Photoassisted Degradation of Dye Pollutants. 8. Irreversible Degradation of Alizarin Red under Visible Light Radiation in Air-Equilibrated Aqueous TiO₂ Dispersions

Abstract

Alizarin red undergoes rapid photoassisted decomposition in air-equilibrated aqueous TiO2 dispersions under visible light radiation (λ > 420 nm). Proton NMR, chemical oxygen demand (CODCr), UV−visible, IR, GC−MS, and spin-trapping ESR spectroscopic techniques were employed to obtain details of the photodegradation of alizarin red. Peroxides and carbonyl species are the first intermediates observed during the process. The major component of the peroxides produced is H2O2, and no organoperoxides were detected. We have also confirmed that in addition to CO2 and to smaller carbonyl species the principal intermediate produced is phthalic acid, which is unable to degrade further because it does not absorb the actinic visible light radiation (λ > 420 nm). The photodegradation kinetics are discussed in terms of the Langmuir−Hinshelwood model, a case of saturation type kinetics. A mechanism for the photoassisted degradation of alizarin red mediated by TiO2 particles under visible light radiation is proposed.

Photophysical and photocatalytic properties of novel M2BiNbO7 (M = In and Ga)

“…12 Liu et al 20 and Xu and Langford 21 studied that alizarin red and X3B dyes could be decomposed over TiO 2 based on visible light driven dye-sensitized phenomena. Tang et al 8 reported that photocatalytic degradation of MB over TiO 2 was also owing to dye-sensitized process under visible light irradiation.…”

“…The result indicated that the rate of MB photolysis was almost the same as that of MB degradation with TiO 2 as the catalyst, suggesting that TiO 2 was inactive to MB photocatalytic degradation under visible light irradiation. 12 Liu et al 20 and Xu and Langford 21 studied that alizarin red and X3B dyes could be decomposed over TiO 2 based on visible light driven dye-sensitized phenomena. Tang et al 8 reported that photocatalytic degradation of MB over TiO 2 was also owing to dye-sensitized process under visible light irradiation.…”

Influência da intensidade luminosa na fotodegradação de efluente têxtil

“…According to Liu et al (1999), the greater decolourisation in relation to mineralization is due to the fact that only those organic species excited by visible light may be degraded with the help of catalyst particles.…”

“…The photogenerated electrons from CB and the hole from VB may migrate to the surface and take part in the oxidation-reduction reactions on the interface (Nogueira and Jardim, 1998;Galindo et al, 2000;Gouvêa et al, 2000).…”

“…In the heterogeneous photocatalysis using semiconductors, the degradation reaction rate depends on many parameters, including the reactor geometry, semiconductor nature and concentration, oxygen concentration, organic compound concentration, luminous intensity, temperature, pH, presence of interfering species and agitation intensity (Mills and Hunte, 1997).…”