Synthesis of a novel amorphous metal-organic framework containing rich N and S groups for efficient adsorption of Ag(I) in aqueous solutions

Industrial wastewater containing heavy metal Ag(I) causes irreversible harm to human health through food chain, necessitating effective removal methods. According to hard-soft acids-bases (HSAB) theory, nitrogen (N) and sulfur (S) functional groups form stable chelates with Ag(I). In this study, 2-amino-5-sulfanyl-1,3,4-thiadiazole (AST) with three N and two S groups served as organic ligand, and zinc nitrate hexahydrate provided metal center, novel amorphous metal-organic framework (Zn-AST) rich in N and S groups was synthesized via a one-pot solvothermal method. Batch experiments assessed the Zn-AST adsorption properties for Ag(I) in aqueous solutions. In addition, density-functional theory, frontier orbital theory, and molecular electrostatic surface potential analyses were used to elucidate the synthesis and adsorption mechanisms. The maximum adsorption capacity of Zn-AST for Ag(I) was 2932.91 mg/g. The Zn-AST exhibited good selectivity in the presence of Cu(II), Co(II), Ni(II), and Pb(II) ions, the removal rate for Ag(I) was 98.28 %, which was far higher than the values of other ions (all less than 10 %). The main adsorption mechanisms of Ag(I) by the Zn-AST involved electrostatic interactions, the formation of Ag–S bonds, and chelation between Ag and nitrogen functional groups. This study offers a viable strategy for developing unique adsorbents for Ag(I) removal from wastewater.