THE EFFECT OF IRON AND NIOBIUM CO-DOPING RATIO ON THE PHOTOCATALYTIC ACTIVITY OF SOL-GEL DERIVED TITANIUM DIOXIDE

As metal co-dopants, Fe and Nb have been reported to improve the photoquantum efficiency of TiO2 by simultaneously lowering the band gap energy and improving charge separation. In this study, the effects of varying the co-doping ratio of Fe and Nb on the physico- chemical properties and photocatalytic activity of TiO2 photocatalysts prepared using a temperature-controlled sol-gel method were investigated. The combined co-dopant molar loading was held constant (0.25%) while the co-doping ratio of Fe and Nb was varied. The physico- chemical properties of TiO2 were monitored by characterizing the photocatalysts in terms of crystallite phase (XRD), band gap energy (UV-Vis Spectrophotometry), specific surface area (3- point BET), and surface morphology/composition (SEM-EDX). Measurement of the band gap energy confirmed the band gap-lowering effect of Fe, but the lower band gap energy of Nb-TiO2 compared to pure TiO2 indicated that Nb also exhibits a band-gap lowering effect. After 6 hours of photocatalytic testing, 1:2 Fe:Nb-TiO2 displayed the highest photocatalytic activity among the photocatalysts with 64.78% decolorization of the lignin model pollutant under UV illumination and 38.02% under visible light illumination. All co-doped photocatalysts exhibited higher photocatalytic activity compared to pure TiO2 under visible light illumination, confirming the cooperative effects of Fe and Nb towards improving the photocatalytic activity of TiO2.