Effect of oscillating temperature and crystallization on graphene oxide composite pervaporation membrane for inland brine desalination

Membrane distillation (MD) for desalination experienced technical challenges when treating concentrated inland brine with high salinity under industrially-relevant oscillating temperature condition or solar desalination. In this study, we fabricated a composite membrane using graphene oxide (GO) and used it in a pervaporation (PV) process to tackle the issues encountered in the MD processes. The resultant GO composite membranes demonstrated fast water vapor transport through nano-channels between the GO interlayers. In addition, the smoother and negatively charged surface offered by the GO layer hindered the undesired crystal deposition on the membrane surface, and therefore giving a substantially improved performance than the MD process when operated under oscillating temperature. More importantly, the presence of divalent cations in inland brine led to a naturally-occurring crosslinking between the GO nanosheets that offered molecular sieving functionality to the GO layer, preventing the transport of salt ions, as well as GO swelling and therefore providing exceptional performance sustainability, especially under oscillating temperature condition. Interestingly, it was found that GO composite membrane in a PV process for desalination offered greater overall water productivity when operated under the oscillating temperature compared to the constant temperature. These GO composite membranes also demonstrated good performance stability after chemical cleaning and when exposed to minor contaminants found in inland brine such as humic acid.