Photocatalytic discoloration of aqueous malachite green solutions by UV-illuminated TiO2 nanoparticles under air and nitrogen atmospheres:effects of counter-ions and pH

JULIAN ANDRES RENGIFO-HERRERA; LUIS RENE PIZZIO; MIRTA NOEMI BLANCO; CHRISTOPHE ROUSSEL; CESAR PULGARIN

Photochemical and Photobiological Sciences

ROYAL SOC CHEMISTRY

Año: 2011 vol. 10 p. 29 - 35

1474-905X

Under air atmosphere, the photocatalytic discoloration of malachite green (MG) aqueous solutions (atriphenylmethane dye) in the presence of TiO2 and UV light followed an oxidative pathway, involvingan N-demethylation process evidenced by a blue shifting of the main absorption band with a maximumat 618 nm. This oxidative process was affected by the nature of the dye counter-ion and the pH of thesolution. At pH 6.0, the oxidation was found to be faster than at pH 3.0, perhaps due to the poorinteractions between MG and the semiconductor surface. Furthermore, with the presence of oxalate ascounter-ion, the oxidative photocatalytic discoloration was negatively affected mainly at acidic pH.Under nitrogen atmosphere, some evidence was found about the double behaviour of MG wheninvolved in the photocatalytic discoloration reactions pertaining to TiO2 under these conditions. MGcould be simultaneously oxidized, forming N-demethlyated by-products, or reduced, thus leading toleuco-malachite green (LMG) (a colorless and toxic substance) as the main product. The LMGformation is favoured at low pH in the presence of oxalate as counter-ion.