Sorption mechanism and dynamic behavior of graphene oxide as an effective adsorbent for the removal of chlorophenol based environmental-hormones: A DFT and MD simulation study

Chlorophenols are a group of environmental-hormones (EHs) which are carcinogenic, toxic and often precursors to dioxins. Increasing interest in their removal from environment has emerged as a research hotspot in recently years. The adsorption mechanism and dynamic behaviors of four molecules, namely Phenol, 4-chlorophenol (CP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP) onto graphene oxide were investigated by means of plane-wave based Density Functional Theory (DFT) and Molecular Dynamics (MD) simulation. The effects of functional groups, solution, pH value, and substituent etc. have been scrutinized through geometric optimization, binding energy calculations and a series of electronic structure analyses. Based on the computational results, we elucidated the adsorption mechanism of chlorophenols onto GOs in aqueous solution was mainly driven by the hydrophobic effect and ultimately stabilized by the hydrogen bonds and pi-pi interaction. This proposed mechanism was supported by further MD simulations in which a three-state movement was confirmed. It was found that for GOs, the adsorption capacity would be improved by hydroxyl groups which could supply more adsorption sites for the adsorption of chlorophenols. Besides, the adsorption affinity was weakened with increase in number of chloro-groups decorated in the chlorophenols. In addition to the intrinsic properties of the adsorbents and adsorbates, the acidic condition and polar solvent were found to be more favorable, accompanying with the reinforcement of hydrogen-bonds and electrostatic attraction. The combination of DFT method and MD simulations will help to provide insights into the application of graphene oxides for the removal of EHs.