Mercury adsorption study and DFT calculations of sulfur-containing biomass composites prepared by inverse vulcanization

This study introduces an innovative and cost-effective biomass adsorbent, the sulfur/cardanol/potato starch composite (SCP), synthesized through inverse vulcanization for the remediation of mercury-contaminated waters. The SCP was characterized using Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA) and X-ray Diffraction (XRD) to confirm its composition, morphology, and properties. The adsorption capacity of SCP for Hg(II) was 246.88 mg/g with a removal rate of 98.75 %. Adsorption kinetics followed a pseudo-second-order model, indicating chemisorption as the dominant mechanism, while adsorption isotherms were best described by the Langmuir model. Thermodynamic studies confirmed the adsorption process as spontaneous and endothermic. Density Functional Theory (DFT) calculations further elucidate the interaction mechanisms between mercury and the adsorbent, revealing that the thiyl radicals play a crucial role in the adsorption process. The SCP also exhibited a high selectivity for Hg(II) over other co-existing ions and maintains an adsorption capacity over 223.93 mg/g after five regeneration cycles, thus promising practical applications in environmental mercury management.