Sol-gel and impregnated prepared silver TiO₂ semiconductors as photocatalysts for the UV decomposition of 2,4-d: A comparative study of the preparation method

UV-photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid (2,4-d) was studied on Silver-TiO₂ semiconductors prepared by co-gelling silver acetylacetonate and titanium butoxide (TiO₂-Ag) or by incipient impregnation with silver acetylacetonate (0.5 wt% Ag) of bare TiO₂ sol-gel and TiO₂-P25 supports. The comparative study shows that only a slight modification on the specific surface area was obtained on the TiO ₂-Ag sample (60 m²/g) as compared to the TiO₂ sol-gel bare support (65 m²/g). XRD patterns of the samples show anatase as the crystalline phase present in the sol-gel TiO₂ preparations. By means of HRTEM and HAADF-STEM electron microscopy techniques, silver nanoparticles (<12.0 nm) were identified which are very small to be detected by XRD. The photocatalytic oxidation of the herbicide 2,4-d used as a model of contaminant show for the kinetic parameter t_1/2 values of 45 min for the TiO₂-Ag sample, while for the impregnated Ag/TiO ₂ and Ag/P25 nanomaterials t_1/2 was 124 and 66 min, respectively. The higher photoactivity of the TiO₂-Ag photocatalyst is attributed to a combined effect of the silver nanoparticles in interaction with the titania semiconductor.