Photocatalytic activity of transition metals (Mn, Fe, Ag and Ni doped ZnO) nanomaterials synthesised via sol-gel method: Active sites over band gap

Abstract

Dopants with varied stoichiometry values were examined to determine their performances on photocatalysis. The sol-gel method was successfully synthesised using transition metals, namely manganese (Mn), Iron (Fe), silver (Ag) and nickel (Ni), as dopants in ZnO nanostructure. Zn(1-x)Mn(x)O, Zn(1-x)Fe(x)O, Zn(1-x)Ag(x)O and Zn(1-x)Ni(x)O (x=10%) were characterised by using X-ray diffraction (XRD), BET surface area analysis, temperature-programmed desorption of carbon dioxide (TPD–CO2) and UV-Vis spectrophotometer. A phase study on Mn- and Fe-doped ZnO nanoparticles confirmed that both the dopants experienced exceptional crystallinity with single-phase but Ag- and Ni- produced a multi-phases structures. Active sites of catalyst is proven to be an additional factor contributing towards photocatalysis in this work besides band gap and surface area. Temperature-programmed desorption of carbon dioxide (TPD–CO2) showed that the incorporation of Ag into ZnO lattice has enhanced the number of active sites on the surface of the catalyst whereas incorporation of Mn, Fe and Ni in ZnO has reduced it as compared to pure ZnO. Photocatalytic degradation of methyl orange for all stoichiometry of Ag-doped ZnO nanoparticles resulted in lower degradation time. Interestingly, 10% of Ag-doped ZnO achieved the highest degradation rate as much as 97.47 % at 160 minutes, hence emerging as the best amongst all other compositions.