New insights on the understanding of the high adsorption of bisphenol compounds on reduced graphene oxide at high pH values via charge assisted hydrogen bond.

The adsorption characteristics and mechanisms of ionic organic compounds dependent on their dissociation species are still unclear, which hindered the understanding of their environmental behavior and risks. This study compared the sorption of four bisphenol compounds (BCs) on graphite adsorbents, with a specific emphasis on the roles of charge assisted hydrogen bond (CAHB). The negative correlations between the localized orbital locator integrated π over plane index and the single point adsorption coefficient Kd of the four BCs indicated that π-π interaction was an important mechanism for BCs adsorption on graphite adsorbents. Based on the speciation distribution calculation and the modeling of pH-dependent adsorption, the apparent adsorption coefficient of different species were obtained. Except for bisphenol S, the Kd HA- of BC monovalent anions was 2.6 times to one order magnitude higher than that of the neutral species. According to the density functional theory (DFT) calculation, strong CAHB is expected between BC monovalent anions and graphite adsorbents, indicating that CAHB overcame the enhanced electrostatic repulsion and became the dominant adsorption mechanism. This study highlighted the importance of CAHB in the adsorption of ionic organic compounds on carbonaceous materials, which should be carefully taken into consideration for their environmental fate studies.