Photocatalytic Degradation of Malachite Green Dyes With TiO2/WO3 Composite

Abstract

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 C2O4
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.