Fabrication of Polyvinylidene Difluoride Membrane with Enhanced Pore and Filtration Properties by Using Tannic Acid as an Additive

Potential use of tannic acid (TA) as an additive for fabrication of polyvinylidene difluoride (PVDF) membrane was investigated. The TA was introduced by blending into the dope solution with varying concentrations of 0, 1, 1.5, and 2 wt%. The prepared membranes were characterized and evaluated for filtration of humic acid (HA) solution. The stability of the membrane under harsh treatment was also evaluated by one-week exposure to acid and alkaline conditions. The results show that TA loadings enhanced the resulting membrane properties. It increased the bulk porosity, water uptake, and hydrophilicity, which translated into improved clean water flux from 15.4 L/m2.h for the pristine PVDF membrane up to 3.3× for the TA-modified membranes with the 2 wt% TA loading. The flux recovery ratio (FRR) of the TA-modified membranes (FRRs = 78–83%) was higher than the pristine one (FRR = 58.54%), with suitable chemical stability too. The improved antifouling property for the TA-modified membranes was attributed to their enhanced hydrophilicity thanks to improved morphology and residual TA in the membrane matric.

Membranes for the Capture and Screening of Waterborne Plutonium Based on a Novel Pu-Extractive Copolymer Additive

This contribution describes the fabrication of plutonium-adsorptive membranes by non-solvent induced phase separation. The dope solution comprised poly(vinylidene fluoride) (PVDF) and a Pu-extractive copolymer additive of PVDF-g-poly(ethylene glycol methacrylate phosphate) (EGMP) in dimethylformamide (DMF). The effects of casting conditions on membrane permeability were determined for PVDF membranes prepared with 10 wt% PVDF-g-EGMP. Direct-flow filtration and alpha spectrometry showed that membranes containing the graft copolymer could recover Pu up to 59.9 ± 3.0% from deionized water and 19.3 ± 3.5% from synthetic seawater after filtering 10 mL of 0.5 Bq/mL 238Pu. SEM-EDS analysis indicated that the graft copolymer was distributed evenly throughout the entire depth of the copolymer membranes, likely attributing to the tailing observed in the alpha spectra for 238Pu. Despite the reduction in resolution, the membranes exhibited high Pu uptake at the conditions tested, and new membrane designs that promote copolymer surface migration are expected to improve alpha spectrometry peak energy resolutions. Findings from this study also can be used to guide the development of extractive membranes for chromatographic separation of actinides from contaminated groundwater sources.

A Wet-Spinning Process for Producing Carbon Nanotube/Polyvinylidene Fluoride Fibers Having Highly Consistent Electrical and Mechanical Properties

Studies of polymer/carbon nanotube (CNT) fibers typically focus on optimizing the overall properties, and the effects of structural variation on these properties are ignored. Thus, we investigated the longitudinal variation in the properties of CNT/polyvinylidene fluoride (CNT/PVDF) fibers prepared by wet spinning a solution of multi-walled nanotubes, PVDF, and dimethylacetamide. To this end, materials for the CNT/PVDF fiber were selected, and a dope solution was prepared using MWNT, PVDF, and dimethylacetamide (DMAc). To consider the process parameters that would affect the performance of the CNT/PVDF fiber during the wet-spinning process using the dope solution, the initial conditions for wet spinning were selected, including bath concentration, bath temperature, drying temperature, and elongation, and the CNT/PVDF fiber was spun under the corresponding conditions. Additionally, three performance stabilization processes were proposed to improve the initial conditions for wet spinning and manufacturing the fiber. Lastly, to confirm the reliability of the CNT/PVDF fiber in all sections, tensile strength, electrical conductivity, and cross-sectional images were analyzed for the 30 m, 60 m, and 90 m sections of the fiber, and the reliability of the wet-spinning process was verified.

Electrospun polyethersulfone/Ag-Clinoptilolite to remove chemical oxygen demand from real wastewater

Ag-Clinoptilolite/Polyethersulfone (PES/Clin/AgNPs) nanofiber was synthesized through the electrospinning method. The effect of solvent, the amount of Ag-Clinoptilolite, and PES were investigated. Parameters such as electric field, spinning distance, and concentration of the dope solution were studied in order to demonstrate their effects on the electrospinning ability and morphology of the nanofiber. The structure of PES/Clin/AgNPs nanofiber was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) analyses. In the optimum conditions, the nanofibers could be prepared at the size of 250–800 nm. Then, their ability to remove chemical oxygen demand (COD) from real wastewater was studied. The result revealed about 85% removal of COD at pH = 10 and in 10 min for PES/Clin/AgNPs (25%). A successful fabrication method using low-cost natural zeolite and the green polymer was introduced. The reusability of the column was assessed.

Assessment on Performance-properties of Asymmetric Nanofiltration Membranes from Polyethersulfone/n-Methyl-2-pyrrolidone/water Blends with Poly(vinyl pyrrolidone) as Additive

In this study, the effect of poly(vinyl pyrrolidone) (PVP) additive on the fabrication of asymmetric nanofiltration (NF) membranes was investigated in terms of performance, structural details and key properties. On addition of PVP ranging from 2 to 10 wt% into the dope solution, the fabricated NF membranes exhibited significantly different in properties and improved performance. In particular, the membranes made from 2 wt% PVP had the highest water flux and salt rejection of about 3.61 × 10–6 m3/m2s and 44.49 %, respectively. Modeling results revealed that small amount of PVP (2–4 wt%) produced finer structural properties. Moreover, the key properties (rp, ∆x/Ak and ζ) of the fabricated NF membranes were found to be within the range of that of commercial NF membranes.

Morphological Study of Fabricated PVDF Based Hydrophobic Membrane for Different Additives and Coagulation Bath Temperature

The demand of membrane distillation (MD) has increased since last few decades for numerous applications. The membrane used in MD is hydrophobic; therefore, the focus has been emphasised on the development of a suitable membrane with desired microstructure. In this study, the flat sheet hydrophobic membrane of suitable properties has been casted with various additives such as water, ethane-di-ol, and propan-2-ol in dope solution using a non-solvent induced phase separation (NIPS) technique. The effect of water content in dope solution has been studied on casted membrane porosity and contact angle. The maximum contact angle and porosity were found to be 96° and 53.23% at 4 weight percent of water content in dope solution of PVDF polymer and di.methyl.acetamide as solvent. It was found that SEM micrograph when ethane-di-ol and propan-2-ol are used as an additive shows more finger-like pores and nodules, respectively, in the microstructure of the casted membrane. Furthermore, synergistic effects using water with other additives were also identified using SEM micrograph of casted membrane and it was observed that water with ethane-di-ol and propan-2-ol form contact angle of 98° and 105°, respectively, for 2 weight percent each additive in dope. In this study, the membrane was also cast by dissolving PVDF powder in di.methyl.acetamide solvent with lithium chloride and the effect of the temperature difference between coagulation bath and film temperature was investigated using an SEM micrograph. Overall, it was found that water content and temperature difference aid in developing hydrophobic porous membrane of desired properties for MD applications.

PVDF-TiO2 Hollow Fibre Membrane For Water Desalination

The clean water crisis is increasing along with the increasing human population. Sea water is one of the largest water sources that can be utilized on the earth. However, the high salt concentration dissolved in seawater must be treated before it can use. Desalination is the directly technology for treating seawater with PVDF-TiO2 hollow fibre membrane via pervaporation process. The aim of this research was to determine the performance of PVDF-TiO2 hollow fibre membrane against variations in feed temperature in the artificial seawater pervaporation process. Method for fabrication membrane is using dry-wet spinning method. The result showed that the highest flux permeat occurred at feed temperature of 60ºC, namely 8.96 kg.m-2.h-1 with salt rejection > 92.86%. The result via SEM showed that of the membrane surface morphology, there is a white spot on the membrane surface is TiO2 because the dope solution is too thick. The PVDF-TiO2 hollow fiber membrane in this research is can be applied for seawater pervaporation.

Photocatalytic Nanocomposite Polymer-TiO2 Membranes for Pollutant Removal from Wastewater

Photocatalytic TiO2-PVDF/PMMA nano-composites flat sheet membranes were fabricated by phase inversion and then employed in a crossflow filtration pilot to remove model pollutants of various sizes and charge from aqueous solution. The dope solution contained a mixture of PVDF and PMMA as polymers, polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) as additives, triethyl phosphate (TEP) as green solvent and TiO2 as immobilized photo catalyst. After undergoing characterization tests such as SEM morphology thickness, porosity, contact angle and water permeability, the membranes were used to eliminate the model pollutants from synthetic aqueous solution. The impact of the operating conditions (i.e., pH, pressure and initial pollutant concentration) and composition of the doping solution on the performance and photocatalytic and antifouling activity of the membranes was investigated. The results showed that Congo Red and Tartrazine despite their small size were rejected at 99% and 81%, respectively, because of their negative charge, while Ciprofloxacin, which is larger than Tartrazine but of neutral charge, crossed the membrane. The permeability did not decrease with a decline in pollutant concentration but diminished when the pressure increased and was reduced by more than half for wastewater.

Removal of 4-Nitrophenol from Aqueous Solution by Using Polyphenylsulfone-Based Blend Membranes: Characterization and Performance

Among many contaminants in wastewater, organic phenol compounds presented a major concern to endanger the water resources safety. In the present study, blend nanofiltration (NF) membranes comprising polyphenylsulfone (PPSU) and polyethersulfone (PES) were prepared via the non-induced phase separation and their performance was examined against 4-Nitrophenol (4-NP). The PES ratio in the dope solution was varied from 6 to 9 wt.% to probe the impact of PES on the retention and permeation characteristics of the final membranes. A series of experimental tools were employed to estimate the characteristics of the membranes, including surface and cross-section, hydrophilicity, pore size and pore size distribution. Performance evaluation of the NF membranes was conducted considering two operational variables; pH and initial feed solution. About 99% removal of 4-NP along with 6.2 L/m2.h.bar was achieved at the optimum operating conditions as revealed by optimization and mathematical modelling.

Silver-containing polysaccharide-based tricomponent antibacterial fibres for wound care applications

Objective: Polysaccharide-based biomaterials are extensively used in wound care healing due to their unique liquid absorption, gelling properties and biocompatibility properties. They play an important role in controlling infections of highly exuding hard-to-heal wounds. The main objective of this study was to develop silver-containing polysaccharide-based tricomponent antibacterial fibres for use in these complex wounds. Method: The fibres were developed by coating silver-containing alginate and psyllium fibres with hydrolysed chitosan. Dope solution containing alginate, psyllium and silver carbonate was extruded into a coagulation bath containing calcium chloride and hydrolysed chitosan. The developed fibres were tested for liquid absorption, swelling and antibacterial properties against a control fibre (of alginate and psyllium). Results: The developed fibres showed comparatively better liquid absorption, gelling and antibacterial properties than the control fibres. Conclusion: The study concluded that developed fibres could be a preferred choice for application on hard-to-heal wounds with high levels of exudate, to support infection control and faster healing.