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Novel Hollow Mesoporous Silica Spheres/Polymer Hybrid Membrane for Ultrafiltration Huiqing Wu, Beibei Tang,* and Peiyi Wu* The State Key Laboratory of Molecular Engineering of Polymers and Department of Macromolecular Science and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, People’s Republic of China ABSTRACT: A novel hybrid ultrafiltration membrane was prepared by incorporating hollow mesoporous silica spheres (HMSS) into a polymer matrix of brominated polyphenylene oxide (BPPO) using triethanolamine as the amination agent. The hybrid membrane exhibits improved water permeability, thermal stability, and water content, while the rejection to egg albumin maintaining at a high level (>90%). Especially when the addition of HMSS is 1.0 wt %, the water flux of the hybrid membrane reaches a maximum that is almost two times that of the BPPO membrane. The unique properties of HMSS and good interaction between HMSS and polymer contribute to the improvement of membrane performance. The effect of the structures of silica particles on the membrane performance was also investigated, and the results suggest that HMSS with moderate wall thickness is more suitable for the optimization of hybrid membrane properties.
1. INTRODUCTION Nowadays, membrane-based separations are becoming popular in various applications, such as chemical, food, and pharmaceutical industries for concentration purposes, thanks to their low energy requirements, potentially low fabrication cost, and steady-state operation.1 Polymeric membranes are in the most common use, but they suffer from an inherent upper bound on their performance, reflecting a trade-off between their permeability and selectivity.2 Therefore, a hybrid membrane, which comprises a polymeric matrix and inorganic component, has drawn the increasing attention of many researchers. A number of inorganic materials, such as zeolite, carbon nanotubes, graphite, and titanium dioxide, have been used for the formation of hybrid membrane and the enhancement of membrane property.38 Among them, silica materials have been studied extensively because of their structural flexibility, excellent abrasive, optical, electrical, and thermal properties, and unique potential applications. Up to now, silica materials with various structures, such as rod-like particles, nanowires, nanotubes, nanospheres, mesoporous particles, hollow particles, and other complex structures, have been synthesized by different methods.912 Hybrid membranes incorporated with solid silica particles (SiO2) have been reported in many cases, and the results suggest the addition of SiO2 into polymer is beneficial to membrane separation performance either in terms of membrane flux (productivity) or selectivity (separation efficiency) and some other properties including thermal stability and mechanical strength.1316 The improvement of membrane permeability results from the capacity of these fillers to disrupt polymer chain packing and to increase the system free volume.16 In recent years, mesoporous silica materials are developing rapidly because they possess high specific r 2011 American Chemical Society
surface area, large pore volume, tunable pore structures, and welldefined surface property for modification. Most of mesoporous silica materials are prepared using a surfactant template. They usually have uniform pore channels with a diameter range of 210 nm and can be modified in various ways. What is more, mesopores of materials are particularly beneficial to rapid diffusion of molecules, so they provide the possibility for specific separation applications over a range of molecular sizes.17 Mesoporous siliceous MCM-41 molecular sieve was first used as an additive to enhance the gas permeability of a polysulfone membrane by Reid and co-workers.18 Then lots of meaningful works concerned with mesoporous silica/polymer membrane have been reported continuously, and the type and function of hybrid membrane also present a tendency of diversification.1924 Jang et al. reported a complete process for fabricating a hybrid mesoporous silica/polymer membrane on a technologically scalable hollow fiber platform, and the obtained membrane was defect-free with a high gas flux.25 Mekawy and his group developed an ultrafiltration membranes with silica mesostructures, and it could be used effectively in separating silver nanoparticles of uniform morphology and size.26 Zornoza et al. prepared mixed matrix membranes using polyimide Matrimid and mesoporous silica spheres and found permeability of the selective gas increased with the filler, and the selectivity reached a maximum at 8 wt % filler loading.27 Jomekian et al. demonstrated the proper addition of polyethylene oxide (PEO) modified MCM-41 particles into polyvinylidene chloride (PVDC) could effectively Received: July 31, 2011 Revised: December 12, 2011 Published: December 21, 2011 2246
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The Journal of Physical Chemistry C improve membrane performance including hydrophilicity, mechanical property, and especially membrane flux.28 Especially, mesoporous silica particles with a regular spherical geometry, such as hollow spherical nanostructures, have been created for their scientific and technological interests.9,29 In addition to the merits of mesoporous materials, hollow mesoporous silica spheres take the advantages of controllable inner core size, wall thickness, particulate size, and low density, thus being considered as a more promising candidate for numerous applications such as chemical/drug delivery, catalyst, and membrane separation.30,31 However, to the best of our knowledge, the application of hollow mesoporous silica spheres in the field of membrane separation has rarely been reported up until now. Hollow mesoporous silica spheres give rise to a novel kind of hybrid membrane with potential applications, which have not yet been studied. In this research, we developed a novel hollow mesoporous silica spheres (HMSS)/ polymer hybrid membrane based on a brominated polyphenylene oxide (BPPO) matrix. To increase the compatibility between the HMSS and the polymeric component, triethanolamine (TEOA) was introduced into the casting system due to its quaternary amination reaction with BPPO and formation of hydrogen bonds with silanol groups (SiOH) of HMSS.24 The influence of the HMSS loading on the membrane performance was investigated. To gain an insight into the effect of the structures of silica particles on the membrane performance, various silica particles including hollow mesoporous silica spheres with different wall thickness, solid silica particles and mesoporous silica particles were synthesized and incorporated into the BPPO-based polymer matrix. The samples were characterized in terms of FTIR, pure water flux, rejection, water content, SEM, TEM, and TGA.
2. EXPERIMENTAL SECTION 2.1. Materials. Poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) with an intrinsic viscosity of 0.57 103 m3 3 kg1 in chloroform at 25 °C was obtained from the Institute of Chemical Engineering of Beijing, China. Triethanolamine (TEOA), tetraethyl orthosilicate (TEOS), aqueous ammonia (25% w/w), styrene, and N-methyl-2-pyrrolidone (NMP) were purchased from Aladdin Co., Ltd. N-cetyltrimethylammonium bromide (CTAB), chlorobenzene, bromine, ethanol (EtOH), potassium persulfate (KPS), and sodium hydroxide (NaOH) were all of analytical grade and used without further treatment. Egg albumin with an average molecular weight of 45 000 g/mol was used as a probe molecule for rejection tests and supplied by Sinopharm Chemical Reagent Co., Ltd. 2.2. Synthesis of Silica Particles. 2.2.1. Preparation of Polystyrene (PS) Particles. The PS particles used as a template were synthesized by one-stage soap-free emulsion polymerization.32 To a flask, 12.0 g of styrene and 190.0 mL of water were added, and the mixture was vigorously stirred at 300 rpm for about 30 min at room temperature. Then, 0.5 g of KPS (dissolving in 10 mL of water) was added into the mixture. Finally, the mixture was degassed under nitrogen purge, and then polymerization was performed with vigorous stirring at 80 °C for 6 h under nitrogen atmosphere. After completion of the polymerization, the PS particles dispersed in the aqueous solution were obtained after dialysis. The concentration of the PS solution is 1.07% (w/w). 2.2.2. Synthesis of Hollow Mesoporous Silica Spheres (HMSS). The HMSS were synthesized as follows:31,33 0.3227 g of CTAB was dissolved in a mixture of 100 mL of water, 50 mL of EtOH
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(V(EtOH)/V(H2O) = 0.5), and 1 mL of aqueous ammonia. Then, 2.5 mL of PS solution was added into the above CTAB solution, followed by magnetically stirring (250 rpm) for 10 min at 30 °C before adding dropwise 0.4 mL of TEOS. The mixture was continuously stirred at 30 °C for 2 h before the mesoporous silica coated latex was harvested by centrifugation at 8000 rpm for 3 min. The precipitate was washed with copious amounts of water and ethanol, respectively, and then dried at room temperature. Finally, the coated PS were calcined in air at 550 °C for 6 h, and the HMSS were obtained. The wall thickness of HMSS was about 80 nm in the preparation condition and was denominated in HMSS-80. When V(EtOH)/V(H2O) changed from 0.5 to 0.333 and 0.587, HMSS with wall thickness of about 50 and 120 nm were prepared, and they were named HMSS-50 and HMSS-120 according to the wall thickness, respectively. 2.2.3. Synthesis of Solid Silica Particles (SiO2). To a flask, 20 mL of EtOH and 5 mL of aqueous ammonia were added. The mixture of TEOS (0.5 mL) and EtOH (1.0 mL) was rapidly added to the flask and magnetically stirred (100 rpm) for 2 h at 40 °C. Then, the mixture of TEOS (5.0 mL) and EtOH (2.0 mL) were dropwise added into the above solution and then kept for 6 h. The SiO2 was harvested by centrifugation, washing with copious ethanol, and calcining at 550 °C for 6 h. 2.2.4. Synthesis of Mesoporous Silica Spheres (MSS). The MSS were prepared as follows: 0.2915 g of CTAB was dissolved in a mixture of 190 mL of water, 87.5 mL of EtOH, and 1 mL of NaOH solution (2 mol/L). Then, 4.63 mL of TEOS was added into the above solution with magnetic stirring (200 rpm) for 10 min at 80 °C. Finally, the reaction was kept for 24 h at 80 °C. The precipitate was centrifuged, washed, and calcined to remove the surfactant-template. 2.3. Membrane Preparation. The brominated PPO (BPPO) was obtained by the bromination of PPO as described in our previous paper.34,35 The hybrid membrane was prepared as follows. First, a given amount of silica particles was dispersed in NMP and sonicated for 10 min. Then, BPPO was dissolved in the above solution to form an approximately 20 wt % homogeneous solution. Next, TEOA-NMP solution (the ratio of BPPO to TEOA was 8:1) was added. For better dispersion and more sufficient interactions among TEOA, BPPO, and silica particles, the mixture was vigorously stirred for 30 min followed by sonication for 60 min. After removing air bubbles, this solution was cast onto a clean glass plate. Subsequently, the glass plate was horizontally immersed into deionized water at a temperature of 30 °C for at least 24 h to remove the solvent and solidify the membrane structure. Finally, the membranes were washed with deionized water repeatedly and stored in a wet environment. For comparison, a BPPO membrane without silica particles was prepared using the same method. The membrane thickness was approximately 200 μm. 2.4. Characterization. Particles were observed by a high-resolution scanning electron microscope (FE-SEM S-4800, Hitachi) and transmission electron microscopes (JEM-2100F and Hitachi H-600). The surface area was calculated by the BrunauerEmmettTeller (BET) method, and the pore size distribution was calculated by the Barrett JoynerHalenda (BJH) method. The size distribution of the particles was measured by dynamic light scattering (DLS) using a Zetasizer Nano measurement. The surfaces and cross-sections of membranes were observed using a scanning electron microscope (TESCAN 5136MM) and high-resolution FE-SEM S-4800 equipped with EDX 2247
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Figure 2. Nitrogen adsorptiondesorption isotherms and pore size distribution of HMSS-80.
were removed from the water and weighed immediately after blotting the free surface water. Then, they were dried for over 24 h at 60 ( 2 °C in an oven. The water content (W) is deduced from eq 3 W ¼ Figure 1. (a) Schematic of the formation of HMSS; (b) SEM image of PS particles; inset, TEM image of PS particles; (ce) TEM images of HMSS-80; (f) FE-SEM image of HMSS-80.
(QUANTAX 400, Bruker). To better examine the distribution of HMSS, the HMSS/BPPO hybrid membranes were etched on the surface using NMP so that the silica particles can be exposed. Cross-sectional membrane samples were obtained by previous freeze fracturing after immersion in liquid nitrogen. Thermogravimetric analysis (TGA) was performed on a Perkin-Elmer Pyris 1 TGA instrument at a rate of 20 °C/min under a nitrogen atmosphere from 100 to 800 °C. Fourier transform infrared (FT-IR) spectra were recorded on Nicolet Nexus 470. The measurements of pure water flux and protein rejection were performed using a cross-flow membrane module at an operation pressure of 0.2 MPa. The water flux was calculated in eq 1 F ¼
V At
ð1Þ
where V is the total volume of permeated pure water, A is the membrane area, and t is the operation time. The rejection was measured with 0.5 g/L egg albumin solution at an operation pressure of 0.2 MPa. The concentrations of the permeation and feed solutions were determined by an ultravioletvisible spectrophotometer (Lambda 35, PerkinElmer, USA) at 205 nm. The rejection was calculated in eq 2 R ¼ 1
Cp Cf
ð2Þ
where Cp and Cf are the concentrations of the permeation and feed solutions, respectively. The water content of the membranes was determined after equilibrating a sample of membrane in chloride ion form with deionized water at room temperature. The membrane samples
W2 W1 W1
ð3Þ
where W1 and W2 are the weights of the dry and wet membrane samples, respectively.
3. RESULTS AND DISCUSSION 3.1. Characterization of HMSS. The schematic preparation process of HMSS is illustrated in Figure 1a. First, the PS latex was prepared by soap-free emulsion polymerization. Figure 1b shows the TEM and SEM images of PS particles, indicating an average diameter of approximately 500 nm of the monodispersed template particles. The result of DLS measurement suggests the PS particles have a mean diameter of 514 nm with a narrow size distribution (PDI = 0.028), slightly larger than that observed from TEM because of the hydrate layer in aqueous environment. Then, HMSS were synthesized through solgel process of TEOS on the template of PS particles in the presence of the CTAB surfactant and using calcination to remove CTAB and PS template. As shown in Figure 1c,d, the diameter of HMSS increases to about 650 nm with a good particle uniformity after coating the silica on the PS template. The wall thickness of HMSS is about 80 nm (named HMSS-80) and radially oriented mesopores can be clearly observed at a high magnification from Figure 1e,f. Figure 2 displays the nitrogen adsorptiondesorption isotherms and pore size distribution of HMSS-80. The isotherms of HMSS indicate a typical mesoporous material with fair arrangement of pores, large diameter, and a relatively narrow pore-size distribution. The isotherms also show a type IV adsorption behavior without hysteresis and exhibit steep condensation steps, reflecting a high uniformity of mesopores. The samples calcined at 550 °C had a pore size of 2.70 nm, a BET surface area of 794 m2/g, and a pore volume of 0.536 m3/g. 3.2. Characterization of HMSS/BPPO Hybrid Membrane. Figure 3 presents the FT-IR spectra of HMSS, BPPO membrane, 2248
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Figure 3. FT-IR spectra of (a) HMSS; (b) BPPO membrane; and (c) HMSS/BPPO membrane.
Figure 4. (a) SEM image of the hybrid membrane; (b) Si-mapped distribution of the corresponding membrane; (c) SEM image of the cross-section of the hybrid membrane; (d) FE-SEM image of the circled area in panel c.
and HMSS/BPPO hybrid membrane, respectively. In Figure 3a, the bands at 801 and 1089 cm1 are assigned to the symmetrical and asymmetrical vibrations of the bond SiOSi. The band at 961 cm1 is attributed to the vibration of silanol group (SiOH). The band at 1632 cm1 corresponds to H2O adsorbed on the particles. The broad band located at 3432 cm1 is assigned to the superposition of vibrations related both to the physically adsorbed H2O and the silanol groups. The spectrum of BPPO membrane shows several peaks in the Figure 3b, in the range of 3000 2800 cm1 assigned to stretching alkane and aromatic CH (ν(CH)), at 1601 and 1465 cm1 assigned to aromatic CdC stretching (ν(CdC)), at 1382 cm1 assigned to symmetric bending CH3, at 1307 cm1 assigned to CC bridge bond, and at 1193 cm1 assigned to symmetric stretch vibration of the aromatic ether COC. The prominent difference of FT-IR spectrum between BPPO and HMSS/BPPO membrane is the characteristic SiOSi stretching band of HMSS at 1089 cm1.21,36 As is well-known, the compatibility between inorganic and organic phase is one of the most prominent challenges in the formation of hybrid membrane because it has an intensive effect
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Figure 5. TG/DTG curves of BPPO membrane and HMSS/BPPO hybrid membrane.
on the membrane performance. The compatibility between HMSS and polymer matrix can be deduced by Figure 4. Figure 4a shows the SEM image of the surface of the hybrid membrane incorporated with 1.0 wt % of HMSS, and Figure 4b is the Si-mapping image of energy-dispersive spectrometer (EDS) of the corresponding membrane. The EDS spectrum allows the elements present in the membranes to be determined. The EDS mapping (Figure 4b) illustrates that Si is dispersed uniformly in the whole BPPO matrix, and there is no obvious aggregation or gather in the image.20,21,37 The dispersion of the HMSS within the hybrid membrane also can be observed from the crosssectional SEM image in Figure 4c, indicating a homogeneous distribution of particles without apparent segregation or agglomeration. The employment of spheres minimizes agglomeration and improves dispersibility because the spherical shape limits the contact between silica particles, and the sphere size provides a relative low external surface area to volume ratio.27 As can be observed in Figure 4d, which is a magnified image of the circled area in Figure 4c, HMSS are completely surrounded by the polymer, corroborating the good contact between them. First, HMSS with the OH-rich surface may form hydrogen bonding with polymer matrix, which consists of BPPO aminated by TEOA with three hydroxyl groups. Second, HMSS possess pores large enough to readily allow the penetration of polymer chains, resulting in a better wetting and dispersion.18 These two factors contribute to the improvement of interfacial compatibility between the inorganic and organic phases of the hybrid membrane. Figure 5 exhibits the TG/DTG curves of BPPO membrane and HMSS/BPPO hybrid membrane incorporated with 1.0 wt % of HMSS. From the DTG curves, the peak temperature corresponding to the highest decomposition rate for the hybrid membrane (497 °C) is higher than that for the BPPO membrane (490 °C). The result suggests that the addition of HMSS improves the thermal stability of the membrane, as a result of the interactions between HMSS and polymer, which increases the rigidity of polymer chains. The residue at 800 °C for the hybrid membrane is higher than that of BPPO membrane and also higher than that of the theoretical calculated values. Some polymer chains may permeate into the mesoporous channels of HMSS, leading to the improved thermal stability and the higher residue of the hybrid membrane.19,37 3.3. Effect of HMSS Loading on the Membrane Performance. To gain an insight into the influence of HMSS loading on the membrane performance, the hybrid membranes containing HMSS-80 content from 0.5 wt % to 5 wt % were prepared. 2249
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The Journal of Physical Chemistry C The BPPO membrane without HMSS was also prepared for comparison. A plot of pure water flux and rejection to egg albumin vs HMSS content is shown in Figure 6. As the amount of HMSS increases, the pure water flux of the membrane
Figure 6. Effect of HMSS loading on the pure water flux and rejection to egg albumin of HMSS/BPPO hybrid membranes at 0.2 MPa operating pressure.
Figure 7. SEM images of the surfaces of HMSS/BPPO hybrid membranes with different content of HMSS after etching using NMP: (a) 1.0 wt %; (b) 5.0 wt %.
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significantly increases. The flux increases to a maximum that is almost two times that of BPPO membrane at 1.0 wt % of HMSS but decreases at greater amounts of HMSS. At the same time, the egg albumin rejection rates of membranes decreases slightly with increasing amounts of HMSS, remaining at a relatively high level (>90%). The increase in membrane permeability with HMSS loading could be explained taking into account a combination of several factors.19,23,27 First, the mesopores and hollow inner of HMSS provide an additional passageway for water molecules to pass through. Second, the incorporation of HMSS may disrupt polymer chain packing and linking, and it leads to an increase in polymer free volume, which is in favor of the water permeability. Third, the high surface area and large amount of hydroxyl groups on the surface of HMSS contributes to the membrane’s hydrophilicity and water flux. However, an excessive amount of HMSS could cause severe aggregation, declining the specific surface area and the amount of hydroxyl groups on the HMSS surface, thereby resulting in a decrease in water flux. Figure 7 shows the distribution of HMSS in the membrane with different loading, and the SEM images suggest that HMSS can distribute well at low HMSS loading (1 wt %), while it presents severe agglomeration at higher loading, especially when the HMSS loading is 5 wt %. The loss of rejection especially at higher HMSS loadings (3.05.0 wt %) could be due to the generation of small nonselective voids existing between HMSS particles and inorganic organic phases. As a conclusion, adding an appropriate amount of HMSS to BPPO membrane could effectively improve the hybrid ultrafiltrition membrane’s water flux with the resistance of egg albumin above 90%. In our study, a relatively low percentage of inorganic particles is used for the optimization of membrane performance, implying less cost of inorganic material and less influence in the polymer mechanical property. The cross-section SEM images of HMSS/BPPO hybrid membrane are displayed in Figure 8. It could be found that all membranes exhibit a typical asymmetric finger-like structure and that they have no apparent differences. The result demonstrates that the addition of low contents of HMSS does not affect the structures of membrane. Thus, the mechanism of hybrid
Figure 8. SEM images of the cross-sections of HMSS/BPPO hybrid membranes with different content of HMSS: (a) 0 wt %; (b) 1.0 wt %; (c) 2.0 wt %; (d) 3.0 wt %; (e) 5.0 wt %. 2250
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Figure 9. Water content of HMSS/BPPO hybrid membranes with different content of HMSS.
Figure 11. Performance of hybrid membranes incorporated with different silica particles.
Figure 10. (a, b) TEM images of HMSS-50; (c, d) TEM images of HMSS-120; (e) TEM image of SiO2; (f) TEM images of MSS.
membrane structure formation is not affected by the addition of inorganic HMSS.19 Figure 9 illustrates the water contents of hybrid membranes with different content of HMSS. The water content of all hybrid membranes is higher than that of BPPO membrane. The more HMSS loaded, the more water is absorbed in the membrane. The increase in water content of hybrid membranes may be attributed to the water retention of the incorporated HMSS due to the hydrogen bonding of H2O molecules with the SiOH groups and the good adsorption ability of HMSS with meospores, which can be filled with the physically bonded water molecules. 3.4. Effect of Structures of Silica Particles on the Membrane Performance. It has been reported that the structure and morphology of inorganic particles incorporated in the MMM has an effect on membrane performance.21,23 To explore
the influence of the wall thickness, mesoporosity, and hollow structure of hollow mesoporous silica spheres on the membrane performance, various silica particles including hollow mesoporous silica spheres with three different wall thicknesses (HMSS50, HMSS-80, and HMSS-120), solid silica particles (SiO2), and mesoporous silica spheres (MSS) were synthesized, respectivley. Then a series of hybrid membranes containing various particles were prepared and characterized in terms of water flux and egg albumin rejection. In section 3.1, hollow mesoporous silica spheres with a wall thickness of about 80 nm (HMSS-80) were prepared, and herein, two other hollow mesoporous silica spheres were synthesized using the same technique. Hollow mesoporous silica spheres with wall thickness of about 50 nm (HMSS-50) can be observed in Figure 10a,b, and silica particles with wall thickness of about 120 nm (HMSS-120) can be seen in Figure 10c,d. HMSS-80, HMSS-50, and HMSS-120 possess the same morphology except for wall thickness. Figure 10e,f present the TEM image of solid silica particles (SiO2) and mesoporous silica spheres (MSS), respectively, and their size is approximately 650 nm, which is almost the same as that of HMSS to exclude size effects. The performance of hybrid membranes incorporated with different silica particles is summarized in Figure 11. The addition of all kinds of silica particles is 1.0 wt %. All of the hybrid membranes have higher water flux than that of pure BPPO membrane, while the egg albumin rejections present different degrees of reduction. A hybrid membrane based on HMSS, which have secondary wall thickness (HMSS-80), possesses moderate water permeability and the highest rejection. It is 2251
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The Journal of Physical Chemistry C considered that a mesoporous wall with small thickness is beneficial to the fast pass of water molecules. In the case of the same weight of silica spheres, particle number may increase notably due to the smaller sphere size and lower density, thus leading to the aggregation of particles and the generation of nonselective voids. Therefore, the rejection of the HMSS-50/BPPO membrane obviously decreases. Compared with those of the membrane incorporated with HMSS and MSS, SiO2/ BPPO membrane has minimums of both flux and rejection because solid SiO2 without mesoporosity offers no fast pass way for water and reduces the interaction with the polymer phase. The hollow inner, which helps the water transport, may be responsible for the higher water permeation rate of HMSS/BPPO membrane in comparison with that of MSS/BPPO membrane.
4. CONCLUSIONS A novel hollow mesoporous silica spheres (HMSS)/brominated polyphenylene oxide (BPPO) hybrid membrane was prepared using the phase inversion method. The results suggest that the addition of appropriate content of HMSS (1.0 wt %) can significantly increase the water flux of the membrane, while maintaining the rejection to egg albumin at a high level (>90%). The improved performance of the HMSS/BPPO membrane is attributed not only to the unique properties of HMSS, such as mesoporosity, high surface area, large pore volume and hollow inner, but also to the good compatibility between HMSS and polymer. In addition, the thermal stability and water content of the membrane are also improved. To investigate the effect of the structures of silica particles on the membrane performance, various silica particles including hollow mesoporous silica spheres with different wall thickness, solid silica particles, and mesoporous silica particles were synthesized and incorporated into the BPPO matrix to prepare a hybrid membrane. The results illustrate that the hybrid membrane incorporated with HMSS of moderate wall thickness exhibits the best overall properties. ’ AUTHOR INFORMATION Corresponding Author
*Tel: +86-21-65643255. Fax: +86-21-65640293. E-mail: bbtang@ fudan.edu.cn (B.T.);
[email protected] (P.W.).
’ ACKNOWLEDGMENT Financial support of this research was provided by the National Science of Foundation of China (NSFC) (No. 20876028, 20934002, and 20774022) and the National Basic Research Program of China (2005CB623800 and 2009CB930000). ’ REFERENCES (1) Malaisamy, R.; Mahendran, R.; Mohan, D.; Rajendran, M.; Mohan, V. J. Appl. Polym. Sci. 2002, 86, 1749–1761. (2) Freeman, B. D. Macromolecules 1999, 32, 375–380. (3) Choi, J. H.; Jegal, J.; Kim, W. N. J. Membr. Sci. 2006, 284, 406–415. (4) Lu, L. Y.; Sun, H. L.; Peng, F. B.; Jiang, Z. Y. J. Membr. Sci. 2006, 281, 245–252. (5) Jeong, B. H.; Hoek, E. M. V.; Yan, Y. S.; Subramani, A.; Huang, X. F.; Hurwitz, G.; Ghosh, A. K.; Jawor, A. J. Membr. Sci. 2007, 294, 1–7. (6) Lee, H. S.; Im, S. J.; Kim, J. H.; Kim, H. J.; Kim, J. P.; Min, B. R. Desalination 2008, 219, 48–56.
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