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 TiO2–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 t1/2 values of 45 min for the TiO2–Ag sample, while for the impregnated Ag/TiO2 and Ag/P25 nanomaterials t1/2 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.