Multifunctional Graphene Oxide-Based Membranes for Water and Solvent Applications

Graphene oxide (GO), atomically thin sheet of carbon decorated with functionalities such as carboxyl, epoxy, and hydroxyl, has received extensive attention for membrane fabrication. Fast water transport, ease of fabrication, separation on nano scale, mechanical and thermal stability, and stability in solvent media make them a promising candidate for nanofiltration. In this study, two potentially scalable techniques for GO-membrane fabrication, viz. shear alignment and spray coating, were employed. Fabricated GO-membrane consists of highly hydrophilic GO sheets deposited on a commercially available polysulfone substrate. The deposited GO layer has a tendency to delaminate upon a shear exerted by water owing to its high dispersibility. Post-treatment of thermal incubation, resulting in a partial reduction of GO, enhanced the limits of shear stability of GO-membranes up to 1.7 Pa in an aqueous environment. A low rejection of monovalent ions (<5% for NaCl) and moderate rejection of divalent ions (<20% for CaCl₂) for an ionic strength of 0.85 M, and a size exclusion cutoff of 1.3 nm was observed for the GO-membrane. Apart from water treatment, another promising application for these membrane lies in organic solvent nanofiltration (OSN), owing to its exceptional stability in solvent media. More than an order of magnitude higher permeability for isopropanol (20 Liter/m².hr.bar or LMH/bar) was observed for GO-membranes compared to the conventional polymeric OSN membranes, and had a size exclusion cutoff of 3.3 nm. In addition to solute removal on a nanoscale, GO-based systems have also attracted much attention in environmental remediation of toxic organics due to their ability to catalyze redox reactions. In this study, a novel GO-iron nanoparticle (Fe-NP) composite membranes were fabricated by incorporating functional polymers and in-situ synthesis of Fe-NP. Evaluation of catalytic property for remediation of Trichloro ethylene showed 100% removal in the presence of 1.8 mM persulfate, at an operating flux of 2 LMH, pH 6.5 and 23 ^oC. The GO-based platform, with its capabilities of separation on nano scale and nanocomposite catalytic membranes for remediation of toxic organics from water, can further help in achieving the quest for energy-efficient separation and purification.