Photocatalysis with Chromium‐Doped TiO₂: Bulk and Surface Doping

Abstract

The photocatalytic properties of TiO2 modified by chromium are usually found to depend strongly on the preparation method. To clarify this problem, two series of chromium-doped titania with a chromium content of up to 1.56 wt % have been prepared under hydrothermal conditions: the first series (Cr:TiO2) is intended to dope the bulk of TiO2, whereas the second series (Cr/TiO2) is intended to load the surface of TiO2 with Cr. The catalytic properties have been compared in the photocatalytic oxidation of formic acid. Characterization data provides evidence that in the Cr/TiO2 catalysts chromium is located on the surface of TiO2 as amorphous CrOOH clusters. In contrast, in the Cr:TiO2 series, chromium is mostly dissolved in the titania lattice, although a minor part is still present on the surface. Photocatalytic tests show that both series of chromium-doped titania demonstrate visible-light-driven photo-oxidation activity. Surface-doped Cr/TiO2 solids appear to be more efficient photocatalysts than the bulk-doped Cr:TiO2 counterparts.

Insights into the TiO2-Based Photocatalytic Systems and Their Mechanisms

“…The mechanism of cation doping is essentially to tune the Fermi level and electronic structure of d-electron configuration in TiO 2 , thereby to tune the energy levels to absorb the visible light energy and to enhance the overall photocatalytic efficiency of the system as shown in Figure 4a Consequently, there have been many cations doped in TiO2 towards enhancing its PC activities. In such cation doping, TiO2 has been doped with the (i) transition metals such as Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Cd, and W [73][74][75][76][77][78][79][80][81][82][83][84]; (ii) rare-earth metals such as Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, and La [85][86][87][88][89]; and (iii) other metals such as Li, Mg, Ca, Se, Sr, Al, Sn, and Bi [90][91][92][93][94][95][96][97]. In the case of rare earth elements doping, the electronic configurations such as 4f, 5d, and 6s are found to be favorable to tune the band edge positions, density of states, and width of VB and CB via altering the crystal, electronic, and optical structures in TiO2 [98][99][100].…”

Alcohol solvents evaporation-induced self-assembly synthesis of mesoporous TiO2−x−y C x N y nanoparticles toward visible-light driven photocatalytic activity

“…In the recent years, much effort has been devoted to modification of TiO 2 in order to allow the utilization of a wider fraction of visible light (Ould-Chikh et al 2014;Venieri et al 2014;Zhang et al 2014). Until now, the adjusting of the electronic structure of TiO 2 materials is an effective approach, for example, substituting lattice oxygen with nonmetal elements such as C, N, S, F, Cl, or I (Han et al 2014;Huang and Wey 2013;Umadevi et al 2014;Vereb et al 2013;Wang et al 2009).…”

Enhanced visible light photocatalytic activity of Cr3+-doped anatase TiO2 nanoparticles synthesized by sol–gel method

“…Choudhury et al [16] investigated the effect of Cr-doping on the structural, optical and magnetic properties of TiO 2 nanoparticles. The photocatalytic behavior of chromium-doped titania and chromium supported on the surface of titania were studied by Ould-Chikh et al [17].…”