Adsorption of Ca 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 Ca and Na were investigated using batch adsorption experiments, zeta potential measurements, and spectroscopic analysis. When pH increased from 4 to 9, Ca adsorption by GO and the zeta potential of GO increased significantly. Raman spectra suggest that Ca 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 Ca, it was more stable at higher pH in the NaCl solution. The findings of this research provide insights in the adsorption of Ca on GO and fundamental basis for prediction of its effect on the colloidal stability of GO in the environment.