Poly Vinyl Alcohol Composite Membranes Research Articles

Optimization of mass transfer-enhanced chlorine-resistant crosslinked PVA composite membranes for pervaporation desalination

Pervaporation (PV) is characterised by good hydrophilicity and antifouling properties. However, it is still unavoidable to need cleaning during long-term operation. Sodium hypochlorite (NaClO) is a commonly used purifying agent for organic pollutants, but it may cause damage to the polymer membrane. In this study, a grafting method was proposed to enhance the chlorine resistance and water permeability of membrane composite polyvinyl alcohol (PVA) pervaporation membrane. Modified PVA (SPVA) was prepared by grafting 5-sulfosalicylic acid (SSA) to improve the hydrophilicity of the membrane using the sulfonic acid group on SSA. SPVA-FA/PTFE composite membranes were prepared by using perfluoroglutaric acid (PFGA) as crosslinking agent to improve the chlorine resistance of the membranes by utilising the C-F chain contained therein. The water flux was 120.38 ± 1.72 kg/(m2·h), which was 84.2 % higher than that before grafting, when tested at 70 °C and 3.5 wt% NaCl. The chlorine resistance of SPVA-PFGA/PTFE composite membrane was tested in 2000 ppm (pH = 12) NaClO solution for 480 h, and the salt rejection remained above 99.93 %. When desalinating 20 wt% NaCl at 70 °C, the water flux of SPVA-PFGA/PTFE membrane is 51.95 ± 0.6 kg/(m2·h), which has the potential to treat high concentration brine.

Efficient Pervaporation for Ethanol Dehydration: Ultrasonic Spraying Preparation of Polyvinyl Alcohol (PVA)/Ti3C2Tx Nanosheet Mixed Matrix Membranes.

Polyvinyl alcohol (PVA) pervaporation (PV) membranes have been extensively studied in the field of ethanol dehydration. The incorporation of two-dimensional (2D) nanomaterials into the PVA matrix can greatly improve the hydrophilicity of the PVA polymer matrix, thereby enhancing its PV performance. In this work, self-made MXene (Ti3C2Tx-based) nanosheets were dispersed in the PVA polymer matrix, and the composite membranes were fabricated by homemade ultrasonic spraying equipment with poly(tetrafluoroethylene) (PTFE) electrospun nanofibrous membrane as support. Due to the gentle coating of ultrasonic spraying and following continuous steps of drying and thermal crosslinking, a thin (~1.5 μm), homogenous and defect-free PVA-based separation layer was fabricated on the PTFE support. The prepared rolls of the PVA composite membranes were investigated systematically. The PV performance of the membrane was significantly improved by increasing the solubility and diffusion rate of the membranes to the water molecules through the hydrophilic channels constructed by the MXene nanosheets in the membrane matrix. The water flux and separation factor of the PVA/MXene mixed matrix membrane (MMM) were dramatically increased to 1.21 kg·m-2·h-1 and 1126.8, respectively. With high mechanical strength and structural stability, the prepared PGM-0 membrane suffered 300 h of the PV test without any performance degradation. Considering the promising results, it is likely that the membrane would improve the efficiency of the PV process and reduce energy consumption in the ethanol dehydration.

A molecular level based parametric study of transport behavior in different polymer composite membranes for water vapor separation

The membrane dehumidification technology has great energy-saving potential compared to traditional methods. However, the design of composite membrane depends mostly on trial tests. To understand the mechanisms dominating material properties and quantitatively predict the air dehumidification performance of the composite membranes in practical applications, various models combined with different polymeric materials and porous support membranes were developed and investigated by using grand canonical Monte Carlo (GCMC) and Molecular dynamics (MD) simulation methods. The interfacial interactions between the selective layer and the support membrane were analyzed in detail to explore the interface stability and compatibility of various composite membranes. The physical characteristics (density, fractional free volume, solubility parameter and cohesive energy density) and transport properties (solubility, diffusivity, permeability and selectivity) of various composite membranes were parametrically evaluated. The polydimethylsiloxane (PDMS) composite membranes exhibited stronger interfacial interaction in comparison to the PVA composite membranes. The hydrophilicity and polarity of polyvinyl alcohol (PVA) polymer resulted in a stronger interaction between the gas molecules and the PVA membrane. According to the solution–diffusion mechanism, the PVA-PVDF membrane presented the optimal H2O permeability of 3121.38 Barrer among all composite membranes. Generally, polyvinylidene fluoride (PVDF) or polyacrylonitrile (PAN) as the materials of support membrane had good fiber forming characteristics and low gas diffusion resistance, which significantly affects the performance of selective layers. The microscopic mechanisms revealed in this work would lay a solid theoretical foundation for the design of high performance composite membrane for air dehumidification.

Development of antimicrobial nanocomposite scaffolds via loading CZTSe quantum dots for wound dressing applications

The antimicrobial properties of scaffolds designed for use in wound healing are accepted as an important factor in the healing process to accelerate the wound healing process without causing inflammation. For this purpose, chitosan–polyvinyl alcohol composite membranes loaded with Cu2ZnSnSe4 quantum dots (CZTSe QDs) as an antibacterial and cytocompatible biomaterial to regulate the wound healing process were produced. CZTSe QDs particles were synthesized under hydrothermal conditions. Polymer-based nanocomposites with different concentrations of the synthesized nanoparticles were produced by the solvent casting method. After detailed physicochemical and morphological characterizations of CZTSe QDs and composite membranes, antibacterial activities and cell viability were extensively investigated against gram-positive and gram-negative bacterial and yeast strains, and L929 mouse fibroblast cells lines, respectively. The results show that the preparation of composite scaffolds at a QDs concentration of 3.3% by weight has the best antimicrobial activity. Composite scaffold membranes, which can be obtained as a result of an easy production process, are thought to have great potential applications in tissue engineering as wound dressing material due to their high mechanical properties, wettability, strong antibacterial properties and non-toxicity.

UiO-66-NH2/PVA composite Janus membrane with a dense hydrophilic surface layer for strong resistance to fouling and wettability in membrane distillation

Polytetrafluoroethylene (PTFE) hydrophobic membranes used in direct contact membrane distillation (DCMD) processes were prone to fouling and wetting by oil and surfactants, which hampered their broad industrial application. In this work, a new Janus composite membrane was developed by modifying UiO-66-NH2 with polyvinyl alcohol (PVA) as a cross-linking agent and immobilizing the modified UiO-66-NH2 on the PTFE membrane by vacuum filtration. By tuning the ratio of PVA to MOF, an optimally proportioned Janus membrane was obtained, and its performance was tested in DCMD experiments through the use of a sodium chloride feed solution containing hexadecane and sodium dodecyl sulfate. The top layer of this Janus membrane exhibited underwater oleophobicity (130.1 ± 0.96°) and hydrophilicity in the air (54.0 ± 0.92°), while the bottom layer is hydrophobic (132.3 ± 0.97°). Compared to the pristine PTFE membrane, the modified Janus membrane demonstrated promising resistance to both membrane fouling and wetting of oils and surfactants. The desalination rate of 99.99% was still achieved within 24 h with the conductivity remaining lower than 10 μS/cm and the flux maintained at 21.3 L/(m2·h). As a result, the Janus composite membrane developed in this study was shown to be a prospective alternative for treating wastewater containing oily substances and surfactants in a resourceful manner.

Superhydrophilic and underwater superoleophobic in-situ derived 2D Ni-Fe MOF/HNTs composite-enhanced polyvinyl alcohol (PVA) hydrogel membrane for gravity-driven oil/water separation

In this work, we successfully prepared the 2D Ni-Fe MOF-HNTs composites by in-situ hydrothermal growth, followed by enabling it to full into PVA hydrogels, thereupon fabricating the oil/water separation 2D Ni-Fe MOF-HNTs/PVA-decorated stainless steel mesh. The structures and mechanical properties of the composites were identified by a series of characterizations. The results showed that the 2D Ni-Fe MOF nanosheets were gown on the outer surface of HNTs to form the exclusive composite structure and the 2D Ni-Fe MOF-HNTs/PVA composite membrane possessed a more compact pore structure, which exhibited the outstanding mechanical performance and the fatigue resistance ability. The surface property characterizations demonstrated that the 2D Ni-Fe-MOF-HNTs/PVA composite membrane had the superhydrophilic and underwater superoleophobic features. Ultimately, the results of the water flux and separation efficiency on 2D Ni-Fe-MOF-HNTs/PVA composite membrane for oil-water separation and emulsion separation corroborated that it was a promising high-performance separation composite membrane.

MOFs/PVA hybrid membranes with enhanced mechanical and ion-conductive properties

Abstract Nanomaterials have been treated as effective dopants for enhancing mechanical and ion-conductive properties of polymer membranes. Among various nanomaterials, metal–organic frameworks are attracting enormous attention from researchers because of their intriguing structural and functional properties. Here we report a gentle and simple synthesis method of ZIF-8 nanomaterials, which are applied as dopants for polyvinyl alcohol composite membranes. This nanomaterials display uniform size distribution and high purity through various structural investigations. The as-prepared polymer composite membranes present enhanced mechanical and ion-conductive properties compared to pristine samples. This work provides a novel ideal on the design of nanomaterial dopants for high-performance polymer membranes.

A high ZIF-8 loading PVA mixed matrix membrane on alumina hollow fiber with enhanced ethanol dehydration

In this work, a zeolitic imidazolate framework-8 (ZIF-8)/polyvinyl alcohol (PVA) mixed matrix membrane (MMM) was coated onto α-aluminum oxide (α-Al2O3) hollow fibers for ethanol dehydration by utilizing the pervaporation technique. ZIF-8/PVA solution was prepared via a drying-free, water-based method to obtain a uniform distribution MMM. Before coating the MMM onto the hollow fiber, a pristine PVA solution was first dip-coated onto hollow fiber as a gutter layer to prevent phase separation. Different weight ratios of ZIF-8-loaded MMMs were prepared. The results showed that at high ZIF-8 loading (39 wt %), a high permeate flux (685 g/m2 h) and high separation factor (4821) can be observed. Furthermore, compared with free-standing ZIF-8/PVA MMMs, hollow fiber supported ZIF-8/PVA MMMs exhibit a thinner coating thickness but higher pervaporation separation index (approximately 1.5–2 times). The main contribution of this study is not only fabricated the high loading ZIF-8/PVA composite membrane with enhanced performance, but also coated onto the hollow fiber membrane which opens a gate for scale-up production.

Preface

2019 5th International Conference on Advances in Environment Research (ICAER 2019) which was successfully held in Singapore during 13-15 August, 2019. ICAER 2019 was organized by Hong Kong Chemical, Biological & Environmental Engineering Society (HKCBEES), Environment and Agriculture Society (EAS).ICAER 2019 is one of the leading international conferences for presenting novel and fundamental advances in the fields of Advances in Environment Research. It also serves to foster communication among researchers and practitioners working in a wide variety of scientific areas with a common interest in improving Advances in Environment Research related techniques. Prof. Ngai Weng Chan from Universiti Sains Malaysia, Malaysia has been invited to do the welcome address; Prof. Kuo-Lun Tung from National Taiwan University, Taiwan has given his keynote speech”Highly Zeolite-Loaded Polyvinyl Alcohol Composite Membranes for Alkaline Fuel-Cell Electrolytes”; Assoc. Prof. Dr. Shanti Faridah binti Salleh from Universiti Malaysia Sarawak (UNIMAS), Sarawak, Malaysia has shared her keynote speech “Rural Electrification for Sustainable Development: Key Issues and Challenges”; Prof. Ngai Weng Chan from School of Humanities, Universiti Sains Malaysia, Malaysia has also presented his keynote speech”Holistic Urban Water Management Integrating Rainfall Harvesting, Water Conservation and Sustainable Drainage Systems in Universiti Sains Malaysia”.Many researchers, engineers, academicians as well as industrial professionals from all over the world have presented their research results and development activities. There were two sessions for presentations: Environmental Management and Engineering, Renewable Energy and Electric Energy. It is a golden opportunity for the students, researchers and engineers to interact with the experts and specialists to get their advice or consultation on technical matters, sales and marketing strategies.

Fabrication of Photoactuators: Macroscopic Photomechanical Responses of Metal–Organic Frameworks to Irradiation by UV Light

Photoreactive olefinic species are incorporated into a metal-organic framework (MOF), [Zn(bdc)(3-F-spy)] (1). Single crystals of 1 are shown to undergo three types of photomechanical macroscopic deformation upon illumination by UV light. To demonstrate the practical potential of this system, the inclusion of 1 in a PVA (polyvinyl alcohol) composite membrane, by exploiting hydrogen-bonding interactions, is presented. Using this composite membrane, the amplification of mechanical stress to achieve macroscopic actuation behavior is demonstrated. These results pave the way for the generation of MOF-based soft photoactuators that produce clearly defined mechanical responses upon irradiation with light. Such systems are anticipated to have considerable potential in photomechanical energy harvesting and conversion systems.

Fabrication of Photoactuators: Macroscopic Photomechanical Responses of Metal–Organic Frameworks to Irradiation by UV Light

AbstractPhotoreactive olefinic species are incorporated into a metal–organic framework (MOF), [Zn(bdc)(3‐F‐spy)] (1). Single crystals of 1 are shown to undergo three types of photomechanical macroscopic deformation upon illumination by UV light. To demonstrate the practical potential of this system, the inclusion of 1 in a PVA (polyvinyl alcohol) composite membrane, by exploiting hydrogen‐bonding interactions, is presented. Using this composite membrane, the amplification of mechanical stress to achieve macroscopic actuation behavior is demonstrated. These results pave the way for the generation of MOF‐based soft photoactuators that produce clearly defined mechanical responses upon irradiation with light. Such systems are anticipated to have considerable potential in photomechanical energy harvesting and conversion systems.

Gel polymer electrolyte with high performances based on biodegradable polymer polyvinyl alcohol composite lignocellulose

Abstract A novel gel polymer electrolyte (GPE) is prepared based on polyvinyl alcohol (PVA) composite lignocellulose (LC). In this work, mechanical strength of PVA composite LC membranes is significantly enhanced, which endows corresponding GPEs with application potential in lithium ion batteries (LIBs). Meanwhile, when the content of PVA is 5 wt.%, GPE presents high enough liquid electrolyte uptake (425 wt.%) and enough thermal stability. At room temperature, the ion conductivity is 3.92 × 10−3 S cm−1 and lithium ion transference number is up to 0.63. In addition, GPE exhibits electrochemical stability window at 5.2 V (vs. Li/Li+), good compatibility with electrode, excellent initial discharge specific capacity, C-rate and cycling performances.

Highly Zeolite-Loaded Polyvinyl Alcohol Composite Membranes for Alkaline Fuel-Cell Electrolytes.

Having a secure and stable energy supply is a top priority for the global community. Fuel-cell technology is recognized as a promising electrical energy generation system for the twenty-first century. Polyvinyl alcohol/zeolitic imidazolate framework-8 (PVA/ZIF-8) composite membranes were successfully prepared in this work from direct ZIF-8 suspension solution (0–45.4 wt %) and PVA mixing to prevent filler aggregation for direct methanol alkaline fuel cells (DMAFCs). The ZIF-8 fillers were chosen for the appropriate cavity size as a screening aid to allow water and suppress methanol transport. Increased ionic conductivities and suppressed methanol permeabilities were achieved for the PVA/40.5% ZIF-8 composites, compared to other samples. A high power density of 173.2 mW cm−2 was achieved using a KOH-doped PVA/40.5% ZIF-8 membrane in a DMAFC at 60 °C with 1–2 mg cm−2 catalyst loads. As the filler content was raised beyond 45.4 wt %, adverse effects resulted and the DMAFC performance (144.9 mW cm−2) was not improved further. Therefore, the optimal ZIF-8 content was approximately 40.5 wt % in the polymeric matrix. The specific power output was higher (58 mW mg−1) than most membranes reported in the literature (3–18 mW mg−1).

Enhanced separation performance of carbon nanotube–polyvinyl alcohol composite membranes for emulsified oily wastewater treatment under electrical assistance

Abstract Membranes provide an effective solution to treat emulsified oily wastewater, but usually have inherent drawbacks: permeability and selectivity trade-off as well as serious membrane fouling. In this study, carbon nanotube-polyvinyl alcohol (CNT-PVA) composite membranes with high water flux and good electrical conductivity were fabricated and then served as cathode during the filtration of n-hexadecane-in-water emulsion (n-emulsion) and cutting fluid emulsion (c-emulsion) to improve the oil removal efficiency and alleviate membrane fouling. Results show that oil removal rates increase from 85.2% to 97.6% for n-emulsion and from 56.7% to 83.0% for c-emulsion after the application of −1.5 V. The permeation flux after an operation of 60 min with −1.5 V are 2.3 times and 2.2 times of those without potential for n-emulsion and c-emulsion, respectively. Additionally, less oil fouling can be observed from the SEM images of the membrane surface and fouling can be mitigated according to the analysis of fouling model. Cyclic voltammetry and zeta potential analysis demonstrate that electrostatic repulsion rather than electrochemical reactions is responsible for the enhanced oil removal rate and antifouling ability in the filtration process. Furthermore, the results of long term filtration with five runs indicate that the application of potential onto the membranes maintains remarkable stability in high oil removal rate and high flux recovery rate.

Functionalization of polyvinyl alcohol composite membrane by CoOOH for direct borohydride fuel cells

A polyvinyl alcohol anion exchange resin composite membrane was functionalized with CoOOH for use in direct borohydride fuel cells (DBFCs) and is detailed in this report. The CoOOH-functionalized membrane has a higher ionic conductivity and a lower borohydride ion permeability than the membrane without CoOOH. The DBFCs with the CoOOH-functionalized membrane achieved better performance, such as a power density peak at 144mW·cm−2 at 30°C, than did those without CoOOH. Such performance improvement is due to CoOOH functionalization, whereby Co species reduce the crossover of the borohydride ion while maintaining high conductivity for hydroxyl species. With the introduction of the Co species, the conductivity-permeability trade-off dilemma in traditional anion exchange membranes is avoided. Therefore, the functionalization of the membrane helps to elucidate the development of anion exchange membrane fuel cells.

Graphene oxide incorporated novel polyvinyl alcohol composite membrane for pervaporative recovery of acetic acid from vinegar wastewater

A novel polymeric composite membrane consisting of graphene oxide (GO) and poly (vinyl alcohol) (PVA) has been developed and applied in the recovery of acetic acid from vinegar wastewater in a pervaporation unit. The resultant composite membranes designated as (PVA-GO)1 and (PVA-GO)2 were characterized by using X-ray diffractions, scanning electron microscopy, Fourier-transform infrared spectroscopy, atomic force microscopy and thermogravimetric analysis. Membranes were found to attain semi-crystalline to amorphous nature by incorporation of GO to PVA. GO incorporation in the PVA membrane was observed to have a profound influence, as it helped achieve better thermal stability and higher tensile stress compared to pristine PVA membrane. The composite membranes were prone to swelling in presence of water. GO imparted better hydrophilicity of the composite membranes as displayed by a reasonably high degree of volumetric flux of water and separation factor. The study demonstrates that GO can be effectively incorporated within the polymer matrix to tune the mechanical and permeation characteristics of nanocomposites.

Preparation of a Novel Composite Membrane and PtRu/Hollow Carbon Sphere (HCS) Anode Catalyst for Alkaline Direct Methanol Fuel Cell (ADMFC)

This work demonstrated the synthesis process of the anion-exchange nanocomposite membrane based on Poly(vinyl alcohol (PVA) and Quaternary ammonium silica precursor (QASP), which was synthesized by using Glycidytrimethyl ammonium chloride (GTMAC) and 3-Aminopropyl trimethoxysilane (AMPTS). The suitable amount of functional SiO2 fillers was added into the PVA composite polymer membrane to reduce the methanol permeability and also improve the thermal and mechanical properties. A novel and high activity PtRu/Hollow carbon sphere (HCS) was synthesized to use as a catalyst in the anode for methanol oxidation. It was found that this as-prepared PtRu/HCS shows excellent electrochemical activity, as compared with PtRu black. The characteristic properties were examined by thermal gravimetric analysis (TGA), X-ray diffraction (XRD), micro-Raman and FTIR spectroscopies, scanning electron microscopy (SEM), and AC impedance method. It was observed that the maximum ionic conductivity of anion-exchange composite polymer membrane is around 5.12×10-2 S cm-1 at room temperature. It was observed that the highest peak power density of alkaline direct methanol fuel cell (ADMFC) with a 4M KOH + 2M CH3OH fuel was around 70 mW cm-2 at 70oC. The methanol permeability is around 10-6∼10-7 cm2 s-1. The results demonstrate that the PVA/QASP/SiO2 composite membranes exhibit a good candidate for application to ADMFC.

Experimental study and cost evaluation for ethanol separation from fermentation broth using pervaporation

Abstract In this work, the separation of two types of mixtures, ethanol–water mixture and fermented sweet sorghum, was investigated using cellulose acetate supported polyvinyl alcohol composite membranes. The pervaporation (PV) performances of the two mixtures under different operating parameters (ethanol concentrations, operating times and temperatures) were studied. PV performances using sweet sorghum fermentation broth, under all operating parameters, were significantly lower compared to separating ethanol from binary mixtures. Preliminary economic analysis shows that cost of producing 1 l of ethanol from the broth is about 0.9 $/l which is about 1.1 times higher than from the pure binary system.

Proton-Conducting Composite Membranes Derived from Ferroxane-Polyvinyl Alcohol Complex

Abstract A composite membrane composed of iron oxide and polyvinyl alcohol (PVA) was investigated as an alternative electrolyte material for proton exchange membranes (PEMs) in fuel cells using hydrogen as a fuel. Acetic acid (AA)-stabilized lepidocrocite (γ-FeOOH) nanoparticles and goethite (α-FeOOH) nanoparticles (ferroxane) were mixed with dissolved PVA and air-dried to fabricate the PEMs. The ferroxane–PVA composite membrane showed higher proton conductivity than goethite–PVA composite membrane. However, the proton conductivities of the ferroxane–PVA composite membrane decreased as PVA content in the composite membranes increased. Fourier transform infrared spectroscopy analyses of the ferroxane–PVA composite membrane showed that a large portion of AA groups on the surface of ferroxane nanoparticles was lost when mixed with PVA. The tensile force resistance of the composite membrane was much higher compared with ferroxane-derived ceramic membranes.

Polyvinyl Alcohol Based Membrane as Separator for Alkaline Water Electrolyzer

Alkaline water electrolyzer employs nickel based electrodes and asbestos cloth diaphragm. Asbestos is considered as carcinogenic. In order to limit the usage of an asbestos diaphragm, a separator membrane was synthesized from polyvinyl alcohol, glutaraldehyde, N,N,N′N′-Tetramethyl hexane-1,6 diamine, and titanium dioxide. The role of N,N,N′N′-Tetramethyl hexane-1,6 diamine is to improve the dimensional stability of the membrane. The fabricated membranes were characterized by FT-IR, TGA, DSC, and SEM techniques. These fabricated membranes effectively improved the production of hydrogen, more so than the conventional asbestos diaphragm. A current density of 0.38 A/cm2 was achieved when operating the cell with 5 wt% KOH at 30°C at 2 V. Polyvinyl alcohol composite membranes, besides being cheap, showed good electrochemical performance at ambient temperature and pressure than most commercial separator membranes. This comparison gives some insight as to future separator membrane design objectives.