Enhanced water permeation through sodium alginate membranes by incorporating graphene oxides

Pristine graphene oxide (pGO) and reduced graphene oxide (rGO) nanosheets with different physical and chemical structures were prepared, and blended into sodium alginate matrix to fabricate two types of hybrid membranes. Compared with pGO, rGO possessed smaller nanosheet size, more structural defects, less negative charges, less oxygen-containing groups, and more non-oxide regions. The hybrid membranes exhibited brick-and-mortar morphology, unusual crystallinity change, and increased free volume. Swelling resistance and mechanical stability of the hybrid membranes were both enhanced. Pervaporation dehydration was conducted utilizing ethanol/water mixture as model to explore the selective water permeation through hybrid membranes. Due to synergy between permselectivity of water channels and crystallinity of polymer matrix, the hybrid membranes, particularly for rGO-filled membranes, exhibited improved separation performance with increased separation factor and an unusual change of permeation flux. When the rGO content was 1.6wt%, optimum separation performance with a separation factor of 1566 and a permeation flux of 1699g/(m²h) was achieved. The transport mechanism was investigated based on transport property comparison of the two types of membranes, revealing that more water channels with higher selectivity could be constructed and controlled by graphene oxide structure. Moreover, the hybrid membrane displayed a good long-term operation stability.