Heteroaggregation of Graphene Oxide with Minerals in Aqueous Phase.

Broad applications of graphene oxide (GO) will result in its release into aquatic environments, where clay minerals and metal (hydr)oxides are commonly present. We therefore investigated the interaction of GO with goethite, kaolinite, montmorillonite, and kaolinite-goethite complex (KGAs). GO significantly enhanced the dispersion of positively charged goethite via heteroaggregation, but no interaction between GO and negatively changed montmorillonite or kaolinite. Electrostatic attraction was a dominant force in GO-goethite heteroaggregation. Sorption/aggregation of GO on goethite followed a linear model. Desorption hysteresis was observed, showing possible irreversible heteroaggregation between GO and goethite, which could be explained by the formation of a sandwich-like structure between GO and goethite. For KGAs, their heteroaggregation with GO occurred when solution pH was lower than 6, and the critical coagulation concentration (CCC) of GO in the presence of KGA increased with increasing pH. The wrapping of KGAs with GO was observed, and the structure of the GO-KGA heteroaggregates depended on both the size and concentration of GO sheets. These findings will provide new insight into the environmental fate, exposure, and impact of GO in water and soil.