The influence of chemical oxidation on the adsorption properties of 3D graphene materials by the enhanced accessibility

Graphene aerogel (GA) and hydrogel (GH) were oxidized using hydrogen peroxide (H2O2) and nitric acid (HNO3), respectively. The oxidized GA enhanced bisphenol A (BPA, hydrophobic) and methyl orange (MO, hydrophilic) adsorption. The accessibility of the air-closed pores in oxidized GA was enhanced due to the increase of oxygen-containing functional groups, exposing some new adsorption sites, as identified by 1H NMR relaxation measurements. The oxidized GH inhibited BPA adsorption but increased MO adsorption. Higher oxygen-containing functional groups form water clusters and occupy adsorption sites for hydrophobic pollutants. Nevertheless, increased hydrophilicity facilitated the adsorption of hydrophilic pollutants. In addition, the adsorption rate of BPA on oxidized GA was decelerated, while that of MO was accelerated. The adsorption rates of both BPA and MO were accelerated on oxidized GH. This study emphasized that oxidation has different effects on the accessibility of air-enclosed pores and the adsorption properties of GA and GH.