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 s urface bond-conjugated TiO2/SiO2 suspension for five commercial dyes, inclu ding cationic dyes, cationic blue X-GRL (CBX) and cationic pink FG (FG), an d 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-hetero cycle N group, whereas, the other three anionic dyes adsorbed on the cataly st surface by a sulfonate group. The mode of adsorption of substrates to th e TiO2/SiO2 particle surface is relevant factor to the formation of NH4+. T he nitrogen of azo group was transformed to NH4+ ions and N-2 gas, and the penta-heterocycle and benzene-ring- su bsti Lute N groups in CBX and FG wer e transformed predominantly to NH4+ ions. The triazine ring and its substit ute groups are much stable in the period of 8 h irradiation. (C) 2001 Elsev ier Science B.V. All rights reserved.