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geopolymer composite membrane derived from fly ash for ultrafast and highly efficient filtration of organic pollutants
Journal Pre-proof Defective Analcime/Geopolymer Composite Membrane Derived from Fly Ash for Ultrafast and Highly Efficient Filtration of Organic Pollutants Ningning Shao (Conceptualization) (Methodology) (Software) (Writing - original draft), Siqi Tang (Data curation) (Formal analysis), Shun Li (Supervision) (Writing - review and editing), Hong Chen (Software) (Supervision), Zuotai Zhang (Writing - review and editing) (Supervision) (Project administration)
PII:
S0304-3894(19)31690-5
DOI:
https://doi.org/10.1016/j.jhazmat.2019.121736
Reference:
HAZMAT 121736
To appear in:
Journal of Hazardous Materials
Received Date:
30 August 2019
Revised Date:
20 November 2019
Accepted Date:
20 November 2019
Please cite this article as: Shao N, Tang S, Li S, Chen H, Zhang Z, Defective Analcime/Geopolymer Composite Membrane Derived from Fly Ash for Ultrafast and Highly Efficient Filtration of Organic Pollutants, Journal of Hazardous Materials (2019), doi: https://doi.org/10.1016/j.jhazmat.2019.121736
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Defective Analcime/Geopolymer Composite Membrane Derived from Fly Ash for Ultrafast and Highly Efficient Filtration of Organic Pollutants
Ningning Shao a,d, Siqi Tang a, Shun Li a, Hong Chen a,c, Zuotai Zhanga,b,c,*
a
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School of Environmental Science and Engineering, Southern University of Science and Technology (SUSTech), Shenzhen 518055, P.R. China b
Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control, Shenzhen 518055, P.R. China
Key Laboratory of Municipal Solid Waste Recycling Technology and Management of
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Shenzhen City, Shenzhen 518055, P.R. China
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c
Institute of Technology for Marine Civil Engineering, Shenzhen Institute of
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Information Technology, Shenzhen 518172, P.R. China
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Corresponding author: Email: [email protected] ; Tel: 86-0755-88018019
Graphical abstract
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Highlights:
Nanofiltration membrane (NFM) was synthesized from fly ash by simple
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method;
Defects in analcime crystals introduced larger voids and channels;
Super-high flux (330-440 L·m-2·h-1·MPa-1) and rejection rate (> 95%) for
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Ultra-low fabrication cost of the NFM (~31.8 $/m2).
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wastewater purification;
Abstract: Nanofiltration membranes (NFMs) are of great interest for water purification attributed by their excellent performance, while the high fabrication cost greatly limits their use. Herein, an ultra-low-cost zeolite-based NFM was developed by a simple hydrothermal method using fly ash as the raw material and used for the high-efficiency filtration of organic pollutants from wastewater. The as-obtained
zeolite membrane was composed of crystalline analcime (ANA) type zeolite and amorphous geopolymer (GP) composite. Benefiting from the defects introduced large cavities and microporous channels in ANA, the ANA/GP composite membrane with a thickness of ~60 m exhibited permeation rates as high as 340-440 L/(m2·h·MPa), and the rejection rates are up to 97 % towards methylene blue. Moreover, the fabrication cost of the ANA/GP membrane is only $31.8/m2, far lower than the reported efficient NFMs. The development of the ANA/GP-NFM paves the way for developing commercially applicable membranes for organics separation and water
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purification.
Keywords: Nanofiltration; Zeolite; Membrane; Fly ash; Water purification
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Abbreviations: Alcian blue
MOF
Metal organic framework
AF
Acid Funhsin
NF
Nanofiltration
ANA
Analcime
NFM
Nanofiltration membrane
BF
Basic fuchsin
CBT
Chrome black T Circulating fluidized bed
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CFBFA
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AB
combustion fly ash
OG
Orange GII
OTCC
Oxytetracycline
PDMS
Polydimethylsiloxane
Metal organic framework
p-NP
p-nitrophenol
CR
Congo Red
RB
Rose bengal
GO
Graphene oxide
RhB
Rhodamine B
GP
geopolymer
RR
Reactive Red
GPM
geopolymer membrane
SCS
sand core slice
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COF
GPM@SCS
SCS supported GPM
TC
tetracycline
MB
Methylene blue
ZM
zeolite membrane
Methyl Green
ZM@SCS
SCS supported ZM
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MG MO
Methyl Orange
1. Introduction Water pollution is among the most critical global challenges of our time. Statistically, over 2 billion people are suffering from contaminated drinking water and
an approximately 245,000 km2 of marine ecosystem is destroyed by the discharge of untreated wastewater (WWAP (United Nations World Water Assessment Programme)/UN-Water, 2018, 2017). With the rapid growth of the global population and urbanization, the demand for clean water is anticipated to increase by 1/3 by 2050 (WWAP (United Nations World Water Assessment Programme)/UN-Water, 2018), which will inevitably end up to generation of more wastewater. Getting access to clean water from the purification of wastewater is one of the best strategies to mitigate the water crisis. Among multifarious contaminants in wastewater, the removal of
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organic pollutants is one of the most difficult challenges. On one hand, organic
pollutants are commonly detected in surface water, groundwater, and drinking water, posing great health threat to ecological health. On the other hand, the concentrations
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of organic pollutants in public aqueous systems are very low (0.1-10 g/L), implying great difficulties and huge cost to remove them using present technologies such as
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photocatalysis and adsorption (Koros and Zhang, 2017).
Membrane-based technologies, such as ion-exchange, reverse osmosis and energy-efficient manner for water
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nanofiltration (NF), are considered the most
purification (Koros and Zhang, 2017; Werber et al., 2016). Particularly, due to the
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nanometer-channel-structure, NF membranes (NFMs) can reject almost all organic molecules with molecular weight cut-off > 200 Da (Hilal et al., 2004; Z. Wang et al.,
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2018) and show less sensitivity to feed quality fluctuations, endowing them with great potential for extensive clean-up of organics in wastewater (Werber et al., 2016).
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Nevertheless, the fabrication of efficient NFMs are mainly centralized at expensive organic materials of graphene oxide (GO) (L. Chen et al., 2017; Koros and Zhang, 2017; Werber et al., 2016; Zhou et al., 2018), metal organic frameworks (MOF) (Li et al., 2016; Zhang et al., 2018), covalent organic frameworks (COF) (Fan et al., 2018), polymers (Tan et al., 2018; P. Wang et al., 2018), etc. Despite these NFMs possess huge permeation rate (usually >100 L/(m2·h·MPa)) and high rejection rate (>95 %) towards organic wastewater, the high manufacturing cost greatly restrain their
commercial applications (Fan et al., 2018). Moreover, due to the complex and rigorous synthesis steps, it is difficult to fabricate perfect membranes with large area and uniform micron or nanometer thickness (Park et al., 2017). Therefore, for practical application, the exploitation of accessible, low-cost, and high-performance NFMs has been a long-standing goal. Zeolites are classical inorganic aluminosilicate materials that usually contain numerous channels less than 2 nm in size, and zeolite membranes (ZMs) are receiving
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increasing attention for various applications, such as catalyst reactors (Zhou et al., 2016) and flow batteries (Yuan et al., 2016). However, ZMs are rarely reported for the physical cut-off of organic pollutants from wastewater mainly because of their much lower permeation rate than organic NFMs (Peng et al., 2018; Zhang et al., 2014).
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Additionally, zeolites are usually synthesized from pure chemical reagents, which
remarkably increase the application cost. To this end, the fabrication of a low-cost and
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high-performance ZM is needed. As an important industrial solid waste worldwide, fly ash disposal is a nerve-wracking problem, especially in developing countries.
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According to the Chinese government report on industrial development (http://www.miit.gov.cn), the output of fly ash in China in 2016 was 541 Mt. Although
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the comprehensive utilization rate is approximately 80 %, more than 100 Mt of fly ash was still left and accumulated. Increasing fly ash heaps are not only harmful to
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environmental sustainability but also resource-wasting. Moreover, due to the complexity of the composition of fly ash and economic limitations, fly ash is currently
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roughly used in construction industries (Hemalatha and Ramaswamy, 2017). Fly ash is in urgent well used towards high-value-added products and applications, such as the synthesis of FA-ZnO nanofibers for the adsorption and photocatalytic degradation of organic dyes (Pant et al., 2019). Additionally, the fabrication of fly ash based microfiltration membranes has also attracted growing attentions (Dong et al., 2006; Zou et al., 2019). Despite all that, the synthesis of fly ash-derived NFM, such as ZM, is rarely reported. Although the synthesis of zeolite from fly ash is not novel,
however, most of the reported works are on the synthesis of zeolite powder (Cardoso et al., 2015; Park et al., 2019), and the integrated synthesis of ZM from fly ash is rarely reported. What’s more, most reported ZM showed unsatisfactory performance. Making materials into bulk device has been a long-term pursuit and will be of great convenience to practical application, hence, we present our study to integrally fabricate easy-accessible, low-cost, and high-performance ZM from fly ash. Herein, we developed a novel low-cost ZM from fly ash that has ultrafast
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permeability and rejection rate for the purification of wastewater containing organic pollutants. The ZM was hydrothermal synthesized from alkaline-activated fly ash. To realize the high-flux peculiarity, the membrane was coated on a porous sintered sand core slice (SCS) support to reduce the membrane thickness, and air bubbles were
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introduced to reduce the water permeation resistance. The SCS supported ZM
(ZM@SCS) was used for the filtration removal of various organic pollutants from
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wastewater. By comparison with available NFMs, the ZM@SCS developed in this
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study shows great potential for large scale application for environmental remediation.
2. Experimental Section
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2.1 Materials
Industrial solid waste of fly ash used in this study was the circulating fluidized
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bed fly ash (CFBFA) collected from the coal gangue power plant of China Coal Group Corporation (Pingshuo, Shanxi Province). Its chemical composition (including
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the content of heavy metals) is shown in Table S1. The particle size distribution (d50 = 9.45 m, d90 = 62.4 m) and granular morphology are shown in Figure S1a and S1b, respectively. For activation of CFBFA, a mixed alkaline activator (AA) was premade by mixing 9.2 wt.% NaOH (99 % pure, Shanghai Aladdin Bio-Chem Technology), 77.4 wt.% aqueous sodium silicate (molar ratio of SiO2/Na2O is 3.2, water content is 63.8 wt. %) and 13.3 wt.% deionized water. The hydrogen peroxide (H2O2, 30 wt. %) and calcium stearate were both purchased from Shanghai Macklin Biochemical Co.,
Ltd. and were used as the foaming agent and foam stabilizer, respectively. Moreover, polydimethylsiloxane (PDMS) from Macklin Biochemical Co., Ltd., was used as the defoaming agent to prevent the generation of large air bubbles. Refractory organic pollutants, such as tetracycline (TC, 99 % pure), p-nitrophenol (p-NP, 98 % pure) and oxytetracycline (OTCC, 99 % pure), were chosen for the filtration removal experiment. Additionally, organic dyes of methylene blue (MB), rhodamine B (RhB) and Congo red (CR) were also chosen for the performance evaluation of the ZM, as
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most available NF studies were on the organic pollutant’s removal.
2.2 Synthesis of zeolite membrane
The fabrication procedures of the ZM are illustrated in Scheme 1a, the condition of which is the optimized condition to obtain the highest-strength geopolymer from
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our previous study (Shao et al., 2015). Typically, 50 g CFBFA, 0.5 g calcium stearate,
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and 60 g AA were mixed and blended to make uniform slurry. The H2O2 (0.2 ml) and PDMS (1 mL) were added into the slurry and stirred rapidly for 30 s. Immediately, the
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well-dispersed slurry was spin-coated on the surface of sintered sand core slices (SCS) and then sealed with a preservative film. Then, the moulds were transferred into a curing box and cured at 60 °C for 24 h. Then, the samples were demoulded, and
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the as-obtained samples were the intermediate SCS-supported geopolymer membranes (GPM@SCS). Then, the GPMs were transferred into a Teflon reactor and
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hydrothermally treated at 180 ℃ for 16 h and then dried at 80 °C overnight. The final obtained samples were the target product of SCS-supported ZM (ZM@SCS). In order
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to control the thickness of ZM layer, we firstly coated enough amount of coating precursor on SCS, then the much thicker ZM layer was further polished to control its thickness.
2.3 Characterization X-ray diffraction (XRD) patterns were obtained on a Rigaku Smartlab 9000 diffractometer to determine the phase composition of the as-obtained samples.
Brunauer-Emmett-Teller (BET) analysis was used to determine the size distribution and specific area of the pores, which were measured by N2 adsorption-desorption on an ASAP 2020plus apparatus at 77 K. Mercury intrusion porosimeter (MIP, AutoPore IV) was also used to determine the large pores distribution of as-obtained ZM sample. The MIP test was performed on small block samples of approximately 1-2 cm3 in volume and 3-5g in total mass, and the conducted contact angel was 130 o. Before MIP test, samples need to be vacuum-dried at 60 oC for 24 h. The morphology of the samples was examined by field-emission scanning electron microscopy (FESEM,
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Zeiss Merlin). High-resolution transmission electron microscopy (HRTEM) images, high-angle annular dark-field scanning transmission electron microscopy (STEM-
HAADF) and elemental mapping images were taken on an FEI Titan Themis G2-300
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scanning transmission electron microscope at 300 kV. The microscope was equipped
with a probe spherical aberration corrector that enabled sub-Ångstrom imaging using
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STEM-HAADF detectors. A UV-visible (UV-vis) spectrophotometer (Cary 60, Agilent Tech.) was used to determine the concentration of organic pollutants (MB,
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RhB and CR). High-performance liquid chromatography (HPLC, Agilent Technologies 1260) was used to determine the concentrations of TC, p-NP and
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OTCC. In addition, heavy metals concentration in CFBFA and their leaching from ZM during filtration was detected by inductively coupled plasma mass spectrometer
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(ICP-MS, Thermo Scientific iCAP RQ). The theoretical analysis of ANA crystal, including crystal microstructure model,
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channel and pore size, and crystal defects, was simulated and calculated by Materials Studio (version 8.0).
2.4 Filtration removal of organic pollutants The organic pollutants were removed by vacuum filtration of the corresponding organic pollutant solutions through the ZM@SCS, and the experimental equipment is shown in Figure S2. The gap between the ZM@SCS and funnel was sealed with
commercial fish tank sealant. The vacuum filter used a water-circulating pump, for which the maximum vacuum was 0.098 MPa. For each filtration removal experiment, 20 mL of the 100 ppm corresponding solution was filtered 3 times. Then, the filtrate was collected to test the residual concentration of the organic pollutants. Additionally, to evaluate the long-term-use feasibility and demonstrate the physical cut-off mechanism but not the adsorption effect, we also carried out the ZM@SCS for cyclic filtration of MB. For each cyclic filtration experiment, 50 mL of
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100 ppm MB solution was conducted to filter through the ZM and the filtrate was collected for MB concentration measurement. The total cyclic time was 15.
2.5 Adsorption experiment by zeolite membrane
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To evaluate the contribution of adsorption to the removal of organic dyes, we
carried out an adsorption experiment by immersing ~100 mg sample of ZM layer into
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100 mL of 100 ppm MB solution. To avoid destroying the large pores and pin holes in ZM, the sample was crushed into small blocks but not grinded into powder. Then, we
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collected the blocky sample in 0.6~2 mm (by meshes sieving) for experiment. The adsorption experiment was conducted for 4 h and the residual MB concentration was
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analysed at chosen times (10, 20, 30, 60, 90, 120, 180, 240 min).
2.6 Acid and alkali resistance of zeolite membrane
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The acid and alkali resistance of the prepared ZM was tested according to the Chinese Standard GB/T 34242-2017 towards NFM. Typically, the acid and alkaline
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resistance experiments were conducted by immersing the as-prepared ZMs in acid solution (HCl, 0.01 M) and alkaline solution (NaOH, 0.01 M) for 12 h at 40 oC, respectively. After that, the samples were dried for 24 h at 60 oC. The changes of the surface morphology and phase composition of the ZM after the acid and alkali treatment were tested. The changes of the permeation rate and rejection rate towards MB solution were also tested to evaluate the acid and alkali resistance of the ZM.
3. Results and discussion 3.1 Characterization of zeolite membrane The XRD patterns of the samples at different fabrication steps are shown in Figure 1a, phase evolution has been observed during the fabrication process of ZM. The CFBFA contains quartz (SiO2), anhydrite (CaSO4), hematite (Fe2O3) and lime (CaO) as its main crystal phases, whereas it is mainly amorphous. However, after alkaline activation, the anhydrite and lime phases disappeared, and an obvious hump
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between 20 and 40° (2 theta) was noted, which is indicative of amorphous
geopolymer (GP) gels (Guo et al., 2010). Furthermore, after hydrothermal treatment, a highly crystalline phase of analcime (ANA) zeolite (JCPDS# 99-0007,
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Na(AlSi2O6)H2O) was clearly noted. Some impurity peaks were also observed, which were assigned to epistilbite (JCPDS# 75-0743, Na0.95Ca2.85Al6Si18O48(H2O)14) and
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Zeolite Phi (JCPDS#38-0261, Na1.98Al2Si4.55O13.09·5.49H2O). Thus, the as-obtained ZM was considered to be a composite membrane that was mainly composed of
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crystalline ANA, uncrystallized amorphous GP gels and unreacted CFBFA. In addition, the effect of hydrothermal time and H2O2 dosage on the formation of the
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ANA phase was also investigated (see Figure S3), from which we learned that a 16 h hydrothermal time and 0.2 mL H2O2 dosage are the proper parameters to obtain highly crystalline ANA. As the foaming agent, the increase of H2O2 dosage would
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lead to the increase of ZM porosity. So, we think the introduced pores by H2O2 play
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important roles in the formation of ANA crystal during hydrothermal process. From the cross-sectional SEM image (Figure 1b), the as-obtained ZM@SCS had
a ZM layer thickness of approximately 60 m, and the ZM tightly adhered to the SCS support. From the top-view image (Figures 1c and S4), the ZM is observed to be unconsolidated and with numerous crystals, 100-500 nm in size, filling the surface and inner spaces. Importantly, the vast amount of crystals did not exist independently in the ZM but were bound by a continuous host material, which was considered to be
the unreacted amorphous GP gels. The cross-sectional image (Figure 1d) indicates that the ZM contains vast amount of pin holes (<200 nm), which are believed beneficial to reduce the membrane resistance and increase the water flux. To further investigate the distribution of large pores in ZM layer, we also conducted the sample for MIP test and the result is shown in Figure S5. According to Wu et al. (Wu et al., 2019), the pores of GP based materials can be divided into 3 types: gel pores (2-10 nm), mesopores (10-50 nm), and capillary pores (> 50 nm). The peak value represents the most frequently occurring pore diameter in the interconnected pore structure of
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cementitious sample (Pipilikaki et al., 2009). In this study, the critical pore diameters are noted at 30-150 nm and 1-2 m, indicating the importance of capillary holes in transporting organic wastewater and reducing membrane resistance. Hence, the
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observed pin holes in Figure 1d are believed to be the mesopores and capillary pores. Nevertheless, in our opinion, these pin holes will not affect the membrane rejection
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performance towards organic pollutants, as the ZM is thick enough (tens of micron scale) and there will always be ANA crystals to intercept the pollutant molecule.
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To illustrate the composition of the nanosized crystals, TEM-EDS mapping result (Figures 1e-g) indicate that the crystal was composed of Si, Al, Na and O with an
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atomic ratio of 2:1:1:5, which matches the elemental composition in the ANA chemical formula. For the binder material between the ANA crystals, the TEM and
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STEM-HAADF characterizations (Figure S6) demonstrated it to be calcic amorphous phase, which was believed to be the unreacted glass phase of fly ash or the amorphous
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calcium aluminosilicate hydrate (C-A-S-H) gel(Myers et al., 2013; Walkley et al., 2016). C-A-S-H gel, a typical binder phase in GP materials, is a complex amorphous material with a partially cross-linked tobermorite structure (Myers et al., 2013), and the dense structure leaves no space for organic pollutants to flow through. Therefore, the ANA nanometre channels are believed to play the key role when applying the ZM@SCS for filtration removal of organic pollutants. To predict the feasibility of the ZM@SCS for NF rejection of organic pollutants,
small block materials from ZM fractions were sampled for BET analysis, and the result is shown in Figures 2a and S7. Notably, the ZM shows a hierarchical porous structure of approximately 65 vol. % mesopores and 25 vol. % micropores. The significant amount of mesopores are believed to be those pores dispersed in the ZM matrix (see Figure 1d), attributed to which the membrane resistance could be significantly reduced. The micropore diameters were measured to be 0.64, 0.93 and 1.27 nm (inset image of Figure 2a), which were believed to be derived from the ANA nanocrystals. However, as shown in Figure 2b, the idealized ANA crystal is a highly
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cross-linked 3D network with 4, 6 and 8 rings as its fundamental building units. The highly distorted 8-ring unit (Figure 2b right) contains the largest ANA channel with
dimensions of 1.6×4.2 Å, which is much lower than the values from the BET analysis.
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Delicately, the BET pore size value is correlated (0.93 and 1.27 nm are approximately 1.5 and 2.0 times of 0.64 nm). Therefore, in our comprehensive analysis, we
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considered the as-obtained ANA zeolite to be a crystal with partial defects. To verify our assumption, the ZM sample was carried out for high-resolution 29Si
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NMR detection, and the result is shown in Figure 2c. From the NMR spectrum, it was observed that the main peak was split into 8 separate single peaks centred at -71.6, -
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82.7, -92.5, -96.7, -102.4, -107.8, -112, -116.2 ppm. In particular, the peaks at -92.5, 96.7, -102.4 and -107.8 ppm are the characteristic peaks of an ANA zeolite, and these
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peaks were attributed to the Q4(3Al), Q4(2Al), Q4(1Al), and Q4(0Al) of the siliconoxygen tetrahedra coordination conditions, respectively (Lippmaa et al., 1981;
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Ramdas and Klinowski, 1984). The peaks at 112 and 116.2 ppm were attributed to the unreacted silicate derived from fly ash (Criado et al., 2008; Peng et al., 2015). The peaks at -71.6 and -82.7 ppm were assigned to the features of the uncrystallized GP gel (Duxson et al., 2005; Favier et al., 2015) and the low intensities indicated relatively thorough conversion of ANA from the amorphous GP gels. To demonstrate that the as-obtained ANA in ZM is partially defected in its structure, we first hypothesized that the as-obtained ANA was a perfect crystal, and then the Si/Al molar
ratio of ANA could be calculated from the following equation, which is proposed according to the theory from Engelhardt (Engelhardt and Michel, 1987): 𝑆𝑖 ⁄𝐴𝑙 =
𝑄 4 (3𝐴𝑙)+𝑄4 (2𝐴𝑙)+𝑄 4 (1𝐴𝑙)+𝑄 4 (0𝐴𝑙)
(I)
3 4 2 1 𝑄 (3𝐴𝑙)+ 𝑄4 (2𝐴𝑙)+ 𝑄4 (1𝐴𝑙) 4 4 4
where Q4(3Al), Q4(2Al), Q4(1Al) and Q4(0Al) represent the corresponding quantified peak results (see Figure 2c). The detailed explanation of this equation is given in Section 1.1 in supplementary information.
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Based on the above hypothesis, the final Si/Al molar ratio was calculated to be 3.45 > 2, which is much higher than the standard Si/Al ratio of the perfect ANA
crystal. Therefore, it was concluded that the above hypothesis was invalid and that the as-obtained ANA crystal contained significant defects. The presence of ANA defects
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means that the Si-O tetrahedron and Al-O tetrahedron units were not all tetra-
coordinated with the others, which yielded much larger channels or cavities. With this
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analysis result, the framework of the as-obtained ANA crystals was simulated to show partial defects, where the 4-, 6-, and 8-ring structures were partially replaced by much
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larger rings due to the lost or partially coordinated of the internal bridging Si-O or AlO tetrahedrons. For instance, as shown in Figure 2d, a simulated 14-ring structure
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exhibits a diameter of approximately 0.6-0.7 nm, which is consistent with the BET value. Additionally, 0.9 and 1.2 nm rings could also be achieved in the same way. To
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further verify the ANA crystal defects, the sample was carried out for high-resolution HAADF-STEM and HRTEM detection and the images are shown in Figures 2e, 2f
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and S8. From Figure 2e, it is clearly noted that the ANA crystal contained numerous dark dots in its matrix, which were believed to be the cavities or channels derived from crystal defects. A high-resolution lattice image (Figures 2f and S8) shows that these dark dot areas were voids, revealing the existence of crystal defects. Moreover, these voids were 0.5-2 nm in diameter, which would make it easier for water molecules to pass through but did not affect their resistance to large organic molecules.
Based on the above results, we confirmed the existence of ANA crystal defects, and these defects enabled the formation of larger cavities or channels than those in a perfect ANA crystal. Hence, due to the existence of these large cavities or channels, the resulting ANA-ZM is considered to be more suitable for NF of organic pollutants from wastewater than perfect ANA crystals. In the preparation of the ANA-ZM, to minimize the effect of fly ash fluctuations, some key technical parameters need to be optimized, including alkaline activator (AA) composition, mix proportions, curing conditions, and thermal treatment conditions, etc. Therein, the AA composition and
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AA/fly ash mix ratio is the key to control the whole chemical composition of the
reactant system, which plays key role in making same or similar materials from fly
ash. The mechanism of introducing detects into ANA is not clear, further studies need
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to be conducted in this field.
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3.2 Filtration removal of organic pollutants
The as-fabricated ZM@SCS was carried out for the vacuum filtration removal of
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organic pollutants from wastewater using the equipment, as shown in Figure S2. Prior to the filtration removal experiment, the as-obtained ZM@SCS was first polished to thin the surface ZM layer, and the samples of ZM@SCS with different thicknesses of
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the ZM layer are shown in Figure S9a. In this study, 3 kinds of organic dyes (MB, RhB, CR) and 3 kinds of refractory organic pollutants (TC, p-NP, OTCC) with
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concentrations of 100 mg/L were chosen as the target pollutants, and their typical properties are shown in Table S2. From Figure 3a, the intermediate product of
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GPM@SCS with a 64±5 m thick GPM was used for comparison, although the GPM@SCS reached a 99 % rejection rate towards MB, and the permeation rate was only 19 L / (m2·h·MPa). However, after hydrothermal treatment, the obtained ZM@SCS exhibited super-high rejection rates towards the pollutants of MB, RhB, CR, TC and OTCC, and the rejection rates were 96.7, 98.5, 97.7, 98.8 and 98.7 %, respectively. For the p-NP, the rejection rate was only 61.3 %, which likely resulted from its small molecular size (0.62×0.43 nm) that made it easy for the solution to go
through the larger ANA channels. In every case, the permeation rate fall in the range of 340-440 L/(m2·h·MPa), which is an amazing result for a membrane of this thickness and superior to that of most available efficient NFMs (Chen et al., 2018b; P. Chen et al., 2017; Chen et al., 2015; Wang et al., 2016). To investigate the stability and circulating use feasibility of the ZM@SCS for wastewater purification, the membrane was used for cycled filtration removal of MB. As shown in Figure 3b, the sample exhibited excellent stability in both the rejection
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efficiency and permeation rate towards MB with a concentration of 100 mg/L in the wastewater. During the 15 cycles of use, its rejection rate towards MB remained
higher than 95 %, and the permeation rate was also noted to remain at a very high level (340-440 L/m2·h·MPa). From the inset photographs of Figure 3b, it was
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observed that after 15 cycles of use, the rejected MB stayed in the upper surface of the ZM layer of the ZM@SCS without colouring the white SCS, indicating its physical
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cut-off removal mechanism. In addition, the effect of the membrane thickness on the MB filtration performance was also investigated, and the result is shown in Figure S9.
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It is noted that, even at a thickness of hundreds of micrometres, the ZM also showed surprising and competitive permeation rates in comparison with many reported NFMs
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(Chen et al., 2018b; Wang et al., 2016). Notably, the much thicker ZM made it easier to achieve vacuum filtration than the nanometre-sized NFMs because a thicker
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membrane does not crack or break easily, endowing it with a great potential for largescale applications.
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After the 15-times cyclic use for the filtration of MB, the ZM@SCS sample was
conducted for SEM and EDS-mapping characterization (as shown in Figure 3c and 3d). It is obviously noted that, after the cyclic filtration experiment, the ZM layer shows obvious MB deposition on the surface (Figure 3c) when compared with bare ZM layer (see Figure 1c). However, numerous ANA crystals could still be noticed and identified. From the C-mapping image of the selected zone on the cross-section, the element of C is obviously noted on the top surface of the ZM layer but rarely detected
in the inner space, which implies that the rejected MB is basically cut off on the top surface of the ZM. The tiny amount of C detected in the inner space is observed on the site of pin holes, matching well with our assumption that these pin holes or macropores helps to increase the flux but not affect the rejection rate. In addition, to evaluate the contribution of adsorption to the removal of MB, the ZM sample was conducted for an adsorption experiment and the result is shown in Figure S10. It is noted that the ZM sample shows approximately 40 mg/g adsorption capacity, which is believed to attribute to the inner mesopores and capillary pores of ZM. However, the
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adsorption rate is not fast, with about 90 min to basically reach its adsorption-
desorption equilibrium. Therefore, when applying the ZM for filtration experiment
towards organic wastewater, adsorption contributed little to it, mainly because of its
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low adsorption capacity and low adsorption rate. Hence, it is considered that the mechanism of physical cut-off played the key role in the removal of organic
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pollutants.
Based on the above results and analysis, we proposed a mechanism for the
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filtration removal of organic pollutants by the ANA-ZM@SCS, which is depicted in Figure 3c. The as-fabricated ZM was identified as the ANA zeolites were adhesively
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bound by amorphous geopolymer calcic gels. The porous geopolymer matrix greatly reduced the membrane resistance, whereas the micron-sized thickness ensured that the
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water flow would not migrate away from these meso- and macropores directly. Thus, the filled ANA zeolites played a key role in determining the cut-off of these organic
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pollutants. The as-obtained ANA zeolites showed partial defects in their structure, which are beneficial for large channel formation and further reduce the water flow resistance. A small water molecule could easily pass through the hierarchical ANA channels, whereas a macromolecule, such as MB, would be rejected as the MB size is larger than the largest ANA channels.
3.3 Feasibility for practical application As most NFMs are used for dye filtration removal, to highlight the excellent performance of the as-obtained ZM@SCS, we compared the dye rejection efficiencies and permeation rates obtained in this work and various NFMs (see Figure 4a). The most efficient NFMs can reject over 95 % of dye molecules by vacuum filtration, but the water flux nearly fell in the range of 20-300 L/(m2·h·MPa). In this study, the ANA-ZM exhibited approximately 96-98 % rejection efficiencies, and the permeation
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rates reached 440 L / (m2·h·MPa), exceeding almost all the nanometre-thick NFMs. Most importantly, the ANA-ZM was fabricated from the solid waste of FA, which
makes it cost-effective and easily accessible for large-scale applications. To evaluate its feasibility for practical application, the fabrication cost and operational pressure
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between this study and typical NFMs were compared (see Figure 4b). The fabrication cost was calculated according to the corresponding literature, and the detailed
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calculation methods and processes are given in SI-section 1.2 and Tables S3-S7. As shown in Figure 4b, the fabrication cost of most efficient NFMs is over $1,000 /m2,
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and the price for the GO@AAO (Jang et al., 2016) is as high as $18,600 /m2. Although these efficient NFMs possess excellent performance in wastewater
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treatment, the ultrahigh fabrication cost is one of the biggest obstacles preventing their commercial application. Compared with that, the fabrication cost of the ANA-
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ZM@SCS developed in this study is only $31.8/m2. In addition, the operational vacuum pressure is only 0.1 MPa, which is also at the lowest level among efficient
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NFMs. Hence, from both the fabrication cost and operational standpoints, the ANAZM@SCS developed in this work is very feasible for large-scale wastewater treatment.
In addition, to investigate the safety of ZM for its usage of rejecting organic pollutants, we carried out a detection on the leaching heavy metals from ZM, the result was shown in Table 1. The safety evaluation was according to the Chinese Standard (GB8978-1996). From Table 1, we can notice that the leaching concentration
of heavy metals from ZM is much lower than GB8978-1996 limits, indicating its safety for future practical application. The acid and alkali resistance results of the ZM are shown in Figure S11. After acid treatment, as shown in Figure S11a, the ZM shows obvious changes in its morphology, with no ANA crystals observed. In comparison, the alkali treated ZM shows basically no changes in morphology (Figure S11b), indicating that the ZM could resist alkali rinse. The XRD patterns further demonstrated that the as-prepared
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ZM has good alkali resistance, but is not stable in acidic environment (see Figure S11c). In addition, after the acid and alkali treatment, the ZM performances in terms of rejection and permeability were tested. As shown in Figure S11d, compared with
the original ZM, the acid treated ZM (A-ZM) obvious decrease in rejection rate and
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major increase in permeability. However, the alkali treated ZM (B-ZM) shows no
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obvious changes in both rejection rate and permeability.
4. Conclusions
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In summary, an ANA/GP composite membrane with ultralow fabrication cost and excellent molecular cut-off performance was developed in this study. The
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composite membrane showed hierarchical micro- and mesoporous structures in its body and significant defects in the ANA crystals. These features significantly reduced
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the membrane resistance and improved the molecular sieving performance, enabling the membrane to demonstrate a high water flux (340-440 L / (m2·h·MPa)) and an
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effective rejection rate (> 95 %) towards various organic pollutants. Furthermore, the fabrication cost is estimated to be approximately only $31.8/m2, and the operational pressure is 0.1 MPa, both of which are very low. Therefore, the low-cost and highperformance ANA-ZM developed herein is promising for use in separation and purification.
CRediT author statement Ningning Shao: Conceptualization, Methodology, Software, Writing - Original Draft. Siqi Tang: Data curation, Formal analysis. Shun Li: Supervision, Writing - Review & Editing. Hong Chen: Software, Supervision. Zuotai Zhang: Writing- Reviewing and Editing, Supervision, Project
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administration
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Declaration of interests
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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this
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paper.
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The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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Acknowledgement
We gratefully acknowledge supports from National Key R&D Program of China
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(2018YFC1902904) and the Shenzhen Science and Technology Innovation Committee (Grant No. KQJSCX2018032215150778 and JCYJ20170817111443306). Additional support was provided by the Shenzhen Peacock Plan (KQTD20160226195840229) and Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control (Grant No. 2017B030301012) and Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme 2018.
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References Amini, M., Arami, M., Mahmoodi, N.M., Akbari, A., 2011. Dye removal from colored textile wastewater using acrylic grafted nanomembrane. Desalination 267, 107–113. https://doi.org/https://doi.org/10.1016/j.desal.2010.09.014 An, A.K., Guo, J., Jeong, S., Lee, E.-J., Tabatabai, S.A.A., Leiknes, T., 2016. High flux and antifouling properties of negatively charged membrane for dyeing wastewater treatment by membrane distillation. Water Res. 103, 362–371. https://doi.org/https://doi.org/10.1016/j.watres.2016.07.060
ro of
Cardoso, A.M., Horn, M.B., Ferret, L.S., Azevedo, C.M.N., Pires, M., 2015. Integrated synthesis of zeolites 4A and Na–P1 using coal fly ash for application in the formulation of detergents and swine wastewater treatment. J. Hazard. Mater. 287, 69– 77. https://doi.org/https://doi.org/10.1016/j.jhazmat.2015.01.042
-p
Chen, L., Shi, G., Shen, J., Peng, B., Zhang, B., Wang, Y., Bian, F., Wang, J., Li, D., Qian, Z., Xu, G., Liu, G., Zeng, J., Zhang, L., Yang, Y., Zhou, G., Wu, M., Jin, W., Li, J., Fang, H., 2017. Ion sieving in graphene oxide membranes via cationic control of interlayer spacing. Nature 550, 380.
lP
re
Chen, Long, Li, N., Wen, Z., Zhang, L., Chen, Q., Chen, Lina, Si, P., Feng, J., Li, Y., Lou, J., Ci, L., 2018a. Graphene oxide based membrane intercalated by nanoparticles for high performance nanofiltration application. Chem. Eng. J. 347, 12– 18. https://doi.org/https://doi.org/10.1016/j.cej.2018.04.069
na
Chen, Long, Moon, J.-H., Ma, X., Zhang, L., Chen, Q., Chen, Lina, Peng, R., Si, P., Feng, J., Li, Y., Lou, J., Ci, L., 2018b. High performance graphene oxide nanofiltration membrane prepared by electrospraying for wastewater purification. Carbon N. Y. 130, 487–494. https://doi.org/https://doi.org/10.1016/j.carbon.2018.01.062
Jo
ur
Chen, P., Ma, X., Zhong, Z., Zhang, F., Xing, W., Fan, Y., 2017. Performance of ceramic nanofiltration membrane for desalination of dye solutions containing NaCl and Na2SO4. Desalination 404, 102–111. https://doi.org/https://doi.org/10.1016/j.desal.2016.11.014 Chen, Q., Yu, P., Huang, W., Yu, S., Liu, M., Gao, C., 2015. High-flux composite hollow fiber nanofiltration membranes fabricated through layer-by-layer deposition of oppositely charged crosslinked polyelectrolytes for dye removal. J. Memb. Sci. 492, 312–321. https://doi.org/https://doi.org/10.1016/j.memsci.2015.05.068 Criado, M., Fernández-Jiménez, A., Palomo, A., Sobrados, I., Sanz, J., 2008. Effect of the SiO2/Na2O ratio on the alkali activation of fly ash. Part II: 29Si MASNMR Survey. Microporous Mesoporous Mater. 109, 525–534.
https://doi.org/https://doi.org/10.1016/j.micromeso.2007.05.062 Daraei, P., Madaeni, S.S., Salehi, E., Ghaemi, N., Ghari, H.S., Khadivi, M.A., Rostami, E., 2013. Novel thin film composite membrane fabricated by mixed matrix nanoclay/chitosan on PVDF microfiltration support: Preparation, characterization and performance in dye removal. J. Memb. Sci. 436, 97–108. https://doi.org/https://doi.org/10.1016/j.memsci.2013.02.031 Dong, Y., Liu, X., Ma, Q., Meng, G., 2006. Preparation of cordierite-based porous ceramic micro-filtration membranes using waste fly ash as the main raw materials. J. Memb. Sci. 285, 173–181. https://doi.org/https://doi.org/10.1016/j.memsci.2006.08.032
ro of
Duxson, P., Provis, J.L., Lukey, G.C., Separovic, F., van Deventer, J.S.J., 2005. 29Si NMR Study of Structural Ordering in Aluminosilicate Geopolymer Gels. Langmuir 21, 3028–3036. https://doi.org/10.1021/la047336x Engelhardt, G., & Michel, D., High-resolution solid-state NMR of silicates and zeolites, John Wiley & Sons, Chichester, 1987.
re
-p
Fan, H., Gu, J., Meng, H., Knebel, A., Caro, J., 2018. High-Flux Membranes Based on the Covalent Organic Framework COF-LZU1 for Selective Dye Separation by Nanofiltration. Angew. Chemie Int. Ed. 57, 4083–4087. https://doi.org/10.1002/anie.201712816
lP
Favier, A., Habert, G., Roussel, N., d’Espinose de Lacaillerie, J.-B., 2015. A multinuclear static NMR study of geopolymerisation. Cem. Concr. Res. 75, 104–109. https://doi.org/https://doi.org/10.1016/j.cemconres.2015.03.003
na
Guo, X., Shi, H., Dick, W.A., 2010. Compressive strength and microstructural characteristics of class C fly ash geopolymer. Cem. Concr. Compos. 32, 142–147. https://doi.org/https://doi.org/10.1016/j.cemconcomp.2009.11.003
ur
Han, Y., Jiang, Y., Gao, C., 2015. High-Flux Graphene Oxide Nanofiltration Membrane Intercalated by Carbon Nanotubes. ACS Appl. Mater. Interfaces 7, 8147– 8155. https://doi.org/10.1021/acsami.5b00986
Jo
Hemalatha, T., Ramaswamy, A., 2017. A review on fly ash characteristics – Towards promoting high volume utilization in developing sustainable concrete. J. Clean. Prod. 147, 546–559. https://doi.org/https://doi.org/10.1016/j.jclepro.2017.01.114 Hilal, N., Al-Zoubi, H., Darwish, N.A., Mohamma, A.W., Abu Arabi, M., 2004. A comprehensive review of nanofiltration membranes:Treatment, pretreatment, modelling, and atomic force microscopy. Desalination 170, 281–308. https://doi.org/https://doi.org/10.1016/j.desal.2004.01.007 Jang, J.-H., Woo, J.Y., Lee, J., Han, C.-S., 2016. Ambivalent Effect of Thermal
Reduction in Mass Rejection through Graphene Oxide Membrane. Environ. Sci. Technol. 50, 10024–10030. https://doi.org/10.1021/acs.est.6b02834 Kim, D.W., Choi, J., Kim, D., Jung, H.-T., 2016. Enhanced water permeation based on nanoporous multilayer graphene membranes: the role of pore size and density. J. Mater. Chem. A 4, 17773–17781. https://doi.org/10.1039/C6TA06381K Koros, W.J., Zhang, C., 2017. Materials for next-generation molecularly selective synthetic membranes. Nat. Mater. 16, 289. Li, W., Zhang, Y., Su, P., Xu, Z., Zhang, G., Shen, C., Meng, Q., 2016. Metal– organic framework channelled graphene composite membranes for H2/CO2 separation. J. Mater. Chem. A 4, 18747–18752. https://doi.org/10.1039/C6TA09362K
ro of
Li, Y., Su, Y., Zhao, X., He, X., Zhang, R., Zhao, J., Fan, X., Jiang, Z., 2014. Antifouling, High-Flux Nanofiltration Membranes Enabled by Dual Functional Polydopamine. ACS Appl. Mater. Interfaces 6, 5548–5557. https://doi.org/10.1021/am405990g
-p
Li, Y., Wee, L.H., Volodin, A., Martens, J.A., Vankelecom, I.F.J., 2015. Polymer supported ZIF-8 membranes prepared via an interfacial synthesis method. Chem. Commun. 51, 918–920. https://doi.org/10.1039/C4CC06699E
lP
re
Lippmaa, E., Mági, M., Samoson, A., Tarmak, M., Engelhardt, G., 1981. Investigation of the Structure of Zeolites by Solid-State High-Resolution 29Si NMR Spectroscopy. J. Am. Chem. Soc. 103, 4992–4996. https://doi.org/10.1021/ja00407a002
na
Liu, M., Chen, Q., Lu, K., Huang, W., Lü, Z., Zhou, C., Yu, S., Gao, C., 2017. High efficient removal of dyes from aqueous solution through nanofiltration using diethanolamine-modified polyamide thin-film composite membrane. Sep. Purif. Technol. 173, 135–143. https://doi.org/https://doi.org/10.1016/j.seppur.2016.09.023
Jo
ur
Myers, R.J., Bernal, S.A., San Nicolas, R., Provis, J.L., 2013. Generalized Structural Description of Calcium–Sodium Aluminosilicate Hydrate Gels: The CrossLinked Substituted Tobermorite Model. Langmuir 29, 5294–5306. https://doi.org/10.1021/la4000473 Pant, B., Ojha, G.P., Kim, H.-Y., Park, M., Park, S.-J., 2019. Fly-ashincorporated electrospun zinc oxide nanofibers: Potential material for environmental remediation. Environ. Pollut. 245, 163–172. https://doi.org/https://doi.org/10.1016/j.envpol.2018.10.122 Park, H.B., Kamcev, J., Robeson, L.M., Elimelech, M., Freeman, B.D., 2017. Maximizing the right stuff: The trade-off between membrane permeability and selectivity. Science (80-. ). 356, eaab0530. https://doi.org/10.1126/science.aab0530 Park, J., Hwang, Y., Bae, S., 2019. Nitrate reduction on surface of Pd/Sn
catalysts supported by coal fly ash-derived zeolites. J. Hazard. Mater. 374, 309–318. https://doi.org/https://doi.org/10.1016/j.jhazmat.2019.04.051 Peng, L., Xu, X., Yao, X., Liu, H., Gu, X., 2018. Fabrication of novel hierarchical ZSM-5 zeolite membranes with tunable mesopores for ultrafiltration. J. Memb. Sci. 549, 446–455. https://doi.org/https://doi.org/10.1016/j.memsci.2017.12.039 Peng, Z., Vance, K., Dakhane, A., Marzke, R., Neithalath, N., 2015. Microstructural and 29Si MAS NMR spectroscopic evaluations of alkali cationic effects on fly ash activation. Cem. Concr. Compos. 57, 34–43. https://doi.org/https://doi.org/10.1016/j.cemconcomp.2014.12.005
ro of
Pipilikaki, P., and M. Beazi-Katsioti, 2009. The assessment of porosity and pore size distribution of limestone Portland cement pastes." Const. Build. Mater. 23, 1966-1970. Ramdas, S., Klinowski, J., 1984. z9Si-NMR chemical shifts and. Nature 4–6.
-p
Shao, N.-N., Liu, Z., Xu, Y.-Y., Kong, F.-L., Wang, D.-M., 2015. Fabrication of hollow microspheres filled fly ash geopolymer composites with excellent strength and low density. Mater. Lett. 161. https://doi.org/10.1016/j.matlet.2015.09.016
lP
re
Srivastava, H.P., Arthanareeswaran, G., Anantharaman, N., Starov, V.M., 2011. Performance of modified poly(vinylidene fluoride) membrane for textile wastewater ultrafiltration. Desalination 282, 87–94. https://doi.org/https://doi.org/10.1016/j.desal.2011.05.054
na
Tan, Z., Chen, S., Peng, X., Zhang, L., Gao, C., 2018. Polyamide membranes with nanoscale Turing structures for water purification. Science (80-. ). 360, 518 LP – 521. https://doi.org/10.1126/science.aar6308
ur
Tang, H., Ji, S., Gong, L., Guo, H., Zhang, G., 2013. Tubular ceramic-based multilayer separation membranes using spray layer-by-layer assembly. Polym. Chem. 4, 5621–5628. https://doi.org/10.1039/C3PY00617D
Jo
Walkley, B., San Nicolas, R., Sani, M.-A., Rees, G.J., Hanna, J. V, van Deventer, J.S.J., Provis, J.L., 2016. Phase evolution of C-(N)-A-S-H/N-A-S-H gel blends investigated via alkali-activation of synthetic calcium aluminosilicate precursors. Cem. Concr. Res. 89, 120–135. https://doi.org/https://doi.org/10.1016/j.cemconres.2016.08.010 Wang, J., Qin, L., Lin, J., Zhu, J., Zhang, Y., Liu, J., Van der Bruggen, B., 2017. Enzymatic construction of antibacterial ultrathin membranes for dyes removal. Chem. Eng. J. 323, 56–63. https://doi.org/https://doi.org/10.1016/j.cej.2017.04.089 Wang, N., Ji, S., Zhang, G., Li, J., Wang, L., 2012. Self-assembly of graphene oxide and polyelectrolyte complex nanohybrid membranes for nanofiltration and
pervaporation. Chem. Eng. J. 213, 318–329. https://doi.org/https://doi.org/10.1016/j.cej.2012.09.080 Wang, N., Li, X., Wang, L., Zhang, L., Zhang, G., Ji, S., 2016. Nanoconfined Zeolitic Imidazolate Framework Membranes with Composite Layers of Nearly Zero Thickness. ACS Appl. Mater. Interfaces 8, 21979–21983. https://doi.org/10.1021/acsami.6b08581 Wang, P., Wang, M., Liu, F., Ding, S., Wang, X., Du, G., Liu, J., Apel, P., Kluth, P., Trautmann, C., Wang, Y., 2018. Ultrafast ion sieving using nanoporous polymeric membranes. Nat. Commun. 9, 569. https://doi.org/10.1038/s41467-018-02941-6
ro of
Wang, Z., Wang, Zhangxin, Lin, S., Jin, H., Gao, S., Zhu, Y., Jin, J., 2018. Nanoparticle-templated nanofiltration membranes for ultrahigh performance desalination. Nat. Commun. 9, 2004. https://doi.org/10.1038/s41467-018-04467-3
Werber, J.R., Osuji, C.O., Elimelech, M., 2016. Materials for next-generation desalination and water purification membranes. Nat. Rev. Mater. 1, 16018.
re
-p
Wu, M., Ma, T., Su, Y., Wu, H., You, X., Jiang, Z., Kasher, R., 2017. Fabrication of composite nanofiltration membrane by incorporating attapulgite nanorods during interfacial polymerization for high water flux and antifouling property. J. Memb. Sci. 544, 79–87. https://doi.org/https://doi.org/10.1016/j.memsci.2017.09.016
lP
Wu, M., Zhang, Y., Jia, Y., She, W., Liu, G., Wu, Z., Sun, W., 2019. Influence of sodium hydroxide on the performance and hydration of lime-based low carbon cementitious materials. Constr. Build. Mater. 200, 604–615. https://doi.org/https://doi.org/10.1016/j.conbuildmat.2018.12.102
na
WWAP (United Nations World Water Assessment Programme)/UN-Water, 2018. The United Nations World Water Development Report 2018: Nature-Based Solutions for Water. UNESCO, Paris.
Jo
ur
WWAP (United Nations World Water Assessment Programme)/UN-Water, 2017. The United Nations World Water Development Report 2017: Wastewater: The Untapped Resource. UNESCO, Paris. Yu, S., Chen, Z., Cheng, Q., Lü, Z., Liu, M., Gao, C., 2012. Application of thinfilm composite hollow fiber membrane to submerged nanofiltration of anionic dye aqueous solutions. Sep. Purif. Technol. 88, 121–129. https://doi.org/https://doi.org/10.1016/j.seppur.2011.12.024 Yuan, Z., Zhu, X., Li, M., Lu, W., Li, X., Zhang, H., 2016. A Highly IonSelective Zeolite Flake Layer on Porous Membranes for Flow Battery Applications. Angew. Chemie 128, 3110–3114. https://doi.org/10.1002/ange.201510849 Zhang, F., Zheng, Y., Hu, L., Hu, N., Zhu, M., Zhou, R., Chen, X., Kita, H.,
2014. Preparation of high-flux zeolite T membranes using reusable macroporous stainless steel supports in fluoride media. J. Memb. Sci. 456, 107–116. https://doi.org/https://doi.org/10.1016/j.memsci.2014.01.023 Zhang, H., Hou, J., Hu, Y., Wang, P., Ou, R., Jiang, L., Liu, J.Z., Freeman, B.D., Hill, A.J., Wang, H., 2018. Ultrafast selective transport of alkali metal ions in metal organic frameworks with subnanometer pores. Sci. Adv. 4, eaaq0066. https://doi.org/10.1126/sciadv.aaq0066 Zhang, Q., Wang, H., Zhang, S., Dai, L., 2011. Positively charged nanofiltration membrane based on cardo poly(arylene ether sulfone) with pendant tertiary amine groups. J. Memb. Sci. 375, 191–197. https://doi.org/https://doi.org/10.1016/j.memsci.2011.03.033
ro of
Zhang, Y., Su, Y., Peng, J., Zhao, X., Liu, J., Zhao, J., Jiang, Z., 2013. Composite nanofiltration membranes prepared by interfacial polymerization with natural material tannic acid and trimesoyl chloride. J. Memb. Sci. 429, 235–242. https://doi.org/https://doi.org/10.1016/j.memsci.2012.11.059
re
-p
Zhou, C., Wang, N., Qian, Y., Liu, X., Caro, J., Huang, A., 2016. Efficient Synthesis of Dimethyl Ether from Methanol in a Bifunctional Zeolite Membrane Reactor. Angew. Chemie Int. Ed. 55, 12678–12682. https://doi.org/10.1002/anie.201604753
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Zhou, K.-G., Vasu, K.S., Cherian, C.T., Neek-Amal, M., Zhang, J.C., Ghorbanfekr-Kalashami, H., Huang, K., Marshall, O.P., Kravets, V.G., Abraham, J., Su, Y., Grigorenko, A.N., Pratt, A., Geim, A.K., Peeters, F.M., Novoselov, K.S., Nair, R.R., 2018. Electrically controlled water permeation through graphene oxide membranes. Nature 559, 236–240. https://doi.org/10.1038/s41586-018-0292-y
ur
na
Zhu, J., Tian, M., Hou, J., Wang, J., Lin, J., Zhang, Y., Liu, J., Van der Bruggen, B., 2016. Surface zwitterionic functionalized graphene oxide for a novel loose nanofiltration membrane. J. Mater. Chem. A 4, 1980–1990. https://doi.org/10.1039/C5TA08024J
Jo
Zou, D., Qiu, M., Chen, X., Drioli, E., Fan, Y., 2019. One step co-sintering process for low-cost fly ash based ceramic microfiltration membrane in oil-in-water emulsion treatment. Sep. Purif. Technol. 210, 511–520. https://doi.org/https://doi.org/10.1016/j.seppur.2018.08.040
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Figure 1. (a) XRD patterns of FA, GPM and ZM. (b) Cross-sectional SEM image of ZM@SCS. (c) Top-view SEM images of ZM. (d) A magnified SEM image of the cross-section of the ZM layer. (e) TEM observation of a typical zeolite crystal. (f) Transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) maps. (g) The quantitative elemental results of the zeolite crystal.
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Figure 2. (a) Pore diameter distribution of the ZM sample. (b) Typical crystal structure and pore diameter of a perfect analcime zeolite. (c) 29Si nuclear magnetic resonance (NMR) spectra of the as-obtained ZM. (d) Simulated defective analcime crystal structure. (e-f) High-resolution STEM-HAADF images of ANA crystals.
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Figure 3. (a) Rejection and water permeability rates of different organic wastewater through the ZM@SCS (with 60 m thick ZM layer) as well as the intermediate GPM@SCS sample (64±5 m thick) for comparison. (b) Cyclic filtration performance of MB solution through ZM@SCS (inset: digital photographs of ZM@SCS after 15 times use). (c) Top-view SEM image of the ZM after 15 times cyclic use. (d) Cross-section SEM image and EDS-mapping result (inset image) of the selected zone in terms of C element. (e) Proposed mechanism for the filtration removal of organic pollutants by the ANA-ZM@SCS.
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al., 2017; Srivastava et al., 2011; Tang et al., 2013; Wang et al., 2017, 2016, 2012; Z. Wang et al., 2018; Wu et al., 2017; Yu et al., 2012; Zhang et al., 2018, 2011, 2013; Zhu et al., 2016); (b) A comparison between ZM@SCS with other efficient NFMs in the fabrication cost and operation pressure.
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Scheme 1. (a) Schematic illustration of the fabrication steps of the ZM@SCS. (b) Digital photographs of the blank SCS, GPM@SCS and ZM@SCS.
Table 1 Leaching results of heavy metals from ZM during filtration (mg/kg) Sample
Ba
Cr
Zn
Cu
CFBFA
678
219
146
112
Leaching from ZM
< 0.01
0.032
GB8978-1996 limits
—
1.5
< 0.01
1.0
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2.0
0.037
PII:
S0304-3894(19)31690-5
DOI:
https://doi.org/10.1016/j.jhazmat.2019.121736
Reference:
HAZMAT 121736
To appear in:
Journal of Hazardous Materials
Received Date:
30 August 2019
Revised Date:
20 November 2019
Accepted Date:
20 November 2019
Please cite this article as: Shao N, Tang S, Li S, Chen H, Zhang Z, Defective Analcime/Geopolymer Composite Membrane Derived from Fly Ash for Ultrafast and Highly Efficient Filtration of Organic Pollutants, Journal of Hazardous Materials (2019), doi: https://doi.org/10.1016/j.jhazmat.2019.121736
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Defective Analcime/Geopolymer Composite Membrane Derived from Fly Ash for Ultrafast and Highly Efficient Filtration of Organic Pollutants
Ningning Shao a,d, Siqi Tang a, Shun Li a, Hong Chen a,c, Zuotai Zhanga,b,c,*
a
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School of Environmental Science and Engineering, Southern University of Science and Technology (SUSTech), Shenzhen 518055, P.R. China b
Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control, Shenzhen 518055, P.R. China
Key Laboratory of Municipal Solid Waste Recycling Technology and Management of
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Shenzhen City, Shenzhen 518055, P.R. China
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c
Institute of Technology for Marine Civil Engineering, Shenzhen Institute of
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Information Technology, Shenzhen 518172, P.R. China
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Corresponding author: Email: [email protected] ; Tel: 86-0755-88018019
Graphical abstract
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Highlights:
Nanofiltration membrane (NFM) was synthesized from fly ash by simple
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method;
Defects in analcime crystals introduced larger voids and channels;
Super-high flux (330-440 L·m-2·h-1·MPa-1) and rejection rate (> 95%) for
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Ultra-low fabrication cost of the NFM (~31.8 $/m2).
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wastewater purification;
Abstract: Nanofiltration membranes (NFMs) are of great interest for water purification attributed by their excellent performance, while the high fabrication cost greatly limits their use. Herein, an ultra-low-cost zeolite-based NFM was developed by a simple hydrothermal method using fly ash as the raw material and used for the high-efficiency filtration of organic pollutants from wastewater. The as-obtained
zeolite membrane was composed of crystalline analcime (ANA) type zeolite and amorphous geopolymer (GP) composite. Benefiting from the defects introduced large cavities and microporous channels in ANA, the ANA/GP composite membrane with a thickness of ~60 m exhibited permeation rates as high as 340-440 L/(m2·h·MPa), and the rejection rates are up to 97 % towards methylene blue. Moreover, the fabrication cost of the ANA/GP membrane is only $31.8/m2, far lower than the reported efficient NFMs. The development of the ANA/GP-NFM paves the way for developing commercially applicable membranes for organics separation and water
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purification.
Keywords: Nanofiltration; Zeolite; Membrane; Fly ash; Water purification
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Abbreviations: Alcian blue
MOF
Metal organic framework
AF
Acid Funhsin
NF
Nanofiltration
ANA
Analcime
NFM
Nanofiltration membrane
BF
Basic fuchsin
CBT
Chrome black T Circulating fluidized bed
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CFBFA
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AB
combustion fly ash
OG
Orange GII
OTCC
Oxytetracycline
PDMS
Polydimethylsiloxane
Metal organic framework
p-NP
p-nitrophenol
CR
Congo Red
RB
Rose bengal
GO
Graphene oxide
RhB
Rhodamine B
GP
geopolymer
RR
Reactive Red
GPM
geopolymer membrane
SCS
sand core slice
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COF
GPM@SCS
SCS supported GPM
TC
tetracycline
MB
Methylene blue
ZM
zeolite membrane
Methyl Green
ZM@SCS
SCS supported ZM
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MG MO
Methyl Orange
1. Introduction Water pollution is among the most critical global challenges of our time. Statistically, over 2 billion people are suffering from contaminated drinking water and
an approximately 245,000 km2 of marine ecosystem is destroyed by the discharge of untreated wastewater (WWAP (United Nations World Water Assessment Programme)/UN-Water, 2018, 2017). With the rapid growth of the global population and urbanization, the demand for clean water is anticipated to increase by 1/3 by 2050 (WWAP (United Nations World Water Assessment Programme)/UN-Water, 2018), which will inevitably end up to generation of more wastewater. Getting access to clean water from the purification of wastewater is one of the best strategies to mitigate the water crisis. Among multifarious contaminants in wastewater, the removal of
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organic pollutants is one of the most difficult challenges. On one hand, organic
pollutants are commonly detected in surface water, groundwater, and drinking water, posing great health threat to ecological health. On the other hand, the concentrations
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of organic pollutants in public aqueous systems are very low (0.1-10 g/L), implying great difficulties and huge cost to remove them using present technologies such as
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photocatalysis and adsorption (Koros and Zhang, 2017).
Membrane-based technologies, such as ion-exchange, reverse osmosis and energy-efficient manner for water
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nanofiltration (NF), are considered the most
purification (Koros and Zhang, 2017; Werber et al., 2016). Particularly, due to the
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nanometer-channel-structure, NF membranes (NFMs) can reject almost all organic molecules with molecular weight cut-off > 200 Da (Hilal et al., 2004; Z. Wang et al.,
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2018) and show less sensitivity to feed quality fluctuations, endowing them with great potential for extensive clean-up of organics in wastewater (Werber et al., 2016).
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Nevertheless, the fabrication of efficient NFMs are mainly centralized at expensive organic materials of graphene oxide (GO) (L. Chen et al., 2017; Koros and Zhang, 2017; Werber et al., 2016; Zhou et al., 2018), metal organic frameworks (MOF) (Li et al., 2016; Zhang et al., 2018), covalent organic frameworks (COF) (Fan et al., 2018), polymers (Tan et al., 2018; P. Wang et al., 2018), etc. Despite these NFMs possess huge permeation rate (usually >100 L/(m2·h·MPa)) and high rejection rate (>95 %) towards organic wastewater, the high manufacturing cost greatly restrain their
commercial applications (Fan et al., 2018). Moreover, due to the complex and rigorous synthesis steps, it is difficult to fabricate perfect membranes with large area and uniform micron or nanometer thickness (Park et al., 2017). Therefore, for practical application, the exploitation of accessible, low-cost, and high-performance NFMs has been a long-standing goal. Zeolites are classical inorganic aluminosilicate materials that usually contain numerous channels less than 2 nm in size, and zeolite membranes (ZMs) are receiving
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increasing attention for various applications, such as catalyst reactors (Zhou et al., 2016) and flow batteries (Yuan et al., 2016). However, ZMs are rarely reported for the physical cut-off of organic pollutants from wastewater mainly because of their much lower permeation rate than organic NFMs (Peng et al., 2018; Zhang et al., 2014).
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Additionally, zeolites are usually synthesized from pure chemical reagents, which
remarkably increase the application cost. To this end, the fabrication of a low-cost and
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high-performance ZM is needed. As an important industrial solid waste worldwide, fly ash disposal is a nerve-wracking problem, especially in developing countries.
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According to the Chinese government report on industrial development (http://www.miit.gov.cn), the output of fly ash in China in 2016 was 541 Mt. Although
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the comprehensive utilization rate is approximately 80 %, more than 100 Mt of fly ash was still left and accumulated. Increasing fly ash heaps are not only harmful to
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environmental sustainability but also resource-wasting. Moreover, due to the complexity of the composition of fly ash and economic limitations, fly ash is currently
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roughly used in construction industries (Hemalatha and Ramaswamy, 2017). Fly ash is in urgent well used towards high-value-added products and applications, such as the synthesis of FA-ZnO nanofibers for the adsorption and photocatalytic degradation of organic dyes (Pant et al., 2019). Additionally, the fabrication of fly ash based microfiltration membranes has also attracted growing attentions (Dong et al., 2006; Zou et al., 2019). Despite all that, the synthesis of fly ash-derived NFM, such as ZM, is rarely reported. Although the synthesis of zeolite from fly ash is not novel,
however, most of the reported works are on the synthesis of zeolite powder (Cardoso et al., 2015; Park et al., 2019), and the integrated synthesis of ZM from fly ash is rarely reported. What’s more, most reported ZM showed unsatisfactory performance. Making materials into bulk device has been a long-term pursuit and will be of great convenience to practical application, hence, we present our study to integrally fabricate easy-accessible, low-cost, and high-performance ZM from fly ash. Herein, we developed a novel low-cost ZM from fly ash that has ultrafast
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permeability and rejection rate for the purification of wastewater containing organic pollutants. The ZM was hydrothermal synthesized from alkaline-activated fly ash. To realize the high-flux peculiarity, the membrane was coated on a porous sintered sand core slice (SCS) support to reduce the membrane thickness, and air bubbles were
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introduced to reduce the water permeation resistance. The SCS supported ZM
(ZM@SCS) was used for the filtration removal of various organic pollutants from
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wastewater. By comparison with available NFMs, the ZM@SCS developed in this
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study shows great potential for large scale application for environmental remediation.
2. Experimental Section
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2.1 Materials
Industrial solid waste of fly ash used in this study was the circulating fluidized
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bed fly ash (CFBFA) collected from the coal gangue power plant of China Coal Group Corporation (Pingshuo, Shanxi Province). Its chemical composition (including
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the content of heavy metals) is shown in Table S1. The particle size distribution (d50 = 9.45 m, d90 = 62.4 m) and granular morphology are shown in Figure S1a and S1b, respectively. For activation of CFBFA, a mixed alkaline activator (AA) was premade by mixing 9.2 wt.% NaOH (99 % pure, Shanghai Aladdin Bio-Chem Technology), 77.4 wt.% aqueous sodium silicate (molar ratio of SiO2/Na2O is 3.2, water content is 63.8 wt. %) and 13.3 wt.% deionized water. The hydrogen peroxide (H2O2, 30 wt. %) and calcium stearate were both purchased from Shanghai Macklin Biochemical Co.,
Ltd. and were used as the foaming agent and foam stabilizer, respectively. Moreover, polydimethylsiloxane (PDMS) from Macklin Biochemical Co., Ltd., was used as the defoaming agent to prevent the generation of large air bubbles. Refractory organic pollutants, such as tetracycline (TC, 99 % pure), p-nitrophenol (p-NP, 98 % pure) and oxytetracycline (OTCC, 99 % pure), were chosen for the filtration removal experiment. Additionally, organic dyes of methylene blue (MB), rhodamine B (RhB) and Congo red (CR) were also chosen for the performance evaluation of the ZM, as
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most available NF studies were on the organic pollutant’s removal.
2.2 Synthesis of zeolite membrane
The fabrication procedures of the ZM are illustrated in Scheme 1a, the condition of which is the optimized condition to obtain the highest-strength geopolymer from
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our previous study (Shao et al., 2015). Typically, 50 g CFBFA, 0.5 g calcium stearate,
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and 60 g AA were mixed and blended to make uniform slurry. The H2O2 (0.2 ml) and PDMS (1 mL) were added into the slurry and stirred rapidly for 30 s. Immediately, the
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well-dispersed slurry was spin-coated on the surface of sintered sand core slices (SCS) and then sealed with a preservative film. Then, the moulds were transferred into a curing box and cured at 60 °C for 24 h. Then, the samples were demoulded, and
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the as-obtained samples were the intermediate SCS-supported geopolymer membranes (GPM@SCS). Then, the GPMs were transferred into a Teflon reactor and
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hydrothermally treated at 180 ℃ for 16 h and then dried at 80 °C overnight. The final obtained samples were the target product of SCS-supported ZM (ZM@SCS). In order
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to control the thickness of ZM layer, we firstly coated enough amount of coating precursor on SCS, then the much thicker ZM layer was further polished to control its thickness.
2.3 Characterization X-ray diffraction (XRD) patterns were obtained on a Rigaku Smartlab 9000 diffractometer to determine the phase composition of the as-obtained samples.
Brunauer-Emmett-Teller (BET) analysis was used to determine the size distribution and specific area of the pores, which were measured by N2 adsorption-desorption on an ASAP 2020plus apparatus at 77 K. Mercury intrusion porosimeter (MIP, AutoPore IV) was also used to determine the large pores distribution of as-obtained ZM sample. The MIP test was performed on small block samples of approximately 1-2 cm3 in volume and 3-5g in total mass, and the conducted contact angel was 130 o. Before MIP test, samples need to be vacuum-dried at 60 oC for 24 h. The morphology of the samples was examined by field-emission scanning electron microscopy (FESEM,
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Zeiss Merlin). High-resolution transmission electron microscopy (HRTEM) images, high-angle annular dark-field scanning transmission electron microscopy (STEM-
HAADF) and elemental mapping images were taken on an FEI Titan Themis G2-300
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scanning transmission electron microscope at 300 kV. The microscope was equipped
with a probe spherical aberration corrector that enabled sub-Ångstrom imaging using
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STEM-HAADF detectors. A UV-visible (UV-vis) spectrophotometer (Cary 60, Agilent Tech.) was used to determine the concentration of organic pollutants (MB,
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RhB and CR). High-performance liquid chromatography (HPLC, Agilent Technologies 1260) was used to determine the concentrations of TC, p-NP and
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OTCC. In addition, heavy metals concentration in CFBFA and their leaching from ZM during filtration was detected by inductively coupled plasma mass spectrometer
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(ICP-MS, Thermo Scientific iCAP RQ). The theoretical analysis of ANA crystal, including crystal microstructure model,
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channel and pore size, and crystal defects, was simulated and calculated by Materials Studio (version 8.0).
2.4 Filtration removal of organic pollutants The organic pollutants were removed by vacuum filtration of the corresponding organic pollutant solutions through the ZM@SCS, and the experimental equipment is shown in Figure S2. The gap between the ZM@SCS and funnel was sealed with
commercial fish tank sealant. The vacuum filter used a water-circulating pump, for which the maximum vacuum was 0.098 MPa. For each filtration removal experiment, 20 mL of the 100 ppm corresponding solution was filtered 3 times. Then, the filtrate was collected to test the residual concentration of the organic pollutants. Additionally, to evaluate the long-term-use feasibility and demonstrate the physical cut-off mechanism but not the adsorption effect, we also carried out the ZM@SCS for cyclic filtration of MB. For each cyclic filtration experiment, 50 mL of
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100 ppm MB solution was conducted to filter through the ZM and the filtrate was collected for MB concentration measurement. The total cyclic time was 15.
2.5 Adsorption experiment by zeolite membrane
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To evaluate the contribution of adsorption to the removal of organic dyes, we
carried out an adsorption experiment by immersing ~100 mg sample of ZM layer into
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100 mL of 100 ppm MB solution. To avoid destroying the large pores and pin holes in ZM, the sample was crushed into small blocks but not grinded into powder. Then, we
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collected the blocky sample in 0.6~2 mm (by meshes sieving) for experiment. The adsorption experiment was conducted for 4 h and the residual MB concentration was
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analysed at chosen times (10, 20, 30, 60, 90, 120, 180, 240 min).
2.6 Acid and alkali resistance of zeolite membrane
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The acid and alkali resistance of the prepared ZM was tested according to the Chinese Standard GB/T 34242-2017 towards NFM. Typically, the acid and alkaline
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resistance experiments were conducted by immersing the as-prepared ZMs in acid solution (HCl, 0.01 M) and alkaline solution (NaOH, 0.01 M) for 12 h at 40 oC, respectively. After that, the samples were dried for 24 h at 60 oC. The changes of the surface morphology and phase composition of the ZM after the acid and alkali treatment were tested. The changes of the permeation rate and rejection rate towards MB solution were also tested to evaluate the acid and alkali resistance of the ZM.
3. Results and discussion 3.1 Characterization of zeolite membrane The XRD patterns of the samples at different fabrication steps are shown in Figure 1a, phase evolution has been observed during the fabrication process of ZM. The CFBFA contains quartz (SiO2), anhydrite (CaSO4), hematite (Fe2O3) and lime (CaO) as its main crystal phases, whereas it is mainly amorphous. However, after alkaline activation, the anhydrite and lime phases disappeared, and an obvious hump
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between 20 and 40° (2 theta) was noted, which is indicative of amorphous
geopolymer (GP) gels (Guo et al., 2010). Furthermore, after hydrothermal treatment, a highly crystalline phase of analcime (ANA) zeolite (JCPDS# 99-0007,
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Na(AlSi2O6)H2O) was clearly noted. Some impurity peaks were also observed, which were assigned to epistilbite (JCPDS# 75-0743, Na0.95Ca2.85Al6Si18O48(H2O)14) and
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Zeolite Phi (JCPDS#38-0261, Na1.98Al2Si4.55O13.09·5.49H2O). Thus, the as-obtained ZM was considered to be a composite membrane that was mainly composed of
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crystalline ANA, uncrystallized amorphous GP gels and unreacted CFBFA. In addition, the effect of hydrothermal time and H2O2 dosage on the formation of the
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ANA phase was also investigated (see Figure S3), from which we learned that a 16 h hydrothermal time and 0.2 mL H2O2 dosage are the proper parameters to obtain highly crystalline ANA. As the foaming agent, the increase of H2O2 dosage would
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lead to the increase of ZM porosity. So, we think the introduced pores by H2O2 play
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important roles in the formation of ANA crystal during hydrothermal process. From the cross-sectional SEM image (Figure 1b), the as-obtained ZM@SCS had
a ZM layer thickness of approximately 60 m, and the ZM tightly adhered to the SCS support. From the top-view image (Figures 1c and S4), the ZM is observed to be unconsolidated and with numerous crystals, 100-500 nm in size, filling the surface and inner spaces. Importantly, the vast amount of crystals did not exist independently in the ZM but were bound by a continuous host material, which was considered to be
the unreacted amorphous GP gels. The cross-sectional image (Figure 1d) indicates that the ZM contains vast amount of pin holes (<200 nm), which are believed beneficial to reduce the membrane resistance and increase the water flux. To further investigate the distribution of large pores in ZM layer, we also conducted the sample for MIP test and the result is shown in Figure S5. According to Wu et al. (Wu et al., 2019), the pores of GP based materials can be divided into 3 types: gel pores (2-10 nm), mesopores (10-50 nm), and capillary pores (> 50 nm). The peak value represents the most frequently occurring pore diameter in the interconnected pore structure of
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cementitious sample (Pipilikaki et al., 2009). In this study, the critical pore diameters are noted at 30-150 nm and 1-2 m, indicating the importance of capillary holes in transporting organic wastewater and reducing membrane resistance. Hence, the
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observed pin holes in Figure 1d are believed to be the mesopores and capillary pores. Nevertheless, in our opinion, these pin holes will not affect the membrane rejection
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performance towards organic pollutants, as the ZM is thick enough (tens of micron scale) and there will always be ANA crystals to intercept the pollutant molecule.
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To illustrate the composition of the nanosized crystals, TEM-EDS mapping result (Figures 1e-g) indicate that the crystal was composed of Si, Al, Na and O with an
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atomic ratio of 2:1:1:5, which matches the elemental composition in the ANA chemical formula. For the binder material between the ANA crystals, the TEM and
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STEM-HAADF characterizations (Figure S6) demonstrated it to be calcic amorphous phase, which was believed to be the unreacted glass phase of fly ash or the amorphous
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calcium aluminosilicate hydrate (C-A-S-H) gel(Myers et al., 2013; Walkley et al., 2016). C-A-S-H gel, a typical binder phase in GP materials, is a complex amorphous material with a partially cross-linked tobermorite structure (Myers et al., 2013), and the dense structure leaves no space for organic pollutants to flow through. Therefore, the ANA nanometre channels are believed to play the key role when applying the ZM@SCS for filtration removal of organic pollutants. To predict the feasibility of the ZM@SCS for NF rejection of organic pollutants,
small block materials from ZM fractions were sampled for BET analysis, and the result is shown in Figures 2a and S7. Notably, the ZM shows a hierarchical porous structure of approximately 65 vol. % mesopores and 25 vol. % micropores. The significant amount of mesopores are believed to be those pores dispersed in the ZM matrix (see Figure 1d), attributed to which the membrane resistance could be significantly reduced. The micropore diameters were measured to be 0.64, 0.93 and 1.27 nm (inset image of Figure 2a), which were believed to be derived from the ANA nanocrystals. However, as shown in Figure 2b, the idealized ANA crystal is a highly
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cross-linked 3D network with 4, 6 and 8 rings as its fundamental building units. The highly distorted 8-ring unit (Figure 2b right) contains the largest ANA channel with
dimensions of 1.6×4.2 Å, which is much lower than the values from the BET analysis.
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Delicately, the BET pore size value is correlated (0.93 and 1.27 nm are approximately 1.5 and 2.0 times of 0.64 nm). Therefore, in our comprehensive analysis, we
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considered the as-obtained ANA zeolite to be a crystal with partial defects. To verify our assumption, the ZM sample was carried out for high-resolution 29Si
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NMR detection, and the result is shown in Figure 2c. From the NMR spectrum, it was observed that the main peak was split into 8 separate single peaks centred at -71.6, -
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82.7, -92.5, -96.7, -102.4, -107.8, -112, -116.2 ppm. In particular, the peaks at -92.5, 96.7, -102.4 and -107.8 ppm are the characteristic peaks of an ANA zeolite, and these
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peaks were attributed to the Q4(3Al), Q4(2Al), Q4(1Al), and Q4(0Al) of the siliconoxygen tetrahedra coordination conditions, respectively (Lippmaa et al., 1981;
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Ramdas and Klinowski, 1984). The peaks at 112 and 116.2 ppm were attributed to the unreacted silicate derived from fly ash (Criado et al., 2008; Peng et al., 2015). The peaks at -71.6 and -82.7 ppm were assigned to the features of the uncrystallized GP gel (Duxson et al., 2005; Favier et al., 2015) and the low intensities indicated relatively thorough conversion of ANA from the amorphous GP gels. To demonstrate that the as-obtained ANA in ZM is partially defected in its structure, we first hypothesized that the as-obtained ANA was a perfect crystal, and then the Si/Al molar
ratio of ANA could be calculated from the following equation, which is proposed according to the theory from Engelhardt (Engelhardt and Michel, 1987): 𝑆𝑖 ⁄𝐴𝑙 =
𝑄 4 (3𝐴𝑙)+𝑄4 (2𝐴𝑙)+𝑄 4 (1𝐴𝑙)+𝑄 4 (0𝐴𝑙)
(I)
3 4 2 1 𝑄 (3𝐴𝑙)+ 𝑄4 (2𝐴𝑙)+ 𝑄4 (1𝐴𝑙) 4 4 4
where Q4(3Al), Q4(2Al), Q4(1Al) and Q4(0Al) represent the corresponding quantified peak results (see Figure 2c). The detailed explanation of this equation is given in Section 1.1 in supplementary information.
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Based on the above hypothesis, the final Si/Al molar ratio was calculated to be 3.45 > 2, which is much higher than the standard Si/Al ratio of the perfect ANA
crystal. Therefore, it was concluded that the above hypothesis was invalid and that the as-obtained ANA crystal contained significant defects. The presence of ANA defects
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means that the Si-O tetrahedron and Al-O tetrahedron units were not all tetra-
coordinated with the others, which yielded much larger channels or cavities. With this
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analysis result, the framework of the as-obtained ANA crystals was simulated to show partial defects, where the 4-, 6-, and 8-ring structures were partially replaced by much
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larger rings due to the lost or partially coordinated of the internal bridging Si-O or AlO tetrahedrons. For instance, as shown in Figure 2d, a simulated 14-ring structure
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exhibits a diameter of approximately 0.6-0.7 nm, which is consistent with the BET value. Additionally, 0.9 and 1.2 nm rings could also be achieved in the same way. To
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further verify the ANA crystal defects, the sample was carried out for high-resolution HAADF-STEM and HRTEM detection and the images are shown in Figures 2e, 2f
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and S8. From Figure 2e, it is clearly noted that the ANA crystal contained numerous dark dots in its matrix, which were believed to be the cavities or channels derived from crystal defects. A high-resolution lattice image (Figures 2f and S8) shows that these dark dot areas were voids, revealing the existence of crystal defects. Moreover, these voids were 0.5-2 nm in diameter, which would make it easier for water molecules to pass through but did not affect their resistance to large organic molecules.
Based on the above results, we confirmed the existence of ANA crystal defects, and these defects enabled the formation of larger cavities or channels than those in a perfect ANA crystal. Hence, due to the existence of these large cavities or channels, the resulting ANA-ZM is considered to be more suitable for NF of organic pollutants from wastewater than perfect ANA crystals. In the preparation of the ANA-ZM, to minimize the effect of fly ash fluctuations, some key technical parameters need to be optimized, including alkaline activator (AA) composition, mix proportions, curing conditions, and thermal treatment conditions, etc. Therein, the AA composition and
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AA/fly ash mix ratio is the key to control the whole chemical composition of the
reactant system, which plays key role in making same or similar materials from fly
ash. The mechanism of introducing detects into ANA is not clear, further studies need
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to be conducted in this field.
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3.2 Filtration removal of organic pollutants
The as-fabricated ZM@SCS was carried out for the vacuum filtration removal of
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organic pollutants from wastewater using the equipment, as shown in Figure S2. Prior to the filtration removal experiment, the as-obtained ZM@SCS was first polished to thin the surface ZM layer, and the samples of ZM@SCS with different thicknesses of
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the ZM layer are shown in Figure S9a. In this study, 3 kinds of organic dyes (MB, RhB, CR) and 3 kinds of refractory organic pollutants (TC, p-NP, OTCC) with
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concentrations of 100 mg/L were chosen as the target pollutants, and their typical properties are shown in Table S2. From Figure 3a, the intermediate product of
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GPM@SCS with a 64±5 m thick GPM was used for comparison, although the GPM@SCS reached a 99 % rejection rate towards MB, and the permeation rate was only 19 L / (m2·h·MPa). However, after hydrothermal treatment, the obtained ZM@SCS exhibited super-high rejection rates towards the pollutants of MB, RhB, CR, TC and OTCC, and the rejection rates were 96.7, 98.5, 97.7, 98.8 and 98.7 %, respectively. For the p-NP, the rejection rate was only 61.3 %, which likely resulted from its small molecular size (0.62×0.43 nm) that made it easy for the solution to go
through the larger ANA channels. In every case, the permeation rate fall in the range of 340-440 L/(m2·h·MPa), which is an amazing result for a membrane of this thickness and superior to that of most available efficient NFMs (Chen et al., 2018b; P. Chen et al., 2017; Chen et al., 2015; Wang et al., 2016). To investigate the stability and circulating use feasibility of the ZM@SCS for wastewater purification, the membrane was used for cycled filtration removal of MB. As shown in Figure 3b, the sample exhibited excellent stability in both the rejection
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efficiency and permeation rate towards MB with a concentration of 100 mg/L in the wastewater. During the 15 cycles of use, its rejection rate towards MB remained
higher than 95 %, and the permeation rate was also noted to remain at a very high level (340-440 L/m2·h·MPa). From the inset photographs of Figure 3b, it was
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observed that after 15 cycles of use, the rejected MB stayed in the upper surface of the ZM layer of the ZM@SCS without colouring the white SCS, indicating its physical
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cut-off removal mechanism. In addition, the effect of the membrane thickness on the MB filtration performance was also investigated, and the result is shown in Figure S9.
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It is noted that, even at a thickness of hundreds of micrometres, the ZM also showed surprising and competitive permeation rates in comparison with many reported NFMs
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(Chen et al., 2018b; Wang et al., 2016). Notably, the much thicker ZM made it easier to achieve vacuum filtration than the nanometre-sized NFMs because a thicker
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membrane does not crack or break easily, endowing it with a great potential for largescale applications.
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After the 15-times cyclic use for the filtration of MB, the ZM@SCS sample was
conducted for SEM and EDS-mapping characterization (as shown in Figure 3c and 3d). It is obviously noted that, after the cyclic filtration experiment, the ZM layer shows obvious MB deposition on the surface (Figure 3c) when compared with bare ZM layer (see Figure 1c). However, numerous ANA crystals could still be noticed and identified. From the C-mapping image of the selected zone on the cross-section, the element of C is obviously noted on the top surface of the ZM layer but rarely detected
in the inner space, which implies that the rejected MB is basically cut off on the top surface of the ZM. The tiny amount of C detected in the inner space is observed on the site of pin holes, matching well with our assumption that these pin holes or macropores helps to increase the flux but not affect the rejection rate. In addition, to evaluate the contribution of adsorption to the removal of MB, the ZM sample was conducted for an adsorption experiment and the result is shown in Figure S10. It is noted that the ZM sample shows approximately 40 mg/g adsorption capacity, which is believed to attribute to the inner mesopores and capillary pores of ZM. However, the
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adsorption rate is not fast, with about 90 min to basically reach its adsorption-
desorption equilibrium. Therefore, when applying the ZM for filtration experiment
towards organic wastewater, adsorption contributed little to it, mainly because of its
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low adsorption capacity and low adsorption rate. Hence, it is considered that the mechanism of physical cut-off played the key role in the removal of organic
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pollutants.
Based on the above results and analysis, we proposed a mechanism for the
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filtration removal of organic pollutants by the ANA-ZM@SCS, which is depicted in Figure 3c. The as-fabricated ZM was identified as the ANA zeolites were adhesively
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bound by amorphous geopolymer calcic gels. The porous geopolymer matrix greatly reduced the membrane resistance, whereas the micron-sized thickness ensured that the
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water flow would not migrate away from these meso- and macropores directly. Thus, the filled ANA zeolites played a key role in determining the cut-off of these organic
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pollutants. The as-obtained ANA zeolites showed partial defects in their structure, which are beneficial for large channel formation and further reduce the water flow resistance. A small water molecule could easily pass through the hierarchical ANA channels, whereas a macromolecule, such as MB, would be rejected as the MB size is larger than the largest ANA channels.
3.3 Feasibility for practical application As most NFMs are used for dye filtration removal, to highlight the excellent performance of the as-obtained ZM@SCS, we compared the dye rejection efficiencies and permeation rates obtained in this work and various NFMs (see Figure 4a). The most efficient NFMs can reject over 95 % of dye molecules by vacuum filtration, but the water flux nearly fell in the range of 20-300 L/(m2·h·MPa). In this study, the ANA-ZM exhibited approximately 96-98 % rejection efficiencies, and the permeation
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rates reached 440 L / (m2·h·MPa), exceeding almost all the nanometre-thick NFMs. Most importantly, the ANA-ZM was fabricated from the solid waste of FA, which
makes it cost-effective and easily accessible for large-scale applications. To evaluate its feasibility for practical application, the fabrication cost and operational pressure
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between this study and typical NFMs were compared (see Figure 4b). The fabrication cost was calculated according to the corresponding literature, and the detailed
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calculation methods and processes are given in SI-section 1.2 and Tables S3-S7. As shown in Figure 4b, the fabrication cost of most efficient NFMs is over $1,000 /m2,
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and the price for the GO@AAO (Jang et al., 2016) is as high as $18,600 /m2. Although these efficient NFMs possess excellent performance in wastewater
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treatment, the ultrahigh fabrication cost is one of the biggest obstacles preventing their commercial application. Compared with that, the fabrication cost of the ANA-
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ZM@SCS developed in this study is only $31.8/m2. In addition, the operational vacuum pressure is only 0.1 MPa, which is also at the lowest level among efficient
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NFMs. Hence, from both the fabrication cost and operational standpoints, the ANAZM@SCS developed in this work is very feasible for large-scale wastewater treatment.
In addition, to investigate the safety of ZM for its usage of rejecting organic pollutants, we carried out a detection on the leaching heavy metals from ZM, the result was shown in Table 1. The safety evaluation was according to the Chinese Standard (GB8978-1996). From Table 1, we can notice that the leaching concentration
of heavy metals from ZM is much lower than GB8978-1996 limits, indicating its safety for future practical application. The acid and alkali resistance results of the ZM are shown in Figure S11. After acid treatment, as shown in Figure S11a, the ZM shows obvious changes in its morphology, with no ANA crystals observed. In comparison, the alkali treated ZM shows basically no changes in morphology (Figure S11b), indicating that the ZM could resist alkali rinse. The XRD patterns further demonstrated that the as-prepared
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ZM has good alkali resistance, but is not stable in acidic environment (see Figure S11c). In addition, after the acid and alkali treatment, the ZM performances in terms of rejection and permeability were tested. As shown in Figure S11d, compared with
the original ZM, the acid treated ZM (A-ZM) obvious decrease in rejection rate and
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major increase in permeability. However, the alkali treated ZM (B-ZM) shows no
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obvious changes in both rejection rate and permeability.
4. Conclusions
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In summary, an ANA/GP composite membrane with ultralow fabrication cost and excellent molecular cut-off performance was developed in this study. The
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composite membrane showed hierarchical micro- and mesoporous structures in its body and significant defects in the ANA crystals. These features significantly reduced
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the membrane resistance and improved the molecular sieving performance, enabling the membrane to demonstrate a high water flux (340-440 L / (m2·h·MPa)) and an
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effective rejection rate (> 95 %) towards various organic pollutants. Furthermore, the fabrication cost is estimated to be approximately only $31.8/m2, and the operational pressure is 0.1 MPa, both of which are very low. Therefore, the low-cost and highperformance ANA-ZM developed herein is promising for use in separation and purification.
CRediT author statement Ningning Shao: Conceptualization, Methodology, Software, Writing - Original Draft. Siqi Tang: Data curation, Formal analysis. Shun Li: Supervision, Writing - Review & Editing. Hong Chen: Software, Supervision. Zuotai Zhang: Writing- Reviewing and Editing, Supervision, Project
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administration
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Declaration of interests
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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this
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paper.
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The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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Acknowledgement
We gratefully acknowledge supports from National Key R&D Program of China
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(2018YFC1902904) and the Shenzhen Science and Technology Innovation Committee (Grant No. KQJSCX2018032215150778 and JCYJ20170817111443306). Additional support was provided by the Shenzhen Peacock Plan (KQTD20160226195840229) and Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control (Grant No. 2017B030301012) and Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme 2018.
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References Amini, M., Arami, M., Mahmoodi, N.M., Akbari, A., 2011. Dye removal from colored textile wastewater using acrylic grafted nanomembrane. Desalination 267, 107–113. https://doi.org/https://doi.org/10.1016/j.desal.2010.09.014 An, A.K., Guo, J., Jeong, S., Lee, E.-J., Tabatabai, S.A.A., Leiknes, T., 2016. High flux and antifouling properties of negatively charged membrane for dyeing wastewater treatment by membrane distillation. Water Res. 103, 362–371. https://doi.org/https://doi.org/10.1016/j.watres.2016.07.060
ro of
Cardoso, A.M., Horn, M.B., Ferret, L.S., Azevedo, C.M.N., Pires, M., 2015. Integrated synthesis of zeolites 4A and Na–P1 using coal fly ash for application in the formulation of detergents and swine wastewater treatment. J. Hazard. Mater. 287, 69– 77. https://doi.org/https://doi.org/10.1016/j.jhazmat.2015.01.042
-p
Chen, L., Shi, G., Shen, J., Peng, B., Zhang, B., Wang, Y., Bian, F., Wang, J., Li, D., Qian, Z., Xu, G., Liu, G., Zeng, J., Zhang, L., Yang, Y., Zhou, G., Wu, M., Jin, W., Li, J., Fang, H., 2017. Ion sieving in graphene oxide membranes via cationic control of interlayer spacing. Nature 550, 380.
lP
re
Chen, Long, Li, N., Wen, Z., Zhang, L., Chen, Q., Chen, Lina, Si, P., Feng, J., Li, Y., Lou, J., Ci, L., 2018a. Graphene oxide based membrane intercalated by nanoparticles for high performance nanofiltration application. Chem. Eng. J. 347, 12– 18. https://doi.org/https://doi.org/10.1016/j.cej.2018.04.069
na
Chen, Long, Moon, J.-H., Ma, X., Zhang, L., Chen, Q., Chen, Lina, Peng, R., Si, P., Feng, J., Li, Y., Lou, J., Ci, L., 2018b. High performance graphene oxide nanofiltration membrane prepared by electrospraying for wastewater purification. Carbon N. Y. 130, 487–494. https://doi.org/https://doi.org/10.1016/j.carbon.2018.01.062
Jo
ur
Chen, P., Ma, X., Zhong, Z., Zhang, F., Xing, W., Fan, Y., 2017. Performance of ceramic nanofiltration membrane for desalination of dye solutions containing NaCl and Na2SO4. Desalination 404, 102–111. https://doi.org/https://doi.org/10.1016/j.desal.2016.11.014 Chen, Q., Yu, P., Huang, W., Yu, S., Liu, M., Gao, C., 2015. High-flux composite hollow fiber nanofiltration membranes fabricated through layer-by-layer deposition of oppositely charged crosslinked polyelectrolytes for dye removal. J. Memb. Sci. 492, 312–321. https://doi.org/https://doi.org/10.1016/j.memsci.2015.05.068 Criado, M., Fernández-Jiménez, A., Palomo, A., Sobrados, I., Sanz, J., 2008. Effect of the SiO2/Na2O ratio on the alkali activation of fly ash. Part II: 29Si MASNMR Survey. Microporous Mesoporous Mater. 109, 525–534.
https://doi.org/https://doi.org/10.1016/j.micromeso.2007.05.062 Daraei, P., Madaeni, S.S., Salehi, E., Ghaemi, N., Ghari, H.S., Khadivi, M.A., Rostami, E., 2013. Novel thin film composite membrane fabricated by mixed matrix nanoclay/chitosan on PVDF microfiltration support: Preparation, characterization and performance in dye removal. J. Memb. Sci. 436, 97–108. https://doi.org/https://doi.org/10.1016/j.memsci.2013.02.031 Dong, Y., Liu, X., Ma, Q., Meng, G., 2006. Preparation of cordierite-based porous ceramic micro-filtration membranes using waste fly ash as the main raw materials. J. Memb. Sci. 285, 173–181. https://doi.org/https://doi.org/10.1016/j.memsci.2006.08.032
ro of
Duxson, P., Provis, J.L., Lukey, G.C., Separovic, F., van Deventer, J.S.J., 2005. 29Si NMR Study of Structural Ordering in Aluminosilicate Geopolymer Gels. Langmuir 21, 3028–3036. https://doi.org/10.1021/la047336x Engelhardt, G., & Michel, D., High-resolution solid-state NMR of silicates and zeolites, John Wiley & Sons, Chichester, 1987.
re
-p
Fan, H., Gu, J., Meng, H., Knebel, A., Caro, J., 2018. High-Flux Membranes Based on the Covalent Organic Framework COF-LZU1 for Selective Dye Separation by Nanofiltration. Angew. Chemie Int. Ed. 57, 4083–4087. https://doi.org/10.1002/anie.201712816
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Favier, A., Habert, G., Roussel, N., d’Espinose de Lacaillerie, J.-B., 2015. A multinuclear static NMR study of geopolymerisation. Cem. Concr. Res. 75, 104–109. https://doi.org/https://doi.org/10.1016/j.cemconres.2015.03.003
na
Guo, X., Shi, H., Dick, W.A., 2010. Compressive strength and microstructural characteristics of class C fly ash geopolymer. Cem. Concr. Compos. 32, 142–147. https://doi.org/https://doi.org/10.1016/j.cemconcomp.2009.11.003
ur
Han, Y., Jiang, Y., Gao, C., 2015. High-Flux Graphene Oxide Nanofiltration Membrane Intercalated by Carbon Nanotubes. ACS Appl. Mater. Interfaces 7, 8147– 8155. https://doi.org/10.1021/acsami.5b00986
Jo
Hemalatha, T., Ramaswamy, A., 2017. A review on fly ash characteristics – Towards promoting high volume utilization in developing sustainable concrete. J. Clean. Prod. 147, 546–559. https://doi.org/https://doi.org/10.1016/j.jclepro.2017.01.114 Hilal, N., Al-Zoubi, H., Darwish, N.A., Mohamma, A.W., Abu Arabi, M., 2004. A comprehensive review of nanofiltration membranes:Treatment, pretreatment, modelling, and atomic force microscopy. Desalination 170, 281–308. https://doi.org/https://doi.org/10.1016/j.desal.2004.01.007 Jang, J.-H., Woo, J.Y., Lee, J., Han, C.-S., 2016. Ambivalent Effect of Thermal
Reduction in Mass Rejection through Graphene Oxide Membrane. Environ. Sci. Technol. 50, 10024–10030. https://doi.org/10.1021/acs.est.6b02834 Kim, D.W., Choi, J., Kim, D., Jung, H.-T., 2016. Enhanced water permeation based on nanoporous multilayer graphene membranes: the role of pore size and density. J. Mater. Chem. A 4, 17773–17781. https://doi.org/10.1039/C6TA06381K Koros, W.J., Zhang, C., 2017. Materials for next-generation molecularly selective synthetic membranes. Nat. Mater. 16, 289. Li, W., Zhang, Y., Su, P., Xu, Z., Zhang, G., Shen, C., Meng, Q., 2016. Metal– organic framework channelled graphene composite membranes for H2/CO2 separation. J. Mater. Chem. A 4, 18747–18752. https://doi.org/10.1039/C6TA09362K
ro of
Li, Y., Su, Y., Zhao, X., He, X., Zhang, R., Zhao, J., Fan, X., Jiang, Z., 2014. Antifouling, High-Flux Nanofiltration Membranes Enabled by Dual Functional Polydopamine. ACS Appl. Mater. Interfaces 6, 5548–5557. https://doi.org/10.1021/am405990g
-p
Li, Y., Wee, L.H., Volodin, A., Martens, J.A., Vankelecom, I.F.J., 2015. Polymer supported ZIF-8 membranes prepared via an interfacial synthesis method. Chem. Commun. 51, 918–920. https://doi.org/10.1039/C4CC06699E
lP
re
Lippmaa, E., Mági, M., Samoson, A., Tarmak, M., Engelhardt, G., 1981. Investigation of the Structure of Zeolites by Solid-State High-Resolution 29Si NMR Spectroscopy. J. Am. Chem. Soc. 103, 4992–4996. https://doi.org/10.1021/ja00407a002
na
Liu, M., Chen, Q., Lu, K., Huang, W., Lü, Z., Zhou, C., Yu, S., Gao, C., 2017. High efficient removal of dyes from aqueous solution through nanofiltration using diethanolamine-modified polyamide thin-film composite membrane. Sep. Purif. Technol. 173, 135–143. https://doi.org/https://doi.org/10.1016/j.seppur.2016.09.023
Jo
ur
Myers, R.J., Bernal, S.A., San Nicolas, R., Provis, J.L., 2013. Generalized Structural Description of Calcium–Sodium Aluminosilicate Hydrate Gels: The CrossLinked Substituted Tobermorite Model. Langmuir 29, 5294–5306. https://doi.org/10.1021/la4000473 Pant, B., Ojha, G.P., Kim, H.-Y., Park, M., Park, S.-J., 2019. Fly-ashincorporated electrospun zinc oxide nanofibers: Potential material for environmental remediation. Environ. Pollut. 245, 163–172. https://doi.org/https://doi.org/10.1016/j.envpol.2018.10.122 Park, H.B., Kamcev, J., Robeson, L.M., Elimelech, M., Freeman, B.D., 2017. Maximizing the right stuff: The trade-off between membrane permeability and selectivity. Science (80-. ). 356, eaab0530. https://doi.org/10.1126/science.aab0530 Park, J., Hwang, Y., Bae, S., 2019. Nitrate reduction on surface of Pd/Sn
catalysts supported by coal fly ash-derived zeolites. J. Hazard. Mater. 374, 309–318. https://doi.org/https://doi.org/10.1016/j.jhazmat.2019.04.051 Peng, L., Xu, X., Yao, X., Liu, H., Gu, X., 2018. Fabrication of novel hierarchical ZSM-5 zeolite membranes with tunable mesopores for ultrafiltration. J. Memb. Sci. 549, 446–455. https://doi.org/https://doi.org/10.1016/j.memsci.2017.12.039 Peng, Z., Vance, K., Dakhane, A., Marzke, R., Neithalath, N., 2015. Microstructural and 29Si MAS NMR spectroscopic evaluations of alkali cationic effects on fly ash activation. Cem. Concr. Compos. 57, 34–43. https://doi.org/https://doi.org/10.1016/j.cemconcomp.2014.12.005
ro of
Pipilikaki, P., and M. Beazi-Katsioti, 2009. The assessment of porosity and pore size distribution of limestone Portland cement pastes." Const. Build. Mater. 23, 1966-1970. Ramdas, S., Klinowski, J., 1984. z9Si-NMR chemical shifts and. Nature 4–6.
-p
Shao, N.-N., Liu, Z., Xu, Y.-Y., Kong, F.-L., Wang, D.-M., 2015. Fabrication of hollow microspheres filled fly ash geopolymer composites with excellent strength and low density. Mater. Lett. 161. https://doi.org/10.1016/j.matlet.2015.09.016
lP
re
Srivastava, H.P., Arthanareeswaran, G., Anantharaman, N., Starov, V.M., 2011. Performance of modified poly(vinylidene fluoride) membrane for textile wastewater ultrafiltration. Desalination 282, 87–94. https://doi.org/https://doi.org/10.1016/j.desal.2011.05.054
na
Tan, Z., Chen, S., Peng, X., Zhang, L., Gao, C., 2018. Polyamide membranes with nanoscale Turing structures for water purification. Science (80-. ). 360, 518 LP – 521. https://doi.org/10.1126/science.aar6308
ur
Tang, H., Ji, S., Gong, L., Guo, H., Zhang, G., 2013. Tubular ceramic-based multilayer separation membranes using spray layer-by-layer assembly. Polym. Chem. 4, 5621–5628. https://doi.org/10.1039/C3PY00617D
Jo
Walkley, B., San Nicolas, R., Sani, M.-A., Rees, G.J., Hanna, J. V, van Deventer, J.S.J., Provis, J.L., 2016. Phase evolution of C-(N)-A-S-H/N-A-S-H gel blends investigated via alkali-activation of synthetic calcium aluminosilicate precursors. Cem. Concr. Res. 89, 120–135. https://doi.org/https://doi.org/10.1016/j.cemconres.2016.08.010 Wang, J., Qin, L., Lin, J., Zhu, J., Zhang, Y., Liu, J., Van der Bruggen, B., 2017. Enzymatic construction of antibacterial ultrathin membranes for dyes removal. Chem. Eng. J. 323, 56–63. https://doi.org/https://doi.org/10.1016/j.cej.2017.04.089 Wang, N., Ji, S., Zhang, G., Li, J., Wang, L., 2012. Self-assembly of graphene oxide and polyelectrolyte complex nanohybrid membranes for nanofiltration and
pervaporation. Chem. Eng. J. 213, 318–329. https://doi.org/https://doi.org/10.1016/j.cej.2012.09.080 Wang, N., Li, X., Wang, L., Zhang, L., Zhang, G., Ji, S., 2016. Nanoconfined Zeolitic Imidazolate Framework Membranes with Composite Layers of Nearly Zero Thickness. ACS Appl. Mater. Interfaces 8, 21979–21983. https://doi.org/10.1021/acsami.6b08581 Wang, P., Wang, M., Liu, F., Ding, S., Wang, X., Du, G., Liu, J., Apel, P., Kluth, P., Trautmann, C., Wang, Y., 2018. Ultrafast ion sieving using nanoporous polymeric membranes. Nat. Commun. 9, 569. https://doi.org/10.1038/s41467-018-02941-6
ro of
Wang, Z., Wang, Zhangxin, Lin, S., Jin, H., Gao, S., Zhu, Y., Jin, J., 2018. Nanoparticle-templated nanofiltration membranes for ultrahigh performance desalination. Nat. Commun. 9, 2004. https://doi.org/10.1038/s41467-018-04467-3
Werber, J.R., Osuji, C.O., Elimelech, M., 2016. Materials for next-generation desalination and water purification membranes. Nat. Rev. Mater. 1, 16018.
re
-p
Wu, M., Ma, T., Su, Y., Wu, H., You, X., Jiang, Z., Kasher, R., 2017. Fabrication of composite nanofiltration membrane by incorporating attapulgite nanorods during interfacial polymerization for high water flux and antifouling property. J. Memb. Sci. 544, 79–87. https://doi.org/https://doi.org/10.1016/j.memsci.2017.09.016
lP
Wu, M., Zhang, Y., Jia, Y., She, W., Liu, G., Wu, Z., Sun, W., 2019. Influence of sodium hydroxide on the performance and hydration of lime-based low carbon cementitious materials. Constr. Build. Mater. 200, 604–615. https://doi.org/https://doi.org/10.1016/j.conbuildmat.2018.12.102
na
WWAP (United Nations World Water Assessment Programme)/UN-Water, 2018. The United Nations World Water Development Report 2018: Nature-Based Solutions for Water. UNESCO, Paris.
Jo
ur
WWAP (United Nations World Water Assessment Programme)/UN-Water, 2017. The United Nations World Water Development Report 2017: Wastewater: The Untapped Resource. UNESCO, Paris. Yu, S., Chen, Z., Cheng, Q., Lü, Z., Liu, M., Gao, C., 2012. Application of thinfilm composite hollow fiber membrane to submerged nanofiltration of anionic dye aqueous solutions. Sep. Purif. Technol. 88, 121–129. https://doi.org/https://doi.org/10.1016/j.seppur.2011.12.024 Yuan, Z., Zhu, X., Li, M., Lu, W., Li, X., Zhang, H., 2016. A Highly IonSelective Zeolite Flake Layer on Porous Membranes for Flow Battery Applications. Angew. Chemie 128, 3110–3114. https://doi.org/10.1002/ange.201510849 Zhang, F., Zheng, Y., Hu, L., Hu, N., Zhu, M., Zhou, R., Chen, X., Kita, H.,
2014. Preparation of high-flux zeolite T membranes using reusable macroporous stainless steel supports in fluoride media. J. Memb. Sci. 456, 107–116. https://doi.org/https://doi.org/10.1016/j.memsci.2014.01.023 Zhang, H., Hou, J., Hu, Y., Wang, P., Ou, R., Jiang, L., Liu, J.Z., Freeman, B.D., Hill, A.J., Wang, H., 2018. Ultrafast selective transport of alkali metal ions in metal organic frameworks with subnanometer pores. Sci. Adv. 4, eaaq0066. https://doi.org/10.1126/sciadv.aaq0066 Zhang, Q., Wang, H., Zhang, S., Dai, L., 2011. Positively charged nanofiltration membrane based on cardo poly(arylene ether sulfone) with pendant tertiary amine groups. J. Memb. Sci. 375, 191–197. https://doi.org/https://doi.org/10.1016/j.memsci.2011.03.033
ro of
Zhang, Y., Su, Y., Peng, J., Zhao, X., Liu, J., Zhao, J., Jiang, Z., 2013. Composite nanofiltration membranes prepared by interfacial polymerization with natural material tannic acid and trimesoyl chloride. J. Memb. Sci. 429, 235–242. https://doi.org/https://doi.org/10.1016/j.memsci.2012.11.059
re
-p
Zhou, C., Wang, N., Qian, Y., Liu, X., Caro, J., Huang, A., 2016. Efficient Synthesis of Dimethyl Ether from Methanol in a Bifunctional Zeolite Membrane Reactor. Angew. Chemie Int. Ed. 55, 12678–12682. https://doi.org/10.1002/anie.201604753
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Zhou, K.-G., Vasu, K.S., Cherian, C.T., Neek-Amal, M., Zhang, J.C., Ghorbanfekr-Kalashami, H., Huang, K., Marshall, O.P., Kravets, V.G., Abraham, J., Su, Y., Grigorenko, A.N., Pratt, A., Geim, A.K., Peeters, F.M., Novoselov, K.S., Nair, R.R., 2018. Electrically controlled water permeation through graphene oxide membranes. Nature 559, 236–240. https://doi.org/10.1038/s41586-018-0292-y
ur
na
Zhu, J., Tian, M., Hou, J., Wang, J., Lin, J., Zhang, Y., Liu, J., Van der Bruggen, B., 2016. Surface zwitterionic functionalized graphene oxide for a novel loose nanofiltration membrane. J. Mater. Chem. A 4, 1980–1990. https://doi.org/10.1039/C5TA08024J
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Zou, D., Qiu, M., Chen, X., Drioli, E., Fan, Y., 2019. One step co-sintering process for low-cost fly ash based ceramic microfiltration membrane in oil-in-water emulsion treatment. Sep. Purif. Technol. 210, 511–520. https://doi.org/https://doi.org/10.1016/j.seppur.2018.08.040
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Figure 1. (a) XRD patterns of FA, GPM and ZM. (b) Cross-sectional SEM image of ZM@SCS. (c) Top-view SEM images of ZM. (d) A magnified SEM image of the cross-section of the ZM layer. (e) TEM observation of a typical zeolite crystal. (f) Transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) maps. (g) The quantitative elemental results of the zeolite crystal.
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Figure 2. (a) Pore diameter distribution of the ZM sample. (b) Typical crystal structure and pore diameter of a perfect analcime zeolite. (c) 29Si nuclear magnetic resonance (NMR) spectra of the as-obtained ZM. (d) Simulated defective analcime crystal structure. (e-f) High-resolution STEM-HAADF images of ANA crystals.
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Figure 3. (a) Rejection and water permeability rates of different organic wastewater through the ZM@SCS (with 60 m thick ZM layer) as well as the intermediate GPM@SCS sample (64±5 m thick) for comparison. (b) Cyclic filtration performance of MB solution through ZM@SCS (inset: digital photographs of ZM@SCS after 15 times use). (c) Top-view SEM image of the ZM after 15 times cyclic use. (d) Cross-section SEM image and EDS-mapping result (inset image) of the selected zone in terms of C element. (e) Proposed mechanism for the filtration removal of organic pollutants by the ANA-ZM@SCS.
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al., 2017; Srivastava et al., 2011; Tang et al., 2013; Wang et al., 2017, 2016, 2012; Z. Wang et al., 2018; Wu et al., 2017; Yu et al., 2012; Zhang et al., 2018, 2011, 2013; Zhu et al., 2016); (b) A comparison between ZM@SCS with other efficient NFMs in the fabrication cost and operation pressure.
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Scheme 1. (a) Schematic illustration of the fabrication steps of the ZM@SCS. (b) Digital photographs of the blank SCS, GPM@SCS and ZM@SCS.
Table 1 Leaching results of heavy metals from ZM during filtration (mg/kg) Sample
Ba
Cr
Zn
Cu
CFBFA
678
219
146
112
Leaching from ZM
< 0.01
0.032
GB8978-1996 limits
—
1.5
< 0.01
1.0
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2.0
0.037