Adsorption of Cd(II) on mercapto-palygorskite functional materials with different proportions: Performance, mechanism and DFT study

Cd contamination has cosmopolitan harm and urgent needs to be addressed, the mercapto (-SH) modified materials are emerging in the Cd remediation field. In this study, three mercapto-palygorskite functional materials (0.2MP, 0.5MP, 1.0MP) were prepared by trimethoxysilane (MPTMS) and palygorskite (PAL) with different weight ratios (0.2:1, 0.5:1, 1:1), to investigate the effect of -SH proportions differences on material properties and combination configuration with Cd. The results indicated that mercapto groups grafting occurred on the PAL surface, retaining the original mineral structure. The adsorption capacity improved with the increase of -SH ratio, and 1.0MP (30.06 mg·g−1) was up to about 3 times of PAL (10.07 mg·g−1). The Cd stabilization subjected to the pseudo-second-order kinetic, Redlich-Paterson and Langmuir isothermal model, belonging to monolayer homogeneous chemisorption. Multifaceted characterization revealed that MP utilized mercapto and hydroxyl groups to form complexation with Cd as the dominant action mechanism. The electron transfer that took place from -SH to Cd was confirmed by Bader net change. DFT calculation manifested that bidentate complex S-Cd-S (Ead = −1.089 eV) was the best configuration of -SH combined with Cd due to its lower binding energy than the monodentate complex (Ead = −0.579 eV). This study confirms that MP as a friendly functional material offers a bright application prospect in the treatment of Cd contamination.