Photocatalytic Degradation of Textile Reactive Dyes-A Comparative Study Using Nano Silver Decorated Titania-Silica Composite Photocatalysts.

Photocatalytic degradation of commercial textile azo dyes such as Reactive Red 120 (RR 120), Acid Orange 20 (AO 20), Reactive Orange 16 (RO 16) and Congo Red (CR) was studied under UV light and visible light irradiations of wave length 365 nm and 420 nm respectively over bare and modified titania catalysts such as TiO2, 1% Ag/TiO2, 30% TiO2/SiO2 and 1% Ag/30% TiO2/SiO2. On comparison of the catalytic activity of all the synthesized catalysts under UV and Visible irradiations, it was found that the composite catalysts showed higher photocatalytic activity than bare TiO2. Among the catalysts 1% Ag/30% TiO2/SiO2 composite catalyst was the best catalyst for the decolourization of the chosen dyes. Results obtained showed that the time taken for the complete decolourization of dyes was found to be significantly different for different dyes under both UV and visible light irradiations. Among the four dyes, AO 20 decolourised completely (100%) in 2 hrs, whereas Congo Red (CR) decolourised to the least extent (35%) over 1% Ag/30% TiO2/SiO2 under UV light irradiation. Experiments carried out under dark condition in the presence of catalyst revealed very high adsorption of CR (≈60%) over titania catalysts and hence this could be reason for suppressed catalytic activity of 1% Ag/30% TiO2/SiO2. Various optimization studies such as effects of substrate concentration, weight of catalyst and substrate pH were carried out. TOC analysis revealed a very high mineralization of all the dyes.