S. Neelakandan

Separation of macromolecular proteins and rejection of toxic heavy metal ions by PEI/cSMM blend UF membranes

The charged surface modifying macromolecule (cSMM) was blended into the casting solution of poly(ether imide) (PEI) to prepare surface modified ultrafiltration membranes by phase inversion technique. The separation of proteins including bovine serum albumin, egg albumin, pepsin and trypsin was investigated by the fabricated membranes. On increasing cSMM content, solute rejection decreases whereas membrane flux increases. The pore size and surface porosity of the 5 wt% cSMM blend PEI membranes increases to 41.4 Å and 14.8%, respectively. Similarly, the molecular weight cut-off of the membranes ranged from 20 to 45 kDa, depending on the various compositions of the prepared membranes. The toxic heavy metal ions Cu(II), Cr(III), Zn(II) and Pb(II) from aqueous solutions were subjected to rejection by the prepared blended membrane with various concentration of polyethyleneimine (PETIM) as water soluble polymeric ligand. It was found that the rejection behavior of metal ion depends on the PETIM concentration and the stability complexation of metal ion with ligand.

Preparation, characterization and performance of cellulose acetate ultrafiltration membranes modified by charged surface modifying macromolecule

A charged surface modifying macromolecule (cSMM) was synthesized, characterized by FT-IR spectroscopy and blended into the casting solution of cellulose acetate (CA) to prepare surface modified UF membranes by phase inversion technique. With an increasing cSMM additive content from 1 to 4 wt%, pure water flux (PWF) and water content (WC) were increases whereas the hydraulic resistance decreases. Surface characteristic study reveals that the surface hydrophilicity increased in cSMM modified CA membranes. The pore size and surface porosity of the 4 wt% cSMM blend CA membranes increases to 41.26 Å and 0.015%, respectively. Similarly, the molecular weight cut-off (MWCO) of the membranes ranged from 20 to 45 kDa, depending on the various compositions of the prepared membranes. Lower flux decline rate (47.2%) and higher flux recovery ratio (FRR) (89.0%), exhibited by 4 wt% cSMM blend membranes demonstrated its fouling resistant characteristic compared to pristine CA membrane.

Effect of sulfonated graphene oxide on the performance enhancement of acid–base composite membranes for direct methanol fuel cells

Sulfonated poly(1,4-phenylene ether ether sulfone) (SPEES)/poly(ether imide) (PEI)/sulfonated graphene oxide (SGO) based proton exchange membranes (PEMs) were prepared by a solution casting method. The membranes were characterized for their tensile strength, thermal stability, electrochemical properties and physico-chemical properties using a universal testing machine, thermogravimetric analyzer, impedance spectroscopy and water uptake studies respectively. Compared with SPEES/PEI composite (SP) membranes, the ion exchange capacity, hydrophilicity and water uptake of the SP/SGO membranes were enhanced. Surface morphology of the composite membrane was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM images reveal that the nodule size and surface roughness are increased by the incorporation of SGO. Tensile strength and proton conductivity of the composite membranes increased with increasing SGO content. A maximum conductivity of 8.87 × 10−3 S cm−1 was achieved at 25 °C upon addition of 0.8 wt% of SGO. All the SP/SGO membranes exhibited methanol permeability lower than 3.26 × 10−7 cm2 s−1, which was much lower than that of Nafion 117 (3.41 × 10−6 cm2 s−1). Furthermore, the composite membranes exhibited much higher relative selectivity compared with SP and Nafion 117 membranes. It was found that the SP/SGO-0.8 composite membrane appears to be a good candidate for use in DMFC applications.

SPEES/PEI-based highly selective polymer electrolyte membranes for DMFC application

Polymer composite membranes based on sulfonated poly(phenylene ether ether sulfone) (SPEES) membrane with varying concentrations of poly(ether imide) (PEI) were prepared. The sulfonation of PEES was carried out with concentrated sulfuric acid at 10 °C, and the sulfonation degree was maintained as 70 %. The introduction of PEI into the hydrophilic SPEES matrix provided good chemical stability to the membrane. The water uptake, ion exchange capacity, and proton conductivity decrease with increasing PEI content. Scanning electron microscopy (SEM) indicates that PEI particles are homogeneously dispersed into the composite membrane. Thermogravimetric analysis (TGA) showed that all the composite membranes exhibited good thermal stability. On the other hand, the methanol permeability of the composite membranes gradually decreases from 4.23 × 10−7 cm2 s−1 to 8.84 × 10−8 cm2 s−1, which is lower than that of the Nafion 117 membrane. The relative selectivity of the PEI-incorporated SPEES membranes was higher than that of the Nafion membranes. From the observed results, the prepared SPEES/PEI-15 composite membrane can be considered as apposite polymer electrolyte membranes for the application of direct methanol fuel cells (DMFCs).

Performance studies of PEI/SPEI blend ultra-filtration membranes via surface modification using cSMM additives

Sulfonated poly(ether imide) (SPEI) and charged surface modifying macromolecules (cSMM) were synthesized, characterized and blended into the casting solution of poly (ether imide) (PEI) with different compositions to develop surface modified ultra-filtration (UF) membranes by means of improved hydrophilicity. The membranes were prepared by a phase inversion technique and subjected to characterization experiments such as water permeation tests, equilibrium water content (WC), membrane hydraulic resistance (Rm) and protein rejection. Among others, a blend membrane containing 20 wt% SPEI and 5 wt% cSMM in PEI (called M12) exhibited the highest water permeation (440.6 L m−2 h−1 at 345 kPa), highest WC (86.3%) and lowest Rm (0.7 kPa/L m−2 h−1). The M12 membrane also exhibited the highest fluxes of 364.1 L m−2 h−1 and 230.3 L m−2 h−1 (at 345 kPa) with rejections of 31.3% and 62.1%, respectively, when the feed was aqueous trypsin and bovine serum albumin solution (1000 ppm). The difference in contact angle between the top and bottom surface confirmed surface migration of cSMM to the membrane top surface. SEM, AFM and tensile strength measurement revealed that the surface became more porous and rougher, and the mechanical strength was lowered by the blending of SPEI and addition of cSMM. That the M12 membrane achieved a lower internal fouling of 6% and 3.8% and higher flux recovery ratio (FRR) of 94% and 96.2% after UF of trypsin and bovine serum albumin solution explained its better antifouling properties as compared to a pristine PEI membrane.