Simultaneously Controllable Doping Sites and the Activity of a W–N Codoped TiO₂ Photocatalyst

Abstract

Tungsten–nitrogen (W–N) codoping has been known to enhance the photocatalytic activity of anatase TiO2 nanoparticles by utilizing visible light. The doping effects are, however, largely dependent on calcination or annealing conditions, and thus, the massive production of quality-controlled photocatalysts still remains a challenge. Using density functional theory (DFT) thermodynamics and time-dependent DFT computations (TDDFT), we investigate the atomic structures of N doping and W–N codoping in anatase TiO2, as well as the effect of the thermal processing conditions. We find that W and N dopants predominantly constitute two complex structures: an N interstitial site near a Ti vacancy in the triple charge state ((VTi-Ni)3–) and the simultaneous substitutions of Ti by W and the nearest O by N ((WTi-NO)+). The latter case induces highly localized shallow in-gap levels near the conduction band minimum (CBM) and the valence band maximum (VBM), whereas the (VTi-Ni)3– defect complex yielded deep levels (1.9 eV above the VBM). Electronic structures suggest that (WTi-NO)+ improves the photocatalytic activity of anatase by band gap narrowing, while (VTi-Ni)3– degrades the activity by an in-gap state-assisted electron–hole recombination, which explains the experimentally observed deep-level-related photon absorption. Through the real-time propagation of TDDFT, we demonstrate that the presence of (VTi-Ni)3– attracts excited electrons from the conduction band to a localized in-gap state within a much shorter time than the flat band lifetime of TiO2. On the basis of these results, we suggest that calcination under N-rich and O-poor conditions is desirable to eliminate the deep-level states caused by (VTi-Ni)3– and to improve photocatalysis.

Boosting Supercapacitor Performance of TiO2 Nanobelts by Efficient Nitrogen Doping

“…Thus, Al reduction induces oxygen vacancies (V O ). As expected, the signal intensity of EPR decreases in some extent after nitrogen doping, originated from the N 3− substitution into the oxygen vacancies . Moreover, N‐doped TiO 2 NBs also shows weak Ti 3+ signals, which is the result of charge compensation after nitrogen doping …”

Photocatalytic reduction of CO 2 with H 2 O over graphene oxide-supported oxygen-rich TiO 2 hybrid photocatalyst under visible light irradiation: Process and kinetic studies

“…Despite that, pure unmodified TiO 2 suffers from several drawbacks such as low quantum efficiency resulting from rapid recombination of charge carriers and the limit to UV-light absorption due to its wide band gap [29][30][31][32][33]. Great endeavours have been made to resolve these drawbacks, including cationic metal and anionic doping to manipulate the properties of TiO 2 [34][35][36][37][38][39][40][41][42][43][44]. However, these techniques could result in the generation of secondary impurities and oxygen vacancies, respectively, which could ultimately reduce the photocatalytic activity of TiO 2 [45,46].…”

Carbon coated Au/TiO2 mesoporous microspheres: a novel selective photocatalyst

“…Titania (TiO2) has been regarded as one of the most efficient photocatalysts since the first report by Fujishima and Honda [3][4][5][6], because of its high catalytic activity, good stability and low toxicity. After that, huge progress towards improving the photocatalytic efficiency of TiO2 has been made [7], such as band-tailoring by element doping [8,9], constructing mesoporous and/or array structures [10][11][12][13], and plasmonic sensitizing [14,15]. Nevertheless, TiO2 is generally regarded as non-selective because the degradation of organic compounds on TiO2 is enabled by nonselective oxidizing agents (e.g., OH radical) [16].…”