Laminar HNb3O8-based membranes supported on anodic aluminum oxide with enhanced anti-swelling property for organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is an energy-efficient alternative to distillation and evaporation for the separation of mixtures containing organic liquids. Laminar membranes using nanosheets as building blocks have great potential for OSN; however, a swelling of the interlayer spacing causes a severe decrease in the separation performance. Here, we present laminar HNb3O8-based composite membranes fabricated by vacuum filtration on an anodic aluminum oxide support for OSN applications. The laminar HNb3O8 membranes and composite (graphene oxide (GO) and HNb3O8) membranes were found to possess stable structures in various alcohols without severe swelling. As a result, the HNb3O8-based membranes showed higher dye rejections than the GO membrane. Among the HNb3O8-based membranes, the layered GO/HNb3O8 membrane had superior dye rejections in methanol (89.6% for Evans blue, 73.4% for acid red 265, and 43.4% for methyl orange) compared with the GO membranes. Alcohol permeation tests implied that the molecular diameter, rather than the solvent viscosity, was the dominant factor in the superior performance of the layered GO/HNb3O8 membrane. Molecular dynamics simulations suggest a stable GO/HNb3O8 interlayer ranging from around 1.165 to 1.333 nm, and a dense heterolayer formation at the interface between the HNb3O8 and GO layers. This heterolayer formation performs important roles in alcohol permeation and separation of organic dyes. Furthermore, the layered GO/ HNb3O8 membrane showed stable permeation of a model photoresist waste liquid for 6 weeks and an excellent rejection of the photoresist waste, over 91%. We propose that laminar HNb3O8-based membranes have great potential for OSN applications.