Photocatalytic Degradation of Acid Orange Dye Using Silver Impregnated TiO2/SiO2 Composite Catalysts

Titania-silica composite photocatalysts with very high surface area were synthesized via sol gel method and characterized by XRD, BET, DRS and TEM techniques. Both titania and TiO2/SiO2 composite catalysts showed the bandgap around 3.2 eV, but a slight decrease in the bandgap was observed for silver impregnated TiO2/SiO2 composite catalyst. However, a surface plasmon due to the presence of the Ag nano particles were seen around 400-600 nm. Their photocatalytic activities were evaluated towards the degradation of Acid Orange 20, a reactive azo dye, under UV (lambda = 365 nm) and visible (lambda = 420 nm) light irradiations. From the photocatalytic studies the optimum impregnation level of titania required for the complete degradation of Acid Orange 20 over SiO2 was determined. Among the composite catalysts 30% TiO2/SiO2 was found to be the best as it showed 89% of Acid Orange 20 degradation. The activity of composite catalyst was much better than that of pure TiO2 which may be attributed to its higher surface area. In order to improve the photocatalytic activity, silver metal was impregnated over the most active composite catalyst (1% Ag/30% TiO2/SiO2) and tested. Significant increase in both the percentages of decolourisation and degradation of Acid Orange 20 were observed which may be attributed to trapping of electrons by the silver metal ions. Acid Orange 20 was decolourised completely in 2 and 6.5 hrs of UV and visible irradiations respectively. TOC analysis also showed 99.9% and 53% of degradation of Acid Orange 20 in 10 hrs of irradiations of UV and visible light respectively.