Graphene oxide membrane (GOM) is a good candidate for water treatment because of its fast water permeation rate. When being applied in forward osmosis (FO), the freestanding GOM can have high water flux and low reverse salt flux, which is beneficial to the FO process. However, the practical applications of GOM to be used in FO are still unknown. Most of the previous studies used DI water as the feed solution, thus the forward solute transport across the GOM in FO is unknown. Here, the suitable applications of freestanding GOM to be used in FO were investigated by using different types of feed solutions (feed solution containing monovalent, multivalent, or neutral-charged solute). We found that the separation performance for the multivalent ions is generally better than the monovalent ions in FO because they have lower forward solute flux. This suggests that the freestanding GOM is more suitable to treat the solution containing multivalent ions rather than the monovalent ions. Also, by comparing the theoretically calculated results using the Donnan steric pore model and the experimental results, we found that the transport of the solutes across the freestanding GOM is mainly governed by the steric hindrance and the interfacial Donnan exclusion. The EDL screening effect is another mechanism that affects the ion transport in the freestanding GOM, which has been previously ignored. The sensitivity analysis showed that the volumetric charge density is the dominant factor affecting salt transport across the GOM.

Forward solute transport across a freestanding graphene oxide membrane in forward osmosis

ACS Fall 2021

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