Coupling photocatalysts and ferrate oxidation for the removal of the dye rhodamine 6G [Couplage photocatalyse-oxydation par le ferrate (VI) pour le traitement du colorant rhodamine 6G]
Résumé
A limiting factor in photocatalytic oxidation using UV irradiation of titanium dioxide (TiO2) is the recombination of conduction band electrons (e- cb) with electron holes (h+ vb) on TiO2 surface. Coupling ferrate(VI), Fe(VI), known as an “environmentally friendly” oxidant, with UV/TiO2 photocatalysis may involve an oxidation synergism arising from the Fe(VI) scavenging of e- cb and the corresponding beneficial formation of highly reactive Fe(V). This study describes the results of coupling P25 TiO2 and Fe(VI) (pure or Fe(VI) matter synthesized in our laboratory) to remove the dye rhodamine 6G (R6G). Abatement kinetics for R6G, ([R6G]0 = 10-5 M; pH = 8.00 ± 0.05), in presence of TiO2 ([P25] = 0.1 g∙L-1) illuminated under an UV source and/or Fe(VI) ([Fe(VI)]0 = 10-4 M) were followed by spectrophotometry. A synergism was highlighted during the treatment of R6G by UV/TiO2/ pure Fe(VI), leading to a faster abatement and a better mineralization. However, this abatement was not reached when coupling Fe(VI) matter with UV/TiO2. A study of the impact of the inorganic salts present in the Fe(VI) matter on the oxidative activities is presented. Sulfate, SO4 2-, and Fe(OH)3 in particular lead to a high inhibition of TiO2 activity. The monitoring of hydroxyl radical (OH•) production highlighted a physical inhibition of the formation of OH•, probably due to the formation of an inorganic salt layer at the surface of TiO2 and also to the scavenging of OH• in the bulk solution.