Sustainable solutions to remove heavy metal contaminants from the water supply are of critical importance to human health and the environment. Heavy metal decontamination using biomass-derived adsorbents has gained attraction due to its low cost and ability to remove various forms of heavy metals, as well as the availability and reusability of adsorbents. Biomass can be processed via hydrothermal carbonization to produce heavy metal adsorbents. The adsorption of Cu2+ and Pb2+ to 15 oxygen-containing binding sites on a KOH-activated, glucose-derived hydrothermal char molecule was modeled through density functional theory (DFT) calculations, and a new DFT framework to model adsorption while incorporating water solvation effects by explicit addition of water molecules is provided. All DFT calculations were performed on WebMO using the Becke, 3-parameter, Lee–Yang–Parr (B3LYP) exchange-correlation functional and the Los Alamos National Laboratory 2 Double-Zeta (LANL2DZ) basis set. The favorability of adsorption was assessed using the potassium exchange energy (KEE) of each binding site, which is the enthalpy required to exchange a potassium cation bound to the char with a heavy metal cation. The average KEE for Cu2+ is -80 ± 26 kJ/mol, and the average KEE for Pb2+ is -71 ± 29 kJ/mol. Negative KEE values indicate that heavy metal adsorption to the modeled char is energetically favorable. Phenolate-containing sites have the most negative KEEs, indicating more favorable adsorption compared to other binding sites containing carboxylate, carbonyl, or furan moieties. These results suggest that phenolate groups may have a more significant role in heavy metal adsorption than carboxylate groups. Investigation of adsorption to a phenolate motif with varied substituents in the meta and para positions shows that the presence of electron-donating groups yields more negative KEEs and more favorable adsorption.

Computational investigation of Cu2+ and Pb2+ adsorption to hydrothermal char

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