Solar photocatalyzed red dye destruction using a titanium dioxide suspension

Abstract

The destruction of Direct-Red #79 textile dye in dilute aqueous solution was demonstrated by heterogeneous solar photocatalysis over suspended titanium dioxide. Dye oxidation and adsorption mechanisms, TiO2 photocatalysis, and external oxidant (H2O2) addition are discussed. Experimental data are presented which support previous studies reporting first order destruction of organic contaminants using recirculating batch reactor systems. The observance of optimum catalyst concentration, and reaction rate conformance to the Langmuir-Hinshelwood kinetic model were similar to results obtained by others. Dye destruction by free radicals was investigated. Evidence suggesting involvement of these processes is proposed by relating the rate of dye destruction to solution pH and alkalinity levels. Enhancement of dye destruction rate upon hydrogen peroxide addition was examined. Results of total organic carbon analyses, spectrophotometric absorbance measurements, and molecular weight estimations suggested the formation of reaction intermediates and indicated the extent of dye oxidation.