Multifunctional Graphene Oxide-Based Membranes for Water and Solvent Purification

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 in water. 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.