Reactive Dyes In Aqueous Solution Research Articles

Semiconductor-assisted photocatalytic degradation of reactive dyes in aqueous solution

This work reports the semiconductor-assisted photochemical degradation of reactive dyes. In an oxygenated-UV-ZnO system almost total decolorization of Remazol Brilliant Blue R, Remazol Black B, Reactive Blue 221 and Reactive Blue 222 was observed in reaction times of about 60 min. Extending the photochemical treatment up to 120 min, mineralization higher than 80% for all the dyes was observed. During the same period, the residual acute toxicity was significantly reduced only for Remazol Black B. A systematic optimization study carried out by factorial design showed that for the reactive dyes tested, the ZnO semiconductor exhibits a better efficiency than that observed with anatase TiO 2. A synergistic effect in the coupled TiO 2–ZnO system was not observed.

The light stability of azo dyes and azo dyeings IV. Kinetic studies on the role of dissolved oxygen in the photofading of two heterobifunctional azo reactive dyes in aqueous solution

Heterobifunctional reactive derivatives of two previously studied azo chromophores were exposed to light in aqueous solution. In the presence of artificial perspiration, the initial and final rate of photofading depended on the oxygen level of the dye solution. An initial low rate of light-induced dye decomposition was followed by a much higher rate in the final stages of exposure. The lower the initial oxygen concentration the shorter the initial period low dye degradation and the higher the rate of photodegradation in the final stages. Light-induced dye decomposition follows first order kinetics. A reductive mechanism for perspiration assisted, light-induced degradation was supported by results from the photofading of the dyes in the presence of reductive compounds.