Interaction and sorption mechanisms of phthalate plasticizers and Cd²⁺ on biochar

Biochar exhibits significant potential for the remediation of soil contaminated with organic pollutants and heavy metals. A comprehensive understanding of the interfacial interactions and sorption mechanisms of low-hydrophobicity phthalate plasticizers, such as dimethyl phthalate (DMP) and diethyl phthalate (DEP), along with Cd²⁺ on biochar, is essential for the effective remediation of polluted soil environments. This study systematically examines the interaction and sorption mechanisms of PAEs-Cd²⁺ on biochar at both macro and micro levels using sorption batch experiments and molecular dynamics simulations. The sorption of contaminants by biochar occurred through a combination of physical and chemical mechanisms. The presence of coexisting pollutants reduced the sorption capacity of biochar to PAEs but had a minimal effect on Cd²⁺ adsorption. In the co-sorption system, PAEs and Cd²⁺ demonstrated distinct interaction behaviors. Due to its smaller molecular size and higher diffusion coefficient, Cd²⁺ readily bonded to surface sorption sites on biochar and infiltrated its pores. Although PAE-ion complexes enhanced the sorption of pollutants by biochar, PAE molecules, and cluster structures primarily accumulated on the biochar surface, interacting with heavy metals through electrostatic forces. This interaction reduced the contribution of pore filling to pollutant sorption and weakened the desorption hysteresis capacity of biochar. The intraparticle diffusion model had similar results. Thus, a larger specific surface area and an abundant pore structure are crucial factors in improving the co-sorption capacity of biochar. This study offers novel insights into the sorption behavior of PAEs and Cd²⁺ on biochar within organic-inorganic composite pollution.