Molecular simulation of adsorption thermodynamics and dynamics behavior of GOs at air-water interface

The adsorption of two-dimensional (2-D) graphene oxide (GO) nanosheets at the air-water interface has broad technological implications for GO-based functional material preparations. Molecular-level understanding of the adsorption mechanism and interfacial behaviour is of great significance. Here, the adsorption free energy of GO nanosheets at the air-water interface was simulated, in which the effect of functional groups and deprotonation has been investigated. It was observed that the neutral GOs are generally thermodynamically favourable for the interface adsorption, while the deprotonated GO sheet has no such interface activity. Although the carboxyl group can enhance the interface adsorption minimum in the free energy profile, thereby improving the interfacial activity of the GO sheet, the oxidisation degree on GO is the main controlling factor determining the interface affinity. The interfacial morphology and dynamics of GO nanosheets have also been simulated, in which a parallel movement with a 2-D anisotropic rotation along the interface was revealed. Our simulation results provide new insights into the adsorption mechanism and behaviour of GO at the air-water interface.