Properties Of Polyvinylidene Fluoride Membrane Research Articles

Increasing the hydrophilicity and antifouling properties of polyvinylidene fluoride membranes by doping novel nano-hybrid ZnO@ZIF-8 nanoparticles for 4-nitrophenol degradation

ZIF-8 modification can reduce aggregation of ZnO (a typical photocatalyst), and enhances antifouling property of PVDF membranes. In this study, we developed a novel membrane by adding ZnO@ZIF-8 nanoparticles into polyvinylidene fluoride (PVDF) substrates by using non-solvent induced phase separation (NIPS) method. Filtration test with bovine serum albumin (BSA) showed that the modified membrane has good pure water flux (395 L m−2 h−1, PWF) and high flux recovery rate (94%, FRR). Furthermore, the SiO2:ZnO@ZIF-8 membrane showed high separation effect in 4-NP degradation test under light condition, with the flux achieved about 321 L m−2 h−1 during filtration process. The degradation efficiency reached 81.5%, the apparent rate constant (Kapp/min−1) was 0.211 min−1. Besides, in prolonged 4-nitrophenol (4-NP) degradation test, the SiO2:ZnO@ZIF-8 membrane maintained higher flux and degradation rate. Thus, we reported a novel membrane with a prominent antifouling property.

Azo dye removal via surfactant-assisted polyvinylidene fluoride membrane

Background: Recently, concerns have been raised regarding the environmental and public health safety of azo dyes, the most widely used synthetic dyes. The membrane technique has been introduced as one of the efficient methods for dye removal treatments. Polyvinylidene fluoride (PVDF) membrane manipulated by surfactants was studied for removal of the azo dye, carmoisine. Methods: PVDF membrane was prepared via non-solvent-induced phase separation (NIPS) and used to remove the azo dye, carmoisine. Three nonionic surfactants including Tween 20, Tween 60, and Tween 80 were used individually as additives in casting solutions to improve PVDF membrane properties. Results: Fourier-transform infrared spectroscopy (FTIR) demonstrated the presence of functional groups of carbonyl (C=O) and hydroxyl (OH), assigned to Tween molecules, in the membrane chemical structure. All Tween species caused a decrease in the surface hydrophobicity of PVDF membranes illustrated by the reduced contact angles. Each Tween at a 2% concentration in the dope solution led to an increase in the pore-size of PVDF membranes, which was estimated by scanning electron microscopy (SEM). However, this impact was reversed at Tween concentrations of 4%. Membranes were assessed for dye removal efficiency and permeate flux in a cross-flow system. Permeability of PVDF membranes improved (~78%) with adding Tween 80 at a concentration of 2%. Tween 60 at a 2% concentration resulted in a ~45% increase in dye removal efficiency of PVDF membranes. And, atomic force microscopy (AFM) showed that Tween 60 increased membrane surface roughness. Conclusion: Surfactant-mediated changes in the surface properties of PVDF membrane improved dye removal efficacy.

Improving the hydrophilic and antifouling properties of polyvinylidene fluoride membrane by incorporation of novel nanohybrid GO@SiO2 particles

Novel high-flux and antifouling membranes were prepared by introducing the “three-dimensional structure” nanohybrid particle (GO@SiO2) and polyvinylpyrrolidone (PVP) into polyvinylidene fluoride (PVDF) casting solution. GO@SiO2 nanohybrid particle was produced via in situ hydrolysis and condensation of precursor tetraethoxysilane (TEOS) on the surfaces of graphene oxide (GO) nanosheets, and the nanohybrid membranes were first prepared through phase inversion by an immersion precipitation technique. Compared with PVDF/PVP, PVDF/SiO2/PVP and PVDF/GO/PVP membranes, PVDF/GO@SiO2/PVP membrane had outstanding performance in hydrophilicity, surface roughness, and mechanical force. The rejection rate of bovine serum albumin (BSA) exceeded 78.5% under high water flux (1232L/(m2h)) and the membrane flux recovery rate was highest (BSA=77.5%, sodium alginate (SA)=82.1%). To investigate the antifouling properties of the nanohybrid membrane further, the adhesion forces of foulant and membrane were determined using our own foulant probes with an atomic force microscope (AFM). The results showed that the adhesion forces between PVDF/GO@SiO2/PVP membrane and foulants (BSA and SA) were far smaller than the adhesive forces of the foulants with the PVDF/PVP membrane. The results showed that the new nanohybrid membrane had the best overall properties and antifouling ability, and it provides a new method for improving the performance of PVDF membranes.

Structure and properties of PVDF membrane with PES-C addition via thermally induced phase separation process

Polyvinylidene fluoride (PVDF) membrane and PVDF membrane with phenolphthalein polyethersulfone (PES-C) addition were prepared via thermally induced phase separation (TIPS) method by using diphenyl carbonate (DPC) and dimethyl acetamide (DMAc) as mixed diluents. The effects of coagulation temperature and pre-evaporation time on structure and properties of membranes were studied. The changes of sewage flux in MBR and the attenuation coefficient of sewage flux were investigated. The resistance distributions of PVDF and PVDF/PES-C membranes were compared by resistance analysis. Membrane composition and structure were characterized by ATR-FTIR, TGA, SEM and AFM. The foulant on membranes was analyzed by FTIR. The contact angle of PVDF/PES-C membrane was lower than that of PVDF membrane. A thinner skin layer and a porous cellular support layer formed in PVDF/PES-C membrane and resulted in a higher porosity and pure water flux. The pure water flux and porosity of PVDF/PES-C membrane increased with rising coagulation temperature and decreased with extending pre-evaporation time. The flux attenuation coefficient, the cake layer resistance and internal fouling resistance of PVDF/PES-C membrane in MBR were smaller than those of PVDF membrane in MBR. The FTIR spectrum of foulant on membrane indicated that the foulant on PVDF/PES-C membrane was mostly composed of protein and polysaccharide, while the foulant on pure PVDF membrane included biopolymer clusters besides protein and polysaccharide.

Effect of preparation conditions on the morphology, polymorphism and mechanical properties of polyvinylidene fluoride membranes formed via thermally induced phase separation

Polyvinylidene fluoride (PVDF) membranes were prepared from PVDF/sulfolane (SFL) solutions using the thermally induced phase separation (TIPS) method. The effects of PVDF concentration and dissolving temperature on the morphology, polymorphism and mechanical properties of such prepared membranes were investigated. Field emission scanning electron microscopy (FESEM) was performed to observe the membrane morphology, and X-ray diffraction (XRD) along with differential scanning calorimetry (DSC) was used to analyze the crystalline structure and thermal behaviors of membranes, respectively. Based on the experimental results, PVDF mainly crystallized into α phase in the overall membranes for all the investigated cases. As the PVDF concentration in the casting solution was raised, the total crystallinity and tensile strength of the membranes increased, while the porosity decreased. With the increase in dissolving temperature, the total crystallinity and porosity of the membranes increased slightly; however, the tensile strength decreased. The FESEM photomicrographs of cross-sections of membranes indicated that an interconnected bi-continuous structure was obtained in the PVDF/SFL (30 wt.% PVDF) system with a dissolving temperature of 120 °C, while the rest of the investigated membranes showed spherical or irregular particle structure, consequently, the tensile strength was improved from 3.5 to 7.5 MPa, and the energy consumption of membrane preparation was reduced.

Properties of polyvinylidene fluoride membranes at low degrees of sulphonation and their characterization by concentration potential coupled with A.C. impedance measurements

Membranes consisting of polyvinylidene fluoride at low degrees of sulphonation have been prepared in different experimental conditions. Because of the presence of ionogenic SO 3H groups, they exhibit ion exchange properties and ionic conductivity. Their electrochemical properties have been characterized by concentration potential coupled with an a.c. impedance method, in the frequency range of 5—10 7 Hz. It was found that the electrical resistance (10 2—10 6ω-cm) decreases with increasing HCl concentration, while, in some cases, the permselectivity is near to unity even at 0.1 M electrolyte concentration. These results are explained by assuming the presence of a very compact film, responsible for the high permselectivity, and of a thick porous part, having high electrical resistance where salt invasion readily occurs.

The contrastive study of chemical treatment on the properties of hydrophobic PVDF membrane

In this study, polyvinylidene fluoride (PVDF) flat membranes were treated with potassium hydroxide (KOH), sodium hydroxide (NaOH) and sodium hypochlorite (NaOCl). The effects of temperature, treatment duration and chemical concentration towards the properties of PVDF membrane were contrastively studied. Following treatment, membrane became much brittle with a reduced nominal elongation to as low as 61%. Temperature elevation and prolonged treatment time accelerated the chemical reaction with PVDF as shown by further decline in the membrane stability. Nevertheless, the treatment conditions employed in this study are considered too mild for the dehydrofluorination process to occur. FTIR analysis indicated no carbon-carbon double bond formation and DSC analysis showed insignificant changes in the melting temperature. All treated membrane was observed to have larger pore size as a result of stretching on surface structure. Comparatively, acquired results showed that NaOCl has the most detrimental impact on the PVDF membrane stability, followed by NaOH and KOH.