Modified Polyvinylidene Fluoride Membrane Research Articles

Novel strategy for membrane biofouling control in MBR with CdS/MIL-101 modified PVDF membrane by in situ visible light irradiation

Novel control strategies for membrane biofouling with eco-friendly photocatalytic technology are critically needed in practical operation of membrane bioreactors (MBRs). In this study, a metal-organic frameworks (MOF) based photocatalytic membrane was firstly applied in an anammox MBR for a long-term biofouling control, where bacteria were inactivated and foulants were degraded simultaneously, with environmentally friendly and renewable visible light energy. By physicochemical characterization, the synthesized photocatalyst of CdS/MIL-101 showed superior visible-light photocatalytic ability, and the 1 wt% CdS/MIL-101 modified membrane C2 showed enhanced hydrophilicity and water permeability compared with the pristine membrane C0. In the long-term operation of anammox MBRs under waterproof lights irradiation, the filtration cycles of C2 (25–26 d) were obviously extended compared with C0 (10–14 d), while their average total nitrogen removal efficiencies were comparable up to 84%, indicating an excellent biofouling alleviation effect by using C2 with a satisfactory nitrogen removal performance maintained. By analysis of the biofilm on the fouled membranes, the organic foulants (especially extracellular polymeric substances) were degraded, and the live bacteria were inactivated effectively by the photocatalytic reactions of CdS/MIL-101 on C2. In the antimicrobial tests against model bacteria, C2 exhibited remarkable antimicrobial effect against both Gram-negative and Gram-positive bacteria with visible light irradiation by destruction of cell integrity with the inhibition rate of 92% for Escherichia coli and 95% for Staphylococcus aureus, respectively. In the model foulants (bovine serum albumin, sodium alginate, and humic acid) filtration tests, C2 showed higher antifouling capabilities, lower flux declining rates, and higher foulants rejection rates under visible light irradiation compared with C0. The reactive species of ·OH, e– and h+ generated on C2 were verified to play the predominant role in the anti-biofouling processes by simultaneous bacteria inactivation and foulants degradation. The findings offer a novel insight into the biofouling controlling in MBRs by simultaneous bacteria inactivation and foulants degradation with an eco-friendly method.

Enhancing the Antibacterial Properties of PVDF Membrane by Hydrophilic Surface Modification Using Titanium Dioxide and Silver Nanoparticles

This work investigates polyvinylidene fluoride (PVDF) membrane modification to enhance its hydrophilicity and antibacterial properties. PVDF membranes were coated with nanoparticles of titanium dioxide (TiO2-NP) and silver (AgNP) at different concentrations and coating times and characterized for their porosity, morphology, chemical functional groups and composition changes. The results showed the successfully modified PVDF membranes containing TiO2-NP and AgNP on their surfaces. When the coating time was increased from 8 to 24 h, the compositions of Ti and Ag of the modified membranes were increased from 1.39 ± 0.13 to 4.29 ± 0.16 and from 1.03 ± 0.07 to 3.62 ± 0.08, respectively. The water contact angle of the membranes was decreased with increasing the coating time and TiO2-NP/AgNP ratio. The surface roughness and permeate fluxes of coated membranes were increased due to increased hydrophilicity. Antimicrobial and antifouling properties were investigated by the reduction of Escherichia coli cells and the inhibition of biofilm formation on the membrane surface, respectively. Compared with that of the original PVDF membrane, the modified membranes exhibited antibacterial efficiency up to 94% against E. coli cells and inhibition up to 65% of the biofilm mass reduction. The findings showed hydrophilic improvement and an antimicrobial property for possible wastewater treatment without facing the eminent problem of biofouling.

Poly (vinyl alcohol) modification of poly(vinylidene fluoride) microfiltration membranes for oil/water emulsion separation via an unconventional radiation method

Owing to inherent hydrophobicity, most polymer membranes suffer from serious fouling by organic pollutants, which severely deteriorates separation performances and reduce membrane lifetimes. Thus, surface hydrophilic modifications are essential to the development and application of various polymer membranes. Here, an unconventional but simple one-step approach was used to modify the surface of poly(vinylidene fluoride) (PVDF) membranes to produce good hydrophilicity and underwater superoleophobicity. This method directly anchored hydrophilic poly(vinyl alcohol) (PVA) onto PVDF membrane surfaces under γ-ray irradiation but without any vinyl additives. The obtained modified PVDF membranes possessed excellent separation performances for various oil-in-water emulsions, with oil rejection up to 99.5% and filtration flux up to 6.9 × 102 L m−2 h−1 bar−1 under ultralow pressure (0.084 bar). In addition, oil fouling was confirmed to be almost reversible on modified PVDF membranes, which made the flux recovery remarkably improved, from 33% of pristine PVDF membrane to 98% of modified membranes, and they also exhibited outstanding oil-fouling resistance to high viscosity oils. This study demonstrated that this unconventional radiation method was facile and effective for tailoring the performance of polymer membranes with saturated functional compounds, which could benefit the development of various functional membranes and other materials.

Simple Amphoteric Charge Strategy to Reinforce Superhydrophilic Polyvinylidene Fluoride Membrane for Highly Efficient Separation of Various Surfactant-Stabilized Oil-in-Water Emulsions.

Long-term efficient separation of highly emulsified oily wastewater is challenging. Reported herein is the preparation of a reinforced superhydrophilic, underwater superoleophobic membrane with demulsification properties using active iron nanoparticles in situ generated on a polydopamine (PDA)/polyethylenimine (PEI)-modified polyvinylidene fluoride (PVDF) membrane surface. A stable zwitterionic structure is fabricated on the membrane surface and provides it with an excellent capability of binding a hydration layer, leading to enhanced superhydrophilic/underwater superoleophobic properties. The interaction between the membrane surface and water is quantified using the relaxation time of water. After iron nanoparticles in situ anchoring, the superhydrophilic, underwater superoleophobic PDA/PEI modified PVDF membrane shows more stable flux behaviors, higher oil separation efficiency, demulsification, and excellent antioil-fouling properties for various anionic, nonionic, and cationic surfactant-stabilized oil-in-water emulsions in a crossflow filtration system. The reinforced hydration layer and the amphoteric charged demusification properties of the membrane play important roles in enhancing the membrane separation performance. The reinforced membrane also exhibits excellent cleaning and reusability performance in long-term operations. The outstanding separation performance, as well as the simple and cost-effective fabrication process of the membrane with various favorable properties, highlight its promise in practical emulsified oily water applications.

Bifunctional NiAlFe LDH-coated membrane for oil-in-water emulsion separation and photocatalytic degradation of antibiotic

A new NiAlFe layered double hydroxide/polydopamine/polyvinylidene fluoride (NiAlFe LDH/PDA/PVDF) membrane was fabricated by in-situ growth of LDH on the PDA modified PVDF membrane. The as-prepared membrane possesses a nano/microscale rough structural surface and displays the superior wettability of superhydrophilicity in air and underwater superoleophobicity. Combining the favourable features of superwettability and hierarchical rough structure, the NiAlFe LDH/PDA/PVDF membrane could effectively separate a series of oil-in-water emulsions with high efficiency (>99%) and high permeation flux (925–1913 L m−2 h−1 bar−1). Besides, owing to the light harvest ability of NiAlFe LDH, the relevant membrane also can be applied as a photocatalysis paper for the light-driven treatment of antibiotic residue in aqueous solution. In which, NiAlFe LDH/PDA/PVDF membrane can effectively degrade typical antibiotic tetracycline within 20 min under UV light irradiation, exhibiting excellent photocatalytic activity. In addition, cyclic experiments demonstrate that NiAlFe LDH/PDA/PVDF membrane has excellent stability and reusability both in oil-in-water emulsion separation and photocatalytic reaction. In general, the findings of this research demonstrate that photo-response LDH modified membranes have potential multiple applications in wastewater treatment.

Reducing the pathogenicity of wastewater with killer vapor-induced phase separation membranes

While smart antibacterial surfaces with bacteria-killing/bacteria-releasing properties have been reported, no strategy existed up to date to prepare phase-inversion membranes having these capabilities in one single step, without any surface-modification. We addressed this challenge by synthesizing two copolymers made of butyl methacrylate (BMA) units and of 2-(dimethylamino)ethyl methacrylate (DMAEMA), poly(BMA-r-DMAEMA), or (trimethylamino)ethyl methacrylate chloride (TMAEMA), poly(BMA-r-TMAEMA), both miscible with poly(vinylidene fluoride) (PVDF), and prepared membranes by the vapor-induced phase separation process. Results showed that all membranes were able to kill almost 100% of bacteria that came into contact with the surface. A washing procedure with a saline solution of sodium hexametaphosphate permitted to regenerate the membrane modified with poly(BMA-r-TMAEMA). Strong hydration of the interface between positively-charged brushes and dead bacteria after docking with hexametaphosphate anions, combined to the excess of negative charges, results in bacteria release following conformational changes of poly(BMA-r-TMAEMA) polyelectrolyte brushes. However, the membrane modified with poly(BMA-r-DMAEMA) could not be regenerated, likely because poly(BMA-r-DMAEMA) does not behave as a polyelectrolyte. Results also reveal that poly(BMA-r-TMAEMA)-modified PVDF membranes were able to kill various species of bacteria, and that multiple cycles could be successively run. The prepared MF membranes are able to kill the majority of microorganisms once they contact the membrane during filtration. Domains of applications are numerous from wastewater-treatment to healthcare applications, wherever bacteria are wanted dead after separation.

Facile hydrophilic modification of PVDF membrane with Ag/EGCG decorated micro/nanostructural surface for efficient oil-in-water emulsion separation

Wettability of porous materials is crucial for the separation of emulsified oil/water mixtures. Herein, high hydrophobicity of polyvinylidene fluoride (PVDF) membrane has been facilely transformed to high hydrophilicity and underwater superoleophobicity via single-step coating of plant-derived epigallocatechin gallate (EGCG) and silver ion (Ag+) in aqueous solution. EGCG can chelate with Ag+ and in-situ reduced it into Ag nanoparticle, meanwhile Ag/EGCG composite was adhered on membrane surface due to the high surface binding affinity of EGCG. The hydrophilic EGCG and formed micro/nanostructure together improved membrane hydrophilicity and oleophobicity. The optimally Ag/EGCG modified PVDF membrane possesses high permeate flux (e.g. 735 L/(m2h) for diesel-in-water emulsion, while it is zero for pristine PVDF membrane) under a low operation pressure of 0.5 bar and high oil rejections in the treatment of surfactant-stabilized oil-in-water emulsions consisting of micro/nano scale droplets. In addition, the membrane exhibits excellent antifouling property with a flux recovery ratio of 98.1% and satisfactory reusability in a 5-cycle test. Moreover, the membrane possessed desired stability during long-term rinsing test and Ag leaching test. This work would offer new insights into surface hydrophilic manipulation of porous membrane towards practical oil emulsion purification.

Antibiofouling performance and mechanisms of a modified polyvinylidene fluoride membrane in an MBR for wastewater treatment: Role of silver@silica nanopollens

Biofouling remains to be one of major obstacles in membrane bioreactors (MBRs), calling for the development of antibiofouling membranes. Silver nanoparticles (AgNPs), being a kind of broad spectrum bactericidal agent, have been widely used for modifying membrane; however, uncontrollable release of AgNPs and thus a short lifetime of modified membranes are thorny issues for the AgNPs-modified membranes. In this study, silica nanopollens were used as AgNPs nanocarriers for membrane modification (ASNP-M), which could improve silver delivery efficacy, avoid agglomeration and control Ag+ release towards bacteria. At a silver loading of 107.7 ± 10.9 μg Ag/cm2, ASNP-M effectively inhibited growth of Escherichia coli and Staphylococcus aureus, with an Ag+ release rate of 0.5 μg/(cm2 d). Long-term MBR tests showed that ASNP-M exhibited a significantly reduced transmembrane pressure increase rate of 0.88 ± 0.34 kPa/d which was much lower than that of two control membranes, i.e., pristine membrane (M0) (2.32 ± 0.86 kPa/d) and Ag@silica nanospheres (without spikes) modified membrane (ASNS-M) (2.25 ± 1.28 kPa/d). No significant adverse influences on the pollutant removal were also observed in the reactor. Foulants analysis revealed that biofilm of ASNP-M was thinner and comprised of mainly dead cells, and only organic matter with strong adhesion properties was allowed to attach onto the membrane surface. Bacterial community analysis suggested that the incorporation of Ag@silica nanopollens inhibited colonization of bacteria which are capable of causing membrane biofouling (e.g., Proteobacteria and Actinobacteria). These findings highlight the potential of the antibiofouling membrane to be used in MBRs for wastewater treatment and reclamation.

Hydrophilic hierarchical carbon with TiO2 nanofiber membrane for high separation efficiency of dye and oil-water emulsion

Hierarchical carbon hybrid materials have gained more attention in recent times especially in the separation of pollutants from wastewater. In this study, a novel ternary composite of graphitic carbon nitride (G-C3N4) decorated on reduced graphene oxide (RGO) with titanium dioxide (TiO2) nanohybrids was synthesized using hydrothermal approach to modify the electrospun PVDF membranes for the separation of oil and dye in wastewater. The characteristic functional groups of G-C3N4, RGO and TiO2 (G-C3N4,/RGO/TiO2) nanohybrids were confirmed by X-ray diffraction (XRD) and X-ray photon electron spectroscopy. Moreover, the prepared membranes were also studied using field emission scanning electron microscope and X-ray photoelectron spectroscopy. Interestingly, the PVDF modified membranes displayed excellent thermal stability with lower contact angle, increased surface roughness and surface charges. It was due to the tunable covalent π-π interfaces among G-C3N4 and RGO 2D hierarchical structured nanosheets. Besides due to the reasonable hierarchical structure formation of chemical and physical defense mechanism, the modified membranes exhibited outstanding antifouling performance and different oil water emulsion rejections. The pure water flux for GT-4 membrane was around 1261.2 ± 2 L/m2.h and exhibited high oil water removal efficiency above 95.4 ± 0.1% for different oils. The modified PVDF membranes also exhibited higher rejection rate of about 94.2 ± 0.5% for methylene blue dye removals. These studies confirm the formation of hydration layer and hierarchical structure for membranes which can be employed in oil water emulsion separation and dye rejection studies.

Fabrication of hyperbranched polyether demulsifier modified PVDF membrane for demulsification and separation of oil-in-water emulsion

Membrane-based treatment for oil-in-water emulsion remains a significant challenge. The main difficulties are to solve membrane fouling and to destroy the emulsion system to achieve high-efficiency emulsion separation. Herein, chemical demulsification combined with membrane separation technology was proposed for oil/water separation from the emulsion. A hyperbranched phenol-amine resin block polyether demulsifier (AE2311) was grafted onto surface of styrene-co-maleic anhydride (SMA) blend polyvinylidene fluoride (PVDF) membrane by alcoholysis reaction. The successful preparation of the demulsifier modified PVDF membrane was characterized by X - rayphotoelectron spectroscopy (XPS), attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and atomic force microscope (AFM). The obtained AE2311@SMA/PVDF membrane with grafting time of 9 h exhibited superhydrophilic (water contact angle of 0°) and underwater superoleophobic properties (underwater oil contact angle over 150°). The modified membrane can break the O/W emulsion and allow water to pass through. The separation efficiency for dichloroethane-in-water, kerosene-in-water, toluene-in-water and petroleum ether-in-water emulsions were all recorded over 99.0%, which indicates that the modified membrane has excellent capability for oil-water separation. Moreover, the modified membrane can be reused and exhibited long-term operation stability owing to the excellent underwater anti-fouling performance. The intrinsic mechanism for the oil/water separation is the synergistic effect of the chemical demulsification of AE2311, the hydrophilic and underwater super hydrophobic properties of the membrane surface, and the sieving effect of the ultrafiltration membrane. The demulsifier functionalized membrane provides a new idea for the fabrication membrane of oil-water emulsion separation in the future.

Fouling resistance of 3-[[3-(trimethoxysilane)-propyl] amino] propane-1-sulfonic acid zwitterion modified poly (vinylidene fluoride) membranes

Zwitterion polymer modified membranes have demonstrated fouling resistance in wide applications. The ubiquitous success in scientific progress, however, has not yet brought significant breakthrough in the application of such membranes in wastewater treatment. Limitation of zwitterion materials in membrane is seldomly discussed. In this paper, we aimed to bring an engineering view on the pros-and-cons of zwitterion modified microfiltration membrane in treating solutions containing humic acid (HA) and bovine serum albumin (BSA). A 3-[[3-(trimethoxysilane)-propyl] amino] propane-1-sulfonic acid (TMAPS) grafted zwitterionic PVDF membrane was selected as a model membrane. The membranes were prepared via a two-step “hydroxylation-grafting” method; surface modified PVDF membrane was transformed from hydrophobic to hydrophilic with significant improvement in pure water flux. An 87% increase was obtained in the stable flux for the grafted membrane when treating HA, but very similar flux pattern to the pristine one was found when treating BSA. The membrane resistance model showed that cake layer was the main fouling factor for both foulants. For HA, the cake layer blocking model predicted the membrane flux well; but for BSA, the intermediate blocking model fits best the experimental results. Zwitterion grafted surface failed to show improvement in the fouling resistance even at very low BSA feed concentration. Adsorption experiment indicated that the interaction of BSA to membrane is significantly stronger than HA and membranes independent from the surface characteristics. Present work clarified the limitation of zwitterion modified membranes in treating solutions containing HA-like and protein matters.

Preparation of Mg(OH)2 nanoparticles modified PVDF membranes for efficient dye adsorption and rejection

Preparation of Mg(OH)2 nanoparticles modified PVDF membranes for efficient dye adsorption and rejection

Filtration of BSA through TiO2 photocatalyst modified PVDF membranes

Filtration of BSA through TiO2 photocatalyst modified PVDF membranes

Effectiveness of fouling mechanism for bacterial immobilization in polyvinylidene fluoride membranes for biohydrogen fermentation

Bacterial immobilization was successfully develop using the fouling mechanism on the modified polyvinylidene fluoride membrane surface. The immobilization of bacteria via this method was accomplished through adsorption and entrapment of the bacteria in/on the membrane surface through fouling mechanism. Previously, the membrane was modified by polymerization method to impregnate the iron nanoparticles on the membrane surface in order to increase the surface roughness. The presence of both organic substances and bacterial cells leads to ‘combine fouling’ as the organic substances covalently bind the bacterial cells to the membrane by cross-linking, thus promote the efficiency of bacterial immobilization. The immobilized membrane was used for biohydrogen production via anaerobic fermentation using glucose-based media and it was found that it was capable of augmenting the yield of hydrogen production by 22% relative to the suspended system. This is attributed to the presence of iron on the membrane surfaces which come from the polymerization process that supplies the iron necessary for activating the hydrogenase enzyme in the bacteria, and hence, increase the production of biohydrogen. The metabolites analysis has indicated that the hydrogen production followed the acetic acid pathway.

Scalable fabrication of robust superhydrophobic membranes by one-step spray-coating for gravitational water-in-oil emulsion separation

Hydrophobic anti-wetting membranes have many applications, such as oily wastewater treatment via oil/water separation, desalination via membrane distillation, and carbon capture via gas-liquid membrane contactors. Herein, we used a simple and scalable method to fabricate robust superhydrophobic polyvinylidene fluoride (PVDF) based membranes by one-step spray-coating of fluorinated SiO2 nanoparticles. The prepared PVDF membrane was systematically characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle measurements. The modified PVDF membrane had excellent superhydrophobicity with an extremely high water contact angle up to 171.8 ± 1.1° and a low sliding angle of 1.69 ± 0.13°, due to the fluorinated close-packed hydrophobic SiO2 nanoparticles on the surface. The modified PVDF membrane maintained its relatively stable superhydrophobicity under various harsh conditions, i.e., exposure in hot water, NaOH and HCl, ultrasonication and high-speed flushing, indicating the superior robustness and stability. The prepared membrane also exhibited consistent separation efficiencies up to 99.88 ± 0.03% in water-in-oil emulsions, and superior recyclability and durability over 40 cycles. In addition, spray-coating showed its great promise in engineering various superhydrophobic surfaces on different substrates and excellent scalability in fabricating large-size membranes. This study demonstrates a facilely scalable spray-coating method for engineering robust superhydrophobic surfaces and membranes that can be potentially used for various gas, vapor and water/oil separations.

Enhanced MPBR with polyvinylpyrrolidone-graphene oxide/PVDF hollow fiber membrane for efficient ammonia nitrogen wastewater treatment and high-density Chlorella cultivation

Membrane fouling always as the main obstacle hinders wide application of membrane bioreactor (MBR). Development of antifouling membranes is a promising strategy to overcome this issue. In this study, novel polyvinylpyrrolidone (PVP)-graphene oxide (GO)/PVDF hollow fiber membrane with enhanced hydrophilicity and antifouling property was synthesized by assembling PVP-GO nanocomposites via chemical grafting method. The PVP-GO/PVDF membrane was successfully applied into algae-membrane photo-bioreactor (MPBR) with solids retention times (SRTs) of 30 d for high ammonia-nitrogen wastewater treatment at hydraulic retention times (HRTs) of 24 h. The permeability, removal performance and influence on extracellular polymeric substance (EPS) of algae-MPBR with modified PVDF membrane were compared to a control traditional system operated in parallel. Compared with pristine PVDF membrane, PVP-GO/PVDF membrane exhibited improved hydrophilicity (contact angle decreased from 97 to 62°), better permeability (1.7 times) and attractive flux recover rate (96%) in MPBR filtration, which was attributed to uniformly dispersed PVP-GO nanocomposites as spatial brushes for mitigating foulants on membrane surface. In terms of contaminants degradation, COD, NH4-N+ and NO3-N removal efficiency of algae-MPBR with modified membranes were kept above 97.8, 93.1 and 68.7%, much higher than traditional MBR. Moreover, remarkable reduction in hydrophobic proteins amount of EPS on fouling layer was observed for PVP-GO/PVDF membrane. The biomass concentration was maintained around 780 mg/L after 16 days and average biomass production rate reached as high as 45 mg/L d. These results indicated that PVP-GO/PVDF membrane exhibited superior antifouling performance for high-density microbes harvesting and efficient treatment for high ammonia-nitrogen wastewater.

Fouling-resistant PVDF nanofibre membranes for the desalination of brackish water in membrane distillation

In the current study, pristine PVDF nanofibre membranes were successfully modified with silica nanoparticles (SiO2NPs) or with organically-functionalised (silanised) silica nanoparticles (f-SiO2NPs). The superhydrophobic f-SiO2NPs-modified PVDF membranes (contact angle = 156 ± 6°) showed enhanced water flux and lower flux decays than those of pristine and SiO2NPs-modified PVDF membranes under both low salinity (LS) and high salinity (HS) feed solution conditions. Nevertheless, the higher organic content of the LS feed exacerbated fouling and wetting in both pristine and modified membranes (i.e., flux decays of up to 73.6% in uncoated membrane samples). These results indicate the efficiency of the silanisation of f-SiO2NPs in attaining super-hydrophobicity and enhanced performance in modified PVDF membranes. However, fouling and wetting still had a negative impact on the performance of the f-SiO2NPs-modified PVDF membranes. To provide anti-fouling properties, a hydrophilic layer consisting of silver nanoparticles (AgNPs) and functionalised multi-walled carbon nanotubes (f-MWCNTs) was coated on the pristine and modified membranes. This layer significantly decreased the flux decay and enhanced the resistance towards a decay in salt rejection of pristine, SiO2NPs-modified, and f-SiO2NPs-modified PVDF membranes under both LS and HS feed solution conditions. The adsorption of foulants also changed the surface characteristics of both coated and uncoated membranes, as evidenced by a decrease in contact angle and increase in interfacial free energy. The hydrophilic coating layer provided fouling-resistance properties, high salt rejection, and low flux decays to hydrophobic PVDF nanofibre membranes, demonstrating the high potential of this technique to produce potable water from brackish water in Membrane Distillation processes.

Poly (3, 4-ethylenedioxythiophene) modified polyvinylidene fluoride membrane for visible photoelectrocatalysis and filtration

A polyvinylidene fluoride (PVDF) organic conductive membrane with photoelectric activity was successfully developed via printing of oxidant (FeCl3·6H2O) layer by layer and then chemical vapor deposition (CVD) of Poly (3, 4-ethylenedioxythiophene) (PEDOT). Four kinds of membranes were prepared by changing the number of oxidant coatings layers. The structure and photoelectric properties of four membranes were well characterized. The photocurrent density of 3.7 × 10−4 A indicated that the four-oxidant coating layers membrane achieved the best performance in photo-electricity activity. A comprehensive study of degradation efficiency under different photoelectric conditions was carried out. Results showed that the photoelectrocatalytic removal of tetracycline hydrochloride was 1.6 and 7.9 times higher than that of photocatalysis and photolysis, respectively, under a voltage of 3 V assisted with visible light irradiation. The anti-interference and stability tests in continuous filtration process demonstrated that the dissolved organic matters (DOMs) can result in a 30% fluctuation on removal rate. The streaming potential tests of DOMs adsorption on membrane surface indicated that the more obvious the adsorption phenomenon was, the degradation of tetracycline hydrochloride was weaker. The degradation intermediates were identified and pathways were proposed in this work. The photoelectrocatalysis of PEDOT modified PVDF membrane provided a new potential for water purification.

Plasma-induced poly(acrylic acid)-TiO2 coated polyvinylidene fluoride membrane for produced water treatment: Synchrotron X-Ray, optimization, and insight studies

A super-hydrophilic, polyvinylidene fluoride (PVDF) membrane was obtained through plasma-induced poly (acrylic acid) (PAA) polymerization followed by titanium dioxide nano particles (TiO2 NPs) self-assembly for oily produced water treatment. Fractional factorial design method was applied to investigate the effects of experimental factors and their interactions on membrane modification. The mechanism of TiO2 NPs self-assembly was explored through synchrotron-based X-ray analyses and comprehensive membrane characterization. It was found that nano-TiO2 was immobilized onto the membrane surface through PAA layer without valence change. For the first time, the mechanism of nano-TiO2 immobilization was confirmed to be the coordination of Ti4+ with carboxylic group. After modification, the TiO2 NPs were strongly and uniformly fixed on membrane surface, dramatically improving the hydrophilicity of the PVDF membrane surface. The permeation flux was increased more than four times, and the oil rejection rate was higher than 92%. The modified PVDF membrane has great potential in the application for various water-recovery systems, and this study provided a new insight into the nature of functionalized polymer membrane.

Antifouling behaviour of PVDF/TiO2 composite membrane: a quantitative and qualitative assessment

The composite membranes of PVDF/TiO2 were prepared by a phase-inversion technique. Different amounts of TiO2 with respect to the weight of the polymer were incorporated in the casting solution to study qualitatively and quantitatively the antifouling property of the membrane. The membrane morphology was studied using a high-resolution scanning electron microscopy and atomic force microscopy, whereas the crystalline nature was studied using X-ray diffraction method. The interfacial interactions between foulants and TiO2 immobilized membranes were also evaluated using the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) approach. The XDLVO theory revealed an increase in repulsive interactive energy barrier with an increase in TiO2 loading, thus causing to improve the antifouling property of the membrane. Intercalation of TiO2 nanoparticles efficiently improved the porosity and wettability of the polymeric membranes, which could be confirmed by the contact angle analyzer analysis. The modified PVDF membranes exhibited excellent antimicrobial properties against Gram-negative Escherichia coli as confirmed from the halo zone and activity test. The permeation experimental results also showed high protein rejection of bovine serum albumin and humic acid (foulant) for membranes with optimum TiO2 loading of 0.01 g/g of PVDF polymer. However, at a concentration of 0.02 g TiO2/g of PVDF a negative effect on the membrane property was observed due to the former non-uniform distribution.