Preparation, characterisation and testing of catalytic polymeric membranes in the oxidation of benzene to phenol
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Polyvinylidene fluoride
Membrane Distillation
Polyvinylidene fluoride
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Membrane Distillation
Cationic polymerization
Zeta potential
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Membrane separation processes are promising methods for wastewater treatment. Membrane fouling limits their wider use; however, this may be mitigated using photocatalytic composite materials for membrane preparation. This study aimed to investigate photocatalytic polyvinylidene fluoride (PVDF)-based nanocomposite membranes for treating model dairy wastewater containing bovine serum albumin (BSA). Membranes were fabricated via physical coating (with TiO2, and/or carbon nanotubes, and/or BiVO4) and blending (with TiO2). Another objective of this study was to compare membranes of identical compositions fabricated using different techniques, and to examine how various TiO2 concentrations affect the antifouling and cleaning performances of the blended membranes. Filtration experiments were performed using a dead-end cell. Filtration resistances, BSA rejection, and photocatalytic cleanability (characterized by flux recovery ratio (FRR)) were measured. The surface characteristics (SEM, EDX), roughness (measured by atomic force microscopy, AFM), wettability (contact angle measurements), and zeta potential of the membranes were also examined. Coated PVDF membranes showed higher hydrophilicity than the pristine PVDF membrane, as evidenced by a decreased contact angle, but the higher hydrophilicity did not result in higher fluxes, unlike the case of blended membranes. The increased surface roughness resulted in increased reversible fouling, but decreased BSA retention. Furthermore, the TiO2-coated membranes had a better flux recovery ratio (FRR, 97%) than the TiO2-blended membranes (35%). However, the TiO2-coated membrane had larger total filtration resistances and a lower water flux than the commercial pristine PVDF membrane and TiO2-blended membrane, which may be due to pore blockage or an additional coating layer formed by the nanoparticles. The BSA rejection of the TiO2-coated membrane was lower than that of the commercial pristine PVDF membrane. In contrast, the TiO2-blended membranes showed lower resistance than the pristine PVDF membrane, and exhibited better antifouling performance, superior flux, and comparable BSA rejection. Increasing the TiO2 content of the TiO2-blended membranes (from 1 to 2.5%) resulted in increased antifouling and comparable BSA rejection (more than 95%). However, the effect of TiO2 concentration on flux recovery was negligible.
Polyvinylidene fluoride
Filtration (mathematics)
Zeta potential
Biofouling
Ultrafiltration (renal)
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The field of membrane distillation (MD) is currently enjoying a great deal of interest and its possible fields of application are being explored. However, penetration of liquid feed in membrane pores (wetting phenomenon) has caused in the lack of overall attention in the MD processes. Even though commercial polymeric membranes (e.g., polyvinylidene fluoride (PVDF), polypropylene (PP), and polytetrafluoroethylene) show intrinsic hydrophobicity, the pore wetting may still take place for treatment of solutions with surface tensions lower than water. Depositing nanoparticles (nPs) on membrane surface to form a microstructure on top of macrostructure (physical property rather than a chemical property of surface) as it is in natural superhydrophobic surfaces such as lotus leaf can increase water repelling effect of membranes.In this paper, membrane pore wetting behavior is investigated by depositing/grafting SiO2 nanoparticles on the surface of commercially available polypropylene membrane. Dip coating method is used to deposit nPs for increasing the membrane surface roughness, water contact angle and consequently reducing membrane wettability. The effect of experiment parameters on the superhydrophobicity and permeability of nano-coating membranes are examined herein to explore the optimum preparing conditions. Atomic force microscope (AFM) and contact angle goniometry measurements are applied to study the influences of surface coating on the surface structure and performance of the original and coated membranes.Moreover, membrane distillation tests are performed for modified and virgin flat sheet PP membranes. By comparing the performance of the original and modified membranes in direct contact membrane distillation experiments in the presence of a surfactant (sodium dodecyl sulphate, SDS), the influence of coating on membrane pore wetting and contamination degree of permeate with a surfactant is shown.
Membrane Distillation
Polymeric membrane
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Membrane Distillation
Polyvinylidene fluoride
Phase inversion
Membrane Fouling
Biofouling
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Membrane Distillation
Polyvinylidene fluoride
Electrospinning
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In this research work, novel perfluorooctanoic acid-modified melamine (PFOM) was synthesized as a hydrophobic filler using a facile one-pot synthesis. PFOM incorporating polyvinylidene fluoride (PVDF) solution was cast on a cellulose sheet to prepare a dual-layered membrane employing the phase-inversion technique for direct contact membrane distillation (DCMD) application. The influence of PFOM to tailor the dual-layered membrane performance was then investigated. The long perfluoro chain in PFOM hydrophobic fillers increased the surface roughness of the membranes due to its random overlapping with PVDF backbone, and these membranes exhibited a higher water contact angle value. The increase in pore size and membrane porosity did not significantly influence the liquid entry pressure of water (LEPw). The microporous membranes displayed good mechanical strength for use in the test setup. Pure water permeation was the highest (6.9 kg m-2 h-1) for membrane (M1) with 1 wt% of PFOM when tested with a simulated sea-water solution (3.5% w/v NaCl) in the direct contact distillation mode. These membranes also achieved the theoretical salt-rejection of 99.9%, thus confirming the potential of these membranes to be investigated for large scale membrane distillation (MD) applications like desalination of seawater.
Membrane Distillation
Polyvinylidene fluoride
Phase inversion
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Membrane distillation (MD) is a thermal-driven membrane separation process which recently garners interest from academic and industry due to its low energy requirements and the ability to integrate with renewable energy. In this work, two different additives, i.e. polyethersulfone (PES) and ethylene glycol (EG), were added into dope solutions consisting of polyvinylidene fluoride (PVDF) and 1-methyl-2-pyrrolidone (NMP) to prepare membranes for MD applications. The membranes were characterized with respect to thickness, pore size, porosity, and water contact angle using scanning electron microscope and water contact goniometer. Compared with the membranes made from pure PVDF and PVDF–EG system, it is found that PVDF–EG–PES membrane displayed improved characteristics i.e. having optimum porosity, large pore size, and thin membrane thickness coupled with finger-like structure extended from both inner and outer layers of the membrane. In addition to this, the permeate flux of PVDF–EG–PES membrane during MD application was also reported to be the highest among all the membranes studied when tested under same process conditions. With respect to membrane performance stability, the results showed that PVDF–EG–PES membrane could achieve a very consistent permeate flux while maintaining high NaCl rejection throughout 20 h operation, indicating the potential of this membrane in MD process.
Membrane Distillation
Polyvinylidene fluoride
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In this study, styrene-butadiene-styrene (SBS) was used to develop a novel functionalized electrospun membrane for the effective treatment of heavy metals in direct contact membrane distillation (DCMD) applications. Functionalization was achieved by the addition (doping) of the super hydrophobic Al2O3 nanoparticles (Al NPs) within the matrix of the membrane during electrospinning. Neat (pristine nondoped) and doped SBS membranes were tested. The performance of the SBS membranes were also compared with fabricated polyvinylidene fluoride membranes with and without doping with Al NPs. The membrane characteristics were tested via Fourier transform infrared, scanning electron microscopy, pore size, and porosity investigations. The wettability of the membranes was investigated with respect to the liquid entry pressure (LEP) and contact angle. The performance of the membranes was tested in a DCMD setting for its ability to treat water containing salt (NaCl) and heavy metals (Cr (VI), Cd, Pb) in various concentration in a single and multicomponent systems. The SBS member exhibited excellent hydrophobicity characteristics such as a high LEP (16.87 psi) and contact angle (141° ± 2°). It also had superior permeate flux rate compared to the other prepared membranes (54.4 LMH). The addition of the Al2O3 nanoparticles enhance the performance of the membranes substantially. Slight decline in the flux was observed after 14 hours of continuous operating time that could be attributed to agglomeration, adsorption, or temperature polarization effects. The SBS AL NPs membranes also demonstrated excellent flux for saline solutions of varied concentrations with 99% salt rejection.
Membrane Distillation
Polyvinylidene fluoride
Electrospinning
Surface Modification
Phase inversion
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Membrane Distillation
Polyvinylidene fluoride
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