Template-Assisted Fabrication of Thin-Film Composite Forward

Apr 20, 2016 - Among all water and wastewater treatment processes, membrane ... in some areas of water purification, agricultural irrigation, food pro...
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Template-Assisted Fabrication of Thin-Film Composite ForwardOsmosis Membrane with Controllable Internal Concentration Polarization Jingguo Li,† Qing Liu,† Xue Li,† Yanbiao Liu,*,‡ and Jianping Xie*,† †

Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, 117585, Singapore NUS Environmental Research Institute, National University of Singapore, 5A Engineering Drive 1, #02-01, 117411, Singapore

‡

S Supporting Information *

ABSTRACT: The internal concentration polarization (ICP) of solutes in the porous substrate layer may reduce the water flux of a forward-osmosis (FO) membrane. Here we present an efficient design by using a novel silica template strategy to address this ICP issue. In particular, a thin-film composite (TFC) FO membrane was prepared by incorporating silica nanoparticles (SiNPs) into the poly(ether sulfone) (PES) support layer, followed by the removal of the as-encapsulated SiNPs by hydrofluoric acid (HF) etching, leading to the formation of a highly porous and interconnected-pore structure of the support layer. Such porous structure favors the salt back diffusion in the substrate layer, leading to an improved net osmotic pressure across the selective layer. In addition, the HF treatment also contributes to a more hydrophilic top polyamide layer, further improving the performance of the membrane. The effects of the silica template on the morphology and properties of the as-designed TFC FO membrane are systematically investigated, and two major contributors for the enhanced water flux of the membrane have also been identified. The materials and strategy developed in this study will be of potential for the fabrication of high-quality FO membranes.

1. INTRODUCTION

FO utilizes the different osmotic pressure of the solutions across the semipermeable synthetic membrane to extract clean water and to concentrate impaired feed streams at minimal energy consumption.20,21 Like other polymeric membrane materials, FO membranes also share the major benefits of polymeric materials. However, it still remains as a grand challenge to fabricate a high performance FO membrane for practical applications. Recently, several efficient methods have been developed to improve the permeability of the membrane, such as the optimization of the interfacial polymerization,22,23 incorporation with suitable nanomaterials,24−26 and posttreatment with certain chemicals.27,28 However, the FO membrane features an intrinsic asymmetric structure, which

The rapid population growth and fast industrialization and urbanization over the past decades have stimulated the exploration of alternative water resources.1 The issues related to water resources may become worse if no effective technical solutions can be provided. Among all water and wastewater treatment processes, membrane technologies are considered to be the most promising because of their low cost, high selectivity, and easy integration into other technologies.2 Some membrane technologies such as reverse osmosis,3 nanofiltration,4 and ultrafiltration,5,6 are widely applied in various situations.7−9 As a more recently developed membrane technology, forward osmosis (FO) benefits from operational advantages and low fouling tendencies,10−15 and FO is achieving increasing acceptance in some areas of water purification, agricultural irrigation, food processing, and power generation.16−19 © 2016 American Chemical Society

Received: Revised: Accepted: Published: 5327

March 4, 2016 April 14, 2016 April 20, 2016 April 20, 2016 DOI: 10.1021/acs.iecr.6b00874 Ind. Eng. Chem. Res. 2016, 55, 5327−5334

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Industrial & Engineering Chemistry Research

effect. Furthermore, the pore structures of the support layer could also be controlled by using the pore-generating SiNPs with different parameters (e.g., size, shape, and surface chemistry).

could have a severe effect of internal concentration polarization (ICP) within the porous support layer, thus leading to a significant performance drop during operation.29,30 To address the ICP issue, the substrate layer of a FO membrane may need to have features such as high porosity and low tortuosity.31 However, the current FO membrane substrates are generally prepared via a phase inversion route, and the as-prepared substrates typically have a tortuous sponge-like structure on top of a finger-like structure.32 The sponge-like structure is formed with small pores segregated by dense walls and it is gets denser as it nears the top surface, which is considered the major reason for ICP.33 Therefore, the osmotic driving force in practical settings is often lower than the theoretical value (as shown in Supporting Information, Figure S1), especially when the draw solutions are at a high concentration (where the water flux becomes more “self-limiting”).34,35 There is therefore a pressing need to develop efficient strategies to prepare a highly porous support layer that could largely mitigate the ICP effect. Extensive efforts have been recently devoted to design high quality FO membranes with a reduced ICP effect in the support layer. There have been a number of successful attempts.36−38 For example, a polymeric nanofiber was recently used as the support layer for FO membranes, which could effectively minimize the S value (= thickness × tortuosity/porosity) of the membrane, thus improving its water productivity.33 Nanofibers of other polymer matrixes have also been demonstrated to be effective as a support layer for FO membranes.8,39 Although the use of nanofibers as a support layer could address the ICP issue to some extent, the fabrication of nanofibers often involves some complicated and time-consuming procedures, which may constrain their further applications in practical settings. In addition, the interactions between the active layer and the nanofiber support are relatively weak, which could pose another challenge to their practical applications. Another efficient strategy to mitigate the ICP effect is to dope porous zeolite nanocomposites in the support layer.24 This strategy could largely address the ICP effect; however, like other zeolite-doped membranes, the zeolite nanocomposite substrates often suffer a severe ion exchange problem between the zeolite substrates and the multivalent cations. In addition, even at a moderate acidic environment, a dealumination reaction may exist in the zeolite substrate, leading to the decomposition of the membrane. The above two effects will significantly reduce the stability of the zeolite, affecting its separation performance as well as its durability in a long-term operation. Hence, it is desirable to develop more practical and promising solutions to address the ICP issue in FO membranes. This challenging issue could be addressed by using the emerging nanotechnology in membranes. In particular, silica nanoparticles (SiNPs) have recently emerged as one of the most popular nanomaterial in the membrane field. For example, some studies used SiNPs as additives (physical dopants) in the top selective layer or substrate layer,5,6,40 to improve the hydrophilicity of the membrane; however, this strategy only achieved a limited success due to the intrinsic self-blocking effect of the doped SiNPs. To address this issue, and bearing in mind the major ICP obstacle of FO membranes, we hypothesized that the incorporation of SiNPs in the support layer, followed by a complete removal of the as-encapsulated SiNPs (therefore SiNPs in the present study are serving as a pore-generating template, which is distinctly different from the previous work using SiNPs as physical dopants), may generate a highly porous support layer that may feature a tunable ICP

2. EXPERIMENTAL SECTION 2.1. Materials. Poly(ether sulfone) (PES), N-methyl-2pyrrolodinone (NMP, > 99.5%), polyethylene glycol (PEG, Mn = 400 g/mol), hexane, ethanol, and sodium chloride were purchased from Merck. The deionized water used in the experiments was produced by a Milli-Q ultrapure water system (Millipore, USA). m-Phenylenediamine (MPD, > 99%), 1,3,5benzenetricarbonyl trichloride (TMC, 98%), hydrofluoric acid (HF), and silica nanoparticles (SiNPs, 20−30 nm in size) were purchased from Sigma-Aldrich Chemical Co. All chemicals were used as received. 2.2. Membrane Fabrication. The PES substrates were prepared by the Loeb−Sourirajan wet-phase inversion method. The PES polymers were first dried overnight to remove the moisture content before use. Followed by that, a different amount of SiNPs (0, 0.5, 1, 3, and 5 wt %) was mixed with PES, PEG-400, NMP, and water to form a homogeneous casting solution. The casting solutions were degassing prior to the casting onto a glass plate with a 100 μm casting knife. Then the as-casted membranes were immediately immersed into a water coagulation bath at room temperature and the mixed solutions were kept for 24 h to ensure a complete precipitation. In a typical fabrication of a TFC FO membrane, the membrane substrate was first immersed in a 2 wt % MPD in DI water for 1 min. A filter paper was then used to remove the water droplets on the membrane surface. Thereafter, the top surface of the membrane was brought to contact with the 0.05 wt % TMC solution in n-hexane for 30 s, leading to the formation of a polyamide thin film layer. The newly prepared TFC FO membranes with different silica content were immersed in a 20 wt % HF aqueous solution for 24 h to completely remove the encapsulated SiNPs from the support layer. After the HF treatment, the resultant membranes were referred to as HF/ TFC-0, HF/TFC-0.5, HF/TFC-1, HF/TFC-3, and HF/TFC-5 for the TFC membranes with a weight percentage of doped SiNPs of 0, 0.5, 1, 3, and 5, respectively. Finally, these membrane samples were stored in DI water at room temperature before use. 2.3. Composition, Morphology, Surface Roughness, and Contact Angles. An X-ray photoelectron spectrometer (XPS, Krotos Analytical Ltd., England) was used to monitor the chemical changes of the as-prepared silica-doped TFC membranes before and after the HF treatment. The morphology of membranes was examined by field emission scanning electric microscopy (FESEM, JEOL JSM-6700F), for which the membrane samples were prepared in liquid nitrogen followed by the platinum coating using a JEOL-1100E ion sputtering device. The surface roughness of the as-fabricated TFC membranes was studied by atomic force microscopy (AFM, Nanoscope IIIa, Digital Instrument, USA) in the tapping mode at room temperature. Images in the range of 5 μm × 5 μm were obtained, and the mean roughness (Ra) was used for the membrane surface characterization. Photoluminescence was recorded on a PerkinElmer LS55 fluorescence spectrometer. The water contact angle was measured by a contact angle goniometer (Rame Hart) at room temperature using Milli-Q water as the probe liquid to determine the surface hydrophilicity of the membranes. The 5328

DOI: 10.1021/acs.iecr.6b00874 Ind. Eng. Chem. Res. 2016, 55, 5327−5334

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Industrial & Engineering Chemistry Research

Figure 1. Schematic illustration of the fabrication process of the silica-templated TFC membrane.

pressure of the draw solution; πfeed is the osmotic pressure of the feed solution; and D is the salt diffusion coefficient.

immediate contact angles were recorded and calculated by the software once the water drops touched the membrane surface. Ten readings were obtained at different random locations, and an average contact angle was calculated to minimize the experimental error. For the average surface pore size of the substrate membrane, the software “ImageJ” was used to analyze the high-resolution FESEM images and the average pore size was obtained by more than 100 counts. 2.4. Membrane Porosity. Membrane porosity ε is defined as the total pore volume divided by the membrane volume. Porosity of the support can be determined by the gravimetric method according to the following equation: ε=

⎞ ⎛ Aπ draw + B ⎟⎟ = ln⎜⎜ D ⎝ Aπfeed + B + Jw ⎠

Jw S

2.6. FO Performance. The membrane test module consists of one water channel on each side of the membrane with a dimension of 2.0 cm in length and 1.0 cm in width. The effective membrane area is 2 cm2. No spacer was used in the testing. Both the draw solution (2 mol L−1 NaCl) and feed solution (DI water) flowed counter-currently through the filtration cell at the same volumetric flow rate of 0.3 L min−1, and they were recirculated. Two different membrane orientations were tested at room temperature, with either the selective layer against the feed solution (FO mode) or against the draw solution (pressure retarded osmosis (PRO) mode). The water permeation flux, Jw (L m−2 h−1, LMH), is determined by eq 6, based on the absolute weight change of the feed and the effective membrane area, Am (m2):

(w2 − w1)/ρ1 (w2 − w1)/ρ1 + w1/ρm

(1)

where w1 is the dry weight of the PES substrate membrane, w2 is the total weight of the PES substrate saturated with water, ρ1 is the density of water, and ρm is the density of the PES material (ρm, 1.37 g cm−3). 2.5. Mass Transport Performance. The water permeability (A), salt permeability (B), and salt rejection (R) of the as-fabricated TFC membranes before and after the HF treatment were determined by a stainless steel dead-end stirred cell under RO mode. The experiments were conducted three times and an average value was reported. The effective membrane area was 2 cm2, and all tests were performed at room temperature. The water permeability A is determined based on eq 2, where Jw is the volumetric water flux and ΔP is the applied pressure.

A = Jw /ΔP

Jw =

Js =

(2)

1−R (ΔP − Δπ ) R

(C tVt) − (C0V0) 1 Δt Am

(7)

where Ct (mol L ) and Vt (L) are the salt concentration and the volume of the feed solution at time t, respectively; C0 (mol L−1) and V0 (L) are the initial salt concentration and the volume of the feed solution, respectively.

(3)

3. RESULTS AND DISCUSSION The preparation of silica-templated FO membrane was simple and only involved two steps. As illustrated in Figure 1 (with more details in the Experimental Section), the first step was the preparation of the TFC membrane. In a typical preparation process, the silica-doped PES substrate membranes (hereafter referred to as PES-0, PES-0.5, PES-1, PES-3, and PES-5 for the PES membranes with a weight percentage of doped SiNPs of 0,

The salt permeability B is calculated from eq 4 based on the solution-diffusion model, where Δπ is the osmotic pressure across the membrane B=A

(6)

−1

Cp Cf

Δw 1 Δt A m

where Δw (kg) is the absolute weight change of water permeated across the TFC FO membrane over a predetermined time Δt (h) during the FO measurements. The reverse salt flux, Js (g m−2 h−1, gMH) was determined from the conductivity increment in the feed when deionized water was used as the feed solution:

The salt rejection R is determined from eq 3, where Cp is the permeate salt concentration and Cf is the feed concentration

R=1−

(5)

(4)

The membrane structure parameter (S) is determined by fitting A and B value into the eq 5, wherein πdraw is the osmotic 5329

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Figure 2. FESEM images of the pristine PES substrate membrane (PES-0) (a) before and (d) after the HF treatment; and PES-5 substrate membrane (b, c) before and (e, f) after the HF treatment at different magnifications.

Figure 3. Overview FESEM images of cross-section of (a) HF/TFC-0 and (c) HF/TFC-5 membrane; and magnifications of top section FESEM images of (b) HF/TFC-0 and (d) HF/TFC-5 membrane.

0.5, 1, 3 and 5, respectively) were first fabricated by the LoebSourirajan wet-phase inversion method.41,42 A selective polyamide thin film layer was then introduced by an interfacial polymerization of m-phenylenediamine (MPD) and 1,3,5benzenetricarbonyl trichloride (TMC), leading to the formation of thin film composite (TFC) membranes (hereafter referred to as TFC-0, TFC-0.5, TFC-1, TFC-3, and TFC-5 for the TFC membranes with a weight percentage of doped SiNPs of 0, 0.5, 1, 3, and 5, respectively). The second step was the post-treatment of the above TFC membranes with a diluted hydrofluoric acid (HF) solution (20 wt %) for 24 h. As illustrated in Figure 1, the imbedded SiNPs in the PES layer will be completely removed, generating a more porous substrate skin layer, which could favor water and salt diffusion. The asfabricated membranes were washed copiously with deionized water to remove any HF residual, and the final membrane

samples are respectively described as HF/TFC-0, HF/TFC-0.5, HF/TFC-1, HF/TFC-3, and HF/TFC-5, which also correspond to the above descriptions of the as-prepared PES and TFC membranes. To assess the morphology difference of the substrate membranes before and after the removal of the SiNP template, the substrate membrane morphologies (only PES-0 and PES-5 were chosen for a purpose of clear comparison) were examined by field emission scanning electron microscopy (FESEM). As shown in Figure 2a, the pristine PES substrate membrane (PES-0) shows a typical dense and smooth surface morphology. No obvious morphology change was seen after the HF treatment (Figure 2d). However, the surface image of the PES-5 substrate membrane (Figure 2b) clearly indicates a unique surface-decorated structure, with a number of worm-like SiNPs clusters formed. A high-resolution top-view image 5330

DOI: 10.1021/acs.iecr.6b00874 Ind. Eng. Chem. Res. 2016, 55, 5327−5334

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Figure 4. FESEM images of the pristine TFC membrane (TFC-0) (a,b) before and (c) after the HF treatment; and TFC-5 membrane (d,e) before and (f) after the HF treatment.

Figure 5. Water flux of the as-prepared TFC membranes in FO process under (a) FO and (b) PRO mode.

membranes was further confirmed by XPS spectra, as listed in Table S2. In addition, we also compared the cross-section morphology of the membranes after the HF treatment. As shown in Figure 3, both cross-section images of the HF/TFC-0 and HF/TFC-5 substrate membranes show a typical spongelike structure on top of the finger-like structure. However, the top section of the substrate of the HF/TFC-5 membrane (Figure 3d) was more porous as compared to that of the HF/ TFC-0 membrane (Figure 3b), which could be attributed to the additional pores generated from the removal of SiNPs (poregenerating template). Moreover, these additional pores may also effectively interconnect the isolated pores segregated by dense PES walls. Such a unique pore structure is favorable for water and salt diffusion. Since the selective polyamide active layer is determinant for the membrane selectivity, it is pivotal to identify the morphology evolution of the active layers as a result of SiNP doping as well as after their removal by the HF treatment. As shown in Figure 4, both TFC-0 and TFC-5 membranes show a typical ridge and valley morphology of polyamides generated by the interfacial polymerization. Interestingly, the polyamide particles for the TFC-5 membrane (Figure 4b,e) were slightly smaller than that in the TFC-0 membrane, which suggests that the silica-incorporated substrate surface may favor the formation of a thicker incipient polyamide film by limiting

(Figure 2c) further suggests that these SiNPs clusters are partially buried inside the PES-5 matrix. X-ray photoelectron spectroscopy (XPS) was further used to verify the encapsulation of SiNPs in the PES layer. As shown in Figure S2, carbon (281.9 eV), oxygen (531.5 eV), and sulfur (164.8 eV) were seen in the XPS spectra of the PES substrate membrane. Besides these peaks, two new characteristic peaks of silicon (101.5 eV for Si 2p and 151.3 eV for Si 2s) were also clearly observed in the PES-5 substrate membrane, confirming the successful incorporation of SiNPs in the PES layer. Table S1 presents the detailed elemental analysis of the as-prepared PES membranes, suggesting that the atomic ratio of silicon was gradually increased as the increase of the weight percentage of silica doping. After the removal of the as-doped SiNPs by HF etching, the resulting PES-5 substrate membrane shows evidently more pores on the membrane surface (Figure 2e) as compared to that of PES-0 (Figure 2d). The average pore size was determined to be 60.0 ± 8.0 nm from the highresolution FESEM image (Figure 2f). It should be noted that a highly porous and low tortuous pore structure in the top part of the substrate membrane will benefit the membrane to overcome the ICP effect.43 In particular, the surface pores could make possible the dense substrate skin layer highly connected, which could significantly facilitate water permeation and salt back diffusion. The complete removal of SiNPs in the 5331

DOI: 10.1021/acs.iecr.6b00874 Ind. Eng. Chem. Res. 2016, 55, 5327−5334

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Industrial & Engineering Chemistry Research the “volcano-like” diffusion reaction.33 That means, for the PES-5 substrate membrane, more MPD monomers are able to contact with the TMC monomers at the initial stage, leading to an accelerated reaction rate, which may form more polyamides in the active layer. Therefore, the polyamide layer tends to grow thicker on the PES-5 substrate membrane as compared to that in the PES-0 substrate membrane (Figure S3). Accompanied with the silica etching process by the HF treatment, the thickness of the ridge-like polyamides was decreased for both TFC-0 and TFC-5 substrate membranes (Figure 4c,f), suggesting a slight thinning effect of the polymeric network due to the HF etching. However, the microstructure of the selective skin surface remained unchanged. The surface morphology evolution was further confirmed by atomic force microscopy (AFM, Figure S4). To evaluate the FO performance of the as-fabricated membranes, the cross-flow experiments were conducted using a laboratory-scale FO system (a detailed setup is illustrated in Figure S5) with an effective membrane area of 2 cm2.41 As shown in Figure 5, before the HF treatment, the water flux of TFC-3 was the highest, ∼30 LMH in FO mode (the selective layer is facing the feed solution), doubling the value of the TFC-0 membrane. The enhanced membrane performance by silica doping is consistent with previous studies, and the improvement is attributed to the increased hydrophilicity of the substrate membrane by silica doping. Surprisingly, the HF/ TFC-5 membrane (∼60 LMH in FO mode) gains 3 times that of the water flux of the HF/TFC-0 membrane; its water flux is about 4 times that of the pristine TFC membrane (TFC-0). This clearly indicates that the performance improvement of the as-designed membranes is mainly caused by the removal of SiNP template with HF, which helps generate a more porous and interconnected-pore substrate layer. Meanwhile, the increased hydrophilicity (Figure S7) and permeability of the polyamide layer (after the HF treatment) could also contribute to the performance of the as-designed membranes. The salt permeability also increased along with the water permeability growth, which is not desired in the practical applications. It should be mentioned that the water-salt selectivity, other than the water permeability, is a key consideration for the design of the FO membrane.44 We have achieved a similar Js/Jw value (salt reverse flux over water flux) for both membranes (Figure S6), which suggests that the as-modified membrane in this study has an improved water management capability compared to the pristine membrane given the same membrane area. This is an important feature as this improvement could help decrease the potential capital and operational cost. A systematic study on the design of various inorganic nanomaterials (e.g., carbon nanotubes) for desalination membrane fabrication may finally produce desirable membranes with high selectivity and high water permeability.44 To further explain why the performance of the as-designed FO membranes has been significantly improved after the HF treatment, the intrinsic performance parameters of the asfabricated TFC membranes before and after the HF treatment were determined under reverse osmosis (RO) mode. Before the HF treatment, the TFC-3 membrane shows the best water permeability and the salt rejection rate for all the silicaincorporated membranes (Table S3). After the HF treatment, however, the water permeability (A) increased gradually from 0.74 ± 0.13 L m−2 h−1 bar−1 of the HF/TFC-0 membrane to 0.88 ± 0.09 L m−2 h−1 bar−1 of the HF/TFC-5 membrane, accompanied by a slight salt rejection rate loss (Table S4). The

higher A value for the HF/TFC-5 membrane may result from the lower water diffusion resistance in the HF/TFC-5 substrate layer. Furthermore, the structure parameter S was employed as a direct indicator of the ICP effect. As listed in Table S3 and Table S4, the S value of the TFC-0 membrane was 3.8 times of that of the HF/TFC-5 membrane, indicating that the structure of the HF/TFC-5 membrane was more favorable for a high water flux, and the contribution of the high water flux is dominated by the reduced structure parameter rather than the improved water permeability. It is worth mentioning that the template method developed in this study targets at fabricating a more porous and less tortuous substrate membrane, which could be effective to address the ICP issue in the FO membranes. Theoretically, the S value is controlled by the membrane tortuosity, thickness, and porosity. As the membrane thickness was fixed for all membranes in this work, the increased porosity and decreased tortuosity were the main reasons for a smaller S value of the HF/TFC-5 membrane. This indicates that the removal of SiNPs within the membrane substrate layer has generated more pores with a highly interconnected pore structure. Therefore, the asprepared HF/TFC-5 membrane with more interconnected porous structure favors the salt back diffusion in the substrate layer, leading to a higher net osmotic driving force across the selective skin layer. In contrast, the relatively low porosity and high tortuosity contributes to a low S value of the TFC-0 membrane, which possesses a thicker sponge-like dense top section in the substrate layer. It is well documented that the conventional TFC membranes may suffer more severe water flux drop in the FO mode as compared to that in the pressure retarded osmosis (PRO; the selective layer is facing the draw solution) mode,8 which mainly due to the severe salt diffusion barrier exists in the tortuous substrate layer. The water flux difference between the FO mode and the PRO mode typically goes up as the draw solution concentration increases, which is in good agreement with our findings in the HF/TFC membranes, as shown in Figure 6.

Figure 6. Water permeability difference of the as-prepared HF/TFC membranes applied in FO process with different draw solution concentrations under FO and PRO mode.

However, the HF/TFC-5 membrane has a more balanced behavior in both the FO and PRO modes (Figure 6). That is because the salt back diffusion resistance in the FO mode has been greatly reduced by the interconnected pores in the substrate layer.

4. CONCLUSIONS In summary, we have proposed and demonstrated a novel silica template strategy for the fabrication of TFC FO membrane 5332

DOI: 10.1021/acs.iecr.6b00874 Ind. Eng. Chem. Res. 2016, 55, 5327−5334

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(3) Wang, T.; Dai, L.; Zhang, Q.; Li, A.; Zhang, S. Effects of acyl chloride monomer functionality on the properties of polyamide reverse osmosis (RO) membrane. J. Membr. Sci. 2013, 440, 48−57. (4) Wang, X.; Yeh, T. M.; Wang, Z.; Yang, R.; Wang, R.; Ma, H.; Hsiao, B. S.; Chu, B. Nanofiltration membranes prepared by interfacial polymerization on thin-film nanofibrous composite scaffold. Polymer 2014, 55, 1358−1366. (5) Yin, J.; Kim, E. S.; Yang, J.; Deng, B. Fabrication of a novel thinfilm nanocomposite (TFN) membrane containing MCM-41 silica nanoparticles (NPs) for water purification. J. Membr. Sci. 2012, 423− 424, 238−246. (6) Shen, J. N.; Ruan, H. M.; Wu, L. G.; Gao, C. G. Preparation and characterization of PES−SiO2 organic−inorganic composite ultrafiltration membrane for raw water pretreatment. Chem. Eng. J. 2011, 168, 1272−1278. (7) Chung, T. S.; Zhang, S.; Wang, K. Y.; Su, J.; Ling, M. M. Forward osmosis processes: Yesterday, today and tomorrow. Desalination 2012, 287, 78−81. (8) Dong, H.; Zhang, L.; Chen, H.; Gao, C. Mixed-matrix membranes for water treatment: materials, synthesis and properties. Prog. Chem. 2014, 26, 2007−2018. (9) Kuila, A.; Maity, N.; Chatterjee, D. P.; Nandi, A. K. Temperature triggered antifouling properties of poly(vinylidene fluoride) graft copolymers with tunable hydrophilicity. J. Mater. Chem. A 2015, 3, 13546−13555. (10) Zhou, Z.; Lee, J. Y.; Chung, T. S. Thin film composite forwardosmosis membranes with enhanced internal osmotic pressure for internal concentration polarization reduction. Chem. Eng. J. 2014, 249, 236−245. (11) Wang, Y.; Ou, R.; Ge, Q.; Wang, H.; Xu, T. Preparation of polyethersulfone/carbon nanotube substrate for high-performance forward osmosis membrane. Desalination 2013, 330, 70−78. (12) Tiraferri, A.; Kang, Y.; Giannelis, E. P.; Elimelech, M. Highly hydrophilic thin-film composite forward osmosis membranes functionalized with surface-tailored nanoparticles. ACS Appl. Mater. Interfaces 2012, 4, 5044−5053. (13) Lutchmiah, K.; Verliefde, A. R. D.; Roest, K.; Rietveld, L. C.; Cornelissen, E. R. Forward osmosis for application in wastewater treatment: A review. Water Res. 2014, 58, 179−197. (14) Mazlan, N. M.; Peshev, D.; Livingston, A. G. Energy consumption for desalination - A comparison of forward osmosis with reverse osmosis, and the potential for perfect membranes. Desalination 2016, 377, 138−151. (15) Elimelech, M.; Phillip, W. A. The future of seawater desalination: energy, technology, and the environment. Science 2011, 333, 712−717. (16) Liu, Q.; Li, J.; Zhou, Z.; Xie, J.; Lee, J. Y. Hydrophilic mineral coating of membrane substrate for reducing internal concentration polarization (ICP) in forward osmosis. Sci. Rep. 2016, 6, 19593. (17) Liu, Q.; Zhou, Z.; Qiu, G.; Li, J.; Xie, J.; Lee, J. Y. Surface reaction route to increase the loading of antimicrobial Ag nanoparticles in forward osmosis membranes. ACS Sustainable Chem. Eng. 2015, 3, 2959−2966. (18) Klaysom, C.; Cath, T. Y.; Depuydt, T.; Vankelecom, I. F. Forward and pressure retarded osmosis: potential solutions for global challenges in energy and water supply. Chem. Soc. Rev. 2013, 42, 6959−6989. (19) Zuo, J.; Wang, Y.; Chung, T. S. Novel organic−inorganic thin film composite membranes with separation performance surpassing ceramic membranes for isopropanol dehydration. J. Membr. Sci. 2013, 433, 60−71. (20) Benavides, S.; Oloriz, A. S.; Phillip, W. A. Forward osmosis processes in the limit of osmotic equilibrium. Ind. Eng. Chem. Res. 2015, 54, 480−490. (21) Arena, J. T.; Manickam, S. S.; Reimund, K. K.; Brodskiy, P.; McCutcheon, J. R. Characterization and performance relationships for a commercial thin film composite membrane in forward osmosis desalination and pressure retarded osmosis. Ind. Eng. Chem. Res. 2015, 54, 11393−11403.

with controllable ICP effect. By using SiNPs as pore-generating template, our protocol has successfully generated a highly porous and interconnected-pore structure in the membrane support layer, which favors the salt back diffusion in the substrate layer, thus leading to an improved net osmotic pressure across the selective layer. In addition, the membranes prepared in our SiNP-templated strategy also featured with improved membrane hydrophilicity, another booster for the FO performance. The protocols (e.g., the SiNP-templated strategy) and the TFC membranes developed in this study are important not only because they provide a simple and efficient approach for the fabrication of the FO membrane with controllable ICP, but also because they exemplify the concept of integrating advanced nanotechnology into the membrane technology. However, it should also be noted that the use of HF in the membrane fabrication could suffer some technical, safety, and environmental constraints, and it should be taken into consideration before this method could be further scaled up in the practical setup. Seeking alternative templates other than SiNPs may address this issue, where a more environmental friendly solvent rather than HF could be used in the etching process. Nevertheless, further development of this templating concept may finally address the challenging ICP issue and pave the way of the development of a high-performance FO membrane toward practical applications.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b00874. Experimental details for membrane fabrication and characterization (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was funded under the project entitled “Membrane development for osmotic power generation, Part 1. Materials development and membrane fabrication” (1102-IRIS-11-01) and NUS Grant Number R-279-000-381-279. This research grant is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Environmental & Water Technologies Strategic Research Programme and administered by the Environment & Water Industry Programme Office (EWI) of the PUB. We thank Professor Neal Tai-Shung Chung (Department of Chemical & Biomolecular Engineering, NUS) and Professor Choon Nam Ong (NUS Environmental Research Institute, NERI) for their great help on this project.

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REFERENCES

(1) Subramani, A.; Jacangelo, J. G. Emerging desalination technologies for water treatment: A critical review. Water Res. 2015, 75, 164−187. (2) Zhang, Z. H.; An, Q. F.; Liu, T.; Zhou, Y.; Qian, J. W.; Gao, C. J. Fabrication and characterization of novel SiO2-PAMPS/PSF hybrid ultrafiltration membrane with high water flux. Desalination 2012, 297, 59−71. 5333

DOI: 10.1021/acs.iecr.6b00874 Ind. Eng. Chem. Res. 2016, 55, 5327−5334

Article

Industrial & Engineering Chemistry Research (22) Hu, D.; Xu, Z. L.; Wei, Y. M. A high performance silica− fluoropolyamide nanofiltration membrane prepared by interfacial polymerization. Sep. Purif. Technol. 2013, 110, 31−38. (23) Bano, S.; Mahmood, A.; Kim, S. J.; Lee, K. H. Graphene oxide modified polyamide nanofiltration membrane with improved flux and antifouling properties. J. Mater. Chem. A 2015, 3, 2065−2071. (24) Ma, N.; Wei, J.; Qi, S.; Zhao, Y.; Gao, Y.; Tang, C. Y. Nanocomposite substrates for controlling internal concentration polarization in forward osmosis membranes. J. Membr. Sci. 2013, 441, 54−62. (25) Liang, S.; Kang, Y.; Tiraferri, A.; Giannelis, E. P.; Huang, X.; Elimelech, M. Highly hydrophilic polyvinylidene fluoride (PVDF) ultrafiltration membranes via postfabrication grafting of surfacetailored silica nanoparticles. ACS Appl. Mater. Interfaces 2013, 5, 6694−6703. (26) Ahmad, A. L.; Majid, M. A.; Ooi, B. S. Functionalized PSf/SiO2 nanocomposite membrane for oil-in-water emulsion separation. Desalination 2011, 268, 266−269. (27) Navarro, R.; González, M. P.; Saucedo, I.; Avila, M.; Prádanos, P.; Martínez, F.; Martín, A.; Hernández, A. Effect of an acidic treatment on the chemical and charge properties of a nanofiltration membrane. J. Membr. Sci. 2008, 307, 136−148. (28) González Muñoz, M. P.; Navarro, R.; Saucedo, I.; Avila, M.; Prádanos, P.; Palacio, L.; Martínez, F.; Martín, A.; Hernández, A. Hydrofluoric acid treatment for improved performance of a nanofiltration membrane. Desalination 2006, 191, 273−278. (29) Manickam, S. S.; Gelb, J.; McCutcheon, J. R. Pore structure characterization of asymmetric membranes: Non-destructive characterization of porosity and tortuosity. J. Membr. Sci. 2014, 454, 549−554. (30) Deshmukh, A.; Yip, N. Y.; Lin, S.; Elimelech, M. Desalination by forward osmosis: Identifying performance limiting parameters through module-scale modeling. J. Membr. Sci. 2015, 491, 159−167. (31) Gai, J. G.; Gong, X. L. Zero internal concentration polarization FO membrane: functionalized graphene. J. Mater. Chem. A 2014, 2, 425−429. (32) Li, X.; Chung, T. S.; Chung, T. S. Effects of free volume in thinfilm composite membranes on osmotic power generation. AIChE J. 2013, 59, 4749−4761. (33) Song, X.; Liu, Z.; Sun, D. D. Nano gives the answer: breaking the bottleneck of internal concentration polarization with a nanofiber composite forward osmosis membrane for a high water production rate. Adv. Mater. 2011, 23, 3256−3260. (34) Li, D.; Wang, H. Smart draw agents for emerging forward osmosis application. J. Mater. Chem. A 2013, 1, 14049−14060. (35) Li, P.; Lim, S. S.; Neo, J. G.; Ong, R. C.; Weber, M.; Staudt, C.; Widjojo, N.; Maletzko, C.; Chung, T. S. Short- and long-term performance of the thin-film composite forward osmosis (TFC-FO) hollow fiber membranes for oily wastewater purification. Ind. Eng. Chem. Res. 2014, 53, 14056−14064. (36) Han, G.; Zhang, S.; Li, X.; Widjojo, N.; Chung, T. S. Thin film composite forward osmosis membranes based on polydopamine modified polysulfone substrates with enhancements in both water flux and salt rejection. Chem. Eng. Sci. 2012, 80, 219−231. (37) Duong, P. H. H.; Chisca, S.; Hong, P. Y.; Cheng, H.; Nunes, S. P.; Chung, T. S. Hydroxyl functionalized polytriazole-co-polyoxadiazole as substrates for forward osmosis membranes. ACS Appl. Mater. Interfaces 2015, 7, 3960−3973. (38) Hegab, H. M.; ElMekawy, A.; Barclay, T. G.; Michelmore, A.; Zou, L.; Saint, C. P.; Ginic-Markovic, M. Fine-tuning the surface of forward osmosis membranes via grafting graphene oxide: performance patterns and biofouling propensity. ACS Appl. Mater. Interfaces 2015, 7, 18004−18016. (39) Huang, L.; McCutcheon, J. R. Hydrophilic nylon 6,6 nanofibers supported thin film composite membranes for engineered osmosis. J. Membr. Sci. 2014, 457, 162−169. (40) Bao, M.; Zhu, G.; Wang, L.; Wang, M.; Gao, C. Preparation of monodispersed spherical mesoporous nanosilica−polyamide thin film composite reverse osmosis membranes via interfacial polymerization. Desalination 2013, 309, 261−266.

(41) Li, J.; Yin, L.; Qiu, G.; Li, X.; Liu, Q.; Xie, J. A photo-bactericidal thin film composite membrane for forward osmosis. J. Mater. Chem. A 2015, 3, 6781−6786. (42) Dumée, L.; Lee, J.; Sears, K.; Tardy, B.; Duke, M.; Gray, S. Fabrication of thin film composite poly(amide)-carbon-nanotube supported membranes for enhanced performance in osmotically driven desalination systems. J. Membr. Sci. 2013, 427, 422−430. (43) Pisani, L. Simple expression for the tortuosity of porous media. Transp. Porous Media 2011, 88, 193−203. (44) Werber, J. R.; Deshmukh, A.; Elimelech, M. The critical need for increased selectivity, not increased water permeability, for desalination membranes. Environ. Sci. Technol. Lett. 2016, 3, 112−120.

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DOI: 10.1021/acs.iecr.6b00874 Ind. Eng. Chem. Res. 2016, 55, 5327−5334