Bijay P. Tripathi

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.

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.

Highly charged and stable cross-linked 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid (BAPBDS)-sulfonated poly(ether sulfone) polymer electrolyte membranes impervious to methanol

Disulfonated 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid (BAPBDS) was synthesized as cross-linking agent. In situ cross-linking of sulfonated poly(ether sulfone) (SPES) via sulfonamide linkage was achieved using BAPBDS, for preparing polymer electrolyte membranes (PEMs), without deterioration in membrane functionality due to cross-linking. Effective cross-linking enhanced the membranes’ dimensional, thermal, and chemical stability without impairing the electro-chemical properties such as ion-exchange capacity and proton conductivity. Thus, the properties of the developed PEMs were significantly improved due to more compact structure of the cross-linked SPES membrane (CPES) over membranes without crosslinking. Comparable selectivity parameter (SP) and direct methanol fuel cell (DMFC) performance of the developed membranes, especially CPES-100, with Nafion 117 (N117) indicated their suitability for fuel cell applications.

Highly stable aprotic ionic-liquid doped anhydrous proton-conducting polymer electrolyte membrane for high-temperature applications

Protic ionic-liquid (IL) based polymer electrolyte membranes (PEMs) have been reported for high-temperature fuel cell applications under anhydrous condition. Herein, we report aprotic IL (1-ethyl-3-methylimidazolium ethyl sulfate (EMIES)) and sulfonated poly(ether ether ketone) (SPEEK) based PEMs for fuel cell application under anhydrous condition. Liberated protons from –SO3H groups (SPEEK) due to ionic interaction with EMIES, were responsible for high conductivity under anhydrous conditions. High ionic interaction between the EMIES and SPEEK led to homogeneous mixing. Prepared SPEEK–IL-70 PEM exhibited 0.57 mS cm−1 conductivity (conductivity of EMIES: 3.445 mS cm−1 at room temperature), which was dramatically increased to 18.94 mS cm−1 at 150 °C under anhydrous condition. This enhancement in conductivity was explained due to the well-connected proton conducting channels formed in the polymer matrix because of good miscibility and interaction with EMIES. High stability and good conductivity of SPEEK–IL composite membranes demonstrated their potential application for high-temperature applications.

Functional polyelectrolyte multilayer membranes for water purification applications

A diverse set of supported multilayer assemblies with controllable surface charge, hydrophilicity, and permeability to water and solute was fabricated by pressure driven permeation of poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) solution through poly(ethylene terephthalate) (PET) track-etched membranes. The polyelectrolyte multilayer fabrication was confirmed by means of FTIR, SEM, AFM, ellipsometry, zetapotential, and contact angle characterization. The prepared membranes were characterized in terms of their pure water permeability, flux recovery, and resistance to organic and biofouling properties. The antifouling behavior of the membranes was assessed in terms of protein adsorption and antibacterial behavior. Finally, the membranes were tested for rejection of selected water soluble dyes to establish their usefulness for organic contaminant removal from water. The membranes were highly selective and capable of nearly complete rejection of congo red with sufficiently high fluxes. The feasibility of regenerating the prepared membranes fouled by protein was also demonstrated and good flux recovery was obtained. In summary, the multilayer approach to surface and pore modification was shown to enable the design of membranes with the unique combination of desirable separation characteristics, regenerability of the separation layer, and antifouling behavior.

Bifunctionalized organic-inorganic charged nanocomposite membrane for pervaporation dehydration of ethanol.

Chitosan was modified into N-p-carboxy benzyl chitosan (NCBC) by introducing an aromatic ring grafted with acidic -COOH group and highly stable and cross-linked nanostructured NCBC-silica composite membranes were prepared for pervaporation dehydration of water-ethanol mixture. These membranes were tailored to comprise three regions namely: hydrophobic region, highly charged region and selective region, in which weak acidic group (-COOH) was grafted at organic segment while strong acidic group (-SO(3)H) was grafted at inorganic segment to achieve high stability and less swelling in water-ethanol mixture. Cross-linking density and NCBC-silica content in membrane matrix has been systematically optimized to control the nanostructure of the developed polymer matrix for studying the effects of molecular structure on the swelling, and PV performance. Among prepared membranes, nanocomposite membrane with 3h cross-linking time and 90% (w/w) of NCBC-silica content (PCS-3-3) exhibited 1.66×10(-4)cm(3)(STP) cm/cm(2) s cmHg water permeability (P(W)), while 1.35×10(-7) cm(3)(STP) cm/cm(2) s cmHg ethanol permeability (P(EtOH)) of developed membrane and 1231 PV selectivity factor at 30 °C for separating water from 90% (w/w) ethanol mixture.

Enhanced hydrophilic and antifouling polyacrylonitrile membrane with polydopamine modified silica nanoparticles

A simple and straightforward method for preparing hydrophilic and antifouling ultrafiltration membranes is described. Silica nanoparticles were synthesized and modified by mussel inspired dopamine polymerization. The ultrafiltration membranes were prepared using polyacrylonitrile (PAN) with different ratios of polydopamine modified silica nanoparticles (SiO2-DOPA) via a phase inversion process. Composite membranes containing increasing amounts of SiO2-DOPA were compared to the pure PAN membranes to determine the changes in performance, hydrophilicity, and antifouling characteristics. The composite membranes exhibited higher water permeation and rejection properties compared to those of the neat PAN membrane. During flux decline and recovery experiments, PAN–SiO2-DOPA composite membranes exhibited higher flux recovery than a neat PAN membrane. The best performing membrane recovers more than 75% of its original flux after being washed with deionized water, demonstrating a high resistance to irreversible fouling. The composite membranes were tested for rejection of protein and dye molecules, and the high rejection efficiency with moderately declined fluxes indicates their suitability for separation and water treatment applications.

Antifouling and tunable amino functionalized porous membranes for filtration applications

In an effort to reduce fouling, enhance membrane cleaning, and flux recovery, a hydrophilic polymer with amine functionality was grafted onto an active porous membrane surface. Poly(ethylene glycol) bis-(3-aminopropyl) terminated molecules were grafted on polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride via condensation reaction between the anhydride ring and amine group. Structural analysis, hydrophilicity, water permeability, and rejection performance of the membranes were assessed for its suitability in separation and water purification processes. The hydrophilicity, permeability, and solute rejection property of the membranes increased upon anchoring of amino terminated PEG brushes. The good antifouling behavior (for protein and bacteria) and pure water permeability along with high rejection property showed its suitability for water purification and separation processes.