Influence of gamma-irradiation on the photocatalytic activity of Degussa P25 TiO2

The purpose of this article is to study the influence of gamma irradiation on the sorption capacity and photocatalytic activity of commercially available TiO2 Degussa P25. The photocatalyst was gamma-irradiated at ambient temperature with doses 8–60 kGy (137Cs, dose rate 2 kGy/24 h) and then stored until analysis/tests in liquid N2. X-ray diffraction, SEM, TEM, EPR, and UV–VIS reflectance spectrometry were applied to explore phase composition, crystal cell parameters, crystallite size, textural properties (grain size, and specific surface area), the presence of paramagnetic centers, and UV/VIS absorption of the initial and irradiated samples. The sorption capacity and photocatalytic activity of the products under UVA (17 W, λ max = 365 nm) and sunlight irradiation were studied against Malachite Green 10−5 M aqueous solution, applied as a model pollutant. The sorption capacity varied non-monotonically with the irradiation dose, with clearly expressed maximum and minimum seen at irradiation with doses of 28 and 60 kGy, respectively. The maximum in the photocatalytic activity, both at UV and sunlight illumination, is observed after the dose of 28 kGy is applied; at these conditions, the pollutant degradation rate constant is 1.7/2.7-times higher than the value for the non-irradiated product. The explanation of the obtained results is related mainly to the type and concentration of gamma-generated defects in catalysts, and especially the effect of Ti3+ is discussed. Some of the considered factors may act in opposite directions, causing an extreme point in the relation between the photocatalytic activity and the gamma radiation dose.