Nano SiO2 and TiO2 embedded polyacrylonitrile/polyvinylidene fluoride ultrafiltration membranes: Improvement in flux and antifouling properties

Polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) ultrafiltration (UF) membranes are widely used in drinking water and wastewater applications. These membranes are prone to fouling and membrane efficiency decreases with time under constant operation. Significant improvements/modifications are necessary to apply these polymers as sustainable membrane materials. In this study, PVDF and PAN UF membranes were modified through incorporation of nanoparticles (NPs) namely SiO₂ and TiO₂. PVDF and PAN UF membranes were prepared by phase inversion method from polymer solutions having dispersed SiO₂ and TiO₂ NPs in it. Membrane surface hydrophilicity, charge, roughness, and morphology were studied. Equilibrium water content and molecular weight cut-off of the membranes were also measured. Addition of NPs increased membrane surface hydrophilicity, equilibrium water content, and surface potential. NPs modified membranes exhibited better membrane flux (35–79% higher) and antifouling properties (flux recovery ratio values 28–41% higher) than the virgin membranes.     

Nanocomposite hollow fiber nanofiltration membranes: Fabrication,characterization, and pilot-scale evaluation for surface water treatment

Thin-film nanocomposite (TFN) membranes were fabricated by interfacial polymerization of a polyamide (PA) layer on the shell side of hollow fiber membrane supports. TiO₂ nanoparticle loadings in the thin-film layer were 0.01, 0.05, and 0.20 wt %. Nanoparticle-free PA thin-film composite (TFC) membranes served as the comparative basis. The TFN membranes were characterized in terms of the chemical composition, structure, and surface properties of the separation layer. Incorporating nanoTiO₂ improved membrane permeability up to 12.6-fold. During preliminary laboratory-scale evaluation, TFN membranes showed lower salt rejection but higher TOC rejection in comparisons with the corresponding values for TFC controls. Based on the performance in lab-scale tests, TFN membranes with 0.01 wt % nanoTiO₂ loading were selected for an evaluation at the pilot scale with synthetic surface water as the feed. While the permeate flux during long-term pilot-scale operation gradually decreased for TFC membranes, TFN membranes had a higher initial permeate flux that gradually increased with time. The TOC rejection by TFN and TFC membranes was comparable. We conclude that TFN membranes show promise for full-scale surface water treatment applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48205.     

Morphological effects of spherical SiO2 and hexagonal mesoporous MCM-41 nanoparticles in polyacrylonitrile mixed matrix membranes on the biofouling mitigation in short-term filtration

In this study, the morphology of the nanostructures is evaluated on the surface characterization and performance of the polyacrylonitrile (PAN) ultrafiltration mixed matrix membranes (MMM). To this end, silica nanoparticles (NPs) such as spherical (SiO₂) and hexagonal mesoporous (MCM-41) with high hydrophilicity were incorporated at 0.5, 1, and 2 wt%. Attenuated total reflectance-Fourier transform infrared analysis illustrated the placement of NP on the surface of the MMM. Atomic force microscopy studies also showed that SiO₂ NP added to PAN exhibited a smoother surface than MCM-41 NP. Field-emission scanning electron microscope analysis of the MMM identified that all membranes are composed of a finger-like porous structure. Contact angle measurements indicate that the morphology of the NPs has no significant effect on MMM hydrophilicity. Moreover, the performance of the MMM was evaluated, and regardless of NP morphology, the MMM showed better permeate flux with increased loading. A higher pure water flux was observed in the PAN-MCM41-1% membrane (237 L/m² h), possibly because of inherent porosity and high hydrophilicity of MCM-41 compared to SiO₂ NP. Further, the PAN-SiO₂-1% membrane exhibited superior antifouling properties due to a lower surface roughness. The present studies reveal that the morphology of the NP greatly influence on the structure, permeation, and antifouling properties of PAN membranes.     

Nanoparticles modified Polyacrylonitrile/Polyacrylonitrile – Polyvinylidenefluoride blends as substrate of high flux anti-fouling nanofiltration membranes

Thin-film composite nanofiltration membranes were prepared by interfacial polymerization reaction of piperazine and trimesoylchloride on virgin and nanoparticles (SiO₂/TiO₂) modified Polyacrylonitrile/70:30 and 30:70 Polyacrylonitrile – Polyvinylidenefluoride blend ultrafiltration substrates. The membranes were characterized for surface hydrophilicity and potential, surface and cross-sectional morphology and equilibrium water content. Pure water permeability and differential rejection of multi (MgSO₄) and monovalent salts (NaCl) of the membranes were studied. Nanofiltration (NF) membranes prepared on nanoparticle modified UF substrates exhibit higher flux than the membranes prepared on virgin UF substrates. NF membranes prepared on TiO₂ modified substrates are exhibiting higher flux than the other membranes. Membrane prepared on TiO₂ modified 70:30 blend substrate exhibits the highest rejection ratio (4.63) of divalent to monovalent salts. Nanofiltration membranes prepared on nanoparticle modified substrates are displaying comparatively higher flux recovery ratio (FRR) and lower total fouling ratio (TFR) values than the NF membranes prepared on virgin ultrafiltration substrates.     

Effective incorporation of TiO2 nanoparticles into polyamide thin‐film composite membranes

The effectiveness of TiO₂ nanoparticles in improving the performance of polyamide (PA) thin‐film composite (TFC) membranes has been investigated. PA TFC membranes were prepared by interfacial polymerization with m‐phenylenediamine (MPD) and 1,3,5‐benzene tricarbonyl trichloride (TMC) where TiO₂ particles were added during and after interfacial polymerization. To distribute the TiO₂ nanoparticles uniformly in the PA films, colloidally stable TiO₂ sols were synthesized and added to the aqueous MPD solution rather than to an organic TMC solution. Through the use of different incorporation methods, TiO₂ particles were located on the top surface, in PA film layer, and in both positions. In the case of dense PA layers, the hydrophilicity of the membranes was significantly improved due to the presence of TiO₂ particles, resulting in an increased water flux. On the other hand, the enhancement of water flux was less significant when TiO₂ particles were incorporated into a loose PA film that was prepared with additives. In addition, a BSA fouling test confirmed that TiO₂ nanoparticles effectively improve the antifouling properties of the membranes for both dense and loose PA films. This effect is possibly due to increased hydrophilicity, covering of the fouling space, and a reduction in surface roughness. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43383.     

Improved separation performance of polyamide based reverse osmosis membrane incorporated with poly(dopamine) coated carbon nanotubes

A series of polyamide thin-film nanocomposite (PA TFN) membranes have been fabricated by incorporating hydrophilic poly(dopamine) (PDA) coated carbon nanotubes (CNTs@PDA) into the PA selective layer via interfacial polymerization. The effects of PDA coating thickness on surface characteristics and separation performances of membranes are studied in detail. The PDA coating makes the surface of PA TFN membrane more hydrophilic, smoother and less electronegative. The desalination performance is obviously influenced by the coating thickness of PDA and the loading concentration of PDA@CNTs. The water fluxes of PDA@CNTs incorporated PA TFN membranes have been improved without sacrificing NaCl rejections. When the loading concentration is 0.0010%, the maximum water flux is 48.1 L m⁻² h increasing by 45% compared with that of pristine PA membrane. Meanwhile, the NaCl rejection is up to 99.8%. The CNTs@PDA incorporated PA TFN membranes exhibit better anti-fouling property and separation performance durability. This work proves that CNTs@PDA has great potential application in PA TFN membranes.     

Solution-blow spun PLA/SiO2 nanofiber membranes toward high efficiency oil/water separation

With the ever frequent of industrial organic solvent emissions and oil spillages, the development of high efficiency oil/water separation materials has attracted extensive attention. Here, PLA-based nanofiber membranes modified with metal oxides (SiO₂, TiO₂, Al₂O₃, and CeO₂) are fabricated through blow spinning the mixed solution of polylactic acid (PLA) and metal oxide nanoparticles (NPs). Results shows that the addition of SiO₂ NPs significantly increases the hydrophobicity of the membranes, while maintaining the excellent superoleophilicity. The PLA/SiO₂ nanofiber membranes demonstrate a higher separation performance than pure PLA, PLA/TiO₂, PLA/Al₂O₃, and PLA/CeO₂ nanofiber membranes with high separation efficiency (~100%) and permeation flux (17,800 L m⁻² h⁻¹ for n-heptane), as well as prominent oil adsorption capacity (19.9 g/g for n-hexane). The successful fabrication of metal oxides modified PLA nanofiber membranes with high separation and adsorption ability, and excellent durability hold great application potential in the field of oily wastewater treatment.     

Modification of Thin Film Composite PVA/PAN Membranes for Pervaporation Using Aluminosilicate Nanoparticles

The effect of the modification of the polyvinyl alcohol (PVA) selective layer of thin film composite (TFC) membranes by aluminosilicate (Al₂O₃·SiO₂) nanoparticles on the structure and pervaporation performance was studied. For the first time, PVA-Al₂O₃·SiO₂/polyacrylonitrile (PAN) thin film nanocomposite (TFN) membranes for pervaporation separation of ethanol/water mixture were developed via the formation of the selective layer in dynamic mode. Selective layers of PVA/PAN and PVA-Al₂O₃·SiO₂/PAN membranes were formed via filtration of PVA aqueous solutions or PVA-Al₂O₃·SiO₂ aqueous dispersions through the ultrafiltration PAN membrane for 10 min at 0.3 MPa in dead-end mode. Average particle size and zeta potential of aluminosilicate nanoparticles in PVA aqueous solution were analyzed using the dynamic light scattering technique. Structure and surface properties of membranes were studied using scanning electron microscopy (SEM), atomic force microscopy (AFM) and water contact angle measurements. Membrane performance was investigated in pervaporation dehydration of ethanol/water mixtures in the broad concentration range. It was found that flux of TFN membranes decreased with addition of Al₂O₃·SiO₂ nanoparticles into the selective layer due to the increase in selective layer thickness. However, ethanol/water separation factor of TFN membranes was found to be significantly higher compared to the reference TFC membrane in the whole range of studied ethanol/water feed mixtures with different concentrations, which is attributed to the increase in membrane hydrophilicity. It was found that developed PVA-Al₂O₃·SiO₂/PAN TFN membranes were more stable in the dehydration of ethanol in the whole range of investigated concentrations as well as at different temperatures of the feed mixtures (25 °C, 35 °C, 50 °C) compared to the reference membrane which is due to the additional cross-linking of the selective layer by formation hydrogen and donor-acceptor bonds between aluminosilicate nanoparticles and PVA macromolecules.     

Structural and performance properties of UV-assisted TiO2 deposited nano-composite PVDF/SPES membranes

In this research, the surface of poly (vinylidene fluoride) (PVDF)/sulfonated polyethersulfone (SPES) blend membrane prepared via immersion precipitation was modified by depositing of TiO₂ nano-particles followed by UV irradiation to activate their photocatalytic property. The membranes were characterized by FTIR, SEM, AFM, contact angle, dead end filtration (pure water flux and BSA solution flux), antifouling analysis and antibacterial activity. The FTIR spectrum confirmed the presence of OH functional groups on the PVDF/SPES membrane structure, which was the key factor for deposition, and self-assembly of TiO₂ nanoparticles on the membrane surface. The SEM and AFM images indicated that the TiO₂ nanoparticles were deposited on the PVDF/SPES membrane. The contact angle measurements showed that the hydrophilicity of PVDF/SPES membrane was strongly improved by TiO₂ deposition and UV irradiation. The filtration results indicated that the initial flux of TiO₂ deposited PVDF/SPES membranes was lower than the initial flux of neat PVDF/SPES membrane. However, the former membranes showed lower flux decline compared to the neat PVDF/SPES membrane. The BSA rejection of modified membranes was improved. The fouling analysis demonstrated that the TiO₂ deposited PVDF/SPES membranes showed the fewer tendencies to fouling. The results of antibacterial study showed that the UV irradiated TiO₂ deposited PVDF/SPES membranes possess high antibacterial property.     

Preparation of graphene oxide/polyamide composite nanofiltration membranes for enhancing stability and separation efficiency

Polyamide (PA) NF membranes are synthesized on a hollow fiber support by the interfacial polymerization (IP) of piperazine (PIP) and trimesoyl chloride (TMC). Then, GO is coated on the PA layer to decorate the NF membrane surface (denoted GO/PA-NF). This strategy aims to improve the hydrophilicity, chlorine resistance and separation stability of the membrane. The optimization, chemical composition, morphology, and hydrophilicity of the synthesized GO/PA-NF membrane are characterized. Results indicate that the optimized GO/PA-NF in terms of rejection rate and flux are with 0.05 wt% GO. The rejection of GO/PA-NF for Na2SO₄ and MgSO₄ is 99.4% and 96.9%, respectively. Even if the GO/PA-NF is immersed in 1000 ppm NaClO solution for 48 h, the NF membrane still maintains stable salt rejection. The developed NF membranes exhibit excellent treatment performance on dying wastewater. The permeate flux and rejection of GO/PA-NF toward Congo red solution are determined to be 44.2 L/m²h and 100%, respectively. Compared with the PA membrane, GO/PA-NF presents a higher rejection for Na₂SO₄ (99.4%) and a lower rejection for NaCl (less than 20%), which shows that the NF membranes have a better divalent/monovalent salt separation performance. This study highlights the superior performance of GO/PA-NF and shows its high potential for application in wastewater treatment.     

Cellulose triacetate/LUDOX-SiO2 nanocomposite for synthesis of pervaporation desalination membranes

A series of cellulose triacetate/Ludox-silica nancomposite pervaporation membranes was successfully prepared via solution casting, aiming to improve the performance of cellulose triacetate membranes for desalination. The fabricated nanocomposite membranes were characterized to study the membrane morphology, chemical composition, mechanical properties, and surface hydrophilicity. Furthermore, the desalination performance was investigated as a function of silica (SiO₂) loading (ranging from 1 to 4 wt%) and feed concentration at 30 and 60 g/L of sodium chloride (NaCl). Pervaporation experiments showed that incorporating 4 wt% SiO₂ into a cellulose triacetate (CTA) membrane increased the water flux by a factor 2.5 compared with pristine CTA (from 2.2 to 6.1 kg m⁻² h⁻¹) for a 30 g/L NaCl feed solution at 70°C, while the salt rejection remained above 99%. The CTA/4 wt% SiO₂ membrane was found to have only 21% flux reduction when tested with a 60 g/L NaCl feed solution, without changes in membrane selectivity. This suggests that the developed CTA/Ludox-SiO₂ nanocomposite pervaporation membrane is suitable for desalination.     

SiO2-modified nanocomposite nanofiltration membranes with high flux and acid resistance

Thin-film nanocomposite (TFN) nanofiltration (NF) membranes with superior properties were prepared using hydrophilic SiO₂ (HGPN-SiO₂) nanoparticles as the inorganic modifying monomer by an interfacial polymerization (IP) process. The effects of HGPN-SiO₂ on the morphology and surface properties of the prepared NF membranes were characterized by attenuated total reflectance–Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, surface zeta potential, and static contact angle. The addition of HGPN-SiO₂ can effectively improve the permeate flux of the NF membranes. When the HGPN-SiO₂ concentration in the aqueous phase was 0.08 wt %, the permeate flux of the TFN-NF membrane was twice that of the pure NF membrane. Furthermore, the acid resistance of the TFN-NF membrane was clearly improved with the addition of HGPN-SiO₂. Under neutral conditions, the TFN-NF membrane showed superior flux and salt rejection stability in a long-running operation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47436.     

Inorganic nanoparticles incorporated in polyacrylonitrile-based mixed matrix membranes for hydrophilic,ultrafast, and fouling-resistant ultrafiltration

Mixed matrix membrane (MMM) structures and performances are greatly affected by the distribution of nanoparticles in the polymeric matrix. Until now, there has been little research on the effects of nanoparticle distribution states on polyacrylonitrile (PAN)-based MMM structures and performances. In this paper, different intermolecular interactions between nanoparticles and PAN molecules were generated by in situ fabricated amino-functionalized SiO₂ and TiO₂ nanoparticles to create absolutely different distribution states of nanoparticles in a PAN matrix. The results indicated that, due to the strong interactions between amino and cyano groups, SiO₂ is distributed in the PAN membranes homogeneously, while most of the TiO₂ migrates to the membrane's top surfaces or the walls of pores or even escape from the membranes during the nonsolvent index phase separation (NIPS) process. PAN-TiO₂ MMMs have more hydrophilic top surfaces, higher porosity, larger mean pore size, and stronger antifouling performances than pure PAN and PAN-SiO₂ membranes. The PAN-TiO₂ MMMs have an ultrahigh water flux of 1204.6 L/(m² h), which is more than 44 times that of PAN membranes. And the good pore structures and hydrophilicity of the membranes derived from special interactions between in situ TiO₂ nanoparticles and PAN molecules can give high-performance PAN-based ultrafiltration membranes a bright future. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47902.     

Synthesis and characterization of low content of different SiO2 materials composite poly (vinylidene fluoride) ultrafiltration membranes

A comparison of the morphology and performance of virgin poly (vinylidene fluoride) (PVDF) ultrafiltration (UF) membrane, and PVDF-composite membranes with low content of two different SiO₂ (N-SiO₂ and M-SiO₂ particles) was carried out. Cross-sectional area and surface morphology of the membranes were observed by scanning electron microscopy and atomic force microscopy. Surface hydrophilicity of the porous membranes was determined through the measurement of a contact angle. Performance tests were conducted on the composite membranes through water flux and bovine serum albumin (BSA) retention. Average pore size and surface porosity were calculated based on the permeate flux. Thermal stability and mechanical stability were determined by thermogravimetric analysis and tensile stress tests. The results indicate that N-SiO₂/PVDF (P-N) membranes possessed larger average pore size and porosity, which led to higher water flux and a slight decline in BSA retention. On the other hand, M-SiO₂/PVDF (P-M) membranes had better mechanical stability and anti-fouling performance with enhanced membrane hydrophilicity and decreased membrane surface roughness. Both of the P-N and P-M membranes exhibited typical asymmetric morphology and improved thermal stability.     

Enhancing antifouling performance of poly(l‐lactide) membranes by TiO2 nanoparticles

Poly(l ‐lactide) (PLLA)/TiO₂ composite membranes were fabricated by immersion precipitation method. The resulting membranes were characterized using various methods including XRD, ATR‐FTIR, TGA, DSC, SEM, goniometer, and molecular weight cut‐off. The antifouling performance of the membrane was investigated through the filtration experiments of the oil/water emulsion. XRD, SEM, and ATR‐FTIR results indicated that TiO₂ was successfully introduced into the membrane, while DSC and TGA indicated the enhancement of thermal stability of membrane. The improvement of membrane hydrophilicity was confirmed by goniometer. In addition, the pore size and porosity on the membrane surface varied obviously with increasing the TiO₂ loading. It was concluded that PLLA/TiO₂ composite membranes had better antifouling and recycling performance compared with the pure PLLA membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43542.     

Cellulose acetate (CA) hybrid membrane prepared by phase inversion method combined with chemical reaction with enhanced permeability and good anti-fouling property

The CA hybrid membrane with enhanced anti-fouling property and higher permeability was prepared by nonsolvent induced phase separation method combined with chemical reaction. The impacts of different solvents (N-methyl-2-pyrrolidone, N, N- Dimethylacetamide, Dimethyl sulfoxide and N, N-Dimethylformamide), organic acids (citric acid/fumaric acid) and titanium dioxide (TiO₂) nanoparticles (NPs) on the separation performance and thermal stability of CA hybrid membranes were investigated. Results showed that the introduction of organic acids to membrane matrix caused asymmetry in the membrane structure with more uniform pore size distribution and higher porosity (82.5%). This is attributed to the production of CO₂ bubbles by a reaction between organic acid in the casting solution and salt in the coagulation bath. Meanwhile, a tremendous rise in anti-fouling property (from 89.7% to 94%), pure water flux (from 329.7 to 821.5 L/m² h) and permeation flux (from 265.8 to 546.3 L/m² h) indicates a significant improvement in the hydrophilicity and the permeability of prepared membranes. In addition, a significant improvement in thermal stability (by 90°C) was achieved owing to the formation of dative bonds between TiO₂ NPs and CA polymer. Therefore, this approach can significantly improve the anti-fouling property and the separation performance of the CA membrane.     

Synthesis and Characterization of Polycarbonate/TiO2 Ultrafiltration Membranes: Critical Flux Determination

A novel polycarbonate (PC) membrane was modified with titanium dioxide via nonsolvent-induced phase separation method to improve its hydrophilicity and antifouling properties in a submerged membrane system for the removal of humic acid (HA) both with and without polyaluminum chloride (PAC) coagulant. The effect of TiO₂ additive on the morphology and performance of the nanocomposite membranes was studied by atomic force microscopy, field emission scanning electron microscopy, energy dispersive X-ray, mechanical properties, water contact angle, porosity, pure water flux, rejection tests, and antifouling parameters. The obtained results revealed that a higher critical flux was achieved by the PC/TiO₂ nanocomposite membrane. The flux recovery ratio of the neat PC membrane increased with the addition of TiO₂ nanoparticles and without PAC coagulant. HA removal for the PC nanocomposite membrane was higher than that of the neat PC membrane with and without PAC coagulant.     

Enhanced water flux through ultrafiltration polysulfone membrane via addition‐removal of silica nano‐particles: Synthesis and characterization

In the present paper, hierarchically structured ultrafiltration polysulfone (PSf) membrane was prepared to explore the effect of addition and subsequent removal of SiO₂ nano‐particles on the membrane morphology, hydrophilicity, and separation properties. The PSf based membranes namely PSf, PSf/SiO₂ and PSf/WSiO₂ (i.e. SiO₂ nano‐particles was acid‐washed and removed from PSf/SiO₂), were synthesized and characterized by different characterization methods. Pure water flux through the membranes was determined using a filtration unit operating at a continuous dead‐end flow mode. The modification enhanced the morphology, hydrophobicity, porosity and transport properties of the modified membranes, although the molecular weight cut‐off (MWCO) of the membranes was not changed considerably. In comparison, PSf/WSiO₂ membrane exhibited excellent pure water flux (about 4.5 times the flux of PSf, and 17 times the flux of PSf/SiO₂), although antifouling property of PSf/SiO₂ in separation of bovine serum albumin (BSA) was better than that of PSf and PSf/WSiO₂ membranes. The results suggested that the addition/removal of sacrificial solid fillers within/from a membrane matrix may provide a promising strategy to enhance PSf membrane transport property. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43556.     

Thin film composite forward osmosis membranes with poly(2‐hydroxyethyl methacrylate) grafted nano‐TiO2 as additive in substrate

The poly(2‐hydroxyethyl methacrylate) grafted titanium dioxide nanoparticles were synthesized and added to the substrate of flat‐sheet thin film composite forward osmosis (TFC‐FO) membranes. The hydrophilicity of substrate was improved, which was advantageous to enhance the water flux of TFC‐FO membranes. The membranes containing a 3 wt % TiO₂‐PHEMA in the substrate exhibited a finger‐like structure combined with sponge‐like structure, while those with lower or without TiO₂‐PHEMA content showed fully finger‐like structures. As for FO performance, the TFC‐FO membranes with 3 wt % TiO₂‐PHEMA content achieved the highest water flux of 42.8 LMH and 24.2 LMH against the DI water using 2M NaCl as the draw solution tested under the active layer against draw solution (AL‐DS) mode and active layer against feed solution (AL‐FS) mode, respectively. It was proven that the hydrophilic property of membrane substrates was a strong factor influencing the water flux in FO tests. Furthermore, the structural parameter was remarkably decreased with an increase of TiO₂‐PHEMA content in membrane substrate, indicating the reducing of internal concentration polarization. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43719.     

PVDF–TiO2 composite hollow fiber ultrafiltration membranes prepared by TiO2 sol–gel method and blending method

Organic–inorganic polyvinylidene fluoride (PVDF)–titanium dioxide (TiO₂) composite hollow fiber ultrafiltration (UF) membranes were prepared by TiO₂ sol–gel method and blending method, respectively. The membranes were characterized in terms of microstructure, hydrophilicity, permeation performance, thermal stability, and mechanical strength. The experimental results indicated that PVDF–TiO₂ composite UF membranes exhibited significant differences in surface properties and intrinsic properties because of the addition of inorganic particles. The TiO₂ particles improved the membrane strength and thermal stability of PVDF–TiO₂ composite UF membranes. In particular, hydrophilicity and permeability increased dramatically with the increase of TiO₂, whereas the retention property of UF membranes was nearly unchanged. However, high TiO₂ concentration induced the aggregation of particles, resulting in the decline of hydrophilicity and permeability. Compared with PVDF–TiO₂ composite hollow fiber UF membranes prepared by TiO₂ blending method, PVDF–TiO₂ composite hollow fiber UF membranes prepared by TiO₂ sol–gel method formed a dispersed inorganic network, and the stronger interaction between inorganic network and polymeric chains led to TiO₂ particles being uniformly dispersed in UF membranes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009