Preparation of a Novel Poly(vinylidene fluoride) Ultrafiltration

Jan 27, 2016 - In tests of membrane performance, the APTES-HNT/PVDF ... (1) Traditional treatments for oil/water separation including gravity separati...
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Preparation of a Novel Poly(vinylidene fluoride) Ultrafiltration Membrane by Incorporation of 3‑AminopropyltriethoxysilaneGrafted Halloysite Nanotubes for Oil/Water Separation Guangyong Zeng,†,‡ Yi He,*,†,‡,§ Yingqing Zhan,†,‡ Lei Zhang,†,‡ Heng Shi,†,‡ and Zongxue Yu*,†,‡ †

College of Chemistry and Chemical Engineering, ‡Oil & Gas Field Applied Chemistry Key Laboratory of Sichuan Province, and State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, P. R. China §

ABSTRACT: Halloysite nanotubes (HNTs) were modified by a simple surface covalent functionalization with 3aminopropyltriethoxysilane (APTES). A novel poly(vinylidene fluoride) (PVDF) ultrafiltration membrane was then prepared by incorporating different ratios of APTES-HNTs. The Fourier-transform infrared (FT-IR), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM) results demonstrated that the HNTs were successfully modified by the introduction of APTES. The morphologies of the membranes were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). In tests of membrane performance, the APTES-HNT/PVDF membrane exhibited a higher pure-water flux (PWF) and a lower contact angle (CA) than a pure PVDF membrane and an HNT/PVDF membrane, respectively, which was attributed to the homogeneous dispersion of nanoparticles in the membrane matrix. In addition, the oil removal capacities of the membrane were improved, and all of the oil-rejection ratios were greater than 90% when the novel membrane was used to separate four different types of oil/water emulsions. The APTES-HNT/PVDF membrane showed a durable oil resistance with a flux recovery ratio (FRR) that could still reach 82.9% after three fouling/washing cycles. The enhancement of the antifouling properties was caused by a decrease of the surface roughness. As a result, APTES-HNTs will provide a new material for the fabrication of antifouling membranes for practical applications in oil/water separations.

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INTRODUCTION With the increasing economic development of society, the environment is being seriously polluted and damaged. Oily wastewater is a common pollution problem that is harmful to life and reproduction.1 Traditional treatments for oil/water separation including gravity separation, flotation, and coagulation have low separation efficiencies or consume a great deal of energy.2 In recent years, as an advanced water treatment technology, membrane technology has also been successfully applied for oil/water separations.3−5 However, because of the hydrophobic surfaces, polymer membranes are easily polluted by contaminants in practical application, which reduces the separation performance of membranes.6−8 To improve the fouling resistance of membranes in the oil/ water separation process, the incorporation of inorganic nanoparticles into membranes has been extensively studied.9−11 Hydrophilic nanoparticles not only can enhance the filtration rate of oily wastewater but can also help to decrease concentration polarization and prevent many oil droplets from aggregating on the surface of the membrane.12 Yan et al.13 prepared Al2O3 −PVDF tubular membranes to treat oily wastewater from an oil field. The results indicated that the novel membranes exhibited high removals of total organic carbon (TOC), chemical oxygen demand, and oil content. More importantly, the Al2O3−PVDF membrane had favorable antifouling properties, with higher flux recovery and lower contaminant adsorption. In the work of Zhang et al.,14 phosphorylated silica nanotubes (PSNTs) were blended into the PVDF membrane matrix to investigate the oil/water separation performance. Compared with pristine PVDF © 2016 American Chemical Society

membranes, the oil-rejection rate of PSNT/PVDF membranes was increased from 91.5% to 98.4% when the feed solution was 160 mg/L. In addition, other nanoparticles such as multiwalled carbon nanotubes (MWCNTs) and titanium dioxide (TiO2) can also contribute to improving the oil/water separation performances.15−17 However, nanoparticles are prone to aggregate and cannot symmetrically disperse in membranes, which are major drawbacks and need to be overcome by further research.6,18 As a natural hollow tubular material with excellent physical and chemical properties, halloysite nanotubes (HNTs) have also attracted great interest in the field of membrane modification.19−21 Owing to the many hydroxyl groups on the HNT surface, membranes blended with HNTs exhibit good hydrophilicity and antifouling properties and have some potential applications in desalination and wastewater treatment.22−24 In this work, we prepared novel blend membranes by the phase-inversion method. To enhance the dispersion of the nanoparticles in the membrane matrix and strengthen the interfacial interaction between them, the HNTs were functionalized modified by the grafting of 3-aminopropyltriethoxysilane (APTES) as a coupling agent. The effects of additives on the hydrophilicity and antifouling properties of the membranes were studied in detail. More importantly, to explore the Received: Revised: Accepted: Published: 1760

December 16, 2015 January 26, 2016 January 27, 2016 January 27, 2016 DOI: 10.1021/acs.iecr.5b04797 Ind. Eng. Chem. Res. 2016, 55, 1760−1767

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convenience, membranes containing 1−3% APTES-HNTs are denoted as M2-1, M2-2, and M2-3, respectively. For comparison, a pure PVDF membrane (M0) and a 3% HNT/ PVDF membrane (M1) were also prepared according to the above method. 2.4. Characterization of APTES-HNTs. Fourier-transform infrared (FT-IR) spectroscopy (Beijing Rayleigh Analytical Instrument, WQF-520) was used to record the characteristic peaks of HNTs and APTES-HNTs. The thermal stability of the nanoparticles was characterized by thermogravimetric analysis (TGA) (Netzsch, STA449F3) at a heating rate of 10 °C/min in nitrogen atmosphere. In addition, the surface morphologies of pure HNTs and APTES-HNTs were examined by transmission electron microscopy (TEM) (FEI, Tecnai G20). 2.5. Characterization of the Membranes. 2.5.1. Morphologies of the Membranes. Scanning electron microscopy (SEM) (JEOL, JSM-7500F) was used to observe the surface and cross-sectional morphologies of all membranes at different magnifications. To further analyze the surface roughness of the membranes, atomic force microscopy (AFM) (NSK, SPA300HV) was employed. It was performed in tapping mode, and the scan area was 10 μm × 10 μm. 2.5.2. Porosity and Mean Pore Radius. The overall porosity (ε) of each membrane was calculated according to the gravimetric method28 as

performance of the membranes in oil/water separation processes, a series of emulsions were prepared including diesel oil/water (D/W), petroleum ether/water (P/W), n-hexadecane/water (H/W), and vegetable oil/water (V/W). Such a study has never before been reported and might help to broaden the applications of HNT blend membranes.

2. EXPERIMENTAL SECTION 2.1. Materials. Poly(vinylidene fluoride) (PVDF, FR904) was purchased from 3F New Materials Co. Ltd., (Shanghai, China). Halloysite nanotubes (HNTs, diameter 30−70 nm, length 0.5−1.5 μm, purity ≥95%) were obtained from SigmaAldrich. Other chemicals were supplied by Kelong Chemical Reagent Factory (Chengdu, China): 3-aminopropyltriethoxysilane (APTES), polyvinylpyrrolidone (PVP), N,N-dimethylacetamide (DMAc, ≥ 99.5%), petroleum ether, n-hexadecane, and ethanol absolute. All reagents used in this work were employed without further purification. 2.2. Preparation of APTES-HNTs. The modification of HNTs by APTES was performed as follows:25 First, HNTs (1 g) were dispersed into a mixture of ethanol and deionized (DI) water with an ultrasonic cleaner to obtain aqueous solution. Then, APTES (10 mL) was slowly added to the solution, which was refluxed at 343.15 K for 12 h in a three-necked flask. The precipitates were washed repeatedly with DI water. Finally, the APTES-HNTs were obtained after centrifuging and drying in a vacuum oven. 2.3. Preparation of Blend Membranes. APTES-HNT blend membranes (APTES-HNT/PVDF) were synthesized by the phase-inversion method.26 The preparation process is illustrated in Figure 1. Different concentrations of APTES-

ε=

(ω1 − ω2)/ρw (ω1 − ω2)/ρw + ω2 /ρp

(1)

where ω1 and ω2 are the wet and dry weights (g), respectively, of the membrane and ρp and ρw are the densities of PVDF (1.765 g/cm3) and water (0.998 g/cm3), respectively. The mean pore radius (rm) was analyzed according to the Guerout− Elford−Ferry equation rm =

(2.9 − 1.75ε)8μlJ ε × TMP

(2) −4

where μ is the viscosity of water (8.9 × 10 Pa·s), l is the thickness (m) of the membrane, and J is the pure-water flux (L/ m2·h−1) of the membrane. Every test was performed at a pressure (TMP) of 0.1 MPa. 2.5.3. Hydrophilicities and Permeations of the Membranes. The contact angle (CA) of water on each membrane, which can show the hydrophilicity of the membrane, was measured with an XED-SPJ instrument (Beijing Hake). For each measurement, 2.0 μL of DI water was dropped onto membrane surface, and the CA data and images were obtained at room temperature with water spreading over the membrane. The permeation performances of the membranes were tested with a dead-end ultrafiltration experimental device (SINAP, SCM-300). Each newly prepared membrane was prepressured for 0.5 h under a pressure of 0.15 MPa. The pure-water flux (PWF) (Jw.1) is defined as follows29

Figure 1. Preparation process of APTES-HNT/PVDF.

HNTs (1, 2, and 3%, based on the PVDF weight) were added to DMAc (74 g, as the solvent) and dispersed by ultrasonic cleaner for 1 h before addition of PVDF (19 g, as a solute material) and PVP (7 g, as a pore former). Casting solution was obtained after this mixture had been stirred for 8 h at 343.15 K and bubbles released over 24 h in a vacuum-drying oven. Then, the solution was cast onto a glass with a knife at a thickness of 200 μm. After being allowed to evaporate for 0.5 min, the samples were immersed into a coagulation bath filled with DI water.27 The membranes peeled off from the glass and were soaked in DI water at least 24 h before ultrafiltration tests. For

Jw.1 =

V A×t

(3)

where V is the volume of penetrating water (L), A is the effective area (m2), and t is the running time (h). 2.6. Oil/Water Separation Performance. 2.6.1. Preparation of Oil/Water Emulsions. In this study, diesel oil/water (D/W), petroleum ether/water (P/W), n-hexadecane/water (H/W), and vegetable oil/water (V/W) emulsions were prepared to evaluate the oil/water separation performances of 1761

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Industrial & Engineering Chemistry Research ⎛J ⎞ FRR (%) = ⎜⎜ w.2 ⎟⎟ × 100 ⎝ Jw.1 ⎠

the membranes. For each emulsion, the oil and water (1/250, v/v) were mixed for 15 min by ultrasound and stirring, and the concentration of emulsifier (SDS) was 500 mg/L. After emulsification, the floating oil was removed. All of the emulsions were kept stabilized for hours in the laboratory environment before the separation tests. The sizes of the oil droplets in the oil/water emulsions were measured with a laser particle size analyzer (Brookhaven, Zata PALS 190 Plus), and their microscopy images were recorded with a Motic BA300Pol microscope (Nikon, DS-F11), as shown in Figure 2.

(6)

3. RESULTS AND DISCUSSION 3.1. Characterization of APTES-HNTs. Figure 3 shows FTIR spectra of raw HNTs and APTES-HNTs. The peaks

Figure 3. FTIR spectra of (a) raw HNTs and (b) APTES-HNTs.

emerging at 3690 and 3622 cm−1 correspond to the stretching vibrations of Al−OH bonds.25 The peak emerging at 690 cm−1 is the stretching vibration of Si−O bonds.32 These peaks appear in the spectra of both raw HNTs and APTES-HNTs. However, compared with the HNTs, some new peaks were observed at 2928 and 3420 cm−1 for the APTES-HNTs, which correspond to the stretching vibrations of −CH2− and −NH2 groups, respectively.33 These FTIR results confirm the modification of HNTs with APTES. The TGA curves of pristine HNTs and APTES-HNTs are shown in Figure 4. For the two nanomaterials, there is an

Figure 2. Images of oil droplets in oil/water emulsions: (a) D/W, (b) P/W, (c) H/W, and (d) V/W.

2.6.2. Oil Removal. For the oil removal tests, the filtration cell was loaded with a newly prepared oil/water emulsion, which was then stirred at a rate of 200 rpm. The concentration (mg/L) of oil in water was measured with a total organic carbon (TOC) analyzer (Shimadzu, TOC-VCPH). The rejection (R) of each oil ia defined as30 ⎛ Cp ⎞ R (%) = ⎜1 − ⎟ × 100 Cf ⎠ ⎝

(4)

where Cp and Cf are the concentrations (mg/L) of oil in the permeation and feed solutions, respectively. 2.6.3. Antifouling Experiments. The fouling resistance performances of the membranes were characterized by dynamic filtration experiments. The PWF (Jw.1) of each of the membranes was recorded every 5 min. Then, DI water was quickly replaced by the D/W emulsion to obtain the flux (JB). After that, the fouled membranes were removed and immediately washed with DI water for 30 min. Finally, the PWF (Jw.2) was recorded again. The relative flux reduction (RFR) and the flux recovery ratio (FRR) were used to estimate the antifouling abilities of the membranes and were calculated as follows31 ⎛ J ⎞ RFR (%) = ⎜⎜1 − B ⎟⎟ × 100 Jw.1 ⎠ ⎝

Figure 4. TGA curves of (a) raw HNTs and (b) APTES-HNTs.

evident weight loss (nearly 14.5%) from 400 to 550 °C, which is attributed to the decomposition of hydroxyl functional groups (Al−OH) in the structure of the HNTs.34 However, APTES-HNTs exhibited a higher weight loss than raw HNTs between approximately 250 and 400 °C, which is due to the decomposition of organosilane functional groups.35 The results are similar to those of other research36 and also indicate that APTES was successfully introduced onto the surface of the HNTs.

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Membranes. Table 1 reports the micropore sizes of the various membranes investigated in this work. It is clear that the

TEM images of raw HNTs and APTES-HNTs are presented in Figure 5. As shown in Figure 5a, the HNTs were typical

Table 1. Porosities and Mean Pore Radii of Various Membranes membrane M0 M1 M2-1 M2-2 M2-3

porosity (%) 58.3 65.4 64.7 65.1 66.4

(±2.4) (±1.9) (±2.0) (±1.5) (±2.8)

mean pore radius (nm) 35.0 40.6 34.8 38.5 45.9

(±0.4) (±0.8) (±1.0) (±1.3) (±1.5)

additives helped to slightly improve the porosity and mean pore radius of the membranes. As typical hydrophilic materials, HNTs and APTES-HNTs can accelerate the exchange between solvent and nonsolvent during the phase-inversion process.39 However, the addition of nanoparticles also increased the viscosity of the casting solution, which is not favorable for the formation of large pores. In addition, membrane M2-3 exhibited a better pore structure than membrane M1, because of the enhancement of the dispersion of the HNTs. 3.3.2. SEM Images. Cross-sectional SEM images of the different membranes are shown in Figure 7. It is clear that all of the membranes presented typical asymmetric porous structures, with a thin upper skin layer and a fingerlike porous sublayer.40 There were some slight changes between membrane M0 and the other membranes. Compared with the pure PVDF membrane, some large cavities formed in the sublayer upon the addition of HNTs and APTES-HNTs, as a result of the decrease of the solution thermodynamic stability in the coagulating bath. However, the hydrophilic additives also contributed to the formation of larger pore radii and thicker skin layers on the membrane surface, which eventually increased the PWFs and rejection ratios, respectively, of the membrane. These results are consistent with the data in Figure 6 and Table 1. More importantly, the APTES-HNTs were welldispersed in the membrane matrix, as can be seen in Figure 7f (see the yellow circles). The improvement in the dispersion would help to utilize the properties of the HNTs to the greatest extent possible. 3.3.3. AFM Observations. Three-dimensional AFM images including the roughness and surface-area parameters of the different membranes investigated in this work are presented in Figure 8. All membranes exhibited a “peak-and-valley” surface structure, represented by bright and dark regions in the images, respectively. Evidently, the average roughness (Ra) of the membrane surface decreased from 62.8 nm for membrane M0 to 24.5 nm for membrane M2-3 upon the addition of APTESHNTs. In addition, the surface of membrane M2-3 was smoother than that of membrane M1 as a result of the enhancement of the interfacial interaction between the membrane and the nanoparticles upon APTES modification. According to many reports, membranes with lower roughness and surface energy exhibit better antifouling abilities.41,42 The pollutants in water can aggregate and embed in the valleys of the pure PVDF membrane, so that they cannot be cleaned easily and result in irreversible fouling. The smooth surfaces of the APTES-HNT/PVDF membranes effectively contribute to the reduction of the aggregation of pollutants. The antifouling performances of the membranes are discussed in more detail in the following sections.

Figure 5. TEM images of (a) raw HNTs and (b) APTES-HNTs.

cylindrical hollow tubes with an internal diameter of 20−30 nm and an external diameter of 30−70 nm, which could provide some channels to promote the permeation of water.37 However, it is clear that some irregular substance was attached to the surfaces of the HNTs in Figure 5b. The diameter and surface roughness of the APTES-modified nanotubes were markedly increased compared with those of the raw HNTs, which further demonstrates the reaction between APTES and HNTs. 3.2. Contact Angles and Pure-Water Fluxes of the Membranes. The CAs and PWFs of all membranes are shown in Figure 6. Because of the intrinsic hydrophobicity of PVDF,

Figure 6. Pure-water flux and contact-angle images of various membranes.

the CA and PWF of membrane M0 were 84° and 96.8 L·m−2· h−1, respectively. In stark contrast, the hydrophilicity of the membranes were improved significantly by incorporating different amounts of HNTs. A large number of hydrophilic groups (such as −OH) were present on the surface of the HNTs and thus changed the interfacial free energy of the membranes.38 More importantly, membrane M2-3 gave the best results, with CA and PWF values of 58° and 203 L·m−2· h−1, respectively. Compared with that of membrane M1, the PWF of membrane M2-3 increased by 31.2%. This change is attributed to the enhancement of the dispersion of the HNTs in the PVDF matrix after the HNTs had been modified with APTES. 3.3. Morphologies and Microstructures of the Membranes. 3.3.1. Porosities and Mean Pore Radii of the 1763

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Figure 7. Cross-sectional SEM images of membranes (a) M0, (b) M1, (c) M2-1, (d) M2-2, and (e) M2-3. (f) Magnifications of panel e.

Figure 8. Three-dimensional AFM topographies of different membranes: (a) M0, (b) M1, (c) M2-1, (d) M2-2, and (e) M2-3.

3.4. Separation Performances of the Membranes. 3.4.1. Rejection of Oil in Water. Figure 9 shows the oilrejection ratios of membranes M0 and M2-3, which were evaluated with newly prepared D/W, P/W, H/W, and V/W emulsions. Both of these membranes exhibited good oil/water separation performances, and all of the oil-rejection ratios were approximately 90%. It is clear that the pore sizes of the ultrafiltration membranes (dozens of nanometers) were much smaller than the oil-droplet size (thousands of nanometers) in this work. The oil droplets in the emulsions were easily intercepted by the membranes. However, for each emulsion, the rejection ratios of the novel APTES-HNT/PVDF membranes were higher than that of the pure PVDF membrane. This improvement is attributed to the excellent hydrophilicity of the modified HNTs, which prevented many oil droplets from aggregating on the surfaces of the membranes. The oil/water separation effects of membranes M0 and M2-3 are visually displayed in Figure 10. The images of the oil/water

emulsions became much clearer after the emulsions had been filtered through the membranes. 3.4.2. Antifouling Performance. In this study, membranes M0 and M2-3 were chosen for an investigation of antifouling properties and reusability, which involved fouling with the D/ W emulsion and cleaning with DI water. As shown in Figure 11, the flux clearly decreased as DI water was replaced by the D/W emulsion at the beginning of every cycle. This decrease was caused by the formation of an oil cake near the membrane surface. However, both membranes exhibited good flux recoveries after being washed with DI water for 30 min. The FRR of membrane M2-3 reached 91.4% in the first cycle (in Table 2), 18.2% higher than that of membrane M0. More importantly, after three cycles of fouling and cleaning, the FRR of membrane M2-3 was still maintained at 82.9%. The antifouling and rejection mechanisms of the pure PVDF membrane and APTES-HNT-modified membranes are presented in Figure 12. It is known that antifouling properties are closely related to the surface roughness of the membrane. The 1764

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Figure 9. Oil rejections of membranes M0 and M2-3: (a) D/W, (b) P/W, (c) H/W, and (d) V/W.

Figure 10. Images of oil/water emulsions: (a) pristine, (b) after M0 filtration, and (c) after M2-3 filtration.

Table 2. RFR and FRR Data for Membranes in Three Fouling Cycles first cycle

second cycle

third cycle

membrane

RFR (%)

FRR (%)

RFR (%)

FRR (%)

RFR (%)

FRR (%)

M0 M2-3

75.0 61.4

77.3 91.4

78.3 63.5

69.5 88.1

80.4 68.3

63.2 82.9

Figure 11. Antifouling and recycling properties of membranes M0 and M2-3.

roughness and surface energy were reduced upon incorporation of APTES-HNTs, which effectively prevented the aggregation of oil droplets in the membrane valleys and pores of the membrane surface. Moreover, the improvement in the hydrophilicity helped to accelerate the permeation of water, which also further prevented the permeation and aggregation of pollutants. The high water flux could destroy the cake layer formed by the pollutants and eventually enhance the

Figure 12. Antifouling and rejection mechanisms of membranes (a) M0 and (b) M2-3.

antipollution properties of the membrane. Therefore, the irreversible fouling was decreased, and the membrane could be 1765

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via Interfacial Polymerization of Fluorinated Polyamine and Trimesoyl Chloride. Ind. Eng. Chem. Res. 2015, 54, 8302. (9) Li, X.; Wang, M.; Wang, C.; Cheng, C.; Wang, X. Facile Immobilization of Ag Nanocluster on Nanofibrous Membrane for Oil/ Water Separation. ACS Appl. Mater. Interfaces 2014, 6, 15272. (10) Zhou, J.-e.; Chang, Q.; Wang, Y.; et al. Separation of stable oil− water emulsion by the hydrophilic nano-sized ZrO2 modified Al2O3 microfiltration membrane. Sep. Purif. Technol. 2010, 75, 243. (11) Yi, X. S.; Yu, S. L.; Shi, W. X.; et al. The influence of important factors on ultrafiltration of oil/water emulsion using PVDF membrane modified by nano-sized TiO2/Al2O3. Desalination 2011, 281, 179. (12) Chang, Q.; Zhou, J.-e.; Wang, Y.; et al. Application of ceramic microfiltration membrane modified by nano-TiO 2 coating in separation of a stable oil-in-water emulsion. J. Membr. Sci. 2014, 456, 128. (13) Yan, L.; Hong, S.; Li, M. L.; et al. Application of the Al2O3− PVDF nanocomposite tubular ultrafiltration (UF) membrane for oily wastewater treatment and its antifouling research. Sep. Purif. Technol. 2009, 66, 347. (14) Zhang, S.; Wang, R.; Zhang, S.; et al. Development of phosphorylated silica nanotubes (PSNTs)/polyvinylidene fluoride (PVDF) composite membranes for wastewater treatment. Chem. Eng. J. 2013, 230, 260. (15) Vatanpour, V.; Madaeni, S. S.; Moradian, R.; et al. Novel antibifouling nanofiltration polyethersulfone membrane fabricated from embedding TiO2 coated multiwalled carbon nanotubes. Sep. Purif. Technol. 2012, 90, 69. (16) Zirehpour, A.; Rahimpour, A.; Jahanshahi, M.; et al. Mixed matrix membrane application for olive oil wastewater treatment: Process optimization based on Taguchi design method. J. Environ. Manage. 2014, 132, 113. (17) Zhang, Y.; Liu, F.; Lu, Y.; et al. Investigation of phosphorylated TiO2−SiO2 particles/polysulfone composite membrane for wastewater treatment. Desalination 2013, 324, 118. (18) Ghanbari, M.; Emadzadeh, D.; Lau, W. J.; et al. Super hydrophilic TiO2/HNT nanocomposites as a new approach for fabrication of high performance thin film nanocomposite membranes for FO application. Desalination 2015, 371, 104. (19) Hashemifard, S. A.; Ismail, A. F.; Matsuura, T. Mixed matrix membrane incorporated with large pore size halloysite nanotubes (HNTs) as filler for gas separation: Morphological diagram. Chem. Eng. J. 2011, 172, 581. (20) Ghanbari, M.; Emadzadeh, D.; Lau, W. J.; et al. Synthesis and characterization of novel thin film nanocomposite (TFN) membranes embedded with halloysite nanotubes (HNTs) for water desalination. Desalination 2015, 358, 33. (21) Zhang, J.; Zhang, Y.; Chen, Y.; et al. Preparation and Characterization of Novel Polyethersulfone Hybrid Ultrafiltration Membranes Bending with Modified Halloysite Nanotubes Loaded with Silver Nanoparticles. Ind. Eng. Chem. Res. 2012, 51, 3081. (22) Chen, Y.; Zhang, Y.; Zhang, H.; et al. Biofouling control of halloysite nanotubes-decorated polyethersulfone ultrafiltration membrane modified with chitosan-silver nanoparticles. Chem. Eng. J. 2013, 228, 12. (23) Yu, H.; Zhang, Y.; Sun, X.; et al. Improving the antifouling property of polyethersulfone ultrafiltration membrane by incorporation of dextran grafted halloysite nanotubes. Chem. Eng. J. 2014, 237, 322. (24) Zhao, Q.; Hou, J.; Shen, J.; et al. Long-lasting antibacterial behavior of a novel mixed matrix water purification membrane. J. Mater. Chem. A 2015, 3, 18696. (25) Zhang, Y.; He, X.; Ouyang, J.; Yang, H. Palladium nanoparticles deposited on silanized halloysite nanotubes: Synthesis, characterization and enhanced catalytic property. Sci. Rep. 2013, 3, 2948. (26) Liu, F.; Hashim, N. A.; Liu, Y.; et al. Progress in the production and modification of PVDF membranes. J. Membr. Sci. 2011, 375, 1. (27) Xu, Z.; Zhang, J.; Shan, M.; et al. Organosilane-functionalized graphene oxide for enhanced antifouling and mechanical properties of

cleaned easily, which indicates that the novel membranes developed in this work have potential for practical applications in oil/water separations.

4. CONCLUSIONS A novel PVDF oil/water separation membrane was successfully prepared through the incorporation of APTES-grafted HNTs. From the results achieved in this work, we conclude that the APTES-HNTs nanomaterial additives played a significant role in improving the membrane performances. Because of the large number of hydrophilic groups in APTES-HNTs, the blend membranes exhibited good hydrophilicity, with a higher purewater flux and lower contact angle than the pure PVDF membrane. In addition, the successful grafting of APTES on the surface of HNTs, confirmed by FT-IR sepctroscopy and XPS, could effectively solve the problem of nanoparticle aggregation and poor dispersion in the membrane matrix. More importantly, in tests of oil/water separation, the oil rejections and antifouling properties of the membranes were increased by blending APTES-HNTs. These improvements were attributed to a decrease of the roughness and surface energy, which could prevent oil droplets from aggregating, adsorbing, and embedding in the membrane surface and pores. Our future studies will focus on the treatment of actual oily wastewater using this novel type of membrane.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Y.H.). Tel./Fax: +86 02883037315. *E-mail: [email protected] (Z.Y.). Tel./Fax: +86 02883037315. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by Open Fund (PLN1403) of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University).

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REFERENCES

(1) Peterson, C. H. Long-Term Ecosystem Response to the Exxon Valdez Oil Spill. Science 2003, 302, 2082. (2) Tan, B. Y. L.; Tai, M. H.; Juay, J.; Liu, Z.; Sun, D. A study on the performance of self-cleaning oil−water separation membrane formed by various TiO2 nanostructures. Sep. Purif. Technol. 2015, 156, 942. (3) Lin, S.; Lan, W. Waste oil/water emulsion treatment by membrane processes. J. Hazard. Mater. 1998, 59, 189. (4) Howarter, J. A.; Youngblood, J. P. Amphiphile grafted membranes for the separation of oil-in-water dispersions. J. Colloid Interface Sci. 2009, 329, 127. (5) Diban, N.; Aguayo, A. T.; Bilbao, J.; Urtiaga, A.; Ortiz, I. Membrane Reactors for in Situ Water Removal: A Review of Applications. Ind. Eng. Chem. Res. 2013, 52, 10342. (6) Padaki, M.; Surya Murali, R.; Abdullah, M. S.; Misdan, N.; Moslehyani, A.; Kassim, M. A.; Hilal, N.; Ismail, A. F. Membrane technology enhancement in oil−water separation. A review. Desalination 2015, 357, 197. (7) Kang, G.-d.; Cao, Y.-m. Application and modification of poly(vinylidene fluoride) (PVDF) membranesA review. J. Membr. Sci. 2014, 463, 145. (8) Li, Y.; Su, Y.; Zhao, X.; Zhang, R.; Liu, Y.; Fan, X.; Zhu, J.; Ma, Y.; Liu, Y.; Jiang, Z. Preparation of Antifouling Nanofiltration Membrane 1766

DOI: 10.1021/acs.iecr.5b04797 Ind. Eng. Chem. Res. 2016, 55, 1760−1767

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Industrial & Engineering Chemistry Research polyvinylidene fluoride ultrafiltration membranes. J. Membr. Sci. 2014, 458, 1. (28) Cui, Z.; Hassankiadeh, N. T.; Lee, S. Y.; et al. Poly(vinylidene fluoride) membrane preparation with an environmental diluent via thermally induced phase separation. J. Membr. Sci. 2013, 444, 223. (29) Madaeni, S. S.; Zinadini, S.; Vatanpour, V. Preparation of superhydrophobic nanofiltration membrane by embedding multiwalled carbon nanotube and polydimethylsiloxane in pores of microfiltration membrane. Sep. Purif. Technol. 2013, 111, 98. (30) Zhu, X.; Tu, W.; Wee, K.-H.; et al. Effective and low fouling oil/ water separation by a novel hollow fiber membrane with both hydrophilic and oleophobic surface properties. J. Membr. Sci. 2014, 466, 36. (31) Zhang, F.; Zhang, W.; Yu, Y.; et al. Sol−gel preparation of PAAg-PVDF/TiO2 nanocomposite hollow fiber membranes with extremely high water flux and improved antifouling property. J. Membr. Sci. 2013, 432, 25. (32) Zhang, Y.; Xie, Y.; Tang, A.; et al. Precious-Metal Nanoparticles Anchored onto Functionalized Halloysite Nanotubes. Ind. Eng. Chem. Res. 2014, 53, 5507. (33) Moslehyani, A.; Mobaraki, M.; Ismail, A. F.; et al. Effect of HNTs modification in nanocomposite membrane enhancement for bacterial removal by cross-flow ultrafiltration system. React. Funct. Polym. 2015, 95, 80. (34) Yuan, P.; Southon, P. D.; Liu, Z.; et al. Functionalization of Halloysite Clay Nanotubes by Grafting with γ-Aminopropyltriethoxysilane. J. Phys. Chem. C 2008, 112, 15742. (35) Yu, Z.; Zeng, G.; Pan, Y.; et al. Effect of functionalized multiwalled carbon nanotubes on the microstructure and performances of PVDF membranes. RSC Adv. 2015, 5, 75998. (36) Ismail, A. F.; Hashemifard, S. A.; Matsuura, T. Facilitated transport effect of Ag+ ion exchanged halloysite nanotubes on the performance of polyetherimide mixed matrix membrane for gas separation. J. Membr. Sci. 2011, 379, 378. (37) Zhu, J.; Guo, N.; Zhang, Y.; et al. Preparation and characterization of negatively charged PES nanofiltration membrane by blending with halloysite nanotubes grafted with poly(sodium 4styrenesulfonate) via surface-initiated ATRP. J. Membr. Sci. 2014, 465, 91. (38) Duan, L.; Huang, W.; Zhang, Y. High-flux, antibacterial ultrafiltration membranes by facile blending with N-halamine grafted halloysite nanotubes. RSC Adv. 2015, 5, 6666. (39) Wienk, I. M.; Boom, R. M.; Beerlage, M. A. M.; et al. Recent advances in the formation of phase inversion membranes made from amorphous or semi-crystalline polymers. J. Membr. Sci. 1996, 113, 361. (40) Bottino, A.; Camera-Roda, G.; Capannelli, G.; et al. The formation of microporous polyvinylidene difluoride membranes by phase separation. J. Membr. Sci. 1991, 57, 1. (41) Yu, L.; Zhang, Y.; Wang, Y.; et al. High flux, positively charged loose nanofiltration membrane by blending with poly(ionic liquid) brushes grafted silica spheres. J. Hazard. Mater. 2015, 287, 373. (42) Yu, L.; Zhang, Y.; Zhang, H.; et al. Development of a molecular separation membrane for efficient separation of low-molecular-weight organics and salts. Desalination 2015, 359, 176.

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DOI: 10.1021/acs.iecr.5b04797 Ind. Eng. Chem. Res. 2016, 55, 1760−1767