Photocatalytic degradation of the Acid Blue 113 textile azo dye in aqueous suspensions of four commercialized TiO_2 samples

摘要

The apparent first-order rate constant, k_(app), of the Acid Blue 113 textile azo dye photocatalytic disappearance in aqueous suspensions of 4 commercialized TiO_2 samples (50 m~2 g~(-1)-Degussa P25; 54 m~2 g~(-1)-Millennium Chemicals PC50; 250-270 m~2 g~(-1)-Sachtleben Chemie Hombikat UV100; 320 m~2 g~(-1)-Ishihara ST01) was determined from the decrease in the calibrated 566 nm-absorbance of the supernatant. Under the conditions used (1 liter-batch reactor; water-filtered irradiation from a Philips HPK 125-W high-pressure mercury lamp; [TiO_2] = 1 g/L; [dye] = 70 mg/L), the k_(app) ranking was: UV100 > PC50 > P25 > ST01. The corresponding maximal difference in k_(app) was roughly equivalent to that caused by adding an optimal dose of H_2O_2 to the P25 suspension. Taking into account the dye adsorbed amount, q_(ads), in the dark, it is deduced that the recombination rate k_r of photogenerated charges was higher for poorly crystallized TiO_2 samples, as expected; additionally, a low content of impurities is suggested to be at the origin of the low k_r of UV100 relative to ST01. It is also argued that differences in the values of q_(ads) divided by the surface area, S, was less due to pores inaccessible to the dye than to thicker layers of surface tightly bound water for the samples with high S. A FTIR study showed that the dye weakly interacted with TiO_2 and, however, remained the dominant adsorbed species during the degradation. This latter conclusion was in accord with the fact that the dye initial disappearance rates—directly measured or calculated from k_(app)—were almost equal, indicating that the intermediate products of degradation did not significantly compete with the remaining dye for active species.