On the effect of fumed silica particles on the structure, properties and application of PVDF membranes

Efficiency of Fabricated Adsorptive Polysulfone Mixed Matrix Membrane for Acetic Acid Separation

The ultrafiltration mixed matrix membrane (UF MMMs) process represents an applicable approach for the removal of diluted acetic acid at low concentrations, owing to the low pressures applied. The addition of efficient additives represents an approach to further improve membrane porosity and, subsequently, enhance acetic acid removal. This work demonstrates the incorporation of titanium dioxide (TiO₂) and polyethylene glycol (PEG) as additives into polysulfone (PSf) polymer via the non-solvent-induced phase-inversion (NIPS) method to improve the performance of PSf MMMs performance. Eight PSf MMMs samples designated as M0 to M7, each with independent formulations, were prepared and investigated for their respective density, porosity, and degree of AA retention. Morphology analysis through scanning electron microscopy elucidated sample M7 (PSf/TiO₂/PEG 6000) to have the highest density and porosity among all samples with concomitant highest AA retention at approximately 92.2%. The application of the concentration polarization method further supported this finding by the higher concentration of AA solute present on the surface of the membrane compared to that of AA feed for sample M7. Overall, this study successfully demonstrates the significance of TiO₂ and PEG as high MW additives in improving PSf MMM performance.

Characterisation and Mechanical Modelling of Polyacrylonitrile-Based Nanocomposite Membranes Reinforced with Silica Nanoparticles

In this study, neat polyacrylonitrile (PAN) and fumed silica (FS)-doped PAN membranes (0.1, 0.5 and 1 wt% doped PAN/FS) are prepared using the phase inversion method and are characterised extensively. According to the Fourier Transform Infrared (FTIR) spectroscopy analysis, the addition of FS to the neat PAN membrane and the added amount changed the stresses in the membrane structure. The Scanning Electron Microscope (SEM) results show that the addition of FS increased the porosity of the membrane. The water content of all fabricated membranes varied between 50% and 88.8%, their porosity ranged between 62.1% and 90%, and the average pore size ranged between 20.1 and 21.8 nm. While the neat PAN membrane's pure water flux is 299.8 L/m² h, it increased by 26% with the addition of 0.5 wt% FS. Furthermore, thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) techniques are used to investigate the membranes' thermal properties. Finally, the mechanical characterisation of manufactured membranes is performed experimentally with tensile testing under dry and wet conditions. To be able to provide further explanation to the explored mechanics of the membranes, numerical methods, namely the finite element method and Mori-Tanaka mean-field homogenisation are performed. The mechanical characterisation results show that FS reinforcement increases the membrane rigidity and wet membranes exhibit more compliant behaviour compared to dry membranes.

Alkyl Silica Hybrid Nanowire Assembly in Improved Superhydrophobic Membranes for RO Filtration

Alkyl silica membranes and wires were synthesized by a sol-gel method, which has the capacity to control the size of the particles or membranes by controlling the reactions. Trimethoxyoctylsilane (C₈TMOS) was used as a chemical surfactant; poly(vinylpyrrolidone) (PVP) as an emulsifier, dissolved in butanol for emulsion; and tetraethylorthosilicate (TEOS) as a precursor and a source of silica. An assembly of silica wires was fabricated on glass and cotton substrates by the dip-coating technique. Porous membranes and silica wires were observed using scanning electron microscopy (SEM) images. The contact angles of all of the samples were in the range of 140-154° as measured by ImageJ software, which confirmed the hydrophobic nature of the samples. The contact angle was increased by increasing the amount of the surfactant. Phase changes of silica wires and membranes were investigated by thermogravimetric analysis. Chemical bonds of the sample were studied using Fourier transform infrared (FTIR) spectroscopy. The band gap of silica nanowires was measured to be 3.8-3.4 eV using the UV-visible spectrum and decreased as compared to that of bulk silica. These silica-based porous membranes with enhanced transport properties can be used in filtration and separation techniques. This fabricated hybrid silica membrane showed ∼96% salt rejection within a permeation flux of 3.04 L/m² h.

Antimicrobial Hydrophilic Membrane Formed by Incorporation of Polymeric Surfactant and Patchouli Oil

Membrane properties are highly affected by the composition of the polymer solutions that make up the membrane material and their influence in the filtration performance on the separation or purification process. This paper studies the effects of the addition of pluronic (Plu) and patchouli oil (PO) in a polyethersulfone (PES) solution on the membrane morphology, membrane hydrophilicity, and filtration performance in the pesticide removal compound in the water sample. Three types of membranes with the composition of PES, PES + Plu, and PES + Plu + patchouli oil were prepared through a polymer phase inversion technique in an aqueous solvent. The resulting membranes were then analyzed and tested for their mechanical properties, hydrophilicity, antimicrobial properties, and filtration performance (cross-flow ultrafiltration). The results show that all of the prepared membranes could reject 75% of the pesticide. The modification of the PES membrane with Plu was shown to increase the overall pore size by altering the pore morphology of the pristine PES, which eventually increased the permeation flux of the ultrafiltration process. Furthermore, patchouli oil added antimicrobial properties, potentially minimizing the biofilm formation on the membrane surface.

Manufacturing and Characterisation of Polymeric Membranes for Water Treatment and Numerical Investigation of Mechanics of Nanocomposite Membranes

In this study, polyethersulfone (PES) and polyvinylidene fluoride (PVDF) microfiltration membranes containing polyvinylpyrrolidone (PVP) with and without support layers of 130 and 150 μm thickness are manufactured using the phase inversion method and then experimentally characterised. For the characterisation of membranes, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and pore size analysis are performed, the contact angle and water content of membranes are measured and the tensile test is applied to membranes without support layers. Using the results obtained from the tensile tests, the mechanical properties of the halloysite nanotube (HNT) and nano-silicon dioxide (nano SiO₂) reinforced nanocomposite membranes are approximately determined by the Mori–Tanaka homogenisation method without applying any further mechanical tests. Then, plain polymeric and PES and PVDF based nanocomposite membranes are modelled using the finite element method to determine the effect of the geometry of the membrane on the mechanical behaviour for fifteen different geometries. The modelled membranes compared in terms of three different criteria: equivalent stress (von Mises), displacement, and in-plane principal strain. Based on the data obtained from the characterisation part of the study and the numerical analysis, the membrane with the best performance is determined. The most appropriate shape and material for a membrane for water treatment is specified as a 1% HNT doped PVDF based elliptical membrane.

Halloysite Nanotube-Ferrihydrite Incorporated Polyethersulfone Mixed Matrix Membrane: Effect of Nanocomposite Loading on the Antifouling Performance

Membrane filtration is an attractive process in water and wastewater treatment, but largely restricted by membrane fouling. In this study, the membrane fouling issue is addressed by developing polyethersulfone (PES)-based mixed matrix membranes (MMMs) with the incorporation of hydrophilic nanoparticles as an additive. Ultrafiltration MMMs were successfully fabricated by incorporating different loadings of halloysite nanotube-ferrihydrates (HNT-HFO) into a polyethersulfone (PES) matrix and their performance was evaluated for the separation of bovine serum albumin (BSA) solution and oil/water emulsion. The results show that wettability is endowed to the membrane by introducing the additive aided by the presence of abundant -OH groups from the HFO. The loading of additive also leads to more heterogeneous surface morphology and higher pure water fluxes (516.33-640.82 L/m2h) more than twice that of the pristine membrane as reference (34.69 L/m2h) without affecting the rejection. The MMMs also provide much enhanced antifouling properties. The filtration results indicate that the flux recovery ratio of the modified membrane reached 100% by washing with only distilled water and a total flux recovery ratio of >98% ± 0.0471 for HNT-HFO-loaded membranes in comparison with 59% ± 0.0169 for pristine PES membrane.

Effect of hydrophilic silica and dual coagulation bath on structural and mechanical properties of PVDF membrane for membrane distillation

The water scarcity threatens environmental health and human development. Membrane distillation (MD) is one of the most applicable processes for purifying water using a hydrophobic membrane. In this study, the synergetic effect of SiO₂ nanoparticles as well as employing the dual coagulation bath on physical and mechanical properties of Polyvinylidene Fluoride (PVDF) flat-sheet membranes produced by dry-wet phase inversion (DIPS) technique has been investigated. The results of microstructural analysis using Scanning Electron Microscope (SEM) demonstrated that by adding nanoparticles while the pore size decreased noticeably, the percentage of porosity significantly increased. Also, it has been revealed that by utilizing isopropanol as the first coagulation bath the finger-like macro-voids became smaller in size, and the share of sponge-like structures rose remarkably. The membrane performance was tested by Vacuum Membrane Distillation (VMD) for measuring the flux and Liquid Entry Pressure (LEP_w) laboratory setup. It can be seen that by increasing the content of SiO₂ nanoparticles to 6 wt.% while the LEP_w approximately halved, the flux soared to about 10000 g/m²h. Moreover, mechanical testing showed that although the tensile strength of nanocomposite samples fabricated in isopropanol dual coagulation bath was improved by up to 66%, their ductility slightly declined. Furthermore, the hydrophobicity of each membrane was examined via contact angle measurements. Finally, it was found that all membranes completely rejected the NaCl in rejection test. Graphical abstract.

Production of High Flux Poly(Ether Sulfone) Membrane Using Silica Additive Extracted from Natural Resource

This paper reports the application of silica derived from natural biomasses of rice husk and bagasse ashes as membrane modifying agents. The modification was conducted on poly(ether sulfone) (PES) membrane by blending the silica into the dope solution. The modification was aimed to improve the structure and hydraulic performance of the resulting PES membrane. The effects of silica addition to the membrane system were evaluated through the analysis of change in chemical structure using ATR-FTIR, surface morphological change using AFM, and surface hydrophilicity using water contact angle measurement. SEM and AFM images show the silica loading significantly affects the membranes morphologies. Silica loading also promotes hydrophilic property as shown by the decrease in water contact angles from 82° to 52-60° due to the presence of polar groups in some residual silica in the membrane matrix. Silica blending also leads to the formation of membranes with higher permeability of up to three folds but lower humic acid rejection (78-62%). The findings indicate the role of silica to enhance the membrane pore size. The ability of membrane to reject humic acid (of 0.8 nm minimum diameter) indicating that the resulting membranes were in between tight ultrafiltration and nanofiltration type. Nonetheless, applying too-high silica concentration decreased the humic acid rejection most likely due to over enlargement of the membrane pore size.

Improving Water Permeability of Hydrophilic PVDF Membrane Prepared via Blending with Organic and Inorganic Additives for Humic Acid Separation

The removal of impurities from water or wastewater by the membrane filtration process has become more reliable due to good hydraulic performance and high permeate quality. The filterability of the membrane can be improved by having a material with a specific pore structure and good hydrophilic properties. This work aims at preparing a polyvinylidene fluoride (PVDF) membrane incorporated with phospholipid in the form of a 2-methacryloyloxyethyl phosphorylcholine, polymeric additive in the form of polyvinylpyrrolidone, and its combination with inorganic nanosilica from a renewable source derived from bagasse. The resulting membrane morphologies were analyzed by using scanning electron microscopy. Furthermore, atomic force microscopy was performed to analyze the membrane surface roughness. The chemical compositions of the resulting membranes were identified using Fourier transform infrared. A lab-scale cross-flow filtration system module was used to evaluate the membrane's hydraulic and separation performance by the filtration of humic acid (HA) solution as the model contaminant. Results showed that the additives improved the membrane surface hydrophilicity. All modified membranes also showed up to five times higher water permeability than the pristine PVDF, thanks to the improved structure. Additionally, all membrane samples showed HA rejections of 75-90%.

Effect of Pore Characteristics in Polyvinylidene Fluoride/Fumed Silica Membranes on Mass Flux in Solar-Assisted Evaporation Applications

Although important, very little has been demonstrated in the literature to experimentally demonstrate the effects of porosities and pore size on the evaporation flux in polymeric membranes. Additionally, we suspect that a batch-mode setup, i.e., stagnant water, could cause a build-up of heat in the system, influencing the evaporation mass-flux mechanism, and jeopardizing the ability to attain a real correlation between evaporation and effects of pore characteristics. Herein, we fabricate polyvinylidene fluoride membranes containing variable amounts of a Fumed Silica additive to achieve membranes with variable properties, and we investigate the change in the performance of the solar-assisted thin-film evaporation utilizing an in-house built continuous flow evaporation setup (to avoid heat build-up effects in the bulk of the water and demonstrate a continuous flow system). Our membrane design approach had two important advantages: (1) the achievement of similar heat transfer and solar absorbance properties and (2) the achievement of variable pore sizes and volume porosities. We show that the mass flux increased as the mean pore size decreased, indicating that the mode of mass transfer occurred due to the thin-film region of the meniscus from the small fluid velocities near the interface, and we attribute the results to the increase in the capillary pumping effects through the mesoporous channels as they get thinner.

Engineered Slippery Surface to Mitigate Gypsum Scaling in Membrane Distillation for Treatment of Hypersaline Industrial Wastewaters

Membrane distillation (MD) is an emerging thermal desalination process, which can potentially treat high salinity industrial wastewaters, such as shale gas produced water and power plant blowdown. The performance of MD systems is hampered by inorganic scaling, particularly when treating hypersaline industrial wastewaters with high-scaling potential. In this study, we developed a scaling-resistant MD membrane with an engineered "slippery" surface for desalination of high-salinity industrial wastewaters at high water recovery. A polyvinylidene fluoride (PVDF) membrane was grafted with silica nanoparticles, followed by coating with fluoroalkylsilane to lower the membrane surface energy. Contact angle measurements revealed the "slippery" nature of the modified PVDF membrane. We evaluated the desalination performance of the surface-engineered PVDF membrane in direct contact membrane distillation using a synthetic wastewater with high gypsum scaling potential as well as a brine from a power plant blowdown. Results show that gypsum scaling is substantially delayed on the developed slippery surface. Compared to the pristine PVDF membrane, the modified PVDF membranes exhibited a stable MD performance with reduced scaling potential, demonstrating its potential to achieve high water recovery in treatment of high-salinity industrial wastewaters. We conclude with a discussion of the mechanism for gypsum scaling inhibition by the engineered slippery surface.

Morphology and performance of polyvinyl chloride membrane modified with Pluronic F127

Background: Attempts to modify the morphology of membrane for application in industrial separation are being undertaken by many researchers. The present study discusses the morphological modification of polyvinyl chloride (PVC) membrane by combining the hydrophilic surfactant Pluronic F127 (PF127) in a polymer solution to improve the performance of the membrane.  Method: The membrane is formed using the non-solvent induced-phase separation (NIPS) method. PF127 is added to the membrane solution as a membrane modifying agent. The effects of the surfactant concentration in the dope solution on the permeability of pure water, solute rejection, hydrophilic characteristics, and membrane morphology are investigated. Results: Higher concentrations of PF127 had a significant effect on the permeability of pure water. The highest membrane permeation was 45.65 l/m 2.hr.atm with the addition of 7% PF127 additive. Conclusion: PF127 is successfully proposed as a membrane pore-forming agent in this work; the blending of this additive in appropriate amounts in the polymer solution is adequate to improve the performance of the PVC membrane.

Morphology and performance of polyvinyl chloride membrane modified with Pluronic F127

Background: Attempts to modify the morphology of membrane for application in industrial separation are being undertaken by many researchers. The present study discusses the morphological modification of polyvinyl chloride (PVC) membrane by combining the hydrophilic surfactant Pluronic F127 (PF127) in a polymer solution to improve the performance of the membrane.  Method: The membrane is formed using the non-solvent induced-phase separation (NIPS) method. PF127 is added to the membrane solution as a membrane modifying agent. The effects of the surfactant concentration in the dope solution on the permeability of pure water, solute rejection, hydrophilic characteristics, and membrane morphology are investigated. Results: Higher concentrations of PF127 had a significant effect on the permeability of pure water. The highest membrane permeation was 45.65 l/m 2.hr.atm with the addition of 7% PF127 additive. Conclusion: PF127 is successfully proposed as a membrane pore-forming agent in this work; the blending of this additive in appropriate amounts in the polymer solution is adequate to improve the performance of the PVC membrane.

Molecular engineering of organic electroactive materials for redox flow batteries

With high scalability and independent control over energy and power, redox flow batteries (RFBs) stand out as an important large-scale energy storage system.

Preparation of Nano-TiO₂-Coated SiO₂ Microsphere Composite Material and Evaluation of Its Self-Cleaning Property

In order to improve the dispersion of nano-TiO₂ particles and enhance its self-cleaning properties, including photocatalytic degradation of pollutants and surface hydrophilicity, we prepared nano-TiO₂-coated SiO₂ microsphere composite self-cleaning materials (SiO₂–TiO₂) by co-grinding SiO₂ microspheres and TiO₂ soliquid and calcining the ground product. The structure, morphology, and self-cleaning properties of the SiO₂–TiO₂ were characterized. The characterization results showed that the degradation efficiency of methyl orange by SiO₂–TiO₂ was 97%, which was significantly higher than that obtained by pure nano-TiO₂. The minimum water contact angle of SiO₂–TiO₂ was 8°, indicating strong hydrophilicity and the good self-cleaning effect. The as-prepared SiO₂–TiO₂ was characterized by the nano-TiO₂ particles uniformly coated on the SiO₂ microspheres and distributed in the gap among the microspheres. The nano-TiO₂ particles were in an anatase phase with the particle size of 15–20 nm. The nano-TiO₂ particles were combined with SiO₂ microspheres via the dehydroxylation of hydroxyl groups on their surfaces.