Retention of graphene oxide and reduced graphene oxide in porous media: Diffusion-attachment, interception-attachment and straining.

The aggregation, deposition and retention of graphene oxide (GO) and reduced graphene oxide (RGO) were investigated systematically to estimate their mobility in the environment. RGO aggregates faster than GO, resulting in weaker diffusive transfer and a lower deposition rate on oxide surfaces. In NaCl, the critical deposition concentration of RGO (CDCRGO) is smaller than CDCGO on the SiO2 surface, indicating that RGO achieves favorable deposition at lower ionic strength. In CaCl2, Ca2+ bridging causes close CDCGO and CDCRGO. The retention process was observed in the photolithographic SiO2 and Al2O3 micromodels. GO and RGO particles approach collectors mainly via interception before attachment. The interactive forces have a limited effect on the particle retention. The larger RGO aggregates cause greater extent interception and straining, resulting in lower mobility than GO in porous media. The mobility of GO and RGO show different trends in quartz crystal microbalance with dissipation (QCM-D) and in micromodels because the interception and straining mechanisms exist in pore space. Micromodel observation confirms the processes of interception and straining. The combination of QCM-D and micromodel experiments provides the connection of diffusion-attachment, interception-attachment and straining, which comprehensively explains the higher mobility of GO than RGO in porous media.