Vinod K. Shahi

Membrane-based techniques for the separation and purification of proteins: An overview

Membrane processes are increasingly reported for various applications in both upstream and downstream technology, such as microfiltration, ultrafiltration, emerging processes as membrane chromatography, high performance tangential flow filtration and electrophoretic membrane contactor. Membrane-based processes are playing critical role in the field of separation/purification of biotechnological products. Membranes became an integral part of biotechnology and improvements in membrane technology are now focused on high resolution of bioproduct. In bioseparation, applications of membrane technologies include protein production/purification, protein-virus separation. This manuscript provides an overview of recent developments and published literature in membrane technology, focusing on special characteristics of the membranes and membrane-based processes that are now used for the production and purification of proteins.

Crosslinked chitosan/polyvinyl alcohol blend beads for removal and recovery of Cd(II) from wastewater

Crosslinked chitosan/poly(vinyl alcohol) (PVA) beads were prepared by suspension of chitosan-PVA aqueous solution in a mixture of toluene and chlorobenzene. Some quantity of the water was distilled out as an azeotrope along with toluene-chlorobenzene and the droplets were chemically crosslinked by adding glutaraldehyde. The prepared crosslinked beads were characterized by FTIR, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The developed beads were used as an adsorbent for the adsorption of Cd(II) from wastewater. Effect of time, temperature, pH, adsorbent dose and adsorbate concentration on the adsorption of Cd(II) were investigated in batch process and pseudo-first and pseudo-second-order kinetic models were also evaluated. The equilibrium adsorption obeyed Langmuir and Freundlich isotherms as well as the thermodynamic parameters such as DeltaG degrees , DeltaH degrees and DeltaS degrees were calculated. From thermodynamic data, it was found that the adsorption process was endothermic and spontaneous. The maximum adsorption of Cd(II) ions was found to be 73.75% at pH 6 and indicated that developed material could be effectively utilized for the removal of Cd(II) ions from wastewater.

Studies on the electrochemical and permeation characteristics of asymmetric charged porous membranes

Asymmetric charged porous membranes were prepared by imbedding 10% (W/W) ion-exchange resin in cellulose acetate binder. Membrane potential and conductance measurements have been carried out in sodium chloride solutions at different concentrations to investigate the relationship between concentration of fixed charges and electrochemical properties of developed nonselective cation- and anion-exchange membranes. Counterion transport number and permselectivity of these membranes were found to vary due to the presence of ion-exchange resin. The hydrodynamic and electroosmotic permeability of sodium chloride solutions has been studied in order to compute equivalent pore radius. For cation- and anion-exchange membranes good agreement was observed between pore radius values estimated from hydrodynamic and electroosmotic permeability coefficient separately, while for nonselective membranes no correlation was found. Membrane conductance data, along with values of concentration of fixed charges, were used for the estimation of the tortuosity factor, salt permeability coefficient, and frictional coefficient between solute and membrane matrix employing an interpretation by nonequilibrium thermodynamic principles based on frictional forces. Moreover, surface morphological studies of these membranes also have been carried out and the membranes were found to be reasonably homogeneous.

Polymer thin films embedded with metal nanoparticles for electrochemical biosensors applications.

Currently, polymer thin films embedded with metal nanoparticles provided the suitable microenvironment for biomolecules immobilization retaining their biological activity with desired orientation, to facilitate electron transfer between the immobilized enzymes and electrode surfaces, better conformation and high biological activity, resultant in enhanced sensing performance. This article reviews focus on various methods for brief discussion of fabrication of metal nanoparticles-polymer hybrid materials and their applications in different electrochemical biosensors. The performance of hybrid materials based electrochemical biosensor can be improved by synergic properties of the metal nanoparticles and polymer network with biomolecules interface via engineering of morphology, particle size, effective surface area, functionality, adsorption capability and electron-transfer properties. These attractive features to hybrid materials are expected to find applications in a new generation of miniaturized, smart biochip devices.

Studies on transport properties of surfactant immobilized anion-exchange membrane

The permselectivity of an anion-exchange membrane developed in our laboratory has been studied from membrane potential and membrane conductance measurements with the purpose to investigate its variation with electrolyte concentration. The possibility of prevention of reduction in the ion selective character of the membrane with increase in electrolytic concentration upon immobilization of cetyl pyridinium chloride and sodium lauryl sulfate has been explored. A correlation between the extent of immobilized surfactants and improvement in ion selectivity was found. Observations indicate that it is possible to manipulate permselective character of an anionic membrane by immobilization of suitable surfactant. The results have also been used to estimate phenomenological coefficients using non-equilibrium thermodynamics.

Phosphonic acid functionalized aminopropyl triethoxysilane–PVA composite material: organic–inorganic hybrid proton-exchange membranes in aqueous media

Poly(vinyl alcohol)–silica composite proton-exchange membranes were prepared by a sol–gel process in acidic conditions using aminopropyltriethoxysilane as an inorganic precursor and functionalized with phosphonic acid. Phosphorylation of the membranes was confirmed by Fourier transform infrared (FTIR) spectroscopy and ion-exchange capacity (IEC) studies. These membranes were extensively characterized for their thermal and mechanical stabilities, physicochemical and electrochemical properties using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), water uptake studies, proton conductivity and methanol permeability measurements. The silica content in the membrane matrix and the time allowed for the phosphorylation were optimized as functions of the membrane properties. It was observed that the PVA–silica composite acts as an excellent methanol barrier possessing good hydrophilicity and proton conductivity. Moreover, from estimation of the selectivity parameter among all the synthesized membranes, 50% silica composition and 3 h of phosphorylation resulted in the best proton-exchange membrane, which exhibited about 20% more suitability in comparison to Nafion 117 membrane for direct methanol fuel cell applications.

Cross-linked poly(vinyl alcohol)-poly(acrylonitrile-co-2-dimethylamino ethylmethacrylate) based anion-exchange membranes in aqueous media.

Hydroxide anion conducting polymer membranes also termed as anion exchange membranes (AEMs) are recently becoming important materials for electrochemical technology, alkaline fuel cells, and electrolyzers. In this work, the preparation procedure for AEMs based on poly(vinyl alcohol) (PVA) and copolymer of poly(acrylonitrile (PAN)-dimethylamino ethylmethacrylate) (DMAEMA) with strongly basic quaternary ammonium in aqueous media has been reported. This simplified procedure avoids the use of chloromethyl methyl ether (CME), a carcinogen that is harmful to human health, generally used for chloromethylation during AEM preparation. Developed AEMs were extensively characterized by studying physicochemical and electrochemical properties, to assess their suitability for electrodialytic ion separation. These membranes were designed to possess all the required properties of a highly anion conductive membrane such as reasonable water uptake, good ion-exchange capacity (1.18 mequiv g(-1)), high permselectivity (0.90), along with reasonable conductivity (3.45 mS cm(-1)) due to quaternary ammonium group functionality. The membrane conductivity values in conjunction with solution conductivity have been used for the estimation of the isoconductivity point, considering the membrane as a combination of the gel phase and integral phase. Electroosmotic studies revealed quite low mass drag and equivalent pore radius (2.7-4.0 A) of the membrane, which are also desirable properties of an AEM. The excellent electrotransport property of AEM-70 for practical anion separation was concluded from i-v studies. Electrodialytic performance of the AEM-70 membrane revealed its suitability for applications in electromembrane processes.

Functionalized Organic-Inorganic Nanostructured N-p-Carboxy Benzyl Chitosan-Silica-PVA Hybrid Polyelectrolyte Complex as Proton Exchange Membrane for DMFC Applications

Chitosan was modified into N-p-carboxy benzyl chitosan (NCBC) by introducing an aromatic ring grafted with carboxylic acid as the proton conducting group. A preparation procedure of highly conductive and stable organic-inorganic nanostructured NCBC-silica-poly(vinyl alcohol) (PVA), proton exchange membrane (PEM) for direct methanol fuel cell (DMFC), by the sol-gel method in aqueous media has been reported. These PEMs were developed by cross-linking and designed to consist of weak proton conducting (-COOH) groups at organic segments and strong proton conducting (-SO3H) groups at inorganic segments to achieve high charge density and stabilities. Cross-linking density and NCBC-silica content in the membrane matrix were systematically optimized to control their nanostructure, thermal, mechanical, and chemical stabilities, as well as proton and fuel transport properties. Developed PEMs were extensively characterized by studying their physicochemical and electrochemical properties under DMFC operating conditions. As these PEMs were well processed as self-supporting film, they showed high stabilities and proton conductivity and low methanol permeability. Moreover, among all synthesized membranes, PCS-3-3 hybrid PEM exhibited quite a high selectivity parameter in comparison to Nafion117 membrane for DMFC applications.

3-[[3-(Triethoxysilyl)propyl]amino]propane-1-sulfonic Acid−Poly(vinyl alcohol) Cross-Linked Zwitterionic Polymer Electrolyte Membranes for Direct Methanol Fuel Cell Applications

Recently, organic-inorganic nanocomposite zwitterionic polymer electrolyte membranes (PEMs) have attracted remarkable interest for application to the direct methanol fuel cell (DMFC) operated at intermediate temperature (100-200 degrees C). In this paper, we report the synthesis of an organic-inorganic hybrid zwitterionomer silica precursor with ammonium and sulfonic acid functionality by the ring-opening of 3-propanesultone under mild heating conditions and the preparation procedure of a proton-conductive and stable organic-inorganic zwitterion-poly(vinyl alcohol) (PVA) cross-linked PEM by sol-gel in aqueous media. Developed PEMs were extensively characterized by studying their physicochemical and electrochemical properties under DMFC operating conditions. These membranes were designed to possess all of the required properties of a proton-conductive membrane, namely, reasonable swelling, good mechanical, dimensional, and oxidative strength, flexibility, and low methanol permeability along with reasonable proton conductivity (4.85 x 10(-2) S cm(-1)) due to zwitterionic functionality. Moreover, from the selectivity parameter among all developed membranes, ZI-70 [zwitterionomer membrane with 70 wt % of PVA of 3-[[3-(triethoxysilyl)propyl]amino]propane-1-sulfonic acid in the membrane matrix], exhibited the best results in comparison to the Nafion117 membrane for DMFC applications.

Sulfonated polyimide/acid-functionalized graphene oxide composite polymer electrolyte membranes with improved proton conductivity and water-retention properties.

Sulfonated polyimide (SPI)/sulfonated propylsilane graphene oxide (SPSGO) was assessed to be a promising candidate for polymer electrolyte membranes (PEMs). Incorporation of multifunctionalized (-SO3H and -COOH) SPSGO in SPI matrix improved proton conductivity and thermal, mechanical, and chemical stabilities along with bound water content responsible for slow dehydration of the membrane matrix. The reported SPSGO/SPI composite PEM was designed to promote internal self-humidification, responsible for water-retention properties, and to promote proton conduction, due to the presence of different acidic functional groups. Strong hydrogen bonding between multifunctional groups thus led to the presence of interconnected hydrophobic graphene sheets and organic polymer chains, which provides hydrophobic-hydrophilic phase separation and suitable architecture of proton-conducting channels. In single-cell direct methanol fuel cell tests, SPI/SPSGO-8 exhibited 75.06 mW·cm(-2) maximum power density (in comparison with commercial Nafion 117 membrane, 62.40 mW·cm(-2)) under 2 M methanol fuel at 70 °C.