Influence of electronic structures of doped TiO₂on their photocatalysis

Abstract

The modification of bandgap of TiO2 was intensively studied for decades to improve its visible light absorbance efficiency. The practical application potential of TiO2 as photocatalysts for water splitting and water purification has motivated enduring experimental and theoretical research of the doping effects in bulk and nanosized TiO2 using transition metals, rear earths, p‐block metals and metalloids, and non‐metal elments as dopants to decrease the bandgap of TiO2. This review summarized the typical theoretical results of the dopant induced variation in electronic structure, bandgap, and density of states of TiO2. The codoping effects of metal/metal, metal/non‐metal combinations were also introduced briefly to display the modification of electronic structures. Some results were accompanied by experimental results to demonstrate the influence of improved light absorbance efficiency on the photocatalytic performance. The doping effects on the density of states of surface were also summarized briefly. The metal dopants show clear influences on the 3d electrons of titanium to elevate or depress the minimum of conduction band, while the non‐mental dopants mainly interact with the 2p electrons of oxygen to change the position of the maximum of the valence band. The review also noticed the theoretical development of the doping effect with the establishment of novel models, such as the water–TiO2surface interaction. It should be noted that the theoretical models rarely consider the doping induced variation of defect types and concentration, Fermi level position, surface active sites, and charge transport due to the ground state simulation and shortcoming of density functional theory (DFT). The phenomenological explanations of the experimental results are arbitrary in most of the reports. A universal model is required to explain the complex dependence of the process of photocatalysis on the semiconducting properties, such as bandgap, Fermi level, charge transport, and surface states. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Insights into the TiO2-Based Photocatalytic Systems and Their Mechanisms

“…In such cation doping, TiO 2 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 TiO 2 [98][99][100]. In addition, the rare earth elements tend to form complexes through their f -orbital and form various Lewis-based organic compounds, thereby improving the photocatalytic activities of TiO 2 [101,102].…”

Influences of Doping on Photocatalytic Properties of TiO2 Photocatalyst

“…Another path to achieve the abovementioned goal is represented by rare-earth doping [214][215][216][217][218][219]. Compared to transition metals, rare-earth metals with 4f, 5d, and 6s 2 states are considered as the ideal dopants to modify the crystal structure, electronic structure, and optical properties of TiO 2 , which can effectively influence the positions, widths, and density of states of CB and VB [220,221]. Furthermore, rare-earth metals can form complexes with various Lewis-based organic compounds through interaction of the functional groups with their f orbital, thereby improving the photoactivity.…”

Synergistic Effect of Si Doping and Heat Treatments Enhances the Photoelectrochemical Water Oxidation Performance of TiO2 Nanorod Arrays

“…For instance, theoretical calculations show that dopants like Si, Ge, and Pb can mix their s orbitals with Ti 3d orbital and thus change the conduction band edge position of TiO 2 , resulting in the bandgap reduction . Doping with nonmetals like N, C, S, and B also proved to be capable of narrowing the bandgap of TiO 2 . Chen et al employed high pressure hydrogen treatment to compel TiO 2 nanocrystals to form an outer disorder layer, which brought the rising of the valence band maximum and resulted in bandgap narrowing and consequently enhanced the solar absorption .…”