Abstract
Photocatalyzed degradation of phenol in aqueous solution over surface impregnated TiO2 (M = Cu, Cr, V) under UV-Vis (366 nm) and UV (254 nm) irradiation is described. Nanosized photocatalyts were prepared from TiO2-P25 by wet impregnation, and characterized by X-ray diffraction, X-ray fluorescence, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy, Raman spectroscopy, and adsorption studies. No oxide phases of the metal dopants were found, although their presence in the TiO2-P25 lattice induces tensile strain in Cu-impregnated TiO2-P25, whereas compressive strain in Cr- and V-impregnated TiO2-P25. Experimental evidences support chemical and mechanical stability of the photocatalysts. Type IV N2 adsorption–desorption isotherms, with a small H3 loop near the maximum relative pressure were observed. Metal surface impregnated photocatalysts are mesoporous with a similar surface roughness, and a narrow pore distribution around ca. 25 Å. They were chemically stable, showing no metal lixiviation. Their photocatalytic activity was followed by UV-Vis spectroscopy and HPLC–UV. A first order kinetic model appropriately fitted the experimental data. The fastest phenol degradation was obtained with M (0.1%)/TiO2-P25, the reactivity order being Cu > V >> Cr > TiO2-P25 under 366 nm irradiation, while TiO2-P25 > Cu > V > Cr, when using 254 nm radiation. TOC removal under 366 nm irradiation for 300 min showed almost quantitative mineralization for all tested materials, while 254 nm irradiation for 60 min led to maximal TOC removal (ca. 30%). Photoproducts and intermediate photoproducts were identified by HPLC–MS, and appropriate reaction pathways are proposed. The energy efficiency of the process was analysed, showing UV lamps are superior to UVA lamps, and that the efficiency of the surface impregnated catalyst varies in the order Cu > V > Cr.
Highlights
Industry development imply heavy economical charges associated to waste removal, often a cocktail of pollutants harmful to the environment, dangerous for human health, and difficult to degrade by natural mean [1]
Among these, doping and impregnation with transition metal ions lead to an improvement in photocatalytic activity [11,12] through the generation of intermediate energy states in the band gap of TiO2 or trapping of photoexcited electrons [13]
Theoretical calculations suggest band gap reduction in in V and Cr-impregnated P25 is due to the existence of V and Cr 3d orbitals between the valence band (VB) and CB of Cr-doped P25, in the case of V the 3d orbitals are adjacent the conduction band minimum (CBM) so the reduction of Eg relative to non-impregnated TiO2-P25 is lower [59]
Summary
Industry development imply heavy economical charges associated to waste removal, often a cocktail of pollutants harmful to the environment, dangerous for human health, and difficult to degrade by natural mean [1]. Among these, doping and impregnation with transition metal ions lead to an improvement in photocatalytic activity [11,12] through the generation of intermediate energy states in the band gap of TiO2 (increasing Vis light absorption) or trapping of photoexcited electrons (reducing e−/h+ recombination) [13]. Photocatalysts have been used for pollution abatement in water, both in suspension and immobilized over suitable supports Alternative strategies, such as doping TiO2 onto large particles avoid the expensive cost of nanofiltration in real-world environmental applications [14]. We have impregnated TiO2-P25 with different amounts of metals (Cu, Cr, and V), to improve visible light harvesting, and investigated the variables controlling phenol photodegradation, as a model of phenolic pollutants abatement, by heterogeneous photocatalysis with the resulting materials under Vis and UV light. We have impregnated TiO2-P25 with different amounts of metals (Cu, Cr, and V), to improve visible light harvesting, and investigated the variables controlling phenol photodegradation, as a model of phenolic pollutants abatement, by heterogeneous photocatalysis with the resulting materials under Vis and UV light. 0.1%, 0.3%, 0.5%, and 1% of Cu, Cr, and V were used, and the corresponding reaction mechanism for the phenol photocatalyzed degradation was described
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