pH-Dependent adsorption of aromatic compounds on graphene oxide: An experimental, molecular dynamics simulation and density functional theory investigation

This work provides a comprehensive understanding for the pH-dependent adsorption of aromatic compounds (ACs) on graphene oxide (GO). Isothermal and kinetics experiments indicated both adsorption capacity and adsorption rate were suppressed at higher pH, and the mechanisms were revealed by molecular dynamics simulations and density functional theory calculations. More specifically, π-π, hydrogen bond, vdWs, and water-mediated steric hindrance interactions were examined to reveal how pH affected the adsorption capacity, and microscopic dynamic adsorption process was captured to reveal how pH affected the adsorption rate. Results showed the reduced adsorption capacity at higher pH was mediated by increased electrostatic repulsion, weakened π-π interaction, and increased water-mediated steric hindrance. The pH-dependent behaviour of GO was responsible for the effect of pH on adsorption rate. Self-aggregation of GO at lower pH helped to capture ACs and created more favourable adsorption sites. Upon the adsorption of ACs on GO, GO/water/AC/water/GO sandwich-like structure formed, which was also mediated by solution pH. Overall, pH affects the adsorption of ACs on GO by regulating driving forces, adsorption process, and the configuration property of GOAC complex.