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Journal ofMaterials Chemistry A
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aDepartment of Chemical & Biological Eng
Membrane and Water Treatment Techno
University, Hangzhou, 310027, P. R. Ch
+86-571-87952121bXi'an High-Tech Institute, Xi'an, 710025, P
† Electronic supplementary informa10.1039/c3ta12199b
Cite this: J. Mater. Chem. A, 2013, 1,11343
Received 6th June 2013Accepted 18th July 2013
DOI: 10.1039/c3ta12199b
www.rsc.org/MaterialsA
This journal is ª The Royal Society of
Acid and multivalent ion resistance of thin filmnanocomposite RO membranes loaded with silicalite-1nanozeolites†
Hai Huang,a Xinying Qu,a Xiaosheng Ji,a Xin Gao,b Lin Zhang,*a Huanlin Chena
and Lian Houab
The incorporation of NaA nanozeolites into thin film composite (TFC) reverse osmosis (RO) membranes has
been found to elevate water permeability, but the unfavorable acid and multivalent ion sensitivity of NaA
limits the application of the thin film nanocomposite (TFN) membranes for seawater desalination. To
overcome these drawbacks, the chemically stable silicalite-1 nanozeolite was incorporated into the skin
layer of the RO composite membrane via interfacial polymerization. In this paper, the resulting
membrane was characterized with outstanding chemical stability (acid and multivalent cation tolerance)
compared with the NaA mixed membrane. Additionally, silicalite-1 showed better capacity to enhance
membrane permeability than NaA, which can be explained by larger channel pores and a higher water
diffusion rate in silicalite-1. This investigation indicates that the silicalite-1 mixed membrane has great
potential in large-scale seawater desalination because of its excellent permeability and chemical stability.
Introduction
Reverse osmosis (RO) comprises over 50% of installed desali-nation capacity globally.1 The success of RO desalination islargely attributed to the application of thin lm composite(TFC) polyamide (PA) membranes, which ts the high-produc-tivity trend in modern desalination owing to its low hydraulicresistance. To achieve higher permeability TFC PA membranes,considerable effort has been devoted in recent decades bymeans of polymer chemistry, surface modication, post-treat-ment and so on.2–8 Although the conventional methods havebeen shown to effectively enhance membrane permeability, thiscan occur at the expense of membrane rejection. It has becomeimportant to nd new strategies to further elevate the perme-ability without sacricing rejection or other aspects of theperformance.
Several years ago, porous and hydrophilic NaA nanozeoliteswere rst incorporated into an ultra-thin PA layer in a novelapproach to enhance membrane performance.9 This new vari-able was intended to change the dense and cross-linked surfacemorphology of the PA membrane by integrating a microporousstructure (0.42 nm in diameter inside NaA). During the process
ineering, Engineering Research Center of
logy, Ministry of Education, Zhejiang
ina. E-mail: [email protected]; Tel:
. R. China
tion (ESI) available. See DOI:
Chemistry 2013
of RO, water molecules (0.27 nm in diameter)10 can passthrough the separation barrier partly by owing across thesemicropores rather than by simply permeating through thepreviously dense PA layer. In this way, an obviously decreasedhydraulic resistance can be achieved. NaA-incorporated ROmembranes were found to possess increased permeability.11–13
Meanwhile, ion rejection was little changed as commonhydrated ions (0.6–0.9 nm in diameter)14,15 were size-excludedfrom these micropores.
Inspired by this novel concept, many other porous nano-particles were applied in RO membranes. The incorporation ofcarbon nanotubes,16 porous silicon17 and different types ofzeolites (NaX15 and Y types18) demonstrated increased waterpermeability but somewhat decreased ion rejection. Thisrejection deterioration may be explained by tiny voids betweenthe porous nanoparticles and the PA matrix, which would bepassable to salt ions during the separation process.19 It seemsthat NaA performs better than the other nanoparticle candi-dates if considering the harsh rejection requirements in the ROprocess. Here, the hydrophilic surface of NaA, which is rich inhydroxyl groups, may play an important role, as it is morecompatible with the PA matrix, which is rich in hydrophilicamide bonds. This good compatibility leads to fewer voids.19
Moderate acidication is always performed on the feed inmany RO plants for scaling control.20 In an acidic solution, NaAzeolites will undergo a dealumination reaction21 due the exis-tence of alkaline Al in the crystal. Additionally, nearly all prac-tical desalination processes involve a complex feed containingmultivalent cations such as Ca2+, Mg2+ and Sr2+. Upon contact,these multivalent cations will exchange with Na+ inside NaA
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zeolites (ion exchange phenomenon).22 Both reactions willundermine the previous stability of NaA, possibly deterioratingthe separation performance of the resulting NaA–ROmembrane. The poor acid resistance and excellent multivalentcation exchange ability of NaA will reduce the durability of theNaA–PA membrane in long-term applications. Hence, it ismeaningful to nd a more chemically stable substitute for NaAfor incorporation into membranes.
Similar to NaA, silicalite-1 zeolite not only possesses amedium pore size (0.56 nm in diameter),23 between the diam-eter of water molecules and common hydrated ions, but alsopossesses rich hydroxyl groups on its surface. Additionally, sil-icalite-1 is an alumina-free zeolite without counter ions and,therefore, is non-susceptible to acid and multivalent cations. Itis expected that silicalite-1 may be superior to NaA in ROmembranes for desalination applications. Recently, someattention has been focused on assessing the feasibility of sili-cate zeolites in desalination.24,25 A recent investigation fabri-cated mixed PA membranes with silicalite-1 nanocrystalssynthesized in the laboratory, and the obtainedmembranes hada greater hydrophilic surface than the bare PA membrane.25
In this paper, we attempt to conrm that silicalite-1 incor-porated membranes not only possess enhanced permeabilitybut also maintain excellent stability in acid and multivalent ionaqueous solutions. For this purpose, ROmembranes containingdifferent zeolites were fabricated by interfacial polymerization.A comprehensive evaluation of their separation performanceunder different feed solutions was also carried out. This workcould promote the application of porous nanoparticles in ROmembrane processes and will be helpful to explore advancedRO membranes.
Experimental sectionMaterials
Tetraethyl orthosilicate (TEOS, 98%, Aldrich), aluminium iso-propoxide (AIP, 98%, Aldrich), tetrapropylammoniumhydroxide (TPAOH, �20%, Aldrich), tetraethyl ammoniumhydroxide (TEAOH, �40%, Aldrich) and poly(vinyl alcohol)(PVA-1799, Suzhou Chemical Industry Co., Ltd) were used tosynthesise NaA and silicalite-1 zeolite nanocrystals. Trimesoylchloride (TMC, 98%, Aldrich) and m-phenyldiamine (MPD,>99%, Aldrich) were used as received for the interfacial poly-merization of PA. Other chemicals, including sodium chlorideand n-hexane, purchased from Sinopharm Chemical ReagentCo. Ltd, were used without further purication. Polysulfone(ultraltration) membranes were used as the supportmembrane, kindly provided by the Center of Water TreatmentTechnology, Hangzhou, China. Deionized (DI) water producedby a Milli-Q ultrapure water purication system was used forsolution preparation and the ltration study.
Synthesis and characterization of the NaA and silicalite-1zeolite nanocrystals
NaA zeolites were synthesized by the classical hydrothermalmethod described in the literature.26 A certain amount of TEOS
11344 | J. Mater. Chem. A, 2013, 1, 11343–11349
and AIP were dissolved in DI water. Next, the aqueous solutionwas stirred for about 30 min in a sealed polypropylene bottle atroom temperature. TPAOHwas added drop-wise to the preparedsolution. The molar ratio was [Na2O] : [SiO2] : [Al2O3] :[TPAOH] : [H2O] ¼ 0.3 : 4.5 : 0.6 : 9.0 : 400. Aer 10 days ofheating the reaction to reux at 40 �C, a white slurry mixturewas formed. NaA nanocrystals were obtained by repeatedcentrifugation at 12 000 rpm for 6 h and a following rinse withDI water until neutral pH was achieved. The preparation of thesilicalite-1 nanocrystals is similar to NaA, in which TEAOH wasapplied rather than TPAOH in NaA. The molar ratio of thereactive solution was [TEOS] : [TEAOH] : [H2O] : [EtOH] ¼1 : 1.24 : 6.26 : 0.98.
A calcination method was used to remove the template agentfrom the synthesized nanozeolites. To prevent the nanocrystalsfrom aggregating at high temperature, they were blended withan aqueous solution of 2% (w/v) PVA and stirred for 40–60 min.Ultrasonication was performed for 10–20 min for betterdispersion of the nanozeolites. The solution was dried in anoven (80 �C) for 3–5 h and a zeolite–PVA composite was formed.Finally, calcination under oxygen at 550 �C (at a heating rate of1 �C min�1) for 12 h was performed to obtain template-freezeolite nanocrystals with high dispersibility.
X-ray power diffraction (XRD) (X'pert diffractometer using CuKa radiation) was used to evaluate the crystalline structure andscanning electron microscopy (SEM; JSM-5610LV, JEOL, Japan)was used to characterize the nanocrystal morphology and torecord their mean diameter. The size distribution of the parti-cles was determined by manual measurement from the SEMimages. All of the samples were dried in an oven (80 �C) for 30–40 min. Both the XRD and SEM results of the synthesizednanozeolites are shown in the ESI.†
Preparation of the zeolite-incorporated membranes
The bare PA membrane was hand-casted on a polysulfonesubstrate as the control. Aer the support membrane wasimmersed in a 2% (w/v) aqueous MPD solution for about 10min, it was poured out and vertically placed in the atmosphereuntil the excess aqueous solution was removed. The MPD-richsubstrate was dipped into a 0.1% (w/v) TMC solution inn-hexane for 40 s. The nascent PA membrane was heat-cured at60 �C for 20 min, followed by rinsing with DI water to removebyproducts and excess monomers. Zeolite-incorporated PAmembranes were also made in an analogous process, duringwhich the different zeolites (silicalite-1 and NaA) were respec-tively mixed into the TMC–hexane solution. Ultrasonication wasapplied for approximately 30 min before polymerization tocompletely mix the nanozeolites. In this paper, the bare PAmembrane and the membranes containing silicalite-1 and NaAzeolites are labelled as B-PA, S-PA and A-PA, respectively.
Stability test of the membranes under different feedconditions
An acid corrosion test was carried out by applying a 2000 ppmNaCl aqueous solution containing acetic acid (0.5%, v/v, pH 5)during the RO operation. A resistance test with multivalent
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cations was also conducted by subsequently adding CaCl2 to theoriginal NaCl feed to achieve 1000 ppm aer RO operation for2 h. Here, we chose Ca2+ as a typical multivalent ion, rather thanMg2+ or Sr2+, because NaA is more sensitive to Ca2+ than Mg2+
for ion exchange and there is much less Sr2+ than Ca2+ andMg2+
in seawater.
Fig. 2 Contact angle of the membranes.
Membrane characterization and performance assessment
The membrane morphology was imaged by SEM (JSM-5610LV,Japan). A contact angle goniometer (OCA20, Dataphysics, Ger-many) equipped with video capture at room temperature wasemployed to quantify the surface hydrophilicity. For eachsample, ve contact angle tests from different sites were per-formed and the nal results were obtained by calculating theaverage.
A customized cross-ow RO cell (Fig. 1) was used to evaluatethe membrane performance. An aqueous solution containing2000 ppm NaCl was applied as the feed. Prior to measurement,each sample was compressed at 1.6 MPa for 1 h, and thenthe volume of the permeate was collected to calculate the ux(J, L m�2 h�1). The ion rejection (R, %) was evaluated byquantifying the conductivity of the permeate and feed using aconductivity meter.
The permeation ux of the membranes was calculated asfollows:
J ¼ V
SDt
where Dt is the test time (h), V is the volume of permeatecollected during the test (L) and S is the membrane area (m2).
The NaCl rejection of the membranes (%) was calculated asfollows:
R ¼ Cf � Cp
Cf
� 100
where Cf is the feed conductivity and Cp is the permeateconductivity.
Results and discussionContact angle analysis of the membrane surfaces
As presented in Fig. 2, nanozeolite incorporation (includingS-PA and A-PA) rendered the membranes more hydrophilic than
Fig. 1 Schematic diagram of the RO test.
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B-PA. This hydrophilicity enhancement becamemore evident asthe zeolite loading exceeded 0.05% (w/v) in hexane. This couldbe explained by a zeolite-induced kinetic change in the inter-facial polymerization between MPD and TMC. This is proposedto result in more pendant carboxylic groups originating fromthe unreacted acyl chloride of TMC and, consequently,decreased cross-linking of the PA lm.13,27 This is a desirabletrend because a hydrophilic surface is a signicant property interms of good membrane permeability and antifouling.28
Additionally, some of the incorporated zeolites would beexposed to the membrane surface, whichmakes the hydrophiliczeolite body accountable for the increased membrane hydro-philicity to some extent.29,30 Therefore, A-PA, with a slightlymore hydrophilic surface than S-PA, becomes useful since NaAconserved more silanol groups on the surface than the silicalite-1 zeolites.
Desalination performance
The water permeability and NaCl rejection of the threemembranes were characterized using RO tests. As shown in
Fig. 3 The flux of the membranes (B-PA, A-PA, S-PA) with different zeoliteloadings under the operating conditions of 25 �C, 1.6 MPa and 2000 ppm NaCl inthe feed.
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Fig. 4 The rejection of the membranes (B-PA, A-PA, S-PA) with different zeoliteloadings under the operating conditions of 25 �C, 1.6 MPa and 2000 ppm NaCl inthe feed.
Fig. 5 XRD patterns of the NaA (a) and silicalite-1 (b) zeolites before and afterimmersion in acid solution (pH 5) for 12 h.
Fig. 6 Variation of the normalized flux of the membranes (B-PA, A-PA, S-PA) inthe acid corrosion test.
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Fig. 3, aer nanozeolites were incorporated into the PA lm, thepermeability evidently increased in both A-PA and S-PA from 20L m�2 h�1 (B-PA level) to 33.91 L m�2 h�1 (a 70% increase) and66.61 L m�2 h�1 (a 233% increase), respectively. Theseenhancements can be explained by the easier pathway suppliedby the zeolite for water to pass through, namely its internal porechannels.9 Furthermore, the enhancement in hydrophiliciltyshown in Fig. 2 may also facilitate the solubility and diffusion ofwater from the bulk feed to the membrane surface.17
It is notable that S-PA allowed a much higher ux than A-PAand attained good NaCl rejection (96.4%) at a certain zeoliteloading, as suggested by Fig. 3 and 4. This improvement overNaA can be partly interpreted by the silicalite-1 micropores(0.56 nm), which are larger in size than those of NaA (0.42 nm),such that more water molecules can be simultaneously trans-ported through the micropore channels. Additionally, a higherdiffusion rate of water molecules in the silicalite-1 nanocrystalchannels was observed, likely because of the weak H-bondinteractions between the water molecules and frameworkatoms.31 However, in the case of NaA, intrinsic ion–dipoleinteractions are stronger than the H-bond interactions, limitingthe water motion in the channels.31,32
It is notable that an optimal loading amount was found inorder to obtain the greatest permeability, in which A-PA wasabout 0.1% (w/v) and S-PA was about 0.05% (w/v). With higherloading amounts, the membrane permeability droppeddramatically, whichmay have been caused by the aggregation ofnanozeolites at a higher concentration. This aggregationbehavior is mainly driven by colloidal forces33 and is alsodetected in solutions containing other nanomaterials such ascarbon nanotubes,34 graphene35 and fullerene.36 The aggrega-tion behavior of nanozeolites during the PA lm formationprocess will lead to their poor dispersion in the PA matrix17 andinvalidate the water channels inside the nanozeolites, conse-quently weakening the previous enhancement in ux. Insummary, the membrane permeability would decrease in spiteof the improved surface hydrophilicity implied by the contactangle tests.
This journal is ª The Royal Society of Chemistry 2013
Fig. 7 SEMmorphology of B-PA before (a) and after (b) immersion in acid solution (pH 5 for 24 h); A-PA before (c) and after (d) immersion in the same acid solution; S-PA before (e) and after (f) immersion in the same acid solution.
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Zeolite and membrane acid stability
The acid tolerance of the synthesized NaA and silicalite-1 wererst evaluated by immersion into acetic acid solution (pH 5) for12 h in order to simulate the conditions of subsequent acidcorrosion tests of the resulting membranes. XRD analysis(Fig. 5), to supply structural information, was applied to indi-cate any crystalline changes. Fig. 5(a) shows that most of thecharacteristic diffraction peaks of the NaA zeolite disappeared
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aer acid treatment, which indicates the severe collapse of theNaA framework. On the contrary, the silicalite-1 zeolitesexhibited much greater acid stability without signicant struc-tural deterioration, since its characteristic peaks in Fig. 5(b)remained nearly the same. As expected, silicalite-1 was morestable than NaA under acidic conditions.
Three membrane samples including B-PA, A-PA (0.1% (w/v)NaA in hexane) and S-PA (0.05% (w/v) silicate-1 in hexane) were
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Fig. 8 Variation of the normalized rejection and flux of the membranes (B-PA, A-PA, S-PA) after CaCl2 (1000 ppm) addition.
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assessed by an acid corrosion test. The ux and NaCl rejectionwere normalized on the basis of initial ux (J0) and rejection(R0). As shown in Fig. 6, B-PA and S-PA could maintain steadyRO performance during 24 h of operation. On the contrary, adrastic decline in rejection and an increase in ux was found forA-PA. Since it could be ruled out that this occurred due tochanges in the PA matrix because the B-PA sample consistingonly of the polymer showed good acid resistance, the perfor-mance deterioration in A-PA can be reasonably interpreted asdefects introduced by the collapse of the NaA crystal structure asdemonstrated above.
To further investigate the effect of acidic conditions on thezeolite-incorporated membranes, SEM was also applied toprobe the surface of the three samples before and aerimmersion into an acetic acid solution (pH 5) for 24 h. Asindicated in Fig. 7, the surfaces of untreated B-PA and A-PAexhibited a dense “leaf-like” morphology. A-PA was obviouslyrougher than B-PA with an increased specic surface area, somore water molecules can be absorbed by the membrane; thisaccounts for the greater permeability in the RO test. Aer acidimmersion, the B-PA surface became looser, but still dense andnon-porous, as a result of the partial acid-catalyzed hydrolysis ofamido bonds. However, this decrease in the degree of cross-linking did not have a signicant effect on the eventualperformance according to the acid corrosion test describedabove. Hence, this was attributed to a dealumination reactionand subsequent crystalline structure collapse of the NaAzeolites in the PA matrix, as A-PA exhibited many defects visibleby SEM. These defects obviously led to the deteriorated rejec-tion of A-PA. In contrast, there were no visible defects on the“nodular-like” S-PA surface since silicalite-1 has excellent acidresistance.
Membrane stability in the presence of multivalent cations
The three membranes were used in NaCl aqueous solutionswith CaCl2 addition to evaluate the effect of multivalent cations(here, Ca2+ used as an example) on the separation performance.As shown in Fig. 8, A-PA varied tremendously as Ca2+ increased,
11348 | J. Mater. Chem. A, 2013, 1, 11343–11349
with decreased rejection and enhanced permeability. This wasattributed to the increase in NaA pore size caused by an ionexchange process between the compensating Na+ and Ca2+ ionsin the bulk feed. Since two Na+ cations are exchanged with oneCa2+ ion to maintain charge equilibrium, the number of cationsinside the NaA crystals decreased aer ion exchange and moreinternal space was le. Eventually, the effective pore diameter ofthe zeolites increased from the original 0.42 nm to approxi-mately 0.5 nm,37,38 which likely allowedmore water molecules toow through the interconnected channels, and also becomeapproachable to ions. In contrast, S-PA, with no ion exchangereactivity, maintained nearly unchanged levels of rejection andpermeability even aer 16 h of operation. This means that S-PAwould be reliable in the presence of multivalent cations andthus is more feasible for applications in seawater desalination.
Conclusion
Silicalite-1 nanozeolites were incorporated into PA thin lmcomposite membranes, and provided higher membranepermeability as well as enhanced acid and multivalent cationresistance compared to NaA nanozeolite-incorporatedmembranes. The effect of the silicalite-1 nanocrystals on themembrane properties were investigated. Contact angle analysisindicated that the S-PA membrane exhibited a more hydrophilicsurface than the bare PA membrane, and SEM images showedthat the S-PA membrane has a “nodular-like” morphology,unlike the bare PA membranes. Compared with the bare PA andA-PA membranes, the S-PA membranes evaluated by cross-owreverse osmosis tests showed greatly enhanced water perme-ability and improved acid stability. In the multivalent cation(CaCl2) tolerance test, the separation performance of S-PAremained unchanged as there was no ion-change activity withthe silicalite-1 zeolites. All of these results conrm that silica-lite-1 zeolites are superior to NaA zeolites in fabricating thinlm nanocomposite membranes.
Acknowledgements
This project is sponsored by the National Natural ScienceFoundation of China (21076176, 51238006), the NationalBasic Research Program of China (2009CB623402) and theScientic & Technological Innovation Team of Zhejiang Prov-ince (2009R50045).
References
1 M. A. Shannon, P. W. Bohn, M. Elimelech, J. G. Georgiadis,B. J. Marinas and A. M. Mayes, Nature, 2008, 452, 301–310.
2 R. J. Petersen, J. Membr. Sci., 1993, 83, 81–150.3 A. P. Rao, N. V. Desai and R. Rangarajan, J. Membr. Sci., 1997,124, 263–272.
4 I. J. Roh, A. R. Greenberg and V. P. Khare, Desalination, 2006,191, 279–290.
5 A. K. Ghosh, B.-H. Jeong, X. Huang and E. M. V. Hoek,J. Membr. Sci., 2008, 311, 34–45.
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ishe
d on
19
July
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3. D
ownl
oade
d by
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nive
rsity
on
21/0
9/20
13 0
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View Article Online
6 L. Li, S. Zhang, X. Zhang and G. Zheng, J. Membr. Sci., 2008,315, 20–27.
7 G. Chen, S. Li, X. Zhang and S. Zhang, J. Membr. Sci., 2008,310, 102–109.
8 H. Wang, L. Li, X. Zhang and S. Zhang, J. Membr. Sci., 2010,353, 78–84.
9 B. H. Jeong, E. M. V. Hoek, Y. S. Yan, A. Subramani,X. F. Huang, G. Hurwitz, A. K. Ghosh and A. Jawor, J.Membr. Sci., 2007, 294, 1–7.
10 E. R. Nightingale, J. Phys. Chem., 1959, 63, 1381–1387.11 M. L. Lind, D. Eumine Suk, T. V. Nguyen and E. M. V. Hoek,
Environ. Sci. Technol., 2010, 44, 8230–8235.12 M. L. Lind, B.-H. Jeong, A. Subramani, X. Huang and
E. M. V. Hoek, J. Mater. Res., 2009, 24, 1624–1631.13 M. L. Lind, A. K. Ghosh, A. Jawor, X. F. Huang, W. Hou,
Y. Yang and E. M. V. Hoek, Langmuir, 2009, 25, 10139–10145.
14 B. Tansel, J. Sager, T. Rector, J. Garland, R. F. Strayer,L. Levine, M. Roberts, M. Hummerick and J. Bauer, Sep.Purif. Technol., 2006, 51, 40–47.
15 M. Fathizadeh, A. Aroujalian and A. Raisi, J. Membr. Sci.,2011, 375, 88–95.
16 L. Zhang, G.-Z. Shi, S. Qiu, L.-H. Cheng and H.-L. Chen,Desalin. Water Treat., 2011, 34, 19–24.
17 J. Yin, E.-S. Kim, J. Yang and B. Deng, J. Membr. Sci., 2012,423, 238–246.
18 C. Kong, T. Shintani and T. Tsuru, New J. Chem., 2010, 34,2101–2104.
19 H. Huang, X. Qu, H. Dong, L. Zhang and H. Chen, RSC Adv.,2013, 3, 8203–8207.
20 D. Van Thanh, C. Y. Tang, M. Reinhard and J. O. Leckie,Environ. Sci. Technol., 2012, 46, 852–859.
21 K. Shiomori, H. Yoshizawa, K. Fujikubo, Y. Kawano,Y. Hatate and Y. Kitamura, Sep. Sci. Technol., 2003, 38,4057–4077.
This journal is ª The Royal Society of Chemistry 2013
22 M. Barros, P. A. Arroyo, E. F. Sousa-Aguiar andC. R. G. Tavares, Adsorption, 2004, 10, 227–235.
23 L. Li, J. Dong and T. M. Nenoff, Sep. Purif. Technol., 2007, 53,42–48.
24 B. Zhu, L. Zou, C. M. Doherty, A. J. Hill, Y. S. Lin, X. Hu,H. Wang and M. Duke, J. Mater. Chem., 2010, 20, 4675–4683.
25 D. Li, L. He, D. Dong, M. Forsyth and H. Wang, Asia-Pac.J. Chem. Eng., 2012, 7, 434–441.
26 S. Mintova, N. H. Olson, V. Valtchev and T. Bein, Science,1999, 283, 958–960.
27 G. L. Jadav and P. S. Singh, J. Membr. Sci., 2009, 328, 257–267.28 J. Mansouri, S. Harrisson and V. Chen, J. Mater. Chem., 2010,
20, 4567–4586.29 S. Li, Z. J. Li, D. Medina, C. Lew and Y. S. Yan, Chem. Mater.,
2005, 17, 1851–1854.30 Z. Wang, L. H. Wee, B. Mihailova, K. J. Edler and A. M. Doyle,
Chem. Mater., 2007, 19, 5806–5808.31 M. U. Ari, M. G. Ahunbay, M. Yurtsever and A. Erdem-
Senatalar, J. Phys. Chem. B, 2009, 113, 8073–8079.32 J. Y. Wu, Q. L. Liu, Y. Xiong, A. M. Zhu and Y. Chen, J. Phys.
Chem. B, 2009, 113, 4267–4274.33 A. R. Petosa, D. P. Jaisi, I. R. Quevedo, M. Elimelech and
N. Tufenkji, Environ. Sci. Technol., 2010, 44, 6532–6549.34 I. A. Khan, A. R. M. N. Afrooz, J. R. V. Flora, P. A. Schierz,
P. L. Ferguson, T. Sabo-Attwood and N. B. Saleh, Environ.Sci. Technol., 2013, 47, 1844–1852.
35 S. Lin, C.-J. Shih, M. S. Strano and D. Blankschtein, J. Am.Chem. Soc., 2011, 133, 12810–12823.
36 J. Brant, H. Lecoanet and M. R. Wiesner, J. Nanopart. Res.,2005, 7, 545–553.
37 C. R. Melo, H. G. Riella, N. C. Kuhnen, E. Angioletto,A. R. Melo, A. M. Bernardin, M. R. da Rocha and L. daSilva, Mater. Sci. Eng., B, 2012, 177, 345–349.
38 K. Shams and S. J. Mirmohammadi,Microporous MesoporousMater., 2007, 106, 268–277.
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