Influence of adsorption on the photodegradation of various dyes using surface bond-conjugated TiO2/SiO2 photocatalyst

The adsorption and photodegradation have been investigated in illuminated surface bond-conjugated TiO2/SiO2 suspension for five commercial dyes, including cationic dyes, cationic blue X-GRL (CBX) and cationic pink FG (FG), and anionic reactive brilliant red K-2G (K-2G), reactive yellow KD-3G (KD-3G), and acid red B (ARB). Two adsorption modes are proposed. In the TiO2/SiO2 system, CBX and FG (FG) adsorbed on the catalyst surface by a penta-heterocycle N group, whereas, the other three anionic dyes adsorbed on the catalyst surface by a sulfonate group. The mode of adsorption of substrates to the TiO2/SiO2 particle surface is relevant factor to the formation of NH4+. The nitrogen of azo group was transformed to NH4+ ions and N2 gas, and the penta-heterocycle and benzene-ring-substitute N groups in CBX and FG were transformed predominantly to NH4+ ions. The triazine ring and its substitute groups are much stable in the period of 8 h irradiation.