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Heterogeneous activation of peroxymonosulfate via a Ag-La0.8Ca0.2Fe0.94O3−δ perovskite hollow fibre membrane reactor for dye degradation
Separation and Purification Technology 211 (2019) 298–302
Contents lists available at ScienceDirect
Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Heterogeneous activation of peroxymonosulfate via a AgLa0.8Ca0.2Fe0.94O3−δ perovskite hollow fibre membrane reactor for dye degradation ⁎
Teng Maa, Lihong Liub, Bo Menga, , Jun Gaoc, Shaobin Wangb, Shaomin Liub,
T
⁎
a
School of Chemical Engineering, Shandong University of Technology, Zibo 255049, PR China WA School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, WA 6102, Australia c School of Chemistry and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266510, PR China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Cobalt-free perovskite catalyst Peroxymonosulfate oxidation Organic degradation Perovskite hollow fiber
Perovskite oxides have been investigated for their catalytic efficiency for fast aqueous-phase advanced oxidation of dye contaminant. These catalysts in powder are usually dispersed in water but may cause the secondary pollution. In this work, Ag-La0.8Ca0.2Fe0.94O3-δ (Ag-LCF), one typical example of these perovskite catalysts, was fabricated into hollow fibre membrane by the combined phase inversion and sintering method. Such hollow fibres can be readily used as the membrane reactors for dye containing wastewater treatment. The process is based on direct peroxymonosulfate (PMS, HSO5−) oxidation by Ag-LCF membrane material itself therefore avoiding the catalyst loading that is usually required in normal membrane reactor. The catalytic performance of one Ag-LCF hollow fibre membrane was demonstrated by the degradation of methylene blue (MB) with removal efficiency up to 90% compared favourably with other operation modes. Sulfate and hydroxyl radicals play important roles on methylene blue decolouration. Backwashing by acid solution was used to accomplish 94% membrane catalytic efficiency regeneration.
1. Introduction Membrane filtration technologies play important role in water reclamation. Hollow fibre membranes (HFMs), with the highest surface area per unit volume, particularly find increasing commercial applications in areas of microfiltration, ultrafiltration, nanofiltration and reverse osmosis [1–3]. These processes heavily rely on the pore size distribution of the membranes to physically remove ions, harmful molecules and larger suspended particles (e.g., bacteria and viruses) from waste water. Additional chemical treatments are required to decompose the separated contaminants. Alternatively, a HFM reactor incorporated the membrane with an established nanocatalyst may solve the problem by introducing extra antibacterial or photocatalytic properties [4,5]. To load uniform and robust nanoparticles (NPs) on the surface or within the matrix of the membrane scaffold, lots of efforts have been devoted to overcome the weak van der Waals force between the NPs and membrane surface [6]. If these inorganic functional nanomaterials can be made into membranes, the membranes themselves could offer excellent catalytic function. For example, Zhang et al. [7] fabricated nanostructured
⁎
TiO2 hollow fibre membranes with photocatalytic properties for Acid Orange-7 filtration and degradation. Inspired by this work, an attempt is made to prepare perovskite HFMs for peroxymonosulfate (PMS) oxidation and dye containing waste water treatment. PMS is an economic and non-toxic parent oxidant that can be activated by transition metal ions, such as Ag+, Co2+, and Fe2+ to generate highly oxidizing radicals (SO4%− and %OH) for pollutants attenuation as described by the following reactions [8,9]: Mn+ + HSO5‾ → M(n+1)+ + SO4%− + OH‾ (n+1)+
M
SO4%−
+ HSO5‾ → M
n+ %
+
SO5%− +
+ H2O → H + OH + SO4 +
+
H
2‾
SO4%−/%OH + Organic pollutants → degraded products
(1) (2) (3) (4)
Cobalt containing perovskite-type oxides with a general chemical formula ABO3 become attractive catalysts for fast aqueous-phase advanced oxidation [10–12]. However, cobalt leaching may contribute substantially to adverse human health impacts therefore the maximum allowable concentration of Co in drinking water is 0.05 ppm. On the
Corresponding authors. E-mail addresses: [email protected] (B. Meng), [email protected] (S. Liu).
https://doi.org/10.1016/j.seppur.2018.09.077 Received 3 September 2018; Received in revised form 25 September 2018; Accepted 25 September 2018 Available online 26 September 2018 1383-5866/ © 2018 Elsevier B.V. All rights reserved.
Separation and Purification Technology 211 (2019) 298–302
T. Ma et al.
using energy dispersive X-ray spectroscopy (EDS, Oxford INCA 200). The crystal structure of the powder and outer surface of the hollow fibre was characterized using powder X-ray diffraction (XRD, Bruker D8 Advance) using Cu-Kα radiation (λ = 0.15404 nm). The data was collected under a continuous scan mode between 20 and 80° with a step size of 0.02° and a scan rate of 2° min−1. The current and voltage were set at 30 mA and 40 kV, respectively.
contrary, lanthanum is used as a beneficial agent to human health. For instance, La2(CO3)3 has been used as a phosphate binder to treat hyperphosphatemia patients with chronic kidney disease who are undergoing dialysis. Co-free Ag-La0.8Ca0.2Fe0.94O3-δ (Ag-LCF) powder, possessing both Ag and Fe atoms, has been confirmed to efficiently remove organic contaminants through advanced oxidation of PMS [13]. While using fine particles to degrade wastes, an additional step is required to recover the perovskite oxides from the treated water otherwise the treated water will be contaminated by the particulate matters. This concern could be addressed by immobilising the catalyst or employing membrane reactor, which will simplify the overall catalytic system design and process. There is another challenge associated with the use of perovskite powder for PMS activation: weak chemical stability and the need for high temperature regeneration (e.g., calcination at 1000 °C in air) [10,11]. Recently, perovskite oxide HFMs have been intensively exploited for gas separation and methane conversion [14–26]. However, the application of these perovskite membranes for room temperature water treatment has been rarely reported. In this work, we looked at the inherent catalytic efficiency of AgLa0.8Ca0.2Fe0.94O3-δ (Ag-LCF) perovskite hollow fibre as the membrane reactor for dye degradation via the heterogeneous activation of peroxymonosulfate. The selection of Ag-LCF as the hollow fibre material is because of its proven high efficiency and stability in removing the organic and bacterial pollutant. In powder form, Ag-LCF shows better PMS oxidation than pure LCF and simple Fe3O4 oxide [13]. This study may trigger intensive research enthusiasm for the applications of perovskite oxide HFMs in water treatment as this has not been reported so far.
2.4. Membrane evaluation Catalytic degradation of 20 mL methylene blue (MB, 10 ppm) through perovskite/PMS oxidation was evaluated with a 30-cm long HFM at room temperature. The MB solution was pumped into the fibre lumen at a fixed flowrate of 26 mL min−1. A total of 0.2 mL solution sample was withdrawn at given time intervals for concentration measurement. The MB concentration variation was determined by a JASCO V-670 UV-vis/NIR spectrophotometer. The λmax of MB is 665 nm. Organic decomposition efficiency was calculated by Equation (5):
Organic degradation (%) = [(A 0−At)/A 0] × 100%
(5)
where A0 and At are the initial absorbance and the absorbance at time t (min) of MB at 665 nm.
3. Results and discussion 3.1. Characterization of Ag-LCF powder and hollow fibre
2. Experimental
Fig. 1 shows transmission electron microscopy (TEM) and high resolution TEM (HRTEM) images of the prepared Ag-LCF powder calcined at 800 °C for 4 h. The particles were heavily agglomerated with primary sizes ranging from 50 to 100 nm. HRTEM image reveals a regular lattice spacing of 0.27 nm that corresponds to the characteristic (1 2 1) planes of the orthorhombic crystal structure of LCF perovskite oxide [28]. High-angle annular dark field (HAADF) scanning images map the elemental locations of the Ag-LCF nanoparticles (NPs). La, Ca, Fe, and O are homogeneously distributed within NPs. Although the Ag map has a low signal-to-noise ratio, the element distribution is nearly uniform. Some of the bright dots are suggesting the formation of Ag metallic particles, which is in line with the XRD result (Fig. 2) which will be discussed later. All these data reveal that partial Ag atoms are incorporated in the perovskite crystal lattice. Silver and calcium doping have greatly improved the pollutants degradation efficiency due to the decreased Rct and increased number of oxygen vacancies in AgLa0.8Ca0.2Fe0.94O3-δ, which are beneficial to PMS activation [13,28]. Therefore, we use this kind of powder to fabricate hollow fibre membranes. SEM images of the cross-sections and the inner surfaces of Ag-LCF hollow fibres before and after calcination are shown in Fig. 2. The precursor HFM had an outside diameter of 2.7 mm and inner diameter of 2.1 mm. Ag-LCF powders were found to be well dispersed in polymer matrix (Fig. 2b). Although the cross-sectional diameter shrunk to 1.53 mm (outer) and 1.14 mm (inner), respectively, the sintered Ag-LCF HFM maintained the sandwich structure of two short finger-like porous layers separated by a dense core (Fig. 2c). Such asymmetric structures are distinguished by high mechanical strength [27,29]. The inner surface was covered with a defect-free continuous crystal layer (Fig. 2d). The crystal shapes of Ag-LCF are in cobblestone-like morphology, having dimensions of 100 nm to 1 μm. Fig. 2e depicts the powder X-ray diffraction pattern of the crushed Ag-LCF hollow fibre that signifies the presence of the perovskite oxide phase evidenced by the characteristic diffraction peaks at 2θ of 23.94°, 32.36°, 39.94°, 46.42°, and 57.70° (PDF-00-049-1885). However, the XRD also shows a minor intensity peak at 2θ of 38.1°, which is assigned to Ag particle consistent with the previous HRTEM and EDX analysis in Fig. 1.
2.1. Materials and chemicals Metal nitrates such as La(NO3)3·6H2O, Ca(NO3)2·4H2O, Fe (NO3)3·9H2O and other chemicals like citric acid, ethylene glycol, sulfuric acid (H2SO4, 98%), potassium peroxymonosulfate (Oxone® or PMS), 5,5-dimethyl-1-pyrroline N-oxide (DMPO, 99.0%), ethanol (99.5%) were purchased from Sigma-Aldrich. 2.2. Preparation of hollow fibre membranes Silver incorporated La0.8Ca0.2Fe0.94O3-δ (LCF) perovskite powder was prepared via a sol–gel method. Firstly, La(NO3)3·6H2O, Ca (NO3)2·4H2O, Fe(NO3)3·9H2O, and AgNO3 with a molar ratio of 0.80 : 0.20 : 0.94 : 0.05 were dissolved in a mixture of deionized water, citric acid (CA) and ethylene glycol (EG) to form a homogeneous solution at the molar ratios of 1.2 CA : 1.2 EG : 1.0 total metal ions. The pH value of the solution was adjusted to around 8 and heated at 80 °C to produce a transparent gel. The gel was pre-treated at 250 °C for 5 h and subsequently calcined at 800 °C for 4 h to remove the residual carbon and obtain crystalline powder. Ag-LCF hollow fibre membranes were prepared via the phase inversion/sintering technique. The detailed procedures were described elsewhere [27]. In this work, the starting spinning mixture was composed of Ag-LCF powder, polyethersulfone (PESF) (Radel A-300, Ameco Performance, USA) and 1-methyl-2-pyrrolidinone (NMP) (Merck) at weight ratio of 8:4:1. A spinneret with the orifice diameter/inner diameter of 3.0/1.2 mm was applied to form the hollow fibre precursors. Deionized water and tap water were used as the internal and external coagulants, respectively. Sintering was carried out at 1250 °C for 4 h. 2.3. Characterization The morphology of perovskite hollow fibre was observed using scanning electron microscopy (SEM, Zeiss Neon 40EsB FIBSEM). The elemental distribution of the metals on the fibre surface was evaluated 299
Separation and Purification Technology 211 (2019) 298–302
T. Ma et al.
Fig. 1. TEM (a) and HRTEM (b) images of Ag-LCF powder for hollow fibre fabrication. HAADF-STEM images of Ag-LCF (c) and EDX elemental mapping for La, Ca, Fe, Ag, and O.
Fig. 2. SEM images of precursor hollow fibre (a, b) and sintered hollow fibres with heat treatment temperature at 1250 °C (c, d); XRD pattern of the crushed Ag-LCF hollow fibre membrane (e). 300
Separation and Purification Technology 211 (2019) 298–302
T. Ma et al.
chlorine oxidation for pollution abatement, 0.6 mM PMS alone could degrade 56% MB due to the relatively low oxidation potential (E0 (HSO5−/HSO4−) = + 1.82 V vs NHE, [30]. Advanced oxidation processes (AOPs) based on PMS activation by transition metals have received much attention because of higher standard redox potentials of the generated sulfate radical (+ 2.5–3.1 V vs NHE) and hydroxyl radical (+ 1.9–2.7 V vs NHE). Moreover, the process is thermodynamically feasible for the redox cycling of the oxidized metal ions (Eqs. (1) and (2)). Here, the MB degradation significantly increased to 90% in the presence of HFMs. These results validate the enhanced removal of MB is mainly attributed to Ag+ and Fe3+ mediated PMS oxidation. 3.3. Reaction mechanism of Ag-LCF HFM/PMS system To identify the reactive oxygen species responsible for MB degradation in Ag-LCF HFM/PMS system, EPR test using DMPO as the spin-trapping agent was conducted to detect any radicals produced in the AOPs. DMPO reacted with hydroxyl and sulphate radicals to form the typical DMPO-OH and DMPO-SO4 signals, respectively. As can be seen in Fig. 4, both radicals were produced during PMS activation. Ethanol is a widely used scavenger of SO4%− and %OH [31]. To further verify the existence of the radicals, quenching experiments were conducted by adding ethanol (ethanol/PMS at 1000). The degradation rate was notably inhibited, thus proving the presence of sulfate and hydroxyl radicals plays key roles in AOPs.
Fig. 3. Advanced oxidation of methylene blue by Ag-LCF hollow fibre membranes and peroxymonosulfate (PMS) system.
3.4. Stability test of HFM/PMS The stability of the HFM was studied by the recycle test experiments. After the first run, due to surface contamination and coverage/ change of the active sites, the degradation efficiency of membrane was decreased to 50%. Researchers reported that the oxygen permeation through perovskite HFM could be improved after surface acid-modification [27,32]. In our study, as shown in Fig. 5, sulphuric acid treatment (for 5 min) could regenerate the catalyst. The oxidation efficiency maintained at 94% after the fourth run. The catalytic activity dropping in the fifth cycle may be caused by two reasons. The iron ions leached from the catalyst during the reaction could have changed the surface composition of perovskite, hence causing a loss in activity over time. Another reason may be due to the surface coverage of the active sites by the MB degraded intermediates that would give rise to a poorer
Fig. 4. EPR spectrum showing %OH and SO4%− production (with spin trapping agent DMPO) by hollow fibre membrane and PMS.
3.2. Hollow fibre membrane catalytic performance test The catalytic performance of the Ag-LCF membranes was tested by using methylene blue (MB) as a model pollutant. As shown in Fig. 3, after 75 min, less than 10% MB was physically adsorbed by HF membrane surface. Although peroxymonosulfate can provide powerful non-
Fig. 5. Methylene blue degradation profile on reusability of the hollow fiber membrane and PMS (a). SEM images of the hollow fiber membrane after the fifth run (b). 301
Separation and Purification Technology 211 (2019) 298–302
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catalytic performance. Pinholes as an inner surface defect were observed in Fig. 5b. High magnification SEM (inset) shows the exposed particles with an increment in grain size. The membrane wall, especially the dense core remains intact and is capable of preventing waste water leakage from the lumen to the shell side.
[11]
[12]
4. Conclusions
[13]
Silver incorporated perovskite LCF hollow fibre membrane was prepared by the phase inversion spinning/sintering method. The membrane material itself is able to activate PMS for organic pollutant degradation. The membrane reactor exhibits appreciable advantages over the catalyst in powder form, including easy operation, high regeneration efficiency and low energy requirement. The potential of the perovskite LCF hollow fibre membrane in waste water remediation requires further study of the design of novel materials that may directly destruct pollutants without peroxymonosulfate addition.
[14]
[15]
[16] [17] [18]
Acknowledgements
[19]
The authors are thankful for the facilities and scientific and technical assistance of the CHIRI Biosciences Research Precinct core facility and Electron Microscope Facility and X-ray Laboratory, both of which are partially funded by the University, State, and Commonwealth Governments.
[20]
[21]
References
[22] [23]
[1] C.Y. Feng, K.C. Khulbe, T. Matsuura, A.F. Ismail, Recent progresses in polymeric hollow fiber membrane preparation, characterization and applications, Sep. Purif. Technol. 111 (2013) 43–71. [2] A.W. Zularisam, A.F. Ismail, M.R. Salim, Mimi Sakinah, T. Matsuura, Application of coagulation–ultrafiltration hybrid process for drinking water treatment: optimization of operating conditions using experimental design, Sep. Purif. Technol. 65 (2009) 193–210. [3] A.K. Fard, G. McKay, A. Buekenhoudt, H. Al Sulaiti, F. Motmans, M. Khraisheh, M. Atieh, Inorganic membranes: preparation and application for water treatment and desalination, Materials 11 (2018) 74, https://doi.org/10.3390/ma11010074. [4] P. Gunawan, C. Guan, X. Song, Q. Zhang, S.S.J. Leong, C. Tang, Y. Chen, M.B. ChanPark, M.W. Chang, K. Wang, R. Xu, Hollow fiber membrane decorated with Ag/ MWNTs: toward effective water disinfection and biofouling control, ACS Nano 5 (2011) 10033–10040. [5] D.K. Wang, M. Elma, J. Motuzas, W. Hou, F. Xie, X. Zhang, Rational design and synthesis of molecular-sieving, photocatalytic, hollow fiber membranes for advanced water treatment applications, J. Membr. Sci. 524 (2017) 163–173. [6] M.F. Haase, H. Jeon, N. Hough, J.H. Kim, K.J. Stebe, D. Lee, Multifunctional nanocomposite hollow fiber membranes by solvent transfer induced phase separation, 1234, Nat. Commun. 8 (2017), https://doi.org/10.1038/s41467-017-01409-3. [7] X. Zhang, D.K. Wang, D.R.S. Lopez, J.C.D. da Costa, Fabrication of nanostructured TiO2 hollow fiber photocatalytic membrane and application for wastewater treatment, Chem. Eng. J. 236 (2014) 314–322. [8] P. Hu, M. Long, Cobalt-catalyzed sulfate radical-based advanced oxidation: a review on heterogeneous catalysts and applications, Appl. Catal. B. Environ. 181 (2016) 103–117. [9] G.P. Anipsitakis, D.D. Dionysiou, Radical generation by the interaction of transition metals with common oxidants, Environ. Sci. Technol. 38 (2004) 3705–3712. [10] X. Duan, C. Su, J. Miao, Y. Zhong, Z. Shao, S. Wang, H. Sun, Insights into perovskite-
[24]
[25] [26] [27]
[28]
[29] [30]
[31]
[32]
302
catalyzed peroxymonosulfate activation: maneuverable cobalt sites for promoted evolution of sulfate radicals, Appl. Catal. B. Environ. 220 (2018) 626–634. C. Su, X. Duan, J. Miao, Y. Zhong, W. Zhou, S. Wang, Z. Shao, Mixed conducting perovskite materials as superior catalysts for fast aqueous-phase advanced oxidation: a mechanistic study, ACS Catal. 7 (2017) 388–397. J. Miao, J. Sunarso, C. Su, W. Zhou, S. Wang, Z. Shao, SrCo1−xTixO3−δ perovskites as excellent catalysts for fast degradation of water contaminants in neutral and alkaline solutions, Sci. Rep. 7 (2017) 44215. Y. Chu, X. Tan, Z. Shen, P. Liu, N. Han, J. Kang, X. Duan, S. Wang, L. Liu, S. Liu, Efficient removal of organic and bacterial pollutants by Ag-La0.8Ca0.2Fe0.94O3-δ perovskite via catalytic peroxymonosulfate activation, J. Hazard. Mater. 356 (2018) 53–60. Z. Shao, G. Xiong, H. Dong, W. Yang, L. Lin, Synthesis, oxygen permeation study and membrane performance of a Ba0.5Sr0.5Co0.8Fe0.2O3−δ oxygen-permeable dense ceramic reactor for partial oxidation of methane to syngas, Sep. Purif. Technol. 25 (2001) 97–116. Y. Wei, Q. Liao, Z. Li, H. Wang, Enhancement of oxygen permeation through Ushaped oxide hollow fiber membranes by surface modifications, Sep. Purif. Technol. 110 (2013) 74–80. Y. Wei, W. Yang, J. Caro, H. Wang, Dense ceramic oxygen permeable membranes and catalytic membrane reactors, Chem. Eng. J. 220 (2013) 185–203. X. Chen, L. Huang, Y. Wei, H. Wang, Tantalum stabilized SrCoO3−δ perovskite membrane for oxygen separation, J. Membr. Sci. 368 (2011) 159–164. H. Wang, A. Feldhoff, J. Caro, T. Schiestel, S. Werth, Oxygen selective ceramic hollow fiber membranes for partial oxidation of methane, AIChE J. 55 (10) (2009) 2657–2664. X. Tan, Z. Pang, Z. Gu, S. Liu, Catalytic perovskite hollow fibre membrane reactors for methane oxidative coupling, J. Membr. Sci. 302 (2007) 109–114. Y. Hu, R. An, Y. Chu, X. Tana, J. Sunarso, S. Wang, S. Liu, Perovskite hollow fiber membranes supported in a porous and catalytically active perovskite matrix for air separation, Sep. Purif. Technol. 192 (2018) 435–440. Y. Shang, L. Wei, X. Meng, B. Meng, N. Yang, J. Sunarso, S. Liu, CO2-enhanced hydrogen permeability of dual-layered A-site deficient Ba0.95Ce0.85Tb0.05Zr0.1O3-δbased hollow fiber membrane, J. Membr. Sci. 546 (2018) 82–89. H. Wang, C. Tablet, J. Caro, Oxygen production at low temperature using dense perovskite hollow fiber membranes, J. Membr. Sci. 322 (2008) 214–217. X. Zhu, H. Wang, W. Yang, Novel cobalt-free oxygen permeable membrane, Chem. Commun. 1130–1131 (2004). J. Zhu, G. Liu, Z. Liu, Z. Chu, W. Jin, N. Xu, Unprecedented perovskite oxyfluoride membranes with high-efficiency oxygen ion transport paths for low-temperature oxygen permeation, Adv. Mater. 28 (2016) 3511–3515. J. Zhu, S. Guo, Z. Chu, W. Jin, CO2-tolerant oxygen-permeable perovskite-type membranes with high permeability, J. Mater. Chem. A 3 (2015) 22564–22573. H. Wang, S. Werth, T. Schiestel, J. Caro, Perovskite hollow-fiber membranes for the production of oxygen-enriched air, Angew. Chem. Int. Ed. 117 (2005) 7066–7069. D. Yang, N. Yang, B. Meng, X. Tan, C. Zhang, J. Sunarso, Z. Zhu, S. Liu, A-Site excess (La0.8Ca0.2)1.01FeO3−δ (LCF) perovskite hollow fiber membrane for oxygen permeation in CO2-containing atmosphere, Energy Fuels 31 (2017) 4531–4538. S. Palimar, S.D. Kaushik, V. Siruguri, D. Swain, A.E. Viegas, C. Narayana, N.G. Sundaram, Investigation of Ca substitution on the gas sensing potential of LaFeO3 nanoparticles towards low concentration SO2 gas, Dalton Trans. 45 (2016) 13547–13555. S. Liu, L. Liu, Z. Xu, A. Yu, G. Lu, J. Diniz da Costa, Bioceramic macrocapsules for cell immunoisolation, Angew. Chem. Int. Ed. 46 (2007) 3062–3065. A.R. Chesney, C.J. Booth, C.B. Lietz, L. Li, J.A. Pedersen, Peroxymonosulfate rapidly inactivates the disease-associated prion protein, Environ. Sci. Technol. 50 (2016) 7095–7105. W. Tian, H. Zhang, Z. Qian, T. Ouyang, H. Sun, J. Qin, M. Tadé, S. Wang, Breadmaking synthesis of hierarchically Co@C nanoarchitecture in heteroatom doped porous carbons for oxidative degradation of emerging contaminants, Appl. Catal. B. Environ. 225 (2018) 76–83. Z. Wang, H. Liu, X. Tan, Y. Jin, S. Liu, Improvement of the oxygen permeation through perovskite hollow fibre membranes by surface acid-modification, J. Membr. Sci. 345 (2009) 65–73.
Contents lists available at ScienceDirect
Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Heterogeneous activation of peroxymonosulfate via a AgLa0.8Ca0.2Fe0.94O3−δ perovskite hollow fibre membrane reactor for dye degradation ⁎
Teng Maa, Lihong Liub, Bo Menga, , Jun Gaoc, Shaobin Wangb, Shaomin Liub,
T
⁎
a
School of Chemical Engineering, Shandong University of Technology, Zibo 255049, PR China WA School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, WA 6102, Australia c School of Chemistry and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266510, PR China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Cobalt-free perovskite catalyst Peroxymonosulfate oxidation Organic degradation Perovskite hollow fiber
Perovskite oxides have been investigated for their catalytic efficiency for fast aqueous-phase advanced oxidation of dye contaminant. These catalysts in powder are usually dispersed in water but may cause the secondary pollution. In this work, Ag-La0.8Ca0.2Fe0.94O3-δ (Ag-LCF), one typical example of these perovskite catalysts, was fabricated into hollow fibre membrane by the combined phase inversion and sintering method. Such hollow fibres can be readily used as the membrane reactors for dye containing wastewater treatment. The process is based on direct peroxymonosulfate (PMS, HSO5−) oxidation by Ag-LCF membrane material itself therefore avoiding the catalyst loading that is usually required in normal membrane reactor. The catalytic performance of one Ag-LCF hollow fibre membrane was demonstrated by the degradation of methylene blue (MB) with removal efficiency up to 90% compared favourably with other operation modes. Sulfate and hydroxyl radicals play important roles on methylene blue decolouration. Backwashing by acid solution was used to accomplish 94% membrane catalytic efficiency regeneration.
1. Introduction Membrane filtration technologies play important role in water reclamation. Hollow fibre membranes (HFMs), with the highest surface area per unit volume, particularly find increasing commercial applications in areas of microfiltration, ultrafiltration, nanofiltration and reverse osmosis [1–3]. These processes heavily rely on the pore size distribution of the membranes to physically remove ions, harmful molecules and larger suspended particles (e.g., bacteria and viruses) from waste water. Additional chemical treatments are required to decompose the separated contaminants. Alternatively, a HFM reactor incorporated the membrane with an established nanocatalyst may solve the problem by introducing extra antibacterial or photocatalytic properties [4,5]. To load uniform and robust nanoparticles (NPs) on the surface or within the matrix of the membrane scaffold, lots of efforts have been devoted to overcome the weak van der Waals force between the NPs and membrane surface [6]. If these inorganic functional nanomaterials can be made into membranes, the membranes themselves could offer excellent catalytic function. For example, Zhang et al. [7] fabricated nanostructured
⁎
TiO2 hollow fibre membranes with photocatalytic properties for Acid Orange-7 filtration and degradation. Inspired by this work, an attempt is made to prepare perovskite HFMs for peroxymonosulfate (PMS) oxidation and dye containing waste water treatment. PMS is an economic and non-toxic parent oxidant that can be activated by transition metal ions, such as Ag+, Co2+, and Fe2+ to generate highly oxidizing radicals (SO4%− and %OH) for pollutants attenuation as described by the following reactions [8,9]: Mn+ + HSO5‾ → M(n+1)+ + SO4%− + OH‾ (n+1)+
M
SO4%−
+ HSO5‾ → M
n+ %
+
SO5%− +
+ H2O → H + OH + SO4 +
+
H
2‾
SO4%−/%OH + Organic pollutants → degraded products
(1) (2) (3) (4)
Cobalt containing perovskite-type oxides with a general chemical formula ABO3 become attractive catalysts for fast aqueous-phase advanced oxidation [10–12]. However, cobalt leaching may contribute substantially to adverse human health impacts therefore the maximum allowable concentration of Co in drinking water is 0.05 ppm. On the
Corresponding authors. E-mail addresses: [email protected] (B. Meng), [email protected] (S. Liu).
https://doi.org/10.1016/j.seppur.2018.09.077 Received 3 September 2018; Received in revised form 25 September 2018; Accepted 25 September 2018 Available online 26 September 2018 1383-5866/ © 2018 Elsevier B.V. All rights reserved.
Separation and Purification Technology 211 (2019) 298–302
T. Ma et al.
using energy dispersive X-ray spectroscopy (EDS, Oxford INCA 200). The crystal structure of the powder and outer surface of the hollow fibre was characterized using powder X-ray diffraction (XRD, Bruker D8 Advance) using Cu-Kα radiation (λ = 0.15404 nm). The data was collected under a continuous scan mode between 20 and 80° with a step size of 0.02° and a scan rate of 2° min−1. The current and voltage were set at 30 mA and 40 kV, respectively.
contrary, lanthanum is used as a beneficial agent to human health. For instance, La2(CO3)3 has been used as a phosphate binder to treat hyperphosphatemia patients with chronic kidney disease who are undergoing dialysis. Co-free Ag-La0.8Ca0.2Fe0.94O3-δ (Ag-LCF) powder, possessing both Ag and Fe atoms, has been confirmed to efficiently remove organic contaminants through advanced oxidation of PMS [13]. While using fine particles to degrade wastes, an additional step is required to recover the perovskite oxides from the treated water otherwise the treated water will be contaminated by the particulate matters. This concern could be addressed by immobilising the catalyst or employing membrane reactor, which will simplify the overall catalytic system design and process. There is another challenge associated with the use of perovskite powder for PMS activation: weak chemical stability and the need for high temperature regeneration (e.g., calcination at 1000 °C in air) [10,11]. Recently, perovskite oxide HFMs have been intensively exploited for gas separation and methane conversion [14–26]. However, the application of these perovskite membranes for room temperature water treatment has been rarely reported. In this work, we looked at the inherent catalytic efficiency of AgLa0.8Ca0.2Fe0.94O3-δ (Ag-LCF) perovskite hollow fibre as the membrane reactor for dye degradation via the heterogeneous activation of peroxymonosulfate. The selection of Ag-LCF as the hollow fibre material is because of its proven high efficiency and stability in removing the organic and bacterial pollutant. In powder form, Ag-LCF shows better PMS oxidation than pure LCF and simple Fe3O4 oxide [13]. This study may trigger intensive research enthusiasm for the applications of perovskite oxide HFMs in water treatment as this has not been reported so far.
2.4. Membrane evaluation Catalytic degradation of 20 mL methylene blue (MB, 10 ppm) through perovskite/PMS oxidation was evaluated with a 30-cm long HFM at room temperature. The MB solution was pumped into the fibre lumen at a fixed flowrate of 26 mL min−1. A total of 0.2 mL solution sample was withdrawn at given time intervals for concentration measurement. The MB concentration variation was determined by a JASCO V-670 UV-vis/NIR spectrophotometer. The λmax of MB is 665 nm. Organic decomposition efficiency was calculated by Equation (5):
Organic degradation (%) = [(A 0−At)/A 0] × 100%
(5)
where A0 and At are the initial absorbance and the absorbance at time t (min) of MB at 665 nm.
3. Results and discussion 3.1. Characterization of Ag-LCF powder and hollow fibre
2. Experimental
Fig. 1 shows transmission electron microscopy (TEM) and high resolution TEM (HRTEM) images of the prepared Ag-LCF powder calcined at 800 °C for 4 h. The particles were heavily agglomerated with primary sizes ranging from 50 to 100 nm. HRTEM image reveals a regular lattice spacing of 0.27 nm that corresponds to the characteristic (1 2 1) planes of the orthorhombic crystal structure of LCF perovskite oxide [28]. High-angle annular dark field (HAADF) scanning images map the elemental locations of the Ag-LCF nanoparticles (NPs). La, Ca, Fe, and O are homogeneously distributed within NPs. Although the Ag map has a low signal-to-noise ratio, the element distribution is nearly uniform. Some of the bright dots are suggesting the formation of Ag metallic particles, which is in line with the XRD result (Fig. 2) which will be discussed later. All these data reveal that partial Ag atoms are incorporated in the perovskite crystal lattice. Silver and calcium doping have greatly improved the pollutants degradation efficiency due to the decreased Rct and increased number of oxygen vacancies in AgLa0.8Ca0.2Fe0.94O3-δ, which are beneficial to PMS activation [13,28]. Therefore, we use this kind of powder to fabricate hollow fibre membranes. SEM images of the cross-sections and the inner surfaces of Ag-LCF hollow fibres before and after calcination are shown in Fig. 2. The precursor HFM had an outside diameter of 2.7 mm and inner diameter of 2.1 mm. Ag-LCF powders were found to be well dispersed in polymer matrix (Fig. 2b). Although the cross-sectional diameter shrunk to 1.53 mm (outer) and 1.14 mm (inner), respectively, the sintered Ag-LCF HFM maintained the sandwich structure of two short finger-like porous layers separated by a dense core (Fig. 2c). Such asymmetric structures are distinguished by high mechanical strength [27,29]. The inner surface was covered with a defect-free continuous crystal layer (Fig. 2d). The crystal shapes of Ag-LCF are in cobblestone-like morphology, having dimensions of 100 nm to 1 μm. Fig. 2e depicts the powder X-ray diffraction pattern of the crushed Ag-LCF hollow fibre that signifies the presence of the perovskite oxide phase evidenced by the characteristic diffraction peaks at 2θ of 23.94°, 32.36°, 39.94°, 46.42°, and 57.70° (PDF-00-049-1885). However, the XRD also shows a minor intensity peak at 2θ of 38.1°, which is assigned to Ag particle consistent with the previous HRTEM and EDX analysis in Fig. 1.
2.1. Materials and chemicals Metal nitrates such as La(NO3)3·6H2O, Ca(NO3)2·4H2O, Fe (NO3)3·9H2O and other chemicals like citric acid, ethylene glycol, sulfuric acid (H2SO4, 98%), potassium peroxymonosulfate (Oxone® or PMS), 5,5-dimethyl-1-pyrroline N-oxide (DMPO, 99.0%), ethanol (99.5%) were purchased from Sigma-Aldrich. 2.2. Preparation of hollow fibre membranes Silver incorporated La0.8Ca0.2Fe0.94O3-δ (LCF) perovskite powder was prepared via a sol–gel method. Firstly, La(NO3)3·6H2O, Ca (NO3)2·4H2O, Fe(NO3)3·9H2O, and AgNO3 with a molar ratio of 0.80 : 0.20 : 0.94 : 0.05 were dissolved in a mixture of deionized water, citric acid (CA) and ethylene glycol (EG) to form a homogeneous solution at the molar ratios of 1.2 CA : 1.2 EG : 1.0 total metal ions. The pH value of the solution was adjusted to around 8 and heated at 80 °C to produce a transparent gel. The gel was pre-treated at 250 °C for 5 h and subsequently calcined at 800 °C for 4 h to remove the residual carbon and obtain crystalline powder. Ag-LCF hollow fibre membranes were prepared via the phase inversion/sintering technique. The detailed procedures were described elsewhere [27]. In this work, the starting spinning mixture was composed of Ag-LCF powder, polyethersulfone (PESF) (Radel A-300, Ameco Performance, USA) and 1-methyl-2-pyrrolidinone (NMP) (Merck) at weight ratio of 8:4:1. A spinneret with the orifice diameter/inner diameter of 3.0/1.2 mm was applied to form the hollow fibre precursors. Deionized water and tap water were used as the internal and external coagulants, respectively. Sintering was carried out at 1250 °C for 4 h. 2.3. Characterization The morphology of perovskite hollow fibre was observed using scanning electron microscopy (SEM, Zeiss Neon 40EsB FIBSEM). The elemental distribution of the metals on the fibre surface was evaluated 299
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Fig. 1. TEM (a) and HRTEM (b) images of Ag-LCF powder for hollow fibre fabrication. HAADF-STEM images of Ag-LCF (c) and EDX elemental mapping for La, Ca, Fe, Ag, and O.
Fig. 2. SEM images of precursor hollow fibre (a, b) and sintered hollow fibres with heat treatment temperature at 1250 °C (c, d); XRD pattern of the crushed Ag-LCF hollow fibre membrane (e). 300
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chlorine oxidation for pollution abatement, 0.6 mM PMS alone could degrade 56% MB due to the relatively low oxidation potential (E0 (HSO5−/HSO4−) = + 1.82 V vs NHE, [30]. Advanced oxidation processes (AOPs) based on PMS activation by transition metals have received much attention because of higher standard redox potentials of the generated sulfate radical (+ 2.5–3.1 V vs NHE) and hydroxyl radical (+ 1.9–2.7 V vs NHE). Moreover, the process is thermodynamically feasible for the redox cycling of the oxidized metal ions (Eqs. (1) and (2)). Here, the MB degradation significantly increased to 90% in the presence of HFMs. These results validate the enhanced removal of MB is mainly attributed to Ag+ and Fe3+ mediated PMS oxidation. 3.3. Reaction mechanism of Ag-LCF HFM/PMS system To identify the reactive oxygen species responsible for MB degradation in Ag-LCF HFM/PMS system, EPR test using DMPO as the spin-trapping agent was conducted to detect any radicals produced in the AOPs. DMPO reacted with hydroxyl and sulphate radicals to form the typical DMPO-OH and DMPO-SO4 signals, respectively. As can be seen in Fig. 4, both radicals were produced during PMS activation. Ethanol is a widely used scavenger of SO4%− and %OH [31]. To further verify the existence of the radicals, quenching experiments were conducted by adding ethanol (ethanol/PMS at 1000). The degradation rate was notably inhibited, thus proving the presence of sulfate and hydroxyl radicals plays key roles in AOPs.
Fig. 3. Advanced oxidation of methylene blue by Ag-LCF hollow fibre membranes and peroxymonosulfate (PMS) system.
3.4. Stability test of HFM/PMS The stability of the HFM was studied by the recycle test experiments. After the first run, due to surface contamination and coverage/ change of the active sites, the degradation efficiency of membrane was decreased to 50%. Researchers reported that the oxygen permeation through perovskite HFM could be improved after surface acid-modification [27,32]. In our study, as shown in Fig. 5, sulphuric acid treatment (for 5 min) could regenerate the catalyst. The oxidation efficiency maintained at 94% after the fourth run. The catalytic activity dropping in the fifth cycle may be caused by two reasons. The iron ions leached from the catalyst during the reaction could have changed the surface composition of perovskite, hence causing a loss in activity over time. Another reason may be due to the surface coverage of the active sites by the MB degraded intermediates that would give rise to a poorer
Fig. 4. EPR spectrum showing %OH and SO4%− production (with spin trapping agent DMPO) by hollow fibre membrane and PMS.
3.2. Hollow fibre membrane catalytic performance test The catalytic performance of the Ag-LCF membranes was tested by using methylene blue (MB) as a model pollutant. As shown in Fig. 3, after 75 min, less than 10% MB was physically adsorbed by HF membrane surface. Although peroxymonosulfate can provide powerful non-
Fig. 5. Methylene blue degradation profile on reusability of the hollow fiber membrane and PMS (a). SEM images of the hollow fiber membrane after the fifth run (b). 301
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catalytic performance. Pinholes as an inner surface defect were observed in Fig. 5b. High magnification SEM (inset) shows the exposed particles with an increment in grain size. The membrane wall, especially the dense core remains intact and is capable of preventing waste water leakage from the lumen to the shell side.
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4. Conclusions
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Silver incorporated perovskite LCF hollow fibre membrane was prepared by the phase inversion spinning/sintering method. The membrane material itself is able to activate PMS for organic pollutant degradation. The membrane reactor exhibits appreciable advantages over the catalyst in powder form, including easy operation, high regeneration efficiency and low energy requirement. The potential of the perovskite LCF hollow fibre membrane in waste water remediation requires further study of the design of novel materials that may directly destruct pollutants without peroxymonosulfate addition.
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[16] [17] [18]
Acknowledgements
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The authors are thankful for the facilities and scientific and technical assistance of the CHIRI Biosciences Research Precinct core facility and Electron Microscope Facility and X-ray Laboratory, both of which are partially funded by the University, State, and Commonwealth Governments.
[20]
[21]
References
[22] [23]
[1] C.Y. Feng, K.C. Khulbe, T. Matsuura, A.F. Ismail, Recent progresses in polymeric hollow fiber membrane preparation, characterization and applications, Sep. Purif. Technol. 111 (2013) 43–71. [2] A.W. Zularisam, A.F. Ismail, M.R. Salim, Mimi Sakinah, T. Matsuura, Application of coagulation–ultrafiltration hybrid process for drinking water treatment: optimization of operating conditions using experimental design, Sep. Purif. Technol. 65 (2009) 193–210. [3] A.K. Fard, G. McKay, A. Buekenhoudt, H. Al Sulaiti, F. Motmans, M. Khraisheh, M. Atieh, Inorganic membranes: preparation and application for water treatment and desalination, Materials 11 (2018) 74, https://doi.org/10.3390/ma11010074. [4] P. Gunawan, C. Guan, X. Song, Q. Zhang, S.S.J. Leong, C. Tang, Y. Chen, M.B. ChanPark, M.W. Chang, K. Wang, R. Xu, Hollow fiber membrane decorated with Ag/ MWNTs: toward effective water disinfection and biofouling control, ACS Nano 5 (2011) 10033–10040. [5] D.K. Wang, M. Elma, J. Motuzas, W. Hou, F. Xie, X. Zhang, Rational design and synthesis of molecular-sieving, photocatalytic, hollow fiber membranes for advanced water treatment applications, J. Membr. Sci. 524 (2017) 163–173. [6] M.F. Haase, H. Jeon, N. Hough, J.H. Kim, K.J. Stebe, D. Lee, Multifunctional nanocomposite hollow fiber membranes by solvent transfer induced phase separation, 1234, Nat. Commun. 8 (2017), https://doi.org/10.1038/s41467-017-01409-3. [7] X. Zhang, D.K. Wang, D.R.S. Lopez, J.C.D. da Costa, Fabrication of nanostructured TiO2 hollow fiber photocatalytic membrane and application for wastewater treatment, Chem. Eng. J. 236 (2014) 314–322. [8] P. Hu, M. Long, Cobalt-catalyzed sulfate radical-based advanced oxidation: a review on heterogeneous catalysts and applications, Appl. Catal. B. Environ. 181 (2016) 103–117. [9] G.P. Anipsitakis, D.D. Dionysiou, Radical generation by the interaction of transition metals with common oxidants, Environ. Sci. Technol. 38 (2004) 3705–3712. [10] X. Duan, C. Su, J. Miao, Y. Zhong, Z. Shao, S. Wang, H. Sun, Insights into perovskite-
[24]
[25] [26] [27]
[28]
[29] [30]
[31]
[32]
302
catalyzed peroxymonosulfate activation: maneuverable cobalt sites for promoted evolution of sulfate radicals, Appl. Catal. B. Environ. 220 (2018) 626–634. C. Su, X. Duan, J. Miao, Y. Zhong, W. Zhou, S. Wang, Z. Shao, Mixed conducting perovskite materials as superior catalysts for fast aqueous-phase advanced oxidation: a mechanistic study, ACS Catal. 7 (2017) 388–397. J. Miao, J. Sunarso, C. Su, W. Zhou, S. Wang, Z. Shao, SrCo1−xTixO3−δ perovskites as excellent catalysts for fast degradation of water contaminants in neutral and alkaline solutions, Sci. Rep. 7 (2017) 44215. Y. Chu, X. Tan, Z. Shen, P. Liu, N. Han, J. Kang, X. Duan, S. Wang, L. Liu, S. Liu, Efficient removal of organic and bacterial pollutants by Ag-La0.8Ca0.2Fe0.94O3-δ perovskite via catalytic peroxymonosulfate activation, J. Hazard. Mater. 356 (2018) 53–60. Z. Shao, G. Xiong, H. Dong, W. Yang, L. Lin, Synthesis, oxygen permeation study and membrane performance of a Ba0.5Sr0.5Co0.8Fe0.2O3−δ oxygen-permeable dense ceramic reactor for partial oxidation of methane to syngas, Sep. Purif. Technol. 25 (2001) 97–116. Y. Wei, Q. Liao, Z. Li, H. Wang, Enhancement of oxygen permeation through Ushaped oxide hollow fiber membranes by surface modifications, Sep. Purif. Technol. 110 (2013) 74–80. Y. Wei, W. Yang, J. Caro, H. Wang, Dense ceramic oxygen permeable membranes and catalytic membrane reactors, Chem. Eng. J. 220 (2013) 185–203. X. Chen, L. Huang, Y. Wei, H. Wang, Tantalum stabilized SrCoO3−δ perovskite membrane for oxygen separation, J. Membr. Sci. 368 (2011) 159–164. H. Wang, A. Feldhoff, J. Caro, T. Schiestel, S. Werth, Oxygen selective ceramic hollow fiber membranes for partial oxidation of methane, AIChE J. 55 (10) (2009) 2657–2664. X. Tan, Z. Pang, Z. Gu, S. Liu, Catalytic perovskite hollow fibre membrane reactors for methane oxidative coupling, J. Membr. Sci. 302 (2007) 109–114. Y. Hu, R. An, Y. Chu, X. Tana, J. Sunarso, S. Wang, S. Liu, Perovskite hollow fiber membranes supported in a porous and catalytically active perovskite matrix for air separation, Sep. Purif. Technol. 192 (2018) 435–440. Y. Shang, L. Wei, X. Meng, B. Meng, N. Yang, J. Sunarso, S. Liu, CO2-enhanced hydrogen permeability of dual-layered A-site deficient Ba0.95Ce0.85Tb0.05Zr0.1O3-δbased hollow fiber membrane, J. Membr. Sci. 546 (2018) 82–89. H. Wang, C. Tablet, J. Caro, Oxygen production at low temperature using dense perovskite hollow fiber membranes, J. Membr. Sci. 322 (2008) 214–217. X. Zhu, H. Wang, W. Yang, Novel cobalt-free oxygen permeable membrane, Chem. Commun. 1130–1131 (2004). J. Zhu, G. Liu, Z. Liu, Z. Chu, W. Jin, N. Xu, Unprecedented perovskite oxyfluoride membranes with high-efficiency oxygen ion transport paths for low-temperature oxygen permeation, Adv. Mater. 28 (2016) 3511–3515. J. Zhu, S. Guo, Z. Chu, W. Jin, CO2-tolerant oxygen-permeable perovskite-type membranes with high permeability, J. Mater. Chem. A 3 (2015) 22564–22573. H. Wang, S. Werth, T. Schiestel, J. Caro, Perovskite hollow-fiber membranes for the production of oxygen-enriched air, Angew. Chem. Int. Ed. 117 (2005) 7066–7069. D. Yang, N. Yang, B. Meng, X. Tan, C. Zhang, J. Sunarso, Z. Zhu, S. Liu, A-Site excess (La0.8Ca0.2)1.01FeO3−δ (LCF) perovskite hollow fiber membrane for oxygen permeation in CO2-containing atmosphere, Energy Fuels 31 (2017) 4531–4538. S. Palimar, S.D. Kaushik, V. Siruguri, D. Swain, A.E. Viegas, C. Narayana, N.G. Sundaram, Investigation of Ca substitution on the gas sensing potential of LaFeO3 nanoparticles towards low concentration SO2 gas, Dalton Trans. 45 (2016) 13547–13555. S. Liu, L. Liu, Z. Xu, A. Yu, G. Lu, J. Diniz da Costa, Bioceramic macrocapsules for cell immunoisolation, Angew. Chem. Int. Ed. 46 (2007) 3062–3065. A.R. Chesney, C.J. Booth, C.B. Lietz, L. Li, J.A. Pedersen, Peroxymonosulfate rapidly inactivates the disease-associated prion protein, Environ. Sci. Technol. 50 (2016) 7095–7105. W. Tian, H. Zhang, Z. Qian, T. Ouyang, H. Sun, J. Qin, M. Tadé, S. Wang, Breadmaking synthesis of hierarchically Co@C nanoarchitecture in heteroatom doped porous carbons for oxidative degradation of emerging contaminants, Appl. Catal. B. Environ. 225 (2018) 76–83. Z. Wang, H. Liu, X. Tan, Y. Jin, S. Liu, Improvement of the oxygen permeation through perovskite hollow fibre membranes by surface acid-modification, J. Membr. Sci. 345 (2009) 65–73.