Adsorption of Ca²⁺ on single layer graphene oxide

Graphene oxide (GO) holds great promise for a broad array of applications in many fields, but also poses serious potential risks to human health and the environment. In this study, the adsorptive properties of GO toward Ca²⁺ and Na⁺ were investigated using batch adsorption experiments, zeta potential measurements, and spectroscopic analysis. When pH increased from 4 to 9, Ca²⁺ adsorption by GO and the zeta potential of GO increased significantly. Raman spectra suggest that Ca²⁺ was strongly adsorbed on the GO via -COOCa⁺ formation. On the other hand, Na⁺ was adsorbed into the electrical diffuse layer as an inert counterion to increase the diffuse layer zeta potential. While the GO suspension became unstable with increasing pH from 4 to 10 in the presence of Ca²⁺, it was more stable at higher pH in the NaCl solution. The findings of this research provide insights in the adsorption of Ca²⁺ on GO and fundamental basis for prediction of its effect on the colloidal stability of GO in the environment.