PHOTODRADATION OF MALACHITE GREEN DYE USING TIO2 / ACTIVATED CARBON COMPOSITE

This leads to the formation of free electrons in the conduction band and holes in the semiconductor valence band. The energized electrons can either recombine with the holes (and then dissipate the absorbed energy as heat) or the electron-hole pairs can participate in redox reactions. They can react with electron acceptors/donors adsorbed on the surface of the photocatalyst. Alternatively, the solid side at the semiconductor/liquid junction creates an electrical field that separates the electrons-holes pairs that fail to recombine. The electron field allows the holes to migrate to the illuminated part of the TiO2 and the electrons to migrate to the unlit region of the TiO2 particle surface. Essentially, it is accepted that the initial steps of photocatalytic degradation of a species is the reaction with extremely reactive but short-lived hydroxyl radicals (OH● ) or direct hole trapping. The OH● is formed either in the highly hydroxylated semiconductor surface or by direct oxidation of the pollutant molecules under UV radiation. There is also a possibility that both methods of forming OH● occurs in these situation simultaneously. The reduction of adsorbed oxygen species occurs immediately after this process. Dissolved oxygen molecules (in the aqueous system), or other electron acceptors available in the aqueous system can cause this reduction [5, 6, 7].