Mechanistic insights and steric interpretations through statistical physics modelling and density functional theory calculations for the adsorption of the pesticides atrazine and diuron by Hovenia dulcis biochar

Abstract

Atrazine and diuron are two pesticide compounds with very low surface interaction capacity, whose adsorption efficiency remains a challenge in environmental remediation applications. In this work, statistical physics (sta-phy) modelling and density functional theory (DFT) calculations have explored several still unveiled mechanisms involved. A model activated carbon (AC) sample was produced with Hovenia dulcis fruit residues, a local invasive tree species. The adsorption process was spontaneous and endothermic, and the adsorption capacities (Qm) increased as the temperature increased. The number of adsorbate molecules per site (n) decreased as the density of the receptor site (Nm) increased, revealing that the temperature influences the geometry of the molecules during the surface interaction. According to the electrostatic mapping provided by the DFT calculations, it was possible to infer that the obtained Qm values for atrazine, between 42.54 and 73.20 mg g−1, can be a response caused by its own self-repulsion. For diuron, due to its increased neutrality, the potential balance of the electrostatic charges between adsorbate-adsorbent tends to be more effective, resulting in higher Qm values, ranging from 97.91 to 119.7 mg g−1. Therefore, the combination of sta-phy modelling with quantum mechanics calculations is a powerful tool for mechanism interpretation, capable of providing complementary insights into the adsorption process from both adsorbent and adsorbate perspectives.