Synthesis of amine functionalized SiO2 microspheres loaded polymeric hydrogel and its application for simultaneous eviction of divalent metal ions (Pb2+, Cd2+, Cu2+ and Ni2+)

Abstract

Recovery of divalent cationic elements from aquatic system is deliberated as reconciliation of rising industrial growth and access to quality drinking water. Herein we report tactically designed amino functionalized silica core-shell nanoparticle loaded polymeric hydrogel network as benchmark sorbent for divalent metal ions (Pb2+, Cd2+, Cu2+, Ni2+). The simple fabrication method for silica core-shell microspheres involves sol-gel synthesis of the polystyrene (PS) core, afterwards the formation of the silica shell by hydrolysis and condensation reaction, and finally the dissolution of the PS core. The surface of synthesized SiO2 microspheres was amine functionalized before being impregnated within a alginate matrix of polymer to generate amino functionalized SiO2 microsphere loaded polymeric hydrogel [NH2–SiO2MS-Ca-Alg] beads. Combining functionalized silica into polymeric hydrogel structure resulted extraordinary sorption capacities for divalent metal ions [191.4, 70.7, 64.9 and 35.8 mg g−1 respectively for Pb, Cd, Cu and Ni]. Density functional theory calculations were carried out to find out binding energies, preferred binding site of all four studied ions and structural changes due to their sorption. Structural evidence derived from experimental observations corroborate with the DFT analysis and speciation diagram of the divalent metal ion species. Plausible mechanistic pathway and differential uptake of four divalent metal ions were explained based on both experimental findings and theoretical studies. Developed NH2–SiO2 MS-Ca-Alg beads offered outstanding selectivity towards four divalent cations in a single prescription, excellent employability under ambient conditions without affecting essential water quality parameters which are significant breakthroughs for sustainable water remediation applications.