ENVIRONMENTAL PHOTOCHEMISTRY ON SEMICONDUCTOR SURFACES - PHOTOSENSITIZED DEGRADATION OF A TEXTILE AZO-DYE, ACID-ORANGE-7, ON TIO2 PARTICLESUSING VISIBLE-LIGHT

Photosensitized degradation of a textile azo dye, Acid Orange 7, has b een carried out on TiO2 particles using visible fight. Mechanistic det ails of the dye degradation have been elucidated using diffuse reflect ance absorption and FTIR techniques. Degradation does not occur on Al2 O3 surface or in the absence of oxygen. The dependence of the dye degr adation rate on the surface coverage shows the participation of excite d dye and TiO2 semiconductor in the surface photochemical process, Dif fuse reflectance laser flash photolysis confirms the charge injection from the excited dye molecule into the conduction band of the semicond uctor as the primary mechanism for producing oxidized dye radical. The surface-adsorbed oxygen plays an important role in scavenging photoge nerated electrons, thus preventing the recombination between the oxidi zed dye radical and the photoinjected electrons. Diffuse reflectance F TIR was used to make a tentative identification of reaction intermedia tes and end products of dye degradation. The intermediates, 1,2-naphth oquinone and phthalic acid, have been identified during the course of degradation, Though less explored in photocatalysis, the photosensitiz ation approach could be an excellent choice for the degradation of col ored pollutants using visible light.