Photolytic and photocatalytic decolorization of Lauth\'s violet using nano-titanium dioxide: A kinetics study

Photolysis and photocatalysis of Lauth's violet using nano-titanium dioxide at various aqueous buffer and non-buffer pHs. The effects of some various operating parameters such as initial dye concentration, medium pH, illumination time and catalyst amount have been investigated in a photoreactor equipped with high pressure mercury lamp. Spectrophotometric methods supported that the dye is almost completely decolorized. The dye decolorization obeyed from a pseudo-first-order kinetics. The observed rate constants (kobs) of direct photolysis and photocatalysis processes were evaluated for all studied pHs. Rate constants of direct photolysis at buffer were evaluated to be 3.7×10-3, 2.5× 10-2 and 3.0×10-2 min-1 for pHs of 7, 9 and 11 respectively. The rate constants of dye photolysis at non-buffer pHs were found as 8.8×10-2, 7.4×10-2, 1.1×10-1 h-1 for pHs of 5, 7 and 9 respectively. Moreover adsorption constant (KA) and degradation rate (kr) at surface for photocatalytic process were calculated at acidic, neutral and basic media.