同时可控的掺杂位点和W-N共掺杂TiO <sub>2</sub>光催化剂的活性,ACS Catalysis

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同时可控的掺杂位点和W-N共掺杂TiO ₂光催化剂的活性
ACS Catalysis ( IF 11.3 ) Pub Date : 2016-03-25 00:00:00 , DOI: 10.1021/acscatal.6b00104
Heechae Choi ₁ , Dongbin Shin ₂ , Byung Chul Yeo ₁ , Taeseup Song ₃ , Sang Soo Han _{1,

4} , Noejung Park ₂ , Seungchul Kim _{1,

4}

Affiliation

钨-氮（W-N）共掺杂可通过利用可见光增强锐钛矿型TiO ₂纳米颗粒的光催化活性。但是，掺杂效果在很大程度上取决于煅烧或退火条件，因此，大量生产质量控制的光催化剂仍然是一个挑战。使用密度泛函理论（DFT）热力学和时变DFT计算（TDDFT），我们研究了锐钛矿型TiO ₂中N掺杂和W–N共掺杂的原子结构，以及热处理条件的影响。我们发现W和N掺杂剂主要构成两个复杂的结构：在三电荷态（（V _Ti -N _i）^3–），同时用W和Ti替换最近的O，用N（（W _Ti -N _O）⁺）同时替换最近的O。后一种情况会在导带最小值（CBM）和价带最大值（VBM）附近产生高度局部的浅能隙水平，而（V _Ti -N _i）^3–缺陷复合物会产生较深的能级（高于VBM 1.9 eV））。电子结构表明（W _Ti -N _O）⁺通过带隙变窄提高了锐钛矿的光催化活性，而（V _Ti -N _i）^3–间隙内状态辅助的电子-空穴复合降低了活性，这解释了实验观察到的与深能级相关的光子吸收。通过TDDFT的实时传播，我们证明（V _Ti -N _i）^3–的存在在比TiO的平带寿命短得多的时间内将激发的电子从导带吸引到局部带隙状态₂。根据这些结果，我们建议在富氮和贫O条件下进行煅烧可消除（V _Ti -N _i）^3–引起的深能级状态，并改善光催化作用。

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

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.

更新日期：2016-03-25

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