Dye photo-enhancement of TiO2-photocatalyzed degradation of organic pollutants: the organobromine herbicide bromacil

Dye chemicals from the textile industry are a principal source of environme ntal pollution. The industrial effluents must therefore be treated before t heir release into the aqueous environment. However, application of conventi onal biological methods for textile wastewater treatment is limited by unsa tisfactory degradation of the refractory dyes and associated chemicals. In the present study a complete degradation of selected azo- and thiazine-dyes has been achieved by TiO2-solar photocatalytic oxidation (SPO). Here the S PO is accompanied by a reaction of dye sensitization. Enhanced degradation of colourless refractory pollutants has been observed in the combined proce ss, The main advantage of the combined approach is the utilization of visib le light for assisting the degradation of refractory organic pollutants, no t only coloured, but also colourless, which cannot be photosensitized in th e visible region. Although very little is known on the subject, the present results demonstrate that the process is promising for the removal of undes irable toxic chemicals from textile industry wastewater. To simulate such c onditions we have recently studied the dye photosensitized solar photocatal ysis of an uracil derivative. Both UV and visible light are required for en hanced substrate and dye decomposition, irradiation by UV alone decreased t he degradation rate of dye, while visible light alone did not lead to any d ecomposition at all. It seems that the mechanism of the studied reaction in volves a combination of oxidation by hydroxyl radicals, via the hole-electr on semiconductor route, with oxidation by singlet oxygen.