The Impact of Different Functional Groups of Biochar on Mercury Adsorption Investigated by Density Functional Theory

Investigating the impact of biochar functional groups on mercury adsorption performance can provide theoretical guidance for the search and design of high-performance mercury adsorbents. However, due to the highly heterogeneous nature, structural diversity, and surface complexity of biochar, current experimental techniques struggle to elucidate the detailed effects and mechanisms of each functional group. This study employs Density Functional Theory and wavefunction analysis methods to construct eight molecular models with different single and dual functional groups. We calculated and analyzed the adsorption energy, C-Hg bond length, charge transfer, surface electrostatic potential, and electron localization function for each model and adsorption site. Using these methods, we investigated the effects of -CH₃, -CH₂OH, hydroxyl, and cyano groups on mercury adsorption performance at various sites on carbon surfaces. The results indicate that cyano groups significantly enhance mercury adsorption, while hydroxyl groups exhibit specific effects at different sites. Additionally, we proposed interaction mechanisms for two types of dual functional groups—linear superposition and synergistic effects. This study addresses the current gap in understanding the properties of functional groups related to mercury adsorption and provides a more comprehensive theoretical basis for technologies aimed at efficient mercury adsorption under complex practical conditions.