Preparation of Polycrystalline TiO₂ Photocatalysts Impregnated with Various Transition Metal Ions:  Characterization and Photocatalytic Activity for the Degradation of 4-Nitrophenol

Abstract

A set of polycrystalline TiO 2 photocatalysts loaded with various ions of transition metals (Co, Cr, Cu, Fe, Mo, V, and W) were prepared by using the wet impregnation method. The samples were characterized by using some bulk and surface techniques, namely X-ray diffraction, BET specific surface area determination, scanning electron microscopy, point of zero charge determination, and femtosecond pump-probe diffuse reflectance spectroscopy (PP-DRS). The samples were employed as catalysts for 4-nitrophenol photodegradation in aqueous suspension, used as a probe reaction. The characterization results have confirmed the difficulty to find a straightforward correlation between photoactivity and single specific properties of the powders. Diffuse reflectance measurements showed a slight shift in the band gap transition to longer wavelengths and an extension of the absorption in the visible region for almost all the doped samples. SEM observation and EDX measurements indicated a similar morphology for all the particles, and a not homogeneous distribution of the metal species onto the surface of catalyst particles. The impregnated samples revealed recombination rates always higher than that of bare TiO 2 . The photoactivity of TiO 2 was reduced by the presence of transition metal ions with the exception of W, which instead played a beneficial role. The results of femtosecond pumpprobe diffuse reflectance spectroscopy appear quite in accord with the observed photocatalytic activity only for the lowest values of electron-hole recombination rate of the samples.

Photoinduced Dynamics of TiO2 Doped with Cr and Sb

“…For example, TiO 2 absorbs visible light when doped with transition metals. 9 Trivalent chromium cation dopant has been examined along this scheme of sensitization. [9][10][11][12] However, the photocatalytic production of H 2 and O 2 has not yet been achieved with Cr-doped TiO 2 .…”

Enhanced photocatalytic activity of Ce3+–TiO2 for 2-mercaptobenzothiazole degradation in aqueous suspension for odour control

“…The adsorption capacity can be generally improved by adjusting the surface-zero-charge point or by increasing the specific surface area and pore volume of catalysts [4][5][6]. On the other hand, it has been reported that doping with a group of transitional metal ions [5][6][7][8][9][10][11] or depositing some noble metals such as Au [4,[12][13][14] and Pt [15], or coupling metallic oxides [16][17][18][19] with d electronic configuration into TiO 2 lattice could eliminate the recombination of electron-hole pairs significantly and also result in the extension of their wavelength response toward the visible region [20].…”

Photocatalytic Activity and Antibacterial Behavior of Fe3+-Doped TiO2/SnO2 Nanoparticles

“…Because the experimental conditions, preparation methods and standards for the evaluation of photocatalytic activity are there are many argumentative results reported. Some research groups have reported that the presence of these foreign metal species in TiO 2 is generally detrimental for the degradation of organic compounds in aqueous systems (Paola et al, 2000;Navio et al, 1999;Dohshi et al, 2003;Sinha et al, 2001) while some controversial results have also been reported (Choi et al, 1994;Zhang et al, 1998;Yamashita et al, 2002;Araña et al, 2002). The photocatalytic sterilization property of Titanium dioxide (TiO 2 ) has been documented (Watanabe et al, 1999).…”