Tuning of band gap in TiO2 and ZnO nanoparticles by selective doping for photocatalytic applications

Abstract

Metal oxide nanoparticles of TiO2 and ZnO were synthesised using mild hydrothermal solution routes (T = 150–180°C, P = autogeneous, in about 2–16 h) and selectively doped with (Ag+, Sn4+, Sb3+, In3+ = 1–5 M%) in the presence of hexylamine as additive or n-hexanol as surface modifier for tuning the band gap. The synthesised nanoparticles were characterised using powder XRD, UV-Vis, FTIR and SEM. For defects characterisation positron annihilation lifetime spectroscopy (PALS) was employed. X-ray diffraction results revealed that the nanoparticles are highly crystalline and homogeneous in composition. FTIR results demonstrated the presence of various functional groups in the doped TiO2 and ZnO. Doping of TiO2 and ZnO with Ag+ showed decrease in band gap energy to 2·98 eV from 3·31 eV (∼10%) and 3·25 eV from 3·37 eV (∼3·6%) respectively. This has resulted in improved efficiency for the photo degradation in the visible light region for doped TiO2 and ZnO. The authors observed good correlation between the defect densities as revealed by PALS data and tuned band gap energy by dopants.