Synthesis and Characterization of Ti-Nb₂O₅ Catalysts for Discoloration Reaction of Bromophenol Blue and Indigo Carmine Dyes

This work investigated the photodegradation of bromophenol blue (BPB) and indigo carmine (IC) dye under UV–Visible light using pure oxides of titanium and niobium, as well as TiO₂-Nb₂O₅ oxides containing 0.5, 2.5 and 5 wt% of TiO₂, prepared by wet impregnation of Nb₂O₅ with Ti tert-butoxide under inert atmosphere. The results of XRD and Raman spectroscopy showed the presence of anatase TiO₂ phase and T-Nb₂O₅ phase with orthorhombic structure in the pure TiO₂ and Nb₂O₅ oxides, respectively. The Nb₂O₅ oxides doped with TiO₂ presented a T-Nb₂O₅ phase, but there was no formation of TiNb₂O₇. TiO₂ anatase was observed in the mixed oxide with higher Ti content (5 wt% TiO₂). A zeta potential analysis showed positive surface charge values for titanium oxide and negative for niobium oxide and mixed oxides. The addition of up to 5 wt% of the TiO₂ fold the activity of Nb₂O₅ in the discoloration of both dyes. Pure TiO₂ exhibits higher initial activity, which could be related to its positive PZC and higher attraction to sulphonic groups present in the dyes. Despite of the lower initial rate, 2.5 and 5% TiNb catalysts achieved full degradation of the dyes after 4 h of reaction.