Removal of Ag(I) from aqueous solution by thiourea-functionalized silica gel: experimental and theoretical study

Thiourea-functionalized silica gel (HO-SG-GPTS-TS and HE-SG-GPTS-TS) were synthesized by homogeneous and heterogeneous methods, respectively. The feasibility of the as-prepared adsorbents for the remove of Ag(I) from aqueous solution was systemically studied under different solution pH, contact time, temperature, and initial Ag(I) concentration. The adsorption capacity is found to depend on the solution pH and the maximum adsorption capacity is achieved at pH 6. Adsorption kinetic indicates the adsorption can reach equilibrium within 180 min. The adsorption follows pseudo-second order model and is controlled by film diffusion process. Adsorption isotherm shows that the adsorption capacity increases with the increase of initial Ag(I) concentration and temperature. The adsorption isotherm is suitable to be simulated by Langmuir model and is proceeded by chemical mechanism. Thermodynamic parameters suggest the adsorption is a spontaneous, endothermic, and entropy increased process. Density functional theory calculation reveals that the formation of chelates with Ag(I) by S and hydroxyl O atoms dominate the adsorption, and S atom is the main contributor.