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

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• 作者：Heechae Choi ; Dongbin Shin ; Byung Chul Yeo ; Taeseup Song ; Sang Soo Han ; Noejung Park ; Seungchul Kim
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：May 6, 2016
• 年：2016
• 卷：6
• 期：5
• 页码：2745-2753
• 全文大小：529K
• 年卷期：0
• ISSN：2155-5435

文摘

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 ((V_Ti-N_i)^3–) and the simultaneous substitutions of Ti by W and the nearest O by N ((W_Ti-N_O)⁺). The latter case induces highly localized shallow in-gap levels near the conduction band minimum (CBM) and the valence band maximum (VBM), whereas the (V_Ti-N_i)^3– defect complex yielded deep levels (1.9 eV above the VBM). Electronic structures suggest that (W_Ti-N_O)⁺ improves the photocatalytic activity of anatase by band gap narrowing, while (V_Ti-N_i)^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 (V_Ti-N_i)^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 (V_Ti-N_i)^3– and to improve photocatalysis.