Catalytic reduction of 4-nitrophenol using magnetic biostabilise silver nanoparticles

Abstract

Due to their high surface area to volume ratio, silver nanoparticles (AgNPs) have higher reactivity and made them a powerful tool for removal of contaminant in aqueous system. Green synthesis of AgNPs utilizing plant extract has been suggested as possible eco-friendly alternatives to chemical and physical methods. Due to their higher reactivity, AgNPs have tendency to agglomerate resulting in large particle size. Ligand assisted method employing functionalized ligands will covalently anchor the AgNPs onto the solid support thus controlling the AgNPs particle size and preventing agglomeration. In this research, the AgNPs biosynthesised using Cosmos caudatus leaf extract were successfully immobilised onto 3-mercaptopropyltrimethoxysilane (MPTMS) functionalised silica-coated magnetite. The magnetic biostabilised AgNPs were characterised using FTIR, XRF, XRD and AAS analyses. FTIR spectroscopy confirmed that the biomolecules present in the Cosmos caudatus leaf extract act as reducing and capping agents. The amount of sulphur as determined by XRF was 3.52 mmolg^-1. The XRD diffractogram showed that the crystalline AgNPs have been immobilised on the thiol-functionalised silica-coated magnetite. The average crystallite size of AgNPs calculated using Debye Scherrer equation is 27.52 nm. The Ag loading in the magnetic biostabilised AgNPs determined by AAS is 0.42 mmolg^-1. The catalytic performance of AgNPs in the reduction of 4-nitrophenol to 4-aminophenol was investigated. The magnetite supported biostabilised AgNPs show good catalytic activity in the reduction of 4-nitrophenol to 4-aminophenol in the presence of excess NaBH₄. The magnetic catalyst can be efficiently separated from the reaction mixture using an external magnet.