Challenges in Co-Alloyed Titanium Oxynitrides, a Promising Class of Photochemically Active Materials

Abstract

We present a perspective on recent developments in modified TiO 2 photocatalysts for visible light-driven photochemistry with an emphasis on water splitting. We focus on doped and alloyed TiO 2 and in particular address the synergistic effects observed in materials with both transition metal cations and nonmetal anions. Several reports have demonstrated absorption of longer wavelengths (λ = 500−600 nm) by codoped materials compared to the absorption edge of TiO 2 . We review these advances against the backdrop of well-established doped TiO 2 research, suggesting on the basis of compositional analysis and wavelength-resolved measurements of photon conversion efficiency that the increase in visible light absorption is likely due to absorption between defect states rather than true band gap narrowing. We draw a distinction between codoped and co-alloyed materials, stressing the attractive electronic structure of the latter. In highlighting recent literature, data examining the rate of photochemical water splitting or magnitude of anodic current as they depend on the wavelength of incident light are emphasized. Finally, areas for further research are highlighted, particularly in the synthesis of co-alloyed compositions of TiO 2 .

Role of CuO in the modification of the photocatalytic water splitting behavior of TiO2 nanotube thin films

“…Deposition of metal particles to improve the performances of titania thin films by heterojunction, co-catalysis, co-alloying or plasmonic effects has been widely investigated [16][17][18][19], with recent studies remarking also the role of one-dimensional nanoarchitecture (e.g. nanotubes) [20][21][22][23].…”

Photocatalytic Solar Light H2 Production by Aqueous Glucose Reforming

“…Due to the different behaviour of metals and non‐metals, co‐doping was used as a strategy to enhance the photocatalytic activity of TiO 2 , . It is reported that anions and cations generate shallow localized levels near the valence and conduction band edges, allowing the band gap decrease and the shift of the two bands towards less positive and less negative values, respectively . Various N, W co‐doped TiO 2 systems have been prepared and tested under solar light irradiation for oxidation reactions .…”

Experimental and modeling study of visible light responsive photocatalytic oxidation (PCO) materials for toluene degradation

“…While some PCO-based technologies have been evaluated [10–19], research addressing the development and evaluation of visible light driven PCO materials is limited [20–23]. It is known, however, that materials such as TiO 2 can be co-alloyed with niobium (Nb) and oxynitrites to significantly reduce adsorption energy down to 2.0 eV, which enables visible light activation [24–26]. Most evaluations have focused on NO x (NO, NO 2 ) removal using UV lights for outdoor applications [27–32].…”