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UIO-66-NH2 active layer for high-performance desalination
Journal Pre-proof Thin-film nanocomposite nanofiltration membrane with an ultrathin polyamide/UIO-66NH2 active layer for high-performance desalination Yuqiong Gong, Shoujian Gao, Yangyang Tian, Yuzhang Zhu, Wangxi Fang, Zhenggong Wang, Jian Jin PII:
S0376-7388(19)33104-7
DOI:
https://doi.org/10.1016/j.memsci.2020.117874
Reference:
MEMSCI 117874
To appear in:
Journal of Membrane Science
Received Date: 7 October 2019 Revised Date:
18 January 2020
Accepted Date: 22 January 2020
Please cite this article as: Y. Gong, S. Gao, Y. Tian, Y. Zhu, W. Fang, Z. Wang, J. Jin, Thin-film nanocomposite nanofiltration membrane with an ultrathin polyamide/UIO-66-NH2 active layer for high-performance desalination, Journal of Membrane Science (2020), doi: https://doi.org/10.1016/ j.memsci.2020.117874. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
Thin-film Nanocomposite Nanofiltration Membrane with an Ultrathin Polyamide/UIO-66-NH2 Active layer for High-Performance Desalination Yuqiong Gonga,†, Shoujian Gaob,c,†, Yangyang Tianb,c, Yuzhang Zhub,c, Wangxi Fangb,c, Zhenggong Wanga, Jian Jina,b,c,* a
College of Chemistry, Chemical Engineering and Materials Science, Soochow
University, Suzhou, 215123, China. b
i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of
Sciences, Suzhou, 215123, China. c
School of Nano Technology and Nano Bionics, University of Science and Technology
of China, Hefei, 230026, China. †
These authors contributed equally to this work.
* Corresponding author. E-mail address: [email protected] (J. Jin).
Abstract In this work, ultrasmall metal-organic frameworks (MOFs) nanoparticles, UIO-66NH2 nanoparticles were synthesized and embedded in an ultrathin polyamide (PA) active layer via the interfacial polymerization reaction on a polydopamine-wrapped single-walled carbon nanotube film. A thin-film nanocomposite nanofiltration (TFN NF) membrane with a PA/UIO-66-NH2 active layer as thin as 20 ± 3 nm was thus fabricated. The loading mass of the nanoparticles in the TFN NF membrane could be tuned by controlling the nanoparticles concentration in aqueous phase. Benefiting from the ultrathin thickness of active layer and the high loading mass of the MOFs nanoparticles, water permeability up to 46 L m–2 h–1 bar–1 along with a Na2SO4 rejection of 97.1% was achieved, which is 53% increase of the TFC NF membrane without the addition of UIO-66-NH2 nanoparticles. Our membrane owns the thinnest
active layer in the category of TFN NF membranes reported so far and exhibits outstanding desalination performance. Keywords: Thin film nanocomposite membrane, ultrathin active layer, nanofiltration membrane, UIO-66-NH2 nanoparticles, carbon nanotube film.
1. Introduction Nanofiltration (NF) membranes have been widely used for efficient seawater and brackish water desalination, as well as other water purification applications due to their low energy cost, high throughput, high rejection to multivalent salts and some organic molecules [1-3]. To date, the state-of-the-art NF membranes are based on a thin film composite (TFC) structure that contains a porous support layer and a thin polyamide (PA) active layer formed by the interfacial polymerization (IP) reaction of amine and acyl chloride monomers [4-6]. To further improve the permeability and selectivity of TFC membranes, various nanomaterials, such as inorganic nanoparticles, carbon nanotubes, graphene oxide nanosheets, porous metal-organic molecular cages, covalent organic frameworks, and metal-organic frameworks (MOFs), etc. were introduced into the PA layer so as to increase either the water transfer channels, the membrane hydrophilicity, or the membrane surface charge. These gave rise to the rapid development of the so-called thin-film nanocomposite (TFN) membranes [7-14]. As the pioneer of TFN membranes, Hoek et al. first reported the introduction of NaA zeolite nanoparticles in the PA layer and the water permeability of the TFN membrane was greatly improved with less decrease of salt rejection [7]. As a novel porous material, MOFs possess high porosity, uniform pore size and controlled geometry structure. They could be good candidates for fabricating TFN membranes [14]. Up to date, TFN membranes containing various MOFs nanoparticles such as ZIF,
MIL and UIO series have been continuously reported and exhibited either increased water permeability or enhanced rejection [13-20]. Although TFN NF membranes have shown improved desalination performance, they still face the challenge of trade-off between permeability and selectivity [21,22]. In general, the active layer of a TFN NF membrane should be as thin as possible in order to achieve a better performance [23]. As for TFC NF membranes, it might be easy to form an ultrathin PA active layer with thickness of a dozen nanometers via IP process by either controlling the reaction process or choosing specific composite support membranes [24-31]. However, it is difficult to realize on the case of TFN NF membranes. As for TFN NF membranes, the size matching between the nanoparticles and the thickness of PA layer is important to ensure the complete and integrity of the whole membrane [32-35]. In addition, the uniform incorporation of nanoparticles in the ultrathin PA layer without generation of extra defects is still a tough work. In this work, we report the fabrication of a TFN NF membrane with an ultrathin PA/UIO-66-NH2 active layer via the IP reaction on a polydopamine-wrapped singlewalled carbon nanotube (PD/SWCNT) film. To achieve the complete and uniform embedding of nanoparticles in the ultrathin PA layer, ultrasmall UIO-66-NH2 nanoparticles with a size of ~15 nm were synthesized. The nanoparticles with hydrophilic amine ligands could be homogeneously dispersed in the PIP solution. By altering the UIO-66-NH2 concentration in the PIP solution, the loading mass of the nanoparticles in the PA active layer could be tuned. The TFN NF membrane with a PA/UIO-66-NH2 composite active layer as thin as 20 ± 3 nm exhibited largely increased water permeability meanwhile a high rejection for Na2SO4. To the best of our knowledge, our membrane owns the thinnest active layer among TFN NF
membranes reported so far and the membrane performance outperforms all of the other reported TFN NF membranes. 2. Experimental 2.1. Materials The SWCNT powder (OD: 1-2 nm, length: 5-30 µm, purity: > 95%) used herein was commercially available from Nanjing XFNANO Materials Tech Co., Ltd (Nanjing, China). The polyether sulfone microfiltration (PES MF) membrane with an efficient pore size of 0.45 µm was purchased from Yibo Co., Ltd. (Haining, China). Zirconium chloride
(ZrCl4),
2-Aminoterephthalic
acid,
dopamine
hydrochloride
and
Tris(hydroxymethyl)aminomethane were analytical grade and purchased from AlfaAesar. Anhydrous piperazine (PIP) and trimesoyl chloride (TMC) with purity of 99% were purchased from Aladdin Co., Ltd. (Shanghai, China). All the other chemical reagents were analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). Deionized water was used throughout the experiments. 2.2. Synthesis of UIO-66-NH2 nanoparticles The UIO-66-NH2 nanoparticles were synthesized by dissolving 650 mg ZrCl4, 480 mg 2-aminoterephthalic acid and 7.56 g water in 160 mL N,N-dimethylformamide (DMF). Then the DMF solution was sonicated using a Fisher Scientific ultrasonic cell crusher for 2 min to produce a homogeneous solution. Afterwards, the solution was heated at 120 ºC for 24 h. After centrifugation at 10000 rpm for 30 min, the sediments were collected and washed by methanol for 5 times firstly, then washed by water for 8 times. Finally, the UIO-66-NH2 nanoparticles were obtained. 2.3. Preparation of PD/SWCNT film To fabricate PD/SWCNT film, the PD/SWCNT dispersion was firstly prepared according to our previous report [36]. The SWCNT dispersion was fabricated by
adding 40 mg SWCNT powder into 400 mL sodium dodecyl benzene sulfonate (SDBS) water solution with a concentration of 1 g L-1 and sonicating the solution under 10 W for 2 h. The dispersion was then centrifuged at 10000 rpm for 30 min and the supernatant dispersion was collected. Then 150 mL supernatant dispersion was diluted to 450 mL with water, the SDBS in the dispersion was replenished to 1mg mL1
. Dopamine hydrochloride was added into the dispersion with a concentration of 0.1
mg mL-1 and stirred at 40 ºC for 1 h. Then 45 ml 0.1 mol L-1 Tris buffer solution (pH 8.5) was added into the dispersion and further stirred at 40 °C for 23 h. Finally, the dispersion was centrifuged at 10000 rpm for 30 min to collect the supernatant dispersion. The PD/SWCNT film was prepared by filtering 1.5 mL PD/SWCNT dispersion onto a PES MF membrane to form a thin film with an effective area of 11.34 cm2 and dried at 60 °C for 10 min. 2.4. Fabrication of TFC and TFN membranes The TFC and TFN membranes were fabricated via a typical IP reaction of PIP and TMC on the PD/SWCNT/PES MF composite support membrane [27-30]. In this work, the IP process was carried out at a temperature of 25 ℃ and a relative humidity of 60%. To fabricate the TFC membrane, the PD/SWCNT/PES MF composite support membrane was trapped on a clean glass plate where a few drops of PIP water solution (1.25 mg mL-1) were preloaded. Then the PIP solution was dripped to cover the PD/SWCNT film surface for 30 s. The redundant PIP solution was removed until no solution was obviously observed on the film surface. Then the TMC n-hexane solution (1 mg mL-1) was poured on the film surface for 30 s. After removing the redundant TMC solution, the film was immediately immersed in n-hexane for 1 min and then dried at 60 ℃ for 30 min to obtain TFC membrane. To fabricate the TFN membrane, the as-synthesized UIO-66-NH2 nanoparticles was added in the PIP water
solution and sonicated under 10 W for 1 h to form a transparent dispersion with a certain UIO-66-NH2 concentration. Then the IP process was implemented as the same as in the case of TFC membrane preparation process. 2.5. Membrane performance test The desalination performance of the NF membranes was tested on a cross-flow NF apparatus with an efficient test area of 7.06 cm2 at 25 ºC. The salt (Na2SO4, MgSO4, MgCl2, CaCl2, NaCl) concentration was 1000 ppm. The hydraulic transmembrane pressure was 6 bar. Water permeability J (L m–2 h–1 bar–1) was calculated by the following equation (1): J = ∆m/A∆tP
(1)
where ∆m (kg) was the mass increment of the filtrate water during the separation time of ∆t (h), was the density of filtrate water (1 kg L-1), A (m2) was the test area, P (bar) was the hydraulic transmembrane pressure. Salt rejection R (%) was calculated by the following equation (2): R = (1 - Cp/Cf ) × 100%
(2)
where Cp and Cf were the conductivity of filtrate water and feed solution. 2.6. Characterization The transmission electron microscopy (TEM) images were measured on a Tecnai G2 F20 S-Twin field-emission transmission electron microscope. The scanning electron microscopy (SEM) and mapping images were tested on a Quanta FEG 250 scanning electron microscope. The atomic force microscopy (AFM) images were measured on a Bruker Dimension Icon atomic force microscope. Before measuring the TEM and AFM images of the TFC and TFN membranes, the underlying PES membrane was completely dissolved by DMF. To capture the cross-sectional TEM image, the membrane was embedded in epoxy resin and vertically cut into thin sheets. The X-ray
diffraction (XRD) pattern was tested by a Bruker AXS D8 Advance powder X-Ray diffractomer. The dynamic light scattering (DLS) and zeta potential of nanoparticles were measured on a Malvern ZEN3600 Zetasizer Nano series. The surface zeta potential of membranes was measured on an Anton Paar Surpass solid surface analysis. The solution conductivity was measured by a METTLER TOLEDO FE30K conductivity meter. The polyethylene glycol (PEG) concentration was measured by an O.I. Analytical Aurora Model 1030w total organic carbon (TOC) analyzer. 3. Results and discussion 3.1. Synthesis and characterization of UIO-66-NH2 nanoparticles UIO-66-NH2 nanoparticles are chosen in this work for fabricating the TFN membrane because of its good water-stability and controllable particle size. The UIO-66-NH2 nanoparticles were synthesized via the solvothermal reaction of ZrCl4 and 2aminoterephthalic acid with a certain amount of water to tune the nanoparticle size. The addition of water can increase the aggregation rate and thus increase the nucleation rate of UIO-66-NH2, eventually give rise to the formation of extremely small UIO-66-NH2 nanoparticles [37,38]. The TEM image shows the morphology of the synthesized nanoparticles (Fig. 1a). The diameter of the nanoparticles is mainly in the range of 15 ± 5 nm. The XRD pattern reveals the crystalline structure of the nanoparticles (Fig. 1b). Because the nanoparticles are very small, the XRD pattern displays broad reflections. The characteristic peaks at 2θ = 7.4°, 8.4° and 25.9° are attributed to the (111), (002) and (006) planes of the UIO-66-NH2 crystal, in keeping with the previous reports [39]. As for the fabrication of TFN membrane, the quality of nanoparticles dispersity is a key parameter to determine the uniformity of loaded nanoparticles in the resulting PA active layer. To investigate the dispersity of UIO-66NH2 nanoparticles, their size distribution in pure water and in a PIP water solution
(0.2 mg mL-1) was tested using DLS measurement. The UIO-66-NH2 nanoparticles in pure water give a size distribution in the range of 12-18 nm (Fig. 1c) and the nanoparticles in the PIP solution give a similar size distribution in the range of 14-19 nm (Fig. 1d). These results are in accordance with the TEM image, indicating the good dispersity of the nanoparticles both in pure water and in the PIP solution. Fig. 1e is an optical photograph showing the PIP solution containing the nanoparticles. The solution was clearly transparent. When a laser beam is irradiated through the solution, an obvious Tyndall effect appears, demonstrating the nanoparticles are extremely small and homogeneously dispersed in the solution. The good dispersity of UIO-66NH2 nanoparticles in aqueous solution is owing to the abundant hydrophilic amine groups in the nanoparticles. The UIO-66-NH2 nanoparticles are positively charged with zeta potential of 36.5 mV (Fig. S1).
Fig. 1. (a) TEM image and (b) XRD pattern of the UIO-66-NH2 nanoparticles. Size distribution of the nanoparticles (0.2 mg mL-1) in (c) pure water and (d) a PIP water
solution (1.25 mg mL-1). (e) A digital photograph of the transparent PIP solution containing the nanoparticles. When a laser beam is irradiated though the solution, a Tyndall effect appears. 3.2. Morphology and structure characterization of TFN membranes The TFN membrane was fabricated via a typical IP process on a PD/SWCNT/PES composite support. The low concentration of PIP water solution (1.25 mg mL-1) with homogeneously dispersed UIO-66-NH2 nanoparticles (0.2 mg mL-1) and TMC nhexane solution (1 mg mL-1) were used in order to form a thin PA layer. A TFC membrane without the addition of UIO-66-NH2 nanoparticles was also fabricated under the same condition as a control experiment. The surface morphologies of the PD/SWCNT film and the PA NF membranes fabricated on the PD/SWCNT film are revealed by the SEM and AFM images as shown in Fig. 2. The PD/SWCNTs are randomly deposited on the underlying PES MF membrane and interlaced to each other to form a network film with pores of dozens of nanometers (Fig. 2a and 2d). After the IP process, a dense active layer was formed on the PD/SWCNT film for both the TFC membrane (Fig. 2b and 2e) and the TFN membrane (Fig. 2c and 2f). The outlines of PD/SWCNT and UIO-66-NH2 nanoparticles are still visible, indicating the formed active layers are extremely thin. The EDX imaging shows a uniform distribution of Zr element in the TFN membrane (the inset in Fig. 2c), demonstrating the uniform distribution of the UIO-66-NH2 nanoparticles in the active layer. The surface roughness of the PD/SWCNT film was 14.2 nm as measured by the AFM (Fig. 2d). After forming PA layer, the surface roughness decreases to 11.6 nm for the TFC membrane (Fig. 2e). With the nanoparticles embedded in the PA layer, the surface roughness of the TFN membrane increases slightly to 13.4 nm.
Fig. 2. Top-view SEM and AFM images of (a, d) the PD/SWCNT film, (b, e) the PA active layer fabricated on the film, (c, f) the PA/UIO-66-NH2 active layer fabricated on the film. The inserts in b and c are the EDX imaging of Zr element distribution.
Fig. 3 shows the cross-sectional (Fig. 3b) and top-view (Fig. 3c) TEM images of the TFN membrane with the underlying PES MF membrane removed. As shown in Fig. 3b, the PA/UIO-66-NH2 active layer tightly attaches on the PD/SWCNT film to form a bilayer structure. The thickness of the active layer is 20 ± 3 nm, and the thickness of the PD/SWCNT film is 46 ± 5 nm. It can be observed that the UIO-66NH2 nanoparticles are exactly embedded in the ultrathin active layer. To further confirm the embedding of the UIO-66-NH2 nanoparticles in the active layer rather than between the active layer and the PD/SWCNT film, a free-standing PA/UIO-66NH2 film was fabricated at the interface of a PIP/UIO-66-NH2 nanoparticle water solution and a TMC n-hexane solution (Fig. S2). The TEM image clearly shows the uniform embedding of the nanoparticles in the obtained free-standing film. It demonstrates that the UIO-66-NH2 nanoparticles could be successfully embedded within the PA/UIO-66-NH2 active layer fabricated by dispersing the nanoparticles in
the aqueous solution during the IP process. From both the cross-sectional and the topview TEM images, we can’t observe any obvious interfacial defects between the UIO66-NH2 nanoparticles and PA, indicating a good integrity of the active layer.
Fig. 3. (a) A schematic showing the structure of the TFN membrane. (b) Cross-section and (c) top-view TEM images of the PA/UIO-66-NH2 active layer on the PD/SWCNT film.
The dynamic spreading and permeating behaviors of a water droplet (3 μL) on the TFN and TFC membranes were also captured as shown in Fig. 4. The transient water CA of the TFN membrane was 50° which is very similar to that of the TFC membrane (52°), indicating the surface chemical composition of the two membranes is almost the same. This result further demonstrates the UIO-66-NH2 nanoparticles are completely embedded in the UIO-66-NH2/PA active layer and no nanoparticles are exposed outsides PA. As the nanoparticles has a size (~15 nm) very closed to the thickness of the active layer (~20 nm), it further confirms the exact embedding of the nanoparticles and the good integrity of the active layer. It takes 64 s for the water
droplet to permeate into the TFC membrane (Fig. 4b), while it only takes 44 s in the case of the TFN membrane (Fig. 4a). The permeating speed of the water droplet into the TFN membrane is about 1.5 times of that in the case of the TFC membrane, indicating the superior water permeation ability of the TFN membrane.
Fig. 4. Optical images showing the dynamic spreading and permeating behaviors of a water droplet on the (a) TFN membrane and (b) TFC membrane.
3.3. Variation of nanoparticles loading in the PA active layer The variation of UIO-66-NH2 nanoparticles loading in the active layer as a function of the UIO-66-NH2 concentration in the PIP solution was investigated. A series of TFN membranes were fabricated with the UIO-66-NH2 concentration of 0.05, 0.1, 0.2 and 0.4 mg mL-1. Fig. 5 shows the top-view TEM images of the TFN membranes with the PES MF membrane removed. The pure PA active layer in the TFC membrane displays a high transparency with a visible interlacing structure of the underlying PD/SWCNT film (Fig. 5a and b). For the PA/UIO-66-NH2 active layer fabricated
with 0.05 mg mL-1 UIO-66-NH2, there are quite few nanoparticles observed in it (Fig. 5c). With the increase of UIO-66-NH2 concentration, the loading mass of the nanoparticles in the active layer increases gradually (Fig. 5d-f). When the UIO-66NH2 concentration reaches 0.2 mg mL-1, we can observe lots of nanoparticles uniformly distributed throughout the whole active layer (Fig. 5e). Further increasing the UIO-66-NH2 concentration to 0.4 mg mL-1, the active layer shows a very dense distribution of the nanoparticles (Fig. 5f). These results demonstrate the loading mass of the UIO-66-NH2 nanoparticles in the active layer are controllable by tuning the UIO-66-NH2 concentration in the aqueous solution.
Fig. 5. Top-view TEM images of (a) the PD/SWCNT film, (b) the PA active layer fabricated on the film, (c-f) the PA/UIO-66-NH2 active layer fabricated on the film with UIO-66-NH2 concentration of 0.05, 0.1, 0.2 and 0.4 mg mL-1.
3.4. Pore size distribution and surface charge of TFN membranes
To investigate the pore size distribution of the TFN membranes fabricated with different UIO-66-NH2 concentrations in the PIP solution, their rejections to PEG molecules with molecular weight of 200, 400, 600 and 1000 Da were measured. The same measurement was implemented on the TFC membrane as a contrast. The PEG rejection curves are plotted via nonlinear fitting and the molecular weight cutoff (MWCO) which means the molecular weight at a 90% rejection was obtained from the curves (Fig. 6a) The MWCO of the TFC membrane is 396 Da, and it increases to 424, 507, 523 and 565 Da for the TFN membranes fabricated with UIO-66-NH2 concentration of 0.05, 0.1, 0.2 and 0.4 mg mL-1. According to the rejection curves and a probability density function [40-42], the pore radius distribution of the membranes is obtained as shown in Fig. 6b. The mean pore radius of the TFC membrane is 0.24 nm. After introducing the UIO-66-NH2 nanoparticles with concentration of 0.05 and 0.1 mg mL-1, the mean pore radius of the TFN membranes becomes 0.29 and 0.32 nm. Further increasing the UIO-66-NH2 concentration to 0.2 and 0.4 mg mL-1, no more variation of the pore radius distribution appears. According to Donnan principle, the surface charge of a NF membrane is an essential parameter influencing the desalination performance, especially for the rejection of divalent and multivalent ions [43]. The surface charge of the TFC and TFN membranes was evaluated by measuring their surface zeta potential under the pH of 2-11. As shown in Fig. 7a, both the TFC and TFN membranes show a negative surface zeta potential under this pH range, indicating these membranes are negatively charged. Under the neutral condition, these membranes also show a negatively charged surface (Fig. 7b), which is beneficial to the rejection of anions with high valence. With the loading increase of the positively charged UIO-66-NH2 nanoparticles, the surface zeta potential of the TFN membrane changes integrally in the positive direction (Fig. 7a and b).
Fig. 6. (a) PEG rejection curves and MWCOs of the TFC membrane and the TFN membranes fabricated with different UIO-66-NH2 concentrations. (b) Pore radius distribution of the membranes.
Fig. 7. (a) Surface zeta potential curves of the TFC membrane and TFN membranes under different pH. (d) Surface zeta potential of the membranes when the pH is 7.
3.5. Desalination performance of TFN membranes The desalination performance of the TFC and TFN membranes was evaluated by separating a series of salt solutions. As shown in Fig. 8a, the TFC membrane shows water permeability of 30 L m–2 h–1 bar–1 and a Na2SO4 rejection of 98.5%. After introducing the UIO-66-NH2 nanoparticles, the water permeability of the TFN membrane increases sharply to 35, 42, and 46 L m–2 h–1 bar–1 with the UIO-66-NH2 concentration of 0.05, 0.1 and 0.2 mg mL-1. The corresponding Na2SO4 rejection is 98%, 97.6% and 97.1%. Further increasing the UIO-66-NH2 concentration to 0.4 mg
mL-1, the TFN membrane shows a slight decrease of the water permeability of 41 L m–2 h–1 bar–1 with nearly no more change of Na2SO4 rejection. Therefore, the TFN membrane fabricated with UIO-66-NH2 concentration of 0.2 mg mL-1 (TFN-0.2) is chosen for the following test. The separation performance of the TFN-0.2 membrane for Na2SO4, MgSO4, MgCl2, CaCl2 and NaCl is shown in Fig. 8b. The corresponding water permeability is 46, 44, 49, 52 and 54 L m–2 h–1 bar–1, the corresponding salt rejection is 97.1%, 91.2%, 45.8%, 40.8% and 8.1%, respectively. The high rejection of multivalent salts and a low rejection of monovalent salt indicate that the TFN-0.2 membrane has a promising potential to be used where high rejection of monovalent salts is not required, such as softening brackish groundwater, pretreating seawater before reverse osmosis process, treating industrial process streams, decontaminating wastewater, etc. It is worth noting that the pure water permeability of the TFN-0.2 membrane is as high as 63 L m–2 h–1 bar–1. The ultrahigh water permeability of the TFN membrane is attributed to both the ultrathin active layer and the high loading mass of the MOFs nanoparticles. The Na2SO4 rejection is higher than the MgSO4 rejection, and the rejection for divalent ions is much higher than that of monovalent ions, revealing the rejection mechanism of the TFN membrane is the synergistic effect of Donnan exclusion and size sieving.
Fig. 8. (a) Water permeability and Na2SO4 rejection of the TFN membranes fabricated with different UIO-66-NH2 concentrations. (b) Water permeability and salt rejection of the TFN-0.2 membrane.
The performance stability of the TFN-0.2 membrane was also evaluated. During a 72-hour continuous nanofiltration test, the TFN-0.2 membrane shows nearly unchanged water permeability and Na2SO4 rejection (Fig. 9a). Under the applied pressures from 1 bar to 16 bar, the TFN-0.2 membrane also shows stable water permeability with almost no change of Na2SO4 rejection (Fig. S3), indicating the membrane has a good pressure resistance and could withstand the applied pressure up to 16 bar. These results demonstrate that the TFN-0.2 membrane have a good stability
of the high desalination performance. As shown in Fig. 9b, a performance summary of the TFN-0.2 membrane and some advanced TFN NF membranes reported in literatures is made in accordance to water permeability and Na2SO4 rejection (see the references in the supporting information). It clearly shows the overall performance of our TFN NF membrane outperforms all of the other reported TFN NF membranes, especially for the ultrahigh water permeability. For the Na2SO4 rejection, our membrane is also very high. Recently, a water permeance and water/NaCl selectivity upper bound of commercial TFC seawater RO, brackish water RO and NF membranes was established by Tang et al.[44] The performance of the TFN-0.2 membrane is close to the upper bound line among the NF membranes (Fig. S4), and much closer to the line than the TFN NF membranes using UIO-66 nanoparticles.[13,45]
4. Conclusion In summary, we fabricated a TFN NF membrane with an ultrathin PA/UIO-66-NH2 active layer of 20 ± 3 nm via an IP process on a PD/SWCNT film. Before the fabrication, ultrasmall UIO-66-NH2 nanoparticles with size of ~15 nm were synthesized as the nanofiller. The nanoparticles were homogeneously dispersed in the aqueous solution to carry out the IP process and were uniformly embedded in the formed active layer. The nanoparticle loading in the ultrathin active layer was also controllable by adjusting the nanoparticle concentration in the aqueous solution. Benefiting from the ultrathin active layer and the high loading of the MOFs nanoparticles with distinct pore structure, the TFN membrane exhibited ultrahigh water permeability up to 46 L m–2 h–1 bar–1 that was 53% increased to the TFC membrane, simultaneously with a high Na2SO4 rejection of 97.1%. This new type of
TFN NF membrane holds a promising potential for large-scale desalination and other water purification applications, as an alternative of traditional NF membranes.
Fig. 9. (a) Separation performance of the TFN-0.2 membrane during a 72-hour test. (b) A performance summary of the TFN-0.2 (marked by the red star) and other reported TFN NF membranes in accordance to water permeability and Na2SO4 rejection.
Acknowledgment This work was supported by the National Natural Science Funds for Distinguished Young Scholar (51625306), the Key Project of National Natural Science Foundation of China (21433012), the Natural Science Foundation of Jiangsu Province (BK20180259), Joint Research Fund for Overseas Chinese, Hong Kong and Macao
Scholars (21728602), and the National Natural Science Foundation of China (51603229). Funding support from the CAS Pioneer Hundred Talents Program is grateful appreciated as well.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at doi:10.1016/j.memsci.2019.xx.xxx.
References [1] J. Aurell, B. K. Gullett, Aerostat sampling of PCDD/PCDF emissions from the Gulf oil spill in situ burns, Environ. Sci. Technol. 44 (2010) 9431-9437. https://doi.org/10.1021/es103554y. [2] M. R. Esfahani, S. A. Aktij, Z. Dabaghian, M. D. Firouzjaei, A. Rahimpour, J. Eke, I. C. Escobar, M. Abolhassani, L. F. Greenlee, A. R. Esfahani, A. Sadmani, N. Koutahzadeh, Nanocomposite membranes for water separation and purification: Fabrication, modification, and applications, Sep. Purif. Technol. 213 (2019) 465-499. https://doi.org/10.1016/j.seppur.2018.12.050. [3] A. W. Mohammad, Y. H. Teow, W. L. Ang, Y. T. Chung, D. L. Oatley-Radcliffe, N. Hilal, Nanofiltration membranes review: Recent advances and future prospects, Desalination 356 (2015) 226-254. https://doi.org/10.1016/j.desal.2014.10.043. [4] J. E. Cadott, R. J. Petersen, R. E. Larson, E. E. Erickson, A new thin-film composite seawater reverse osmosis membrane, Desalination 32 (1980) 25-31. https://doi.org/10.1016/S0011-9164(00)86003-8.
[5] W. J. Lau, A. F. Ismail, N. Misdan, M. A. Kassim, A recent progress in thin film composite
membrane:
A
review,
Desalination
287
(2012)
190-199.
https://doi.org/10.1016/j.desal.2011.04.004. [6] M. F. J. Solomon, Y. Bhole, A. G. Livingston, High flux membranes for organic solvent nanofiltration (OSN)-Interfacial polymerization with solvent activation, J. Membr. Sci. 423-424 (2012) 371-382. https://doi.org/10.1016/j.memsci.2012.08.030. [7] B. H. Jeong, E. M. V. Hoek, Y. Yan, A. Subramani, X. Huang, G. Hurwitz, A. K. Ghosh, A. Jawor, Interfacial polymerization of thin film nanocomposites: A new concept for reverse osmosis membranes, J. Membr. Sci. 294 (2007) 1-7. https://doi.org/10.1016/j.memsci.2007.02.025. [8] S. R. Lakhotia, M. Mukhopadhyay, P. Kumari, Iron oxide (FeO) nanoparticles embedded thin-film nanocomposite nanofiltration (NF) membrane for water treatment, Sep. Purif. Technol. 211 (2019) 98-107. https://doi.org/10.1016/j.seppur.2018.09.034. [9] J. N. Shen, C. C. Yu, H. M. Ruan, C. J. Gao, B. V. D. Bruggen, Preparation and characterization of thin-film nanocomposite membranes embedded with poly(methyl methacrylate) hydrophobic modified multiwalled carbon nanotubes by interfacial polymerization,
J.
Membr.
Sci.
442
(2013)
18-26.
https://doi.org/10.1016/j.memsci.2013.04.018. [10] G. S. Lai, W. J. Lau, P. S. Goh, A. F. Ismail, N. Yusof, Y. H. Tan, Graphene oxide incorporated thin film nanocomposite nanofiltration membrane for enhanced salt
removal
performance,
Desalination
387
(2016)
14-24.
https://doi.org/10.1016/j.desal.2016.03.007. [11] C. Zhang, X. Si, S. Zhang, B. Pei, J. Gu, Y. Bai, Porous metal–organic molecular cage: a promising candidate to highly improve the nanofiltration performance of thin
film
nanocomposite
membranes,
New
J.
Chem.
43
(2019)
1699-1709.
https://pubs.rsc.org/en/content/articlehtml/2018/nj/c8nj04603d. [12] C. Wang, Z. Li, J. Chen, Z. Li, Y. Yin, L. Cao, Y. Zhong, H. Wu, Covalent organic framework modified polyamide nanofiltration membrane with enhanced performance
for
desalination,
J.
Membr.
Sci.
523
(2017)
273-281.
https://doi.org/10.1016/j.memsci.2016.09.055. [13] Y. He, Y. P. Tang, D. Ma, T.-S. Chung, UiO-66 incorporated thin-film nanocomposite membranes for efficient selenium and arsenic removal, J. Membr. Sci. 541 (2017) 262-270. https://doi.org/10.1016/j.memsci.2017.06.061. [14] M. Kadhom, B. Deng, Metal-organic frameworks (MOFs) in water filtration membranes for desalination and other applications, Appl. Mater. Today 11 (2018) 219-230. https://doi.org/10.1016/j.apmt.2018.02.008. [15] Y. Zhao, Y. Liu, X. Wang, X. Huang, Y. F. Xie, Impacts of metal-organic frameworks on structure and performance of polyamide thin-film nanocomposite membranes,
ACS
Appl.
Mater.
Interfaces
11
(2019)
13724-13734.
https://doi.org/10.1021/acsami.9b01923. [16] Y. Xu, X. Gao, Q. Wang, X Wang, Z. Ji, C. Gao, Highly stable MIL-101(Cr) doped water permeable thin film nanocomposite membranes for water treatment, RSC Adv. 6 (2016) 82669-82675. https://doi.org/10.1039/C6RA16896E. [17] C. Echaide-Górriz, S. Sorribas, C. Télleza, J. Coronas, MOF nanoparticles of MIL-68(Al), MIL-101(Cr) and ZIF-11 for thin film nanocomposite organic solvent nanofiltration
membranes,
RSC
Adv.
6
(2016)
90417-90426.
https://doi.org/10.1039/C6RA17522H. [18] H. Liu, J. Gao, G. Liu, M. Zhang, Y. Jiang, Enhancing permeability of thin film nanocomposite (TFN) membranes via covalent linking of polyamide with the
incorporated metal-organic frameworks, Ind. Eng. Chem. Res. 58 (2019) 8772-8783. https://doi.org/10.1021/acs.iecr.9b00772. [19] J. Wang, Y. Wang, Y. Zhang, A. Uliana, J. Zhu, J. Liu, B. V. d. Bruggen, Zeolitic Imidazolate framework/graphene oxide hybrid nanosheets functionalized thin film nanocomposite membrane for enhanced antimicrobial performance, ACS Appl. Mater. Interfaces 8 (2016) 25508-25519. https://doi.org/10.1021/acsami.6b06992. [20] S. Sorribas, P. Gorgojo, C. Tellez, J, Coronas, A. G. Livingston, High flux thin film nanocomposite membranes based on metal-organic frameworks for organic solvent
nanofiltration,
J.
Am.
Chem.
Soc.
135
(2013)
15201-15208.
https://doi.org/10.1021/ja407665w. [21] R. J. Petersen, Composite reverse osmosis and nanofiltration membrane, J. Membr. Sci. 83 (1993) 81-150. https://doi.org/10.1016/0376-7388(93)80014-O. [22] M. Elimelech, W. A. Phillip, The future of seawater desalination: energy, technology,
and
the
environment,
Science
333
(2011)
712-717.
https://science.sciencemag.org/content/333/6043/712.abstract. [23] A. K. Pabby, S. S. Rizvi, A. M. Sastre, Handbook of membrane separations: chemical, pharmaceutical, food, and biotechnological applications, CRC press, Boca Raton, USA, 2009. [24] S. Karan, Z. Jiang, A. G. Livingston, Sub-10 nm polyamide nanofilms with ultrafast solvent transport for molecular separation, Science 348 (2015) 1347-1351. https://science.sciencemag.org/content/348/6241/1347. [25] J.-J. Wang, H.-C. Yang, M.-B. Wu, X. Zhang, Z.-K. Xu, Nanofiltration membranes with cellulose nanocrystals as an interlayer for unprecedented performance,
J.
Mater.
Chem.
https://doi.org/10.1039/C7TA00501F.
A
5
(2017)
16289-16295.
[26] M.-B. Wu, Y. Lv, H. C. Yang, L. F. Liu, X. Zhang, Z. K. Xu, Thin film composite membranes combining carbon nanotube intermediate layer and microfiltration support for high nanofiltration performances, J. Membr. Sci. 515 (2016) 238-244. https://doi.org/10.1016/j.memsci.2016.05.056. [27] Y. Zhu, W. Xie, S. Gao, F. Zhang, W. Zhang, Z. Liu, J. Jin, Single-walled carbon nanotube film supported nanofiltration membrane with a nearly 10 nm thick polyamide active layer for high-flux and high-rejection desalination, Small 12 (2016) 5034-5041. https://doi.org/10.1002/smll.201601253. [28] Z. Wang, Z. Wang, S. Lin, H. Jin, S. Gao, Y. Zhu, J. Jin, Nanoparticle-templated nanofiltration membranes for ultrahigh performance desalination, Nat. Commun. 9 (2018) 2004. https://doi.org/10.1038/s41467-018-04467-3. [29] S. Gao, Y. Zhu, Y. Gong, Z. Wang, W. Fang, J. Jin, Ultrathin polyamide nanofiltration membrane fabricated on brush-painted single-walled carbon nanotube network
support
for
ion
sieving,
ACS
Nano
13
(2019)
5278-5290.
https://doi.org/10.1021/acsnano.8b09761. [30] Z. Zhou, Y. Hu, C. Boo, Z. Liu, J. Li, L. Deng, X. An, High-performance thinfilm composite membrane with an ultrathin spray-coated carbon nanotube interlayer, Environ.
Sci.
Technol.
Lett.
5
(2018)
243-248.
https://doi.org/10.1021/acs.estlett.8b00169. [31] Z. Yang, Z. Zhou, H. Guo, Z. Yao, X. Ma, X. Song, S.-P. Feng, C. Y. Tang, Tannic acid/Fe3+ nanoscaffold for interfacial polymerization: toward enhanced nanofiltration
performance,
Environ.
Sci.
Technol.
52
(2018)
9341-9349.
https://doi.org/10.1021/acs.est.8b02425. [32] T. Y. Liu, H. G. Yuan, Y. Y. Liu, D. Ren, Y. C. Su, X. Wang, Metal-organic framework nanocomposite thin films with interfacial bindings and self-standing
robustness for high water flux and enhanced ion selectivity, ACS Nano 12 (2018) 9253-9265. https://doi.org/10.1021/acsnano.8b03994. [33] D. Ma, S. B. Peh, G. Han, S. B. Chen, Thin-film nanocomposite (TFN) membranes incorporated with super-hydrophilic metal-organic framework (MOF) UiO-66: toward enhancement of water flux and salt rejection, ACS Appl. Mater. Interfaces 9 (2017) 7523-7534. https://doi.org/10.1021/acsami.6b14223. [34] C. V. Goethem, R. Verbeke, S. Hermans, R. Bernsteinb, I. F. J. Vankelecom, Controlled
positioning
nanocomposites,
J.
of
MOFs
Mater.
in
Chem.
interfacially A
4
polymerized (2016)
thin-film
16368-16376.
https://doi.org/10.1039/C6TA05175H. [35] S. Basu, M. Balakrishnan, Polyamide thin film composite membranes containing ZIF-8 for the separation of pharmaceutical compounds from aqueous streams, Sep. Purif. Technol. 179 (2017) 118-125. https://doi.org/10.1016/j.seppur.2017.01.061. [36] S. J. Gao, Y. Z. Zhu, F. Zhang, J. Jin, Superwetting polymer-decorated SWCNT composite ultrathin films for ultrafast separation of oil-in-water nanoemulsions, J. Mater. Chem. A 3 (2015) 2895-2902. https://doi.org/10.1039/C4TA05624H. [37] A. Schaate, P. Roy, A. Godt. J. Lippke, F. Waltz, M. Wiebcke, P. Behrens, Modulated synthesis of Zr-based metal-organic frameworks: from nano to single crystals,
Chem.
Eur.
J.
17
(2011)
6643-6651.
https://doi.org/10.1002/chem.201003211. [38] X. Lan, N. Huang, J. Wang, T, Wang, A general and facile strategy for precisely controlling the crystal size of monodispersed metal-organic frameworks via separating the nucleation and growth, Chem. Commun 54 (2018) 584-587. https://10.1039/C7CC08244D.
[39] M. Golpour, M. Pakizeh, Preparation and characterization of new PAMOF/PPSU-GO membrane for the separation of KHI from water, Chem. Eng. J. 345 (2018) 221-232. https://doi.org/10.1016/j.cej.2018.03.154. [40] C. Y. Tang, Y. N. Kwon, J. O. Leckie, Effect of membrane chemistry and coating layer on physiochemical properties of thin film composite polyamide RO and NF membranes: I. FTIR and XPS characterization of polyamide and coating layer chemistry,
Desalination
242
(2009)
149-167.
https://doi.org/10.1016/j.desal.2008.04.003. [41] J. Lin, W. Ye, M.-C. Baltaru, Y. P. Tang, N. J. Bernstein, P. Gao, S. Balta, M. Vlad, A. Volodin, A. Sotto, P. Luisi, A. L. Zydney, B. V. D. Bruggen, Tight ultrafiltration membranes for enhanced separation of dyes and Na2SO4 during textile wastewater
treatment,
J.
Membr.
Sci.
514
(2016)
217-228.
https://doi.org/10.1016/j.memsci.2016.04.057. [42] K.-L. Tung, K.-S. Chang, T.-T. Wu, N.-J. Lin, K.-R. Lee, J.-Y. Lai, Recent advances in the characterization of membrane morphology, Curr. Opin. Chem. Eng. 4 (2014) 121-127. https://doi.org/10.1016/j.coche.2014.03.002. [43] Y.-C. Chiang, Y.-Z. Hsub, R.-C. Ruaan, C.-J. Chuang, K.-L. Tung, Nanofiltration membranes synthesized from hyperbranched polyethyleneimine, J. Membrane Sci. 326 (2009) 19-26. https://doi.org/10.1016/j.memsci.2008.09.021. [44] Z. Yang, H. Guo, C. Y. Tang, The upper bound of thin-film composite (TFC) polyamide membranes for desalination, J. Membrane Sci. 590 (2019) 117297. https://doi.org/10.1016/j.memsci.2019.117297. [45] F. Xiao, X. Hu, Y. Chen, Y. Zhang, Porous Zr-based metal-organic frameworks (Zr-MOFs)-incorporated thin-film nanocomposite membrane toward enhanced
desalination performance, ACS Appl. Mater. Interfaces 11 (2019) 47390. https://doi.org/10.1021/acsami.9b17212.
Graphical abstract:
Highlights:
A novel TFN NF membrane with an ultrathin PA/UIO-66-NH2 active layer as thin as 20 ± 3 nm was fabricated.
The nanoparticles are uniformly embedded in the ultrathin active layer, and the nanoparticle loading is highly controllable.
The membrane exhibits ultrahigh water permeability up to 46 L m–2 h–1 bar–1 along with a high Na2SO4 rejection of 97.1%.
The membrane owns the thinnest active layer and outperforms all of the other membranes in the category of reported TFN NF membranes.
Declarations of interest: none
Supporting Information for
Thin-film Nanocomposite Nanofiltration Membrane with an Ultrathin Polyamide/UIO-66-NH2 Active layer for HighPerformance Desalination Yuqiong Gong†, Shoujian Gao†, Yangyang Tian, Yuzhang Zhu, Wangxi Fang, Zhenggong Wang, Jian Jin*
Fig. S1. Zeta potential of UIO-66-NH2 nanoparticles (0.2 mg mL-1) in water. The zeta potential of the nanoparticles is 36.5 mV, indicating the nanoparticles are positively charged.
Fig. S2. A free-standing PA/UIO-66-NH2 thin film fabricated on the interface of a PIP water solution (1.25 mg mL-1) with homogenously dispersed UIO-66-NH2 nanoparticles (0.2 mg mL-1) and a TMC n-hexane solution (1 mg mL-1). (a) A schematic showing the fabrication process. (b) An optical photograph and (c) a topview TEM image of the thin film. As shown in Fig. S2c, the UIO-66-NH2 nanoparticles are successfully and uniformly embedded in the thin film.
Fig. S3. Water permeability and Na2SO4 rejection of the TFN-0.2 membrane under different applied pressures from 1 bar to 18 bar. (Na2SO4 concentration: 1000 ppm).
Fig. S4 Water permeance and water/NaCl selectivity of commercial seawater reverse osmosis (SWRO), brackish water reverse osmosis (BWRO) and NF membranes in the water permeance and selectivity diagram. Reproduced from J. Membrane Sci. 2019, 590, 117297. Copyright 2019 Royal Society of Chemistry. The red star in Fig. S4 represents our TFN-0.2 membrane. The black stars represent the TFN NF membranes using UIO-66 nanoparticles (J. Membr. Sci. 2017, 541, 262; ACS Appl. Mater. Interfaces 2019, 11, 47390). It clearly shows the performance of our TFN NF membrane is close to the upper bound line among the NF membranes, and much closer to the line than the TFN NF membranes using UIO-66 nanoparticles, especially for the higher water permeance.
References in Fig. 9b [1] X. Wei, X. Xu, J. Wu, C. Li, J. Chen, B. Lv, B. Zhu, H. Xiang, SiO2-modified nanocomposite nanofiltration membranes with high flux and acid resistance, J. Appl. Polym. Sci. 47436 (2019) 1-11. [2] M. B. M. Y. Ang, J. M. Pereira, C. A. Trilles, R. R. Aquino, S.-H. Huang, K.-R. Lee, J.-Y. Lai, Performance and antifouling behavior of thin-film nanocomposite
nanofiltration membranes with embedded silica spheres, Sep. Purif. Technol. 210 (2019) 521-529. [3] W. Zhao, H. Liu, N. Meng, M. Jian, H. Wang, X. Zhang, Graphene oxide incorporated thin film nanocomposite membrane at low concentration monomers, J. Membr. Sci. 565 (2018) 380-389. [4] S. Abdikheibari, W. Lei, L. F. Dumèe, N. Milne, K. Baskaran, Thin film nanocomposite
nanofiltration
membranes
from
amine
functionalized-boron
nitride/polypiperazine amide with enhanced flux and fouling resistance, J. Mater. Chem. A 6 (2018) 12066-12081. [5] J. Zheng, M. Li, K. Yu, J. Hu, X. Zhang, L. Wang, Sulfonated multiwall carbon nanotubes assisted thin-film nanocomposite membrane with enhanced water flux and anti-fouling property, J. Membr. Sci. 524 (2017) 344-353. [6] J. Wang, Y. Wang, Y. Zhang, A. Uliana, J. Zhu, J. Liu, B. V. d. Bruggen, Zeolitic imidazolate framework/graphene oxide hybrid nanosheets functionalized thin film nanocomposite membrane for enhanced antimicrobial performance, ACS Appl. Mater. Interfaces 8 (2016) 25508-25519. [7] G. S. Lai, W. J. Lau, P. S. Goh, A. F. Ismail, N. Yusof, Y. H. Tan, Graphene oxide incorporated thin film nanocomposite nanofiltration membrane for enhanced salt removal performance, Desalination 387 (2016) 14-24. [8] Q. Xie, S. Zhang, Z. Hong, H. Ma, B. Zeng, X. Gong, W. Shao, Q. Wang, A novel double-modified strategy to enhance the performance of thin-film nanocomposite nanofiltration membranes: Incorporating functionalized graphenes into supporting and selective layers, Chem. Eng. J. 368 (2019) 186-201.
[9] S. M. Xue, Z.-L. Xu, Y.-J. Tang, C.-H. Ji, Polypiperazine-amide Nanofiltration membrane modified by different functionalized multiwalled carbon nanotubes (MWCNTs), ACS Appl. Mater. Interfaces 8 (2016) 19135-19144. [10] J. Wang, Y. Wang, J. Zhu, Y. Zhang, J. Liu, B. V. d. Bruggen, Construction of TiO2@graphene oxide incorporated antifouling nanofiltration membrane with elevated filtration performance, J. Membr. Sci. 533 (2017) 279-288. [11] Q. Xie, W. Shao, S. Zhang, Z. Hong, Q. Wang, B Zeng, Enhancing the performance of thin-film nanocomposite nanofiltration membranes using MAHmodified GO nanosheets, RSC Adv. 7 (2017) 54898-54910. [12] D. Hu, Z.-L. Xu, C. Chen, Polypiperazine-amide nanofiltration membrane containing silica nanoparticles prepared by interfacial polymerization, Desalination 301 (2012) 75-81. [13] Z. Liao, X. Fang, J. Xie, Q. Li, D. Wang, X. Sun, L. Wang, J. Li, Hydrophilic hollow nanocube-functionalized thin film nanocomposite membrane with enhanced nanofiltration performance, ACS Appl. Mater. Interfaces, 11 (2019) 5344-5352. [14] Q. Xie, S. Zhang, H. Ma, W. Shao, X. Gong, Z. Hong, A novel thin-film nanocomposite nanofiltration membrane by incorporating 3D hyperbranched polymer functionalized 2D graphene oxide, Polymers 10 (2018) 1253. [15] G. S. Lai, W. J. Lau, P. S. Goh, A. F. Ismail, Y. H. Tan, C. Y. Chong, R. KrauseRehberg, S. Awad, Tailor-made thin film nanocomposite membrane incorporated with graphene oxide using novel interfacial polymerization technique for enhanced water separation, Chem. Eng. J. 344 (2018) 524-534. [16] J. Yin, G. Zhu, B. Deng, Graphene oxide (GO) enhanced polyamide (PA) thinfilm nanocomposite (TFN) membrane for water purification, Desalination 379 (2016) 93-101.
[17] T.-Y. Liu, Z.-H. Liu, R.-X. Zhang, Y. Wang, B. V. d. Bruggen, X.-L Wang, Fabrication of a thin film nanocomposite hollow fiber nanofiltration membrane for wastewater treatment, J. Membr. Sci. 488 (2015) 92-102.
Highlights:
A TFN NF membrane with an ultrathin PA/UIO-66-NH2 active layer of 20 ± 3 nm was fabricated.
The nanoparticles are uniformly embedded in the ultrathin active layer.
The membrane exhibits a high water permeability up to 46 L m–2 h–1 bar–1 along with a high Na2SO4 rejection of 97.1%.
The membrane performance outperforms all of the other TFN NF membranes reported previously.
A list of changes to the manuscript: 1. The word “though” has been changed to “into” in the revised manuscript (page 12, line 1, line 2). 2. The sentence “and much closer to the line than the TFN NF membranes using UIO-66 nanoparticles.[13,45]” has been added in the revised manuscript (page 19, line 10-12). 3. The Figure S4 in the revised supporting information has been changed. 4. The references 44-58 (the references in Fig. 9b) in the original manuscript have been removed from the revised manuscript and have been shown in the revised supporting information. The reference 45 has been added in the revised manuscript.
Declaration of interests ☒ 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 paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
S0376-7388(19)33104-7
DOI:
https://doi.org/10.1016/j.memsci.2020.117874
Reference:
MEMSCI 117874
To appear in:
Journal of Membrane Science
Received Date: 7 October 2019 Revised Date:
18 January 2020
Accepted Date: 22 January 2020
Please cite this article as: Y. Gong, S. Gao, Y. Tian, Y. Zhu, W. Fang, Z. Wang, J. Jin, Thin-film nanocomposite nanofiltration membrane with an ultrathin polyamide/UIO-66-NH2 active layer for high-performance desalination, Journal of Membrane Science (2020), doi: https://doi.org/10.1016/ j.memsci.2020.117874. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
Thin-film Nanocomposite Nanofiltration Membrane with an Ultrathin Polyamide/UIO-66-NH2 Active layer for High-Performance Desalination Yuqiong Gonga,†, Shoujian Gaob,c,†, Yangyang Tianb,c, Yuzhang Zhub,c, Wangxi Fangb,c, Zhenggong Wanga, Jian Jina,b,c,* a
College of Chemistry, Chemical Engineering and Materials Science, Soochow
University, Suzhou, 215123, China. b
i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of
Sciences, Suzhou, 215123, China. c
School of Nano Technology and Nano Bionics, University of Science and Technology
of China, Hefei, 230026, China. †
These authors contributed equally to this work.
* Corresponding author. E-mail address: [email protected] (J. Jin).
Abstract In this work, ultrasmall metal-organic frameworks (MOFs) nanoparticles, UIO-66NH2 nanoparticles were synthesized and embedded in an ultrathin polyamide (PA) active layer via the interfacial polymerization reaction on a polydopamine-wrapped single-walled carbon nanotube film. A thin-film nanocomposite nanofiltration (TFN NF) membrane with a PA/UIO-66-NH2 active layer as thin as 20 ± 3 nm was thus fabricated. The loading mass of the nanoparticles in the TFN NF membrane could be tuned by controlling the nanoparticles concentration in aqueous phase. Benefiting from the ultrathin thickness of active layer and the high loading mass of the MOFs nanoparticles, water permeability up to 46 L m–2 h–1 bar–1 along with a Na2SO4 rejection of 97.1% was achieved, which is 53% increase of the TFC NF membrane without the addition of UIO-66-NH2 nanoparticles. Our membrane owns the thinnest
active layer in the category of TFN NF membranes reported so far and exhibits outstanding desalination performance. Keywords: Thin film nanocomposite membrane, ultrathin active layer, nanofiltration membrane, UIO-66-NH2 nanoparticles, carbon nanotube film.
1. Introduction Nanofiltration (NF) membranes have been widely used for efficient seawater and brackish water desalination, as well as other water purification applications due to their low energy cost, high throughput, high rejection to multivalent salts and some organic molecules [1-3]. To date, the state-of-the-art NF membranes are based on a thin film composite (TFC) structure that contains a porous support layer and a thin polyamide (PA) active layer formed by the interfacial polymerization (IP) reaction of amine and acyl chloride monomers [4-6]. To further improve the permeability and selectivity of TFC membranes, various nanomaterials, such as inorganic nanoparticles, carbon nanotubes, graphene oxide nanosheets, porous metal-organic molecular cages, covalent organic frameworks, and metal-organic frameworks (MOFs), etc. were introduced into the PA layer so as to increase either the water transfer channels, the membrane hydrophilicity, or the membrane surface charge. These gave rise to the rapid development of the so-called thin-film nanocomposite (TFN) membranes [7-14]. As the pioneer of TFN membranes, Hoek et al. first reported the introduction of NaA zeolite nanoparticles in the PA layer and the water permeability of the TFN membrane was greatly improved with less decrease of salt rejection [7]. As a novel porous material, MOFs possess high porosity, uniform pore size and controlled geometry structure. They could be good candidates for fabricating TFN membranes [14]. Up to date, TFN membranes containing various MOFs nanoparticles such as ZIF,
MIL and UIO series have been continuously reported and exhibited either increased water permeability or enhanced rejection [13-20]. Although TFN NF membranes have shown improved desalination performance, they still face the challenge of trade-off between permeability and selectivity [21,22]. In general, the active layer of a TFN NF membrane should be as thin as possible in order to achieve a better performance [23]. As for TFC NF membranes, it might be easy to form an ultrathin PA active layer with thickness of a dozen nanometers via IP process by either controlling the reaction process or choosing specific composite support membranes [24-31]. However, it is difficult to realize on the case of TFN NF membranes. As for TFN NF membranes, the size matching between the nanoparticles and the thickness of PA layer is important to ensure the complete and integrity of the whole membrane [32-35]. In addition, the uniform incorporation of nanoparticles in the ultrathin PA layer without generation of extra defects is still a tough work. In this work, we report the fabrication of a TFN NF membrane with an ultrathin PA/UIO-66-NH2 active layer via the IP reaction on a polydopamine-wrapped singlewalled carbon nanotube (PD/SWCNT) film. To achieve the complete and uniform embedding of nanoparticles in the ultrathin PA layer, ultrasmall UIO-66-NH2 nanoparticles with a size of ~15 nm were synthesized. The nanoparticles with hydrophilic amine ligands could be homogeneously dispersed in the PIP solution. By altering the UIO-66-NH2 concentration in the PIP solution, the loading mass of the nanoparticles in the PA active layer could be tuned. The TFN NF membrane with a PA/UIO-66-NH2 composite active layer as thin as 20 ± 3 nm exhibited largely increased water permeability meanwhile a high rejection for Na2SO4. To the best of our knowledge, our membrane owns the thinnest active layer among TFN NF
membranes reported so far and the membrane performance outperforms all of the other reported TFN NF membranes. 2. Experimental 2.1. Materials The SWCNT powder (OD: 1-2 nm, length: 5-30 µm, purity: > 95%) used herein was commercially available from Nanjing XFNANO Materials Tech Co., Ltd (Nanjing, China). The polyether sulfone microfiltration (PES MF) membrane with an efficient pore size of 0.45 µm was purchased from Yibo Co., Ltd. (Haining, China). Zirconium chloride
(ZrCl4),
2-Aminoterephthalic
acid,
dopamine
hydrochloride
and
Tris(hydroxymethyl)aminomethane were analytical grade and purchased from AlfaAesar. Anhydrous piperazine (PIP) and trimesoyl chloride (TMC) with purity of 99% were purchased from Aladdin Co., Ltd. (Shanghai, China). All the other chemical reagents were analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). Deionized water was used throughout the experiments. 2.2. Synthesis of UIO-66-NH2 nanoparticles The UIO-66-NH2 nanoparticles were synthesized by dissolving 650 mg ZrCl4, 480 mg 2-aminoterephthalic acid and 7.56 g water in 160 mL N,N-dimethylformamide (DMF). Then the DMF solution was sonicated using a Fisher Scientific ultrasonic cell crusher for 2 min to produce a homogeneous solution. Afterwards, the solution was heated at 120 ºC for 24 h. After centrifugation at 10000 rpm for 30 min, the sediments were collected and washed by methanol for 5 times firstly, then washed by water for 8 times. Finally, the UIO-66-NH2 nanoparticles were obtained. 2.3. Preparation of PD/SWCNT film To fabricate PD/SWCNT film, the PD/SWCNT dispersion was firstly prepared according to our previous report [36]. The SWCNT dispersion was fabricated by
adding 40 mg SWCNT powder into 400 mL sodium dodecyl benzene sulfonate (SDBS) water solution with a concentration of 1 g L-1 and sonicating the solution under 10 W for 2 h. The dispersion was then centrifuged at 10000 rpm for 30 min and the supernatant dispersion was collected. Then 150 mL supernatant dispersion was diluted to 450 mL with water, the SDBS in the dispersion was replenished to 1mg mL1
. Dopamine hydrochloride was added into the dispersion with a concentration of 0.1
mg mL-1 and stirred at 40 ºC for 1 h. Then 45 ml 0.1 mol L-1 Tris buffer solution (pH 8.5) was added into the dispersion and further stirred at 40 °C for 23 h. Finally, the dispersion was centrifuged at 10000 rpm for 30 min to collect the supernatant dispersion. The PD/SWCNT film was prepared by filtering 1.5 mL PD/SWCNT dispersion onto a PES MF membrane to form a thin film with an effective area of 11.34 cm2 and dried at 60 °C for 10 min. 2.4. Fabrication of TFC and TFN membranes The TFC and TFN membranes were fabricated via a typical IP reaction of PIP and TMC on the PD/SWCNT/PES MF composite support membrane [27-30]. In this work, the IP process was carried out at a temperature of 25 ℃ and a relative humidity of 60%. To fabricate the TFC membrane, the PD/SWCNT/PES MF composite support membrane was trapped on a clean glass plate where a few drops of PIP water solution (1.25 mg mL-1) were preloaded. Then the PIP solution was dripped to cover the PD/SWCNT film surface for 30 s. The redundant PIP solution was removed until no solution was obviously observed on the film surface. Then the TMC n-hexane solution (1 mg mL-1) was poured on the film surface for 30 s. After removing the redundant TMC solution, the film was immediately immersed in n-hexane for 1 min and then dried at 60 ℃ for 30 min to obtain TFC membrane. To fabricate the TFN membrane, the as-synthesized UIO-66-NH2 nanoparticles was added in the PIP water
solution and sonicated under 10 W for 1 h to form a transparent dispersion with a certain UIO-66-NH2 concentration. Then the IP process was implemented as the same as in the case of TFC membrane preparation process. 2.5. Membrane performance test The desalination performance of the NF membranes was tested on a cross-flow NF apparatus with an efficient test area of 7.06 cm2 at 25 ºC. The salt (Na2SO4, MgSO4, MgCl2, CaCl2, NaCl) concentration was 1000 ppm. The hydraulic transmembrane pressure was 6 bar. Water permeability J (L m–2 h–1 bar–1) was calculated by the following equation (1): J = ∆m/A∆tP
(1)
where ∆m (kg) was the mass increment of the filtrate water during the separation time of ∆t (h), was the density of filtrate water (1 kg L-1), A (m2) was the test area, P (bar) was the hydraulic transmembrane pressure. Salt rejection R (%) was calculated by the following equation (2): R = (1 - Cp/Cf ) × 100%
(2)
where Cp and Cf were the conductivity of filtrate water and feed solution. 2.6. Characterization The transmission electron microscopy (TEM) images were measured on a Tecnai G2 F20 S-Twin field-emission transmission electron microscope. The scanning electron microscopy (SEM) and mapping images were tested on a Quanta FEG 250 scanning electron microscope. The atomic force microscopy (AFM) images were measured on a Bruker Dimension Icon atomic force microscope. Before measuring the TEM and AFM images of the TFC and TFN membranes, the underlying PES membrane was completely dissolved by DMF. To capture the cross-sectional TEM image, the membrane was embedded in epoxy resin and vertically cut into thin sheets. The X-ray
diffraction (XRD) pattern was tested by a Bruker AXS D8 Advance powder X-Ray diffractomer. The dynamic light scattering (DLS) and zeta potential of nanoparticles were measured on a Malvern ZEN3600 Zetasizer Nano series. The surface zeta potential of membranes was measured on an Anton Paar Surpass solid surface analysis. The solution conductivity was measured by a METTLER TOLEDO FE30K conductivity meter. The polyethylene glycol (PEG) concentration was measured by an O.I. Analytical Aurora Model 1030w total organic carbon (TOC) analyzer. 3. Results and discussion 3.1. Synthesis and characterization of UIO-66-NH2 nanoparticles UIO-66-NH2 nanoparticles are chosen in this work for fabricating the TFN membrane because of its good water-stability and controllable particle size. The UIO-66-NH2 nanoparticles were synthesized via the solvothermal reaction of ZrCl4 and 2aminoterephthalic acid with a certain amount of water to tune the nanoparticle size. The addition of water can increase the aggregation rate and thus increase the nucleation rate of UIO-66-NH2, eventually give rise to the formation of extremely small UIO-66-NH2 nanoparticles [37,38]. The TEM image shows the morphology of the synthesized nanoparticles (Fig. 1a). The diameter of the nanoparticles is mainly in the range of 15 ± 5 nm. The XRD pattern reveals the crystalline structure of the nanoparticles (Fig. 1b). Because the nanoparticles are very small, the XRD pattern displays broad reflections. The characteristic peaks at 2θ = 7.4°, 8.4° and 25.9° are attributed to the (111), (002) and (006) planes of the UIO-66-NH2 crystal, in keeping with the previous reports [39]. As for the fabrication of TFN membrane, the quality of nanoparticles dispersity is a key parameter to determine the uniformity of loaded nanoparticles in the resulting PA active layer. To investigate the dispersity of UIO-66NH2 nanoparticles, their size distribution in pure water and in a PIP water solution
(0.2 mg mL-1) was tested using DLS measurement. The UIO-66-NH2 nanoparticles in pure water give a size distribution in the range of 12-18 nm (Fig. 1c) and the nanoparticles in the PIP solution give a similar size distribution in the range of 14-19 nm (Fig. 1d). These results are in accordance with the TEM image, indicating the good dispersity of the nanoparticles both in pure water and in the PIP solution. Fig. 1e is an optical photograph showing the PIP solution containing the nanoparticles. The solution was clearly transparent. When a laser beam is irradiated through the solution, an obvious Tyndall effect appears, demonstrating the nanoparticles are extremely small and homogeneously dispersed in the solution. The good dispersity of UIO-66NH2 nanoparticles in aqueous solution is owing to the abundant hydrophilic amine groups in the nanoparticles. The UIO-66-NH2 nanoparticles are positively charged with zeta potential of 36.5 mV (Fig. S1).
Fig. 1. (a) TEM image and (b) XRD pattern of the UIO-66-NH2 nanoparticles. Size distribution of the nanoparticles (0.2 mg mL-1) in (c) pure water and (d) a PIP water
solution (1.25 mg mL-1). (e) A digital photograph of the transparent PIP solution containing the nanoparticles. When a laser beam is irradiated though the solution, a Tyndall effect appears. 3.2. Morphology and structure characterization of TFN membranes The TFN membrane was fabricated via a typical IP process on a PD/SWCNT/PES composite support. The low concentration of PIP water solution (1.25 mg mL-1) with homogeneously dispersed UIO-66-NH2 nanoparticles (0.2 mg mL-1) and TMC nhexane solution (1 mg mL-1) were used in order to form a thin PA layer. A TFC membrane without the addition of UIO-66-NH2 nanoparticles was also fabricated under the same condition as a control experiment. The surface morphologies of the PD/SWCNT film and the PA NF membranes fabricated on the PD/SWCNT film are revealed by the SEM and AFM images as shown in Fig. 2. The PD/SWCNTs are randomly deposited on the underlying PES MF membrane and interlaced to each other to form a network film with pores of dozens of nanometers (Fig. 2a and 2d). After the IP process, a dense active layer was formed on the PD/SWCNT film for both the TFC membrane (Fig. 2b and 2e) and the TFN membrane (Fig. 2c and 2f). The outlines of PD/SWCNT and UIO-66-NH2 nanoparticles are still visible, indicating the formed active layers are extremely thin. The EDX imaging shows a uniform distribution of Zr element in the TFN membrane (the inset in Fig. 2c), demonstrating the uniform distribution of the UIO-66-NH2 nanoparticles in the active layer. The surface roughness of the PD/SWCNT film was 14.2 nm as measured by the AFM (Fig. 2d). After forming PA layer, the surface roughness decreases to 11.6 nm for the TFC membrane (Fig. 2e). With the nanoparticles embedded in the PA layer, the surface roughness of the TFN membrane increases slightly to 13.4 nm.
Fig. 2. Top-view SEM and AFM images of (a, d) the PD/SWCNT film, (b, e) the PA active layer fabricated on the film, (c, f) the PA/UIO-66-NH2 active layer fabricated on the film. The inserts in b and c are the EDX imaging of Zr element distribution.
Fig. 3 shows the cross-sectional (Fig. 3b) and top-view (Fig. 3c) TEM images of the TFN membrane with the underlying PES MF membrane removed. As shown in Fig. 3b, the PA/UIO-66-NH2 active layer tightly attaches on the PD/SWCNT film to form a bilayer structure. The thickness of the active layer is 20 ± 3 nm, and the thickness of the PD/SWCNT film is 46 ± 5 nm. It can be observed that the UIO-66NH2 nanoparticles are exactly embedded in the ultrathin active layer. To further confirm the embedding of the UIO-66-NH2 nanoparticles in the active layer rather than between the active layer and the PD/SWCNT film, a free-standing PA/UIO-66NH2 film was fabricated at the interface of a PIP/UIO-66-NH2 nanoparticle water solution and a TMC n-hexane solution (Fig. S2). The TEM image clearly shows the uniform embedding of the nanoparticles in the obtained free-standing film. It demonstrates that the UIO-66-NH2 nanoparticles could be successfully embedded within the PA/UIO-66-NH2 active layer fabricated by dispersing the nanoparticles in
the aqueous solution during the IP process. From both the cross-sectional and the topview TEM images, we can’t observe any obvious interfacial defects between the UIO66-NH2 nanoparticles and PA, indicating a good integrity of the active layer.
Fig. 3. (a) A schematic showing the structure of the TFN membrane. (b) Cross-section and (c) top-view TEM images of the PA/UIO-66-NH2 active layer on the PD/SWCNT film.
The dynamic spreading and permeating behaviors of a water droplet (3 μL) on the TFN and TFC membranes were also captured as shown in Fig. 4. The transient water CA of the TFN membrane was 50° which is very similar to that of the TFC membrane (52°), indicating the surface chemical composition of the two membranes is almost the same. This result further demonstrates the UIO-66-NH2 nanoparticles are completely embedded in the UIO-66-NH2/PA active layer and no nanoparticles are exposed outsides PA. As the nanoparticles has a size (~15 nm) very closed to the thickness of the active layer (~20 nm), it further confirms the exact embedding of the nanoparticles and the good integrity of the active layer. It takes 64 s for the water
droplet to permeate into the TFC membrane (Fig. 4b), while it only takes 44 s in the case of the TFN membrane (Fig. 4a). The permeating speed of the water droplet into the TFN membrane is about 1.5 times of that in the case of the TFC membrane, indicating the superior water permeation ability of the TFN membrane.
Fig. 4. Optical images showing the dynamic spreading and permeating behaviors of a water droplet on the (a) TFN membrane and (b) TFC membrane.
3.3. Variation of nanoparticles loading in the PA active layer The variation of UIO-66-NH2 nanoparticles loading in the active layer as a function of the UIO-66-NH2 concentration in the PIP solution was investigated. A series of TFN membranes were fabricated with the UIO-66-NH2 concentration of 0.05, 0.1, 0.2 and 0.4 mg mL-1. Fig. 5 shows the top-view TEM images of the TFN membranes with the PES MF membrane removed. The pure PA active layer in the TFC membrane displays a high transparency with a visible interlacing structure of the underlying PD/SWCNT film (Fig. 5a and b). For the PA/UIO-66-NH2 active layer fabricated
with 0.05 mg mL-1 UIO-66-NH2, there are quite few nanoparticles observed in it (Fig. 5c). With the increase of UIO-66-NH2 concentration, the loading mass of the nanoparticles in the active layer increases gradually (Fig. 5d-f). When the UIO-66NH2 concentration reaches 0.2 mg mL-1, we can observe lots of nanoparticles uniformly distributed throughout the whole active layer (Fig. 5e). Further increasing the UIO-66-NH2 concentration to 0.4 mg mL-1, the active layer shows a very dense distribution of the nanoparticles (Fig. 5f). These results demonstrate the loading mass of the UIO-66-NH2 nanoparticles in the active layer are controllable by tuning the UIO-66-NH2 concentration in the aqueous solution.
Fig. 5. Top-view TEM images of (a) the PD/SWCNT film, (b) the PA active layer fabricated on the film, (c-f) the PA/UIO-66-NH2 active layer fabricated on the film with UIO-66-NH2 concentration of 0.05, 0.1, 0.2 and 0.4 mg mL-1.
3.4. Pore size distribution and surface charge of TFN membranes
To investigate the pore size distribution of the TFN membranes fabricated with different UIO-66-NH2 concentrations in the PIP solution, their rejections to PEG molecules with molecular weight of 200, 400, 600 and 1000 Da were measured. The same measurement was implemented on the TFC membrane as a contrast. The PEG rejection curves are plotted via nonlinear fitting and the molecular weight cutoff (MWCO) which means the molecular weight at a 90% rejection was obtained from the curves (Fig. 6a) The MWCO of the TFC membrane is 396 Da, and it increases to 424, 507, 523 and 565 Da for the TFN membranes fabricated with UIO-66-NH2 concentration of 0.05, 0.1, 0.2 and 0.4 mg mL-1. According to the rejection curves and a probability density function [40-42], the pore radius distribution of the membranes is obtained as shown in Fig. 6b. The mean pore radius of the TFC membrane is 0.24 nm. After introducing the UIO-66-NH2 nanoparticles with concentration of 0.05 and 0.1 mg mL-1, the mean pore radius of the TFN membranes becomes 0.29 and 0.32 nm. Further increasing the UIO-66-NH2 concentration to 0.2 and 0.4 mg mL-1, no more variation of the pore radius distribution appears. According to Donnan principle, the surface charge of a NF membrane is an essential parameter influencing the desalination performance, especially for the rejection of divalent and multivalent ions [43]. The surface charge of the TFC and TFN membranes was evaluated by measuring their surface zeta potential under the pH of 2-11. As shown in Fig. 7a, both the TFC and TFN membranes show a negative surface zeta potential under this pH range, indicating these membranes are negatively charged. Under the neutral condition, these membranes also show a negatively charged surface (Fig. 7b), which is beneficial to the rejection of anions with high valence. With the loading increase of the positively charged UIO-66-NH2 nanoparticles, the surface zeta potential of the TFN membrane changes integrally in the positive direction (Fig. 7a and b).
Fig. 6. (a) PEG rejection curves and MWCOs of the TFC membrane and the TFN membranes fabricated with different UIO-66-NH2 concentrations. (b) Pore radius distribution of the membranes.
Fig. 7. (a) Surface zeta potential curves of the TFC membrane and TFN membranes under different pH. (d) Surface zeta potential of the membranes when the pH is 7.
3.5. Desalination performance of TFN membranes The desalination performance of the TFC and TFN membranes was evaluated by separating a series of salt solutions. As shown in Fig. 8a, the TFC membrane shows water permeability of 30 L m–2 h–1 bar–1 and a Na2SO4 rejection of 98.5%. After introducing the UIO-66-NH2 nanoparticles, the water permeability of the TFN membrane increases sharply to 35, 42, and 46 L m–2 h–1 bar–1 with the UIO-66-NH2 concentration of 0.05, 0.1 and 0.2 mg mL-1. The corresponding Na2SO4 rejection is 98%, 97.6% and 97.1%. Further increasing the UIO-66-NH2 concentration to 0.4 mg
mL-1, the TFN membrane shows a slight decrease of the water permeability of 41 L m–2 h–1 bar–1 with nearly no more change of Na2SO4 rejection. Therefore, the TFN membrane fabricated with UIO-66-NH2 concentration of 0.2 mg mL-1 (TFN-0.2) is chosen for the following test. The separation performance of the TFN-0.2 membrane for Na2SO4, MgSO4, MgCl2, CaCl2 and NaCl is shown in Fig. 8b. The corresponding water permeability is 46, 44, 49, 52 and 54 L m–2 h–1 bar–1, the corresponding salt rejection is 97.1%, 91.2%, 45.8%, 40.8% and 8.1%, respectively. The high rejection of multivalent salts and a low rejection of monovalent salt indicate that the TFN-0.2 membrane has a promising potential to be used where high rejection of monovalent salts is not required, such as softening brackish groundwater, pretreating seawater before reverse osmosis process, treating industrial process streams, decontaminating wastewater, etc. It is worth noting that the pure water permeability of the TFN-0.2 membrane is as high as 63 L m–2 h–1 bar–1. The ultrahigh water permeability of the TFN membrane is attributed to both the ultrathin active layer and the high loading mass of the MOFs nanoparticles. The Na2SO4 rejection is higher than the MgSO4 rejection, and the rejection for divalent ions is much higher than that of monovalent ions, revealing the rejection mechanism of the TFN membrane is the synergistic effect of Donnan exclusion and size sieving.
Fig. 8. (a) Water permeability and Na2SO4 rejection of the TFN membranes fabricated with different UIO-66-NH2 concentrations. (b) Water permeability and salt rejection of the TFN-0.2 membrane.
The performance stability of the TFN-0.2 membrane was also evaluated. During a 72-hour continuous nanofiltration test, the TFN-0.2 membrane shows nearly unchanged water permeability and Na2SO4 rejection (Fig. 9a). Under the applied pressures from 1 bar to 16 bar, the TFN-0.2 membrane also shows stable water permeability with almost no change of Na2SO4 rejection (Fig. S3), indicating the membrane has a good pressure resistance and could withstand the applied pressure up to 16 bar. These results demonstrate that the TFN-0.2 membrane have a good stability
of the high desalination performance. As shown in Fig. 9b, a performance summary of the TFN-0.2 membrane and some advanced TFN NF membranes reported in literatures is made in accordance to water permeability and Na2SO4 rejection (see the references in the supporting information). It clearly shows the overall performance of our TFN NF membrane outperforms all of the other reported TFN NF membranes, especially for the ultrahigh water permeability. For the Na2SO4 rejection, our membrane is also very high. Recently, a water permeance and water/NaCl selectivity upper bound of commercial TFC seawater RO, brackish water RO and NF membranes was established by Tang et al.[44] The performance of the TFN-0.2 membrane is close to the upper bound line among the NF membranes (Fig. S4), and much closer to the line than the TFN NF membranes using UIO-66 nanoparticles.[13,45]
4. Conclusion In summary, we fabricated a TFN NF membrane with an ultrathin PA/UIO-66-NH2 active layer of 20 ± 3 nm via an IP process on a PD/SWCNT film. Before the fabrication, ultrasmall UIO-66-NH2 nanoparticles with size of ~15 nm were synthesized as the nanofiller. The nanoparticles were homogeneously dispersed in the aqueous solution to carry out the IP process and were uniformly embedded in the formed active layer. The nanoparticle loading in the ultrathin active layer was also controllable by adjusting the nanoparticle concentration in the aqueous solution. Benefiting from the ultrathin active layer and the high loading of the MOFs nanoparticles with distinct pore structure, the TFN membrane exhibited ultrahigh water permeability up to 46 L m–2 h–1 bar–1 that was 53% increased to the TFC membrane, simultaneously with a high Na2SO4 rejection of 97.1%. This new type of
TFN NF membrane holds a promising potential for large-scale desalination and other water purification applications, as an alternative of traditional NF membranes.
Fig. 9. (a) Separation performance of the TFN-0.2 membrane during a 72-hour test. (b) A performance summary of the TFN-0.2 (marked by the red star) and other reported TFN NF membranes in accordance to water permeability and Na2SO4 rejection.
Acknowledgment This work was supported by the National Natural Science Funds for Distinguished Young Scholar (51625306), the Key Project of National Natural Science Foundation of China (21433012), the Natural Science Foundation of Jiangsu Province (BK20180259), Joint Research Fund for Overseas Chinese, Hong Kong and Macao
Scholars (21728602), and the National Natural Science Foundation of China (51603229). Funding support from the CAS Pioneer Hundred Talents Program is grateful appreciated as well.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at doi:10.1016/j.memsci.2019.xx.xxx.
References [1] J. Aurell, B. K. Gullett, Aerostat sampling of PCDD/PCDF emissions from the Gulf oil spill in situ burns, Environ. Sci. Technol. 44 (2010) 9431-9437. https://doi.org/10.1021/es103554y. [2] M. R. Esfahani, S. A. Aktij, Z. Dabaghian, M. D. Firouzjaei, A. Rahimpour, J. Eke, I. C. Escobar, M. Abolhassani, L. F. Greenlee, A. R. Esfahani, A. Sadmani, N. Koutahzadeh, Nanocomposite membranes for water separation and purification: Fabrication, modification, and applications, Sep. Purif. Technol. 213 (2019) 465-499. https://doi.org/10.1016/j.seppur.2018.12.050. [3] A. W. Mohammad, Y. H. Teow, W. L. Ang, Y. T. Chung, D. L. Oatley-Radcliffe, N. Hilal, Nanofiltration membranes review: Recent advances and future prospects, Desalination 356 (2015) 226-254. https://doi.org/10.1016/j.desal.2014.10.043. [4] J. E. Cadott, R. J. Petersen, R. E. Larson, E. E. Erickson, A new thin-film composite seawater reverse osmosis membrane, Desalination 32 (1980) 25-31. https://doi.org/10.1016/S0011-9164(00)86003-8.
[5] W. J. Lau, A. F. Ismail, N. Misdan, M. A. Kassim, A recent progress in thin film composite
membrane:
A
review,
Desalination
287
(2012)
190-199.
https://doi.org/10.1016/j.desal.2011.04.004. [6] M. F. J. Solomon, Y. Bhole, A. G. Livingston, High flux membranes for organic solvent nanofiltration (OSN)-Interfacial polymerization with solvent activation, J. Membr. Sci. 423-424 (2012) 371-382. https://doi.org/10.1016/j.memsci.2012.08.030. [7] B. H. Jeong, E. M. V. Hoek, Y. Yan, A. Subramani, X. Huang, G. Hurwitz, A. K. Ghosh, A. Jawor, Interfacial polymerization of thin film nanocomposites: A new concept for reverse osmosis membranes, J. Membr. Sci. 294 (2007) 1-7. https://doi.org/10.1016/j.memsci.2007.02.025. [8] S. R. Lakhotia, M. Mukhopadhyay, P. Kumari, Iron oxide (FeO) nanoparticles embedded thin-film nanocomposite nanofiltration (NF) membrane for water treatment, Sep. Purif. Technol. 211 (2019) 98-107. https://doi.org/10.1016/j.seppur.2018.09.034. [9] J. N. Shen, C. C. Yu, H. M. Ruan, C. J. Gao, B. V. D. Bruggen, Preparation and characterization of thin-film nanocomposite membranes embedded with poly(methyl methacrylate) hydrophobic modified multiwalled carbon nanotubes by interfacial polymerization,
J.
Membr.
Sci.
442
(2013)
18-26.
https://doi.org/10.1016/j.memsci.2013.04.018. [10] G. S. Lai, W. J. Lau, P. S. Goh, A. F. Ismail, N. Yusof, Y. H. Tan, Graphene oxide incorporated thin film nanocomposite nanofiltration membrane for enhanced salt
removal
performance,
Desalination
387
(2016)
14-24.
https://doi.org/10.1016/j.desal.2016.03.007. [11] C. Zhang, X. Si, S. Zhang, B. Pei, J. Gu, Y. Bai, Porous metal–organic molecular cage: a promising candidate to highly improve the nanofiltration performance of thin
film
nanocomposite
membranes,
New
J.
Chem.
43
(2019)
1699-1709.
https://pubs.rsc.org/en/content/articlehtml/2018/nj/c8nj04603d. [12] C. Wang, Z. Li, J. Chen, Z. Li, Y. Yin, L. Cao, Y. Zhong, H. Wu, Covalent organic framework modified polyamide nanofiltration membrane with enhanced performance
for
desalination,
J.
Membr.
Sci.
523
(2017)
273-281.
https://doi.org/10.1016/j.memsci.2016.09.055. [13] Y. He, Y. P. Tang, D. Ma, T.-S. Chung, UiO-66 incorporated thin-film nanocomposite membranes for efficient selenium and arsenic removal, J. Membr. Sci. 541 (2017) 262-270. https://doi.org/10.1016/j.memsci.2017.06.061. [14] M. Kadhom, B. Deng, Metal-organic frameworks (MOFs) in water filtration membranes for desalination and other applications, Appl. Mater. Today 11 (2018) 219-230. https://doi.org/10.1016/j.apmt.2018.02.008. [15] Y. Zhao, Y. Liu, X. Wang, X. Huang, Y. F. Xie, Impacts of metal-organic frameworks on structure and performance of polyamide thin-film nanocomposite membranes,
ACS
Appl.
Mater.
Interfaces
11
(2019)
13724-13734.
https://doi.org/10.1021/acsami.9b01923. [16] Y. Xu, X. Gao, Q. Wang, X Wang, Z. Ji, C. Gao, Highly stable MIL-101(Cr) doped water permeable thin film nanocomposite membranes for water treatment, RSC Adv. 6 (2016) 82669-82675. https://doi.org/10.1039/C6RA16896E. [17] C. Echaide-Górriz, S. Sorribas, C. Télleza, J. Coronas, MOF nanoparticles of MIL-68(Al), MIL-101(Cr) and ZIF-11 for thin film nanocomposite organic solvent nanofiltration
membranes,
RSC
Adv.
6
(2016)
90417-90426.
https://doi.org/10.1039/C6RA17522H. [18] H. Liu, J. Gao, G. Liu, M. Zhang, Y. Jiang, Enhancing permeability of thin film nanocomposite (TFN) membranes via covalent linking of polyamide with the
incorporated metal-organic frameworks, Ind. Eng. Chem. Res. 58 (2019) 8772-8783. https://doi.org/10.1021/acs.iecr.9b00772. [19] J. Wang, Y. Wang, Y. Zhang, A. Uliana, J. Zhu, J. Liu, B. V. d. Bruggen, Zeolitic Imidazolate framework/graphene oxide hybrid nanosheets functionalized thin film nanocomposite membrane for enhanced antimicrobial performance, ACS Appl. Mater. Interfaces 8 (2016) 25508-25519. https://doi.org/10.1021/acsami.6b06992. [20] S. Sorribas, P. Gorgojo, C. Tellez, J, Coronas, A. G. Livingston, High flux thin film nanocomposite membranes based on metal-organic frameworks for organic solvent
nanofiltration,
J.
Am.
Chem.
Soc.
135
(2013)
15201-15208.
https://doi.org/10.1021/ja407665w. [21] R. J. Petersen, Composite reverse osmosis and nanofiltration membrane, J. Membr. Sci. 83 (1993) 81-150. https://doi.org/10.1016/0376-7388(93)80014-O. [22] M. Elimelech, W. A. Phillip, The future of seawater desalination: energy, technology,
and
the
environment,
Science
333
(2011)
712-717.
https://science.sciencemag.org/content/333/6043/712.abstract. [23] A. K. Pabby, S. S. Rizvi, A. M. Sastre, Handbook of membrane separations: chemical, pharmaceutical, food, and biotechnological applications, CRC press, Boca Raton, USA, 2009. [24] S. Karan, Z. Jiang, A. G. Livingston, Sub-10 nm polyamide nanofilms with ultrafast solvent transport for molecular separation, Science 348 (2015) 1347-1351. https://science.sciencemag.org/content/348/6241/1347. [25] J.-J. Wang, H.-C. Yang, M.-B. Wu, X. Zhang, Z.-K. Xu, Nanofiltration membranes with cellulose nanocrystals as an interlayer for unprecedented performance,
J.
Mater.
Chem.
https://doi.org/10.1039/C7TA00501F.
A
5
(2017)
16289-16295.
[26] M.-B. Wu, Y. Lv, H. C. Yang, L. F. Liu, X. Zhang, Z. K. Xu, Thin film composite membranes combining carbon nanotube intermediate layer and microfiltration support for high nanofiltration performances, J. Membr. Sci. 515 (2016) 238-244. https://doi.org/10.1016/j.memsci.2016.05.056. [27] Y. Zhu, W. Xie, S. Gao, F. Zhang, W. Zhang, Z. Liu, J. Jin, Single-walled carbon nanotube film supported nanofiltration membrane with a nearly 10 nm thick polyamide active layer for high-flux and high-rejection desalination, Small 12 (2016) 5034-5041. https://doi.org/10.1002/smll.201601253. [28] Z. Wang, Z. Wang, S. Lin, H. Jin, S. Gao, Y. Zhu, J. Jin, Nanoparticle-templated nanofiltration membranes for ultrahigh performance desalination, Nat. Commun. 9 (2018) 2004. https://doi.org/10.1038/s41467-018-04467-3. [29] S. Gao, Y. Zhu, Y. Gong, Z. Wang, W. Fang, J. Jin, Ultrathin polyamide nanofiltration membrane fabricated on brush-painted single-walled carbon nanotube network
support
for
ion
sieving,
ACS
Nano
13
(2019)
5278-5290.
https://doi.org/10.1021/acsnano.8b09761. [30] Z. Zhou, Y. Hu, C. Boo, Z. Liu, J. Li, L. Deng, X. An, High-performance thinfilm composite membrane with an ultrathin spray-coated carbon nanotube interlayer, Environ.
Sci.
Technol.
Lett.
5
(2018)
243-248.
https://doi.org/10.1021/acs.estlett.8b00169. [31] Z. Yang, Z. Zhou, H. Guo, Z. Yao, X. Ma, X. Song, S.-P. Feng, C. Y. Tang, Tannic acid/Fe3+ nanoscaffold for interfacial polymerization: toward enhanced nanofiltration
performance,
Environ.
Sci.
Technol.
52
(2018)
9341-9349.
https://doi.org/10.1021/acs.est.8b02425. [32] T. Y. Liu, H. G. Yuan, Y. Y. Liu, D. Ren, Y. C. Su, X. Wang, Metal-organic framework nanocomposite thin films with interfacial bindings and self-standing
robustness for high water flux and enhanced ion selectivity, ACS Nano 12 (2018) 9253-9265. https://doi.org/10.1021/acsnano.8b03994. [33] D. Ma, S. B. Peh, G. Han, S. B. Chen, Thin-film nanocomposite (TFN) membranes incorporated with super-hydrophilic metal-organic framework (MOF) UiO-66: toward enhancement of water flux and salt rejection, ACS Appl. Mater. Interfaces 9 (2017) 7523-7534. https://doi.org/10.1021/acsami.6b14223. [34] C. V. Goethem, R. Verbeke, S. Hermans, R. Bernsteinb, I. F. J. Vankelecom, Controlled
positioning
nanocomposites,
J.
of
MOFs
Mater.
in
Chem.
interfacially A
4
polymerized (2016)
thin-film
16368-16376.
https://doi.org/10.1039/C6TA05175H. [35] S. Basu, M. Balakrishnan, Polyamide thin film composite membranes containing ZIF-8 for the separation of pharmaceutical compounds from aqueous streams, Sep. Purif. Technol. 179 (2017) 118-125. https://doi.org/10.1016/j.seppur.2017.01.061. [36] S. J. Gao, Y. Z. Zhu, F. Zhang, J. Jin, Superwetting polymer-decorated SWCNT composite ultrathin films for ultrafast separation of oil-in-water nanoemulsions, J. Mater. Chem. A 3 (2015) 2895-2902. https://doi.org/10.1039/C4TA05624H. [37] A. Schaate, P. Roy, A. Godt. J. Lippke, F. Waltz, M. Wiebcke, P. Behrens, Modulated synthesis of Zr-based metal-organic frameworks: from nano to single crystals,
Chem.
Eur.
J.
17
(2011)
6643-6651.
https://doi.org/10.1002/chem.201003211. [38] X. Lan, N. Huang, J. Wang, T, Wang, A general and facile strategy for precisely controlling the crystal size of monodispersed metal-organic frameworks via separating the nucleation and growth, Chem. Commun 54 (2018) 584-587. https://10.1039/C7CC08244D.
[39] M. Golpour, M. Pakizeh, Preparation and characterization of new PAMOF/PPSU-GO membrane for the separation of KHI from water, Chem. Eng. J. 345 (2018) 221-232. https://doi.org/10.1016/j.cej.2018.03.154. [40] C. Y. Tang, Y. N. Kwon, J. O. Leckie, Effect of membrane chemistry and coating layer on physiochemical properties of thin film composite polyamide RO and NF membranes: I. FTIR and XPS characterization of polyamide and coating layer chemistry,
Desalination
242
(2009)
149-167.
https://doi.org/10.1016/j.desal.2008.04.003. [41] J. Lin, W. Ye, M.-C. Baltaru, Y. P. Tang, N. J. Bernstein, P. Gao, S. Balta, M. Vlad, A. Volodin, A. Sotto, P. Luisi, A. L. Zydney, B. V. D. Bruggen, Tight ultrafiltration membranes for enhanced separation of dyes and Na2SO4 during textile wastewater
treatment,
J.
Membr.
Sci.
514
(2016)
217-228.
https://doi.org/10.1016/j.memsci.2016.04.057. [42] K.-L. Tung, K.-S. Chang, T.-T. Wu, N.-J. Lin, K.-R. Lee, J.-Y. Lai, Recent advances in the characterization of membrane morphology, Curr. Opin. Chem. Eng. 4 (2014) 121-127. https://doi.org/10.1016/j.coche.2014.03.002. [43] Y.-C. Chiang, Y.-Z. Hsub, R.-C. Ruaan, C.-J. Chuang, K.-L. Tung, Nanofiltration membranes synthesized from hyperbranched polyethyleneimine, J. Membrane Sci. 326 (2009) 19-26. https://doi.org/10.1016/j.memsci.2008.09.021. [44] Z. Yang, H. Guo, C. Y. Tang, The upper bound of thin-film composite (TFC) polyamide membranes for desalination, J. Membrane Sci. 590 (2019) 117297. https://doi.org/10.1016/j.memsci.2019.117297. [45] F. Xiao, X. Hu, Y. Chen, Y. Zhang, Porous Zr-based metal-organic frameworks (Zr-MOFs)-incorporated thin-film nanocomposite membrane toward enhanced
desalination performance, ACS Appl. Mater. Interfaces 11 (2019) 47390. https://doi.org/10.1021/acsami.9b17212.
Graphical abstract:
Highlights:
A novel TFN NF membrane with an ultrathin PA/UIO-66-NH2 active layer as thin as 20 ± 3 nm was fabricated.
The nanoparticles are uniformly embedded in the ultrathin active layer, and the nanoparticle loading is highly controllable.
The membrane exhibits ultrahigh water permeability up to 46 L m–2 h–1 bar–1 along with a high Na2SO4 rejection of 97.1%.
The membrane owns the thinnest active layer and outperforms all of the other membranes in the category of reported TFN NF membranes.
Declarations of interest: none
Supporting Information for
Thin-film Nanocomposite Nanofiltration Membrane with an Ultrathin Polyamide/UIO-66-NH2 Active layer for HighPerformance Desalination Yuqiong Gong†, Shoujian Gao†, Yangyang Tian, Yuzhang Zhu, Wangxi Fang, Zhenggong Wang, Jian Jin*
Fig. S1. Zeta potential of UIO-66-NH2 nanoparticles (0.2 mg mL-1) in water. The zeta potential of the nanoparticles is 36.5 mV, indicating the nanoparticles are positively charged.
Fig. S2. A free-standing PA/UIO-66-NH2 thin film fabricated on the interface of a PIP water solution (1.25 mg mL-1) with homogenously dispersed UIO-66-NH2 nanoparticles (0.2 mg mL-1) and a TMC n-hexane solution (1 mg mL-1). (a) A schematic showing the fabrication process. (b) An optical photograph and (c) a topview TEM image of the thin film. As shown in Fig. S2c, the UIO-66-NH2 nanoparticles are successfully and uniformly embedded in the thin film.
Fig. S3. Water permeability and Na2SO4 rejection of the TFN-0.2 membrane under different applied pressures from 1 bar to 18 bar. (Na2SO4 concentration: 1000 ppm).
Fig. S4 Water permeance and water/NaCl selectivity of commercial seawater reverse osmosis (SWRO), brackish water reverse osmosis (BWRO) and NF membranes in the water permeance and selectivity diagram. Reproduced from J. Membrane Sci. 2019, 590, 117297. Copyright 2019 Royal Society of Chemistry. The red star in Fig. S4 represents our TFN-0.2 membrane. The black stars represent the TFN NF membranes using UIO-66 nanoparticles (J. Membr. Sci. 2017, 541, 262; ACS Appl. Mater. Interfaces 2019, 11, 47390). It clearly shows the performance of our TFN NF membrane is close to the upper bound line among the NF membranes, and much closer to the line than the TFN NF membranes using UIO-66 nanoparticles, especially for the higher water permeance.
References in Fig. 9b [1] X. Wei, X. Xu, J. Wu, C. Li, J. Chen, B. Lv, B. Zhu, H. Xiang, SiO2-modified nanocomposite nanofiltration membranes with high flux and acid resistance, J. Appl. Polym. Sci. 47436 (2019) 1-11. [2] M. B. M. Y. Ang, J. M. Pereira, C. A. Trilles, R. R. Aquino, S.-H. Huang, K.-R. Lee, J.-Y. Lai, Performance and antifouling behavior of thin-film nanocomposite
nanofiltration membranes with embedded silica spheres, Sep. Purif. Technol. 210 (2019) 521-529. [3] W. Zhao, H. Liu, N. Meng, M. Jian, H. Wang, X. Zhang, Graphene oxide incorporated thin film nanocomposite membrane at low concentration monomers, J. Membr. Sci. 565 (2018) 380-389. [4] S. Abdikheibari, W. Lei, L. F. Dumèe, N. Milne, K. Baskaran, Thin film nanocomposite
nanofiltration
membranes
from
amine
functionalized-boron
nitride/polypiperazine amide with enhanced flux and fouling resistance, J. Mater. Chem. A 6 (2018) 12066-12081. [5] J. Zheng, M. Li, K. Yu, J. Hu, X. Zhang, L. Wang, Sulfonated multiwall carbon nanotubes assisted thin-film nanocomposite membrane with enhanced water flux and anti-fouling property, J. Membr. Sci. 524 (2017) 344-353. [6] J. Wang, Y. Wang, Y. Zhang, A. Uliana, J. Zhu, J. Liu, B. V. d. Bruggen, Zeolitic imidazolate framework/graphene oxide hybrid nanosheets functionalized thin film nanocomposite membrane for enhanced antimicrobial performance, ACS Appl. Mater. Interfaces 8 (2016) 25508-25519. [7] G. S. Lai, W. J. Lau, P. S. Goh, A. F. Ismail, N. Yusof, Y. H. Tan, Graphene oxide incorporated thin film nanocomposite nanofiltration membrane for enhanced salt removal performance, Desalination 387 (2016) 14-24. [8] Q. Xie, S. Zhang, Z. Hong, H. Ma, B. Zeng, X. Gong, W. Shao, Q. Wang, A novel double-modified strategy to enhance the performance of thin-film nanocomposite nanofiltration membranes: Incorporating functionalized graphenes into supporting and selective layers, Chem. Eng. J. 368 (2019) 186-201.
[9] S. M. Xue, Z.-L. Xu, Y.-J. Tang, C.-H. Ji, Polypiperazine-amide Nanofiltration membrane modified by different functionalized multiwalled carbon nanotubes (MWCNTs), ACS Appl. Mater. Interfaces 8 (2016) 19135-19144. [10] J. Wang, Y. Wang, J. Zhu, Y. Zhang, J. Liu, B. V. d. Bruggen, Construction of TiO2@graphene oxide incorporated antifouling nanofiltration membrane with elevated filtration performance, J. Membr. Sci. 533 (2017) 279-288. [11] Q. Xie, W. Shao, S. Zhang, Z. Hong, Q. Wang, B Zeng, Enhancing the performance of thin-film nanocomposite nanofiltration membranes using MAHmodified GO nanosheets, RSC Adv. 7 (2017) 54898-54910. [12] D. Hu, Z.-L. Xu, C. Chen, Polypiperazine-amide nanofiltration membrane containing silica nanoparticles prepared by interfacial polymerization, Desalination 301 (2012) 75-81. [13] Z. Liao, X. Fang, J. Xie, Q. Li, D. Wang, X. Sun, L. Wang, J. Li, Hydrophilic hollow nanocube-functionalized thin film nanocomposite membrane with enhanced nanofiltration performance, ACS Appl. Mater. Interfaces, 11 (2019) 5344-5352. [14] Q. Xie, S. Zhang, H. Ma, W. Shao, X. Gong, Z. Hong, A novel thin-film nanocomposite nanofiltration membrane by incorporating 3D hyperbranched polymer functionalized 2D graphene oxide, Polymers 10 (2018) 1253. [15] G. S. Lai, W. J. Lau, P. S. Goh, A. F. Ismail, Y. H. Tan, C. Y. Chong, R. KrauseRehberg, S. Awad, Tailor-made thin film nanocomposite membrane incorporated with graphene oxide using novel interfacial polymerization technique for enhanced water separation, Chem. Eng. J. 344 (2018) 524-534. [16] J. Yin, G. Zhu, B. Deng, Graphene oxide (GO) enhanced polyamide (PA) thinfilm nanocomposite (TFN) membrane for water purification, Desalination 379 (2016) 93-101.
[17] T.-Y. Liu, Z.-H. Liu, R.-X. Zhang, Y. Wang, B. V. d. Bruggen, X.-L Wang, Fabrication of a thin film nanocomposite hollow fiber nanofiltration membrane for wastewater treatment, J. Membr. Sci. 488 (2015) 92-102.
Highlights:
A TFN NF membrane with an ultrathin PA/UIO-66-NH2 active layer of 20 ± 3 nm was fabricated.
The nanoparticles are uniformly embedded in the ultrathin active layer.
The membrane exhibits a high water permeability up to 46 L m–2 h–1 bar–1 along with a high Na2SO4 rejection of 97.1%.
The membrane performance outperforms all of the other TFN NF membranes reported previously.
A list of changes to the manuscript: 1. The word “though” has been changed to “into” in the revised manuscript (page 12, line 1, line 2). 2. The sentence “and much closer to the line than the TFN NF membranes using UIO-66 nanoparticles.[13,45]” has been added in the revised manuscript (page 19, line 10-12). 3. The Figure S4 in the revised supporting information has been changed. 4. The references 44-58 (the references in Fig. 9b) in the original manuscript have been removed from the revised manuscript and have been shown in the revised supporting information. The reference 45 has been added in the revised manuscript.
Declaration of interests ☒ 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 paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: