Catalytic reduction of methyl blue using biosynthesised gold nanoparticles

Abstract

Gold nanoparticles (AuNPs) have attracted wide attention due to their significant applications in catalysis and environmental remediation. In particular, their high surface area to volume ratio contributes to their higher reactivity and made them a powerful tool for removal of contaminant in aqueous system. Green synthesis of AuNPs utilizing plant extract has been suggested as possible eco-friendly alternatives to chemical and physical methods. Due to their higher reactivity, AuNPs have tendency to agglomerate resulting in large particle size. Ligand assisted method employing functionalize ligands will covalently anchor the AuNPs onto the solid support thus controlling the AuNPs particle size and preventing agglomeration. In this research, a (3-aminopropyl)triethoxysilane (APTES)-functionalized silica-coated magnetite biosynthesized AuNPs was synthesized using Cosmos caudatus aqueous leaf extract as the reducing agent. The magnetic biosynthesised AuNPs were characterized by using FTIR, XRD and AAS analyses. FTIR spectroscopy confirmed that the biomolecules present in the Cosmos Caudatus leaf extract act both as reducing and capping agents. The XRD diffractogram showed that the crystalline AuNPs have been immobilised on the APTES-functionalised silica-coated magnetite. The data obtained from AAS analysis showed that the amount of Au metal present was 5.5 wt%. The reactivity of the magnetic biosynthesised AuNPs was tested in the decolourization of methyl blue in aqueous solution. The concentration of the dye was monitored using UV- Vis Spectrophotometry. The reduction of methyl blue obeyed a pseudo first order reaction with the highest rate constant of 1.74x10^-2 min^-1. The rate constant increases with the increase amount of catalyst. 83% decolourization of methyl blue was achieved suggesting that the catalyst is effective in removing methyl blue.