Experimental and theoretical studies of ZnO and MgO for the rapid coagulation of graphene oxide from aqueous solutions

The biological toxicity and negative environmental effect of graphene oxide (GO) have attracted wide public concern due to its potential risks. To assess the transport behavior and to reduce the environmental hazardous of GO in natural environment, ZnO and MgO were used as coagulant for GO removal from aqueous solutions. The results indicated that GO coagulation on ZnO and MgO were scarcely affected by ionic strength. At neutral pH, the GO removal capacities could reach 232.8 mg/g on MgO and 210.8 mg/g on ZnO. The high removal capacity and short coagulation time showed the enormous advantages for the high-efficiency removal of GO from aqueous solutions, which were important for the real application of MgO and ZnO in reality. The coagulation mechanisms of GO on ZnO and MgO could be attributed to electrostatic attraction and hydrogen bond, which were further demonstrated by DFT calculations. Considering the cost, efficiency, removal capacity and reusability, one can conclude that metal oxides can be promising materials for GO efficient removal by a simple and rapid coagulation process. The findings can provide critical information about the physicochemical behavior of GO in aquatic natural environment, which is significant to decrease the environmental toxicity of GO.