Photocatalytic Degradation of Malachite Green Dyes With TiO2/WO3 Composite

This study summarizes briefly the sources of Malachite green contamination and the wide range of its toxic effects. The photodegradation of this cationic triphenylmethane dye by TiO2 and TiO2/WO3 composite is examined under different experimental conditions. Two types of salts - oxalate and hydrochloride were studied and unexpectedly different kinetics of degradation was observed in the presence of TiO2 or TiO2/WO3 as photocatalysts. The behavior of the hydrochloride dye is almost identical in the presence of both catalysts TiO2 or TiO2/WO3, showing equal rates of degradation. However for the oxalate form the TiO2/WO3 composite is significantly more efficient than pure TiO2. Even more, the apparent rate constant of degradation for oxalate is higher than that obtained for hydrochloride with the same composite TiO2/WO3. It is suggested that initial adsorption of the dye on the surface of the catalyst plays important role and explains the different photocatalytic performance of TiO2/WO3 composite powder. Most probably the sorption of Malachite green oxalate is favored by the C(2)O(4)(2-)ions, this way providing direct photooxidation of the dye. It is also established by UV-VIS comparative analysis that during the proposed photopurification of the pollutants the formation of the colorless carcinogenic Leuco malachite green is negligible.