Elimination of a Cationic Dye (Crystal Violet) in Aqueous Medium by TiO2/UV Oxidation Process

Abstract

The crystal violet, a cationic dye, could be discoloured by TiO₂/   UV process. The experiments have shown on one hand that direct   transformation at 365 nm has led to a feeble percentage of   decolourization (≈ 25 % decoloured for a reaction time of 5 h and   for a concentration of 3 ppm) and in another hand adsorption process   has conducted, in absence of light, to a negligible amount of dye   retention. By contrast, the treatment of the considered solution by   TiO₂/UV at 365 nm has permitted to obtain a better efficiency of   the bleaching process. It has been observed that the decolouration   rate has varied with concentration of the substrate. Indeed, as the   solution becomes more coloured, the colouration disappeared   slowly. Moreover, in all cases, the discolouration process followed   a first-order rate law. The influence of H₂O₂ has led to an improvement   of this process marked thereby, by an acceleration of the   bleaching rate. This fact could be attributed to the participation of   the radicals OH^•, in these reactions. In this case too, the kinetics   behaviour was well represented by first-order rate law. The effects   of salts such as NaCl and Na₂SO₄ have been also investigated and   the obtained results showed a decrease of the decolouration rate   for both cases. The photocatalytic pathway has been well described   by the Langmuir-Hinshelwood kinetics model. The values of the   rate constant (k) and adsorption equilibrium constant (K) are 1.76   M min^-1 and 7.07 M^-1, respectively.