Preparation and characterization of nano-silver/mesoporous titania photocatalysts for herbicide degradation

Hydrothermally synthesized mesoporous titania containing silver; at weight percentages ratio of 1.6 and 3.2, nanoparticles either assembled by polyoxyethylene laurel ether (POL) or sodium dodecylsulphate (SDS) were characterized with XRD. N-2 sorptiometry, DRUV-vis, FIR and TEM. The photocatalytic performance of the catalysts was tested for the oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D; herbicide); through comparison with P25, under visible (lambda > 420 nm) and UV light irradiation. Our results show that TEM measurements evince that dispersed Ag nanoparticles with diameter of 7 and 5 nm are deposited on titania surfaces synthesized using POL and SOS, respectively. XRD and N-2 sorptiometry measurements advocate that Ag atoms were present inside titania pores; as confirmed from decreasing both surface area and pore volume values, as well as attending on titania surfaces upon increasing Ag content prohibiting the growth of anatase phase. The UV-vis absorbance spectra indicated that Ag nanoparticles can shift the absorption maximum to the visible light region as confirmed by the presence of surface plasmon bands at 634 and 700 nm. The apparent rate constants calculated under visible-light illumination for all catalysts were 0.0335 and 0.0289 min(-1); for 1.6 wt.% and 3.2 wt.% Ag/TiO2 templated from POL, as well as 0.0263 and 0.0251 min(-1); for 1.6 wt.% and 3.2 wt.% Ag/TiO2 templated from SOS. The direct involvement of the Ag particles in mediating the electron transfer from the photoexcited TiO2 under band gap excitation is considered to carry out the efficient photo-catalytic oxidation of the 2,4-D besides, the higher efficiency of generation, mobility, and separation of photoinduced electrons and holes. (C) 2010 Elsevier Inc. All rights reserved.