Fabrication of hydrothermally reduced graphene oxide/chitosan composite membranes with a lamellar structure on methanol dehydration

Reduced graphene oxide (rGO) has been prepared through hydrothermal reduction, an environmentally safe reduction of graphene oxide (GO). rGO is used to fabricate a highly compatible and orderly stacked lamellar structure of composite membranes with chitosan (CS). This method also facilitates a continuous large-scale fabrication of membranes. Conventionally, GO and CS are the preferred compounds for this type of fabrication because of their hydrophilic nature. Nevertheless, when they are mixed together, the occurrence of ionic complexation (−COO⁻ H₃⁺ N−R) between the negatively charged carboxylate ions of GO and the positively charged protonated amines of CS create extreme membrane aggregation. Hydrothermal reduction is useful for preventing undesired ionic complexation from mixing rGO and CS because it can remove most carboxylate ions from GO. Consequently, the hydrophilic CS molecular chain is inserted in between the rGO laminates, improving the dispersion and enabling the rGO/CS to stack-up and self-assemble into a lamellar structure. Furthermore, excellent methanol dehydration can be observed through pervaporation, which is attributed to the selective water channels formed in the rGO laminates.