Abstract: A strategy for reductive degradation of azo dye Acid Red 3R (AR3R) by using the in-situ generated heteropoly blue (PW12O404-) was investigated. Heteropoly blue was produced by UV irradiation on aqueous solutions containing posphotungstic acid (photocatalyst) and isopropanol (electron donor). The reduction potential of AR3R was measured by cyclic voltammetry and used to assess the thermodynamic feasibility of reduction of AR3R by heteropoly blue. A dark reaction between AR3R and heteropoly blue was carried out to further confirm and reinforce reductive degradation of AR3R by heteropoly blue. In addition, the effects of various factors such as the photocatalyst amount, isopropanol dosage, dye concentrations, and ionic strength on photodegradation of AR3R were evaluated. The results showed that increase of posphotungstic acid and/or isopropanol concentration accelerated photodegradation of AR3R till a saturation value. The initial rates of photodegradation of AR3R increased with increasing in dye concentration, which could be described by the Langmuir-Hinshelwood equation. However, salt concentration displayed a negative effect on photocatalytic degradation of dye. It was assumed that the charge-transfer within a precomplex formed by photoreduced heteropoly blue and AR3R lead to the reductive degradation of dye and oxidative regeneration of catalyst. This study also indicates that POM/isopropanol/UV system provides a green route for reductive decolorization of azo dyes.

Key words: Polyoxometalate, Photocatalysis, Azo dye, Acid Red 3R, Reductive decolorization