Removal of a synthetic dye "Direct Fast Blue B2RL" via adsorption and photocatalytic degradation using low cost rutile and Degussa P25 titanium dioxide

Removal of a commercial dye (Direct Fast Blue B2RL) has been successfully achieved by rutile TiO2 (R) via adsorption followed by the UV/photocatalytic degradation. The data of adsorption and photocatalytic processes was compared to that obtained using the commonly widespread Degussa P25 TiO2 (D). The parameters which affect both adsorption and photocatalytic processes such as specific surface area (S-BET), particle size, zeta potential, bandgap as well as the effect of pH on the dye structure have been measured and illustrated. Multi ionic forms were obtained for B2RL at different pH values due to the protonation/deprotonation of the functional groups. In both TiO2 types, experimental data for the adsorption processes agreed with Langmuir and Freundlich models in both acidic and neutral media. Whereas, due to repulsion forces, the data fitted only Langmuir model in basic medium suggesting the absence of multilayers. D showed higher adsorption capacities toward B2RL than R in acidic and neutral media. The great difference in the values for the maximum amount of B2RL bound per unit weight of TiO2 (q(m)) between R and D was mainly obtained at low pH, which is not required in the photocatalytic degradation processes. At low pH's, the super tendency of B2RL toward TiO2 surface adsorption blocked the photoactive sites in TiO2 surface. The photocatalytic degradation reaction of different ionic forms of B2RL in the two types of TiO2 has been studied in both solid and liquid systems. It has been concluded that the main photodegradation of B2RL takes place at the surface of the catalyst and the rate constant (k) decreases in solid and liquid systems as follows:- in R the order is pH 12 > pH 5.7 (neutral) > pH 2, while in D the order is pH 5.7 > pH 12 > pH 2. COD analysis confirmed the complete mineralization of B2RL via photocatalytic degradation using both R and D. The influence of different parameters affecting the photocatalytic degradation process such as, initial dye concentration, TiO2 dosage, and light intensity have been studied. Durability of rutile TiO2 and Degussa P25 was also investigated. R and D possessed good performance after repeated running in the photocatalytic degradation system. (C) 2013 International Association for Hydro-environment Engineering and Research, Asia Pacific Division. Published by Elsevier B.V. All rights reserved.