Hydrophilicity Of Polyvinylidene Fluoride Membranes Research Articles

PVDF ultrafiltration membranes containing copper oxide-charcoal based graphene oxide nanohybrids with enhanced performance and antifouling properties

Charcoal based graphene oxide-copper oxide (GO-CuO) nanohybrids were successfully synthesized via the co-precipitation method. It was then used to improve polyvinylidene fluoride (PVDF) ultrafiltration (UF) membrane properties and performance. The PVDF/GO-CuO UF nanocomposite membranes containing different contents of the synthesized GO-CuO nanohybrids were prepared via the phase inversion method. It was found that hydrophilicity of PVDF membrane containing 0.2 wt% of the synthesized GO-CuO nanohybrids increases than the neat PVDF membrane, so that its water contact angle (WCA) decreases from 80.68±1.23° for the neat PVDF membrane to 60.53±5.25° for the modified membrane containing 0.2 wt% of the synthesized GO-CuO nanohybrids. On the other hand, compared to the neat PVDF membrane, pure water flux (PWF) of this modified nanocomposite membrane increases by about 77% (from 101.1±1.82 to 178.87±1.47 LMH) and exhibits 94.28±0.93% rejection of bovine serum albumin (BSA). This improvement is due to increased hydrophilicity, porosity, average membrane pore size, and decreased membrane surface roughness. The results of fouling measurements showed 42%, 60%, and 8% reduction in total fouling ratio (Rt), irreversible fouling ratio (Rir), and reversible fouling ratio (Rr), respectively. This indicated that antifouling properties of the modified membrane is significantly improved. It was found that the fabricated PVDF/GO-CuO nanocomposite membrane exhibits better performance than the neat PVDF membrane. Also, the results showed that this membrane also exhibits better properties and performance than the PVDF/GO and PVDF/CuO nanocomposite membranes. Therefore, it can be concluded that the fabricated PVDF/GO-CuO nanocomposite membrane has excellent potential for water and wastewater treatment applications.

Batch and continuous studies on the removal of heavy metals from aqueous solution using biosynthesised melanin-coated PVDF membranes.

Heavy metals like mercury, chromium, lead and copper present in groundwater at lower concentrations cause severe health issues and can even be fatal when consumed. The biopigment/biopolymer melanin can be reaped from different sources like bacterium, fungus, and human hair. It has excellent heavy metal ion scavenging property and can be exploited for non-biological applications, substantially including water purification. In this work, melanin nanoparticles were derived from the marine bacterium Pseudomonas stutzeri and were coated onto hydrophobic polyvinylidene fluoride (PVDF) membrane as a support, for batch and continuous removal of heavy metal studies. Batch studies on the effect of pH, temperature and adsorbate dose and continuous adsorption studies on the effect of flow rate, adsorbate and adsorbent mass loadings were carried out by using biosynthesised melanin-coated PVDF membranes for the removal of Hg(II), Cr(VI), Pb(II) and Cu(II). Scanning electron microscope (SEM) images revealed the surface morphology, Fourier-transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDS) deciphered the chemical characteristics of melanin-coated PVDF membranes before and after adsorption. Contact angle measurement confirmed the improvement in hydrophilicity of PVDF membrane upon coating with melanin. The maximum removal percentages of heavy metals achieved by melanin-coated PVDF membranes under batch mode operation were 87.6%, 88.45%, 91.8% and 95.8% for mercury, chromium, lead and copper, respectively optimised at 318 K and pH of 3 for chromium and 5 for other metals. However, the continuous mode of operation with a flow rate of 0.5 mL/min having 1 mg/L of heavy metal solution concentration exposed to 50 mg of melanin loading with a working volume of 200 mL showed better removal efficiencies compared with batch mode. The dynamic studies using Thomas and Yoon-Nelson models described the transient stage of the breakthrough curve and the model constants were calculated for column design and scale-up.

Effect of silica nanotubes on characteristic and performance of PVDF nanocomposite membrane for nitrate removal application

In this work, impact of synthesized silica nanotubes (SNTs) on morphology and performance of polyvinylidene fluoride (PVDF) nanocomposite membrane was studied. For this purpose, SNTs were synthesized using hydrothermal method, characterized by different techniques, and finally used as filler in nanocomposite membrane preparation. The PVDF/SNTs nanocomposite membranes were fabricated via phase inversion method at different dosage of SNTs (1–6 wt.%). As-prepared membranes and SNTs were characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and contact angle measurement. The results confirmed by incrementing SNTs dosage, hydrophilicity of PVDF membrane was increased. The effect of SNTs on the membrane performance was studied through nitrate removal at operating pressure of 7 bar. The results showed that the optimal performance parameters (nitrate rejection and pure water permeability (PWP) were obtained at SNTs dosage of 4%. The effect of feed concentration (50, 100, and 150 mg/L) on nitrate separation performance was also investigated and it was found that the maximum rejection of 86% and PWP of 11.58 (L/m2.h.bar) were achieved for optimum PVDF/SNTs membrane at 150 mg/L. Finally, antifouling properties of optimum PVDF/SNTs membrane were investigated.

Impact of sodium hypochlorite cleaning on the surface properties and performance of PVDF membranes

Abstract The adverse effect of sodium hypochlorite (NaClO) cleaning has raised concerns regarding their potential impacts on the membrane materials and activated sludge. In this study, the effect of NaClO cleaning on the physicochemical properties, surface free energy, and fouling propensity of polyvinylidene fluoride (PVDF) membranes was systematically investigated. The Analysis of Variance showed that the variation of NaClO soaking time had a significant effect on the permeability and hydrophilicity of PVDF membranes, while effects of NaClO concentration were insignificant. Results showed that the chemical cleaning with NaClO led to a reduction of membrane mechanical strength, which meant the potential harmful impact on the mechanical stability of membranes. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory analysis results showed that the electron donor components (γ−) of membrane surfaces decreased and the electron acceptor components (γ+) relatively increased with the extension of NaClO exposure time, which facilitated membrane fouling propensity.

A novel hydrophilic treatment of polyvinylidene fluoride membrane based on layer-by-layer assembly

TiO2 nanoparticles with diameter of approximately 20 nm were successfully assembled on polyvinylidene fluoride (PVDF) membranes layer-by-layer so as to improve the hydrophilicity of the PVDF membranes. SEM and droplet imaging system were used to determine microstructure and hydrophilicity of PVDF membranes. The effect of the TiO2 assembling layers on the contact angle (CA) of PVDF membranes was explored. As the number of the assembling layers were 2 and 3, the CAs of the modified PVDF membranes slightly increased at initial frozen time whilst decreased obviously after 1 min. For the modified PVDF membrane with assembling 5 layers TiO2 nanoparticles, the initial CA significantly decreased to 72.1° by approximately 30%. This novel method can be used to develop high performance hydrophilic PVDF membranes with high dispersion of TiO2 in filtration and separation applications.

Effect of doping porous ZrO2 solid superacid shell/void/TiO2 core nanoparticles (ZVT) on properties of polyvinylidene fluoride (PVDF) membranes

In this paper, porous ZrO2 solid superacid shell/void/TiO2 core nanoparticles (ZVT) were firstly prepared and then doped them to polyvinylidene fluoride (PVDF) to prepare a novel composite membrane (ZVT/PVDF composite membrane) through a phase inversion process, enhancing the capabilities of anti-fouling, anti-compaction and hydrophilicity of PVDF membranes. ZVT were investigated through scanning electron microscope (SEM), transmission electron microscope (TEM) and Fourier transform infrared (FT-IR). The results indicate that ZVT with the diameter of around 500nm are uniformly dispersed in PVDF membranes, the thickness of the ZrO2 shell are roughly 50nm and the ZrO2 shell shows a porous structure, and a solid superacid ZrO2 shell on the TiO2 core is formed due to a stretching vibration peak of SO double bond at 1460cm−1 in FT-IR spectra; alternatively, ZrO2 solid superacid shell of ZVT with strong acidity can form hydrophilic surroundings on the surface of PVDF membranes, and abundant hydroxyl groups on the surface of ZVT interact with PVDF chains by hydrogen bonds; furthermore, micro reaction locations (MRL) existing inside channels and surface of PVDF membrane enhance its properties. Therefore, ZVT are desirable functional nanomaterials as fillers of PVDF membranes.

A facile strategy to enhance PVDF ultrafiltration membrane performance via self-polymerized polydopamine followed by hydrolysis of ammonium fluotitanate

In this study, to overcome the inherent hydrophobicity and improve the comprehensive performance of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes, hydrophilic TiO2 particles were utilized to modify PVDF UF membranes. To obtain the strong binding force and homogenous TiO2 distribution on PVDF UF membranes, polydopamine (pDA) as the “bio-glue” was architecturally built between TiO2 and PVDF membranes, and the modification process was facilely designed via self-polymerization of dopamine and subsequent hydrolysis of ammonium fluotitanate. Water contact angle tests proved the significant improvement in the hydrophilicity of PVDF membranes after modification. The morphologies of various membranes before and after modification were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) and the chemical reactions during different modification stages were evaluated by X-ray photoelectron spectroscopy (XPS) tests. It was found that the pDA layer via self-polymerization of dopamine on PVDF membranes could assist TiO2 to tightly and homogeneously bind onto PVDF surface for improving the stability and anti-fouling property of membranes because of the coordination bond (CO···Ti) formed between TiO2 and pDA, and the pore sizes of PVDF membranes obviously decreased after modifications. The possible mechanisms during modifications were discussed. The comprehensive properties of PVDF membranes after such facile modifications had been greatly enhanced according to the results of water flux, bovine serum albumin (BSA) rejection, anti-fouling performance, and TiO2 binding performance characterizations. Both the water flux and BSA rejection could be simultaneously improved at the optimized hydrolysis time. Furthermore, the static and dynamic BSA adsorption tests were carried out. Interestingly, the amounts of BSA adsorption onto modified membranes demonstrated the opposite trends for the static and dynamic BSA adsorption tests. The possible reason was clarified based on the competition between the improved hydrophilicity and the adsorption ability of TiO2. Therefore, TiO2 modified PVDF UF membranes developed by this novel strategy have attractive potential for water environmental remediation.