利用镧系离子掺杂延长{001}/{101}晶面共暴露的TiO_2纳米片电荷分离态以增强其光催化产氢性能（英文）
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摘要
随着工业化的快速发展,化石燃料等不可再生能源的快速消耗,人类将面临不可预测的能源危机.寻找有效的方法来解决能源短缺问题已成为当今的重要研究课题.氢能是一种可以替代化石燃料的清洁可再生能源.利用半导体光催化分解水制氢技术可以将太阳能转化为氢能.目前,在已开发的半导体光催化材料中, TiO_2因具有无毒、稳定、廉价等优点而备受光催化领域关注.但是,在实际应用方面, TiO_2的光催化效率受限于其低的光子利用率和较高的光生电子-空穴复合率.许多研究表明, TiO_2不同晶面的协同作用有利于光生载流子的迁移分离,并且适量的掺杂能够捕获光生电子,从而抑制其复合.而镧系元素因其特殊4f电子结构受到广泛的关注.采用物理或化学方法将镧系离子引入TiO_2晶格中,可以影响光生电子和空穴的动力学过程,延长光生载流子的分离状态,从而提高光催化活性.本文通过简单溶剂热法成功合成了镧系离子掺杂{001}/{101}面共暴露的TiO_2纳米片.X-射线粉末衍射(XRD)、X-射线光电子能谱(XPS)和高分辨透射电子显微镜(HRTEM)的表征结果证明了镧系离子选择性掺杂在TiO_2纳米片{101}面上.结合紫外可见吸收光谱、稳态荧光、瞬态荧光衰减曲线、光电流及莫特-肖特基曲线等手段对镧系离子掺杂TiO_2光催化剂进行了表征,结果表明,镧系离子掺杂TiO_2纳米片增强了对光的吸收,同时延长光生载流子的分离状态,阻碍光生电子和空穴的复合.考察其光催化分解水制氢的性能.研究表明,在相同掺杂量(0.5 mol%RE~(3+)=Ho~(3+), Er~(3+), Tm~(3+), Yb~(3+), Lu~(3+))的TiO_2纳米片中, Yb~(3+)-TiO_2纳米片光催化剂具有优异的产氢活性,在模拟太阳光照射1 h后产氢量是纯TiO_2的4.25倍.同时讨论了不同浓度助催化剂Pt作用下的Yb~(3+)-TiO_2纳米片产氢效果,当Pt含量量为0.3wt%时,光解水产氢活性最佳, Pt/Yb~(3+)-TiO_2纳米片的产氢量是Yb~(3+)-TiO_2的2倍,纯TiO_2的8.5倍.光催化分解水产氢活性的显著提高可以归因于光生电子-空穴对在TiO_2纳米片{001}/{101}面的快速分离,以及镧系离子4f电子轨道对电子的捕获和杂质能级的产生减小了禁带宽度,这不仅延长了光生载流子的分离状态,增加了H~+还原成H_2的机会,而且还可以拓展可见光的吸收范围.可见,利用镧系离子掺杂TiO_2和共暴露{001}/{101}面协同作用是一种实现TiO_2基光催化活性提高的有效方法之一.镧系离子掺杂的策略对提高半导体纳米材料的光催化活性有显著的影响,可能在光催化、光电化学和太阳能电池领域有更广泛的应用.
Ultrathin TiO_2 nanosheets with coexposed {001}/{101} facets have attracted considerable attention because of their high photocatalytic activity. However, the charge-separated states in the TiO_2 nanosheets must be extended to further enhance their photocatalytic activity for H_2 evolution. Herein, we present a successful attempt to selectively dope lanthanide ions into the {101} facets of ultrathin TiO_2 nanosheets with coexposed {001}/{101} facets through a facile one-step solvothermal method. The lanthanide doping slightly extended the light-harvesting region and markedly improved the charge-separated states of the TiO_2 nanosheets as evidenced by UV-vis absorption and steady-state/transient photoluminescence spectra. Upon simulated sunlight irradiation, we observed a 4.2-fold enhancement in the photocatalytic H_2 evolution activity of optimal Yb~(3+)-doped TiO_2 nanosheets compared to that of their undoped counterparts. Furthermore, when Pt nanoparticles were used as cocatalysts to reduce the H_2 overpotential in this system, the photocatalytic activity enhancement factor increased to 8.5. By combining these results with those of control experiments, we confirmed that the extended charge-separated states play the main role in the enhancement of the photocatalytic H_2 evolution activity of lanthanide-doped TiO_2 nanosheets with coexposed {001}/{101} facets.
Ultrathin TiO_2 nanosheets with coexposed {001}/{101} facets have attracted considerable attention because of their high photocatalytic activity. However, the charge-separated states in the TiO_2 nanosheets must be extended to further enhance their photocatalytic activity for H_2 evolution. Herein, we present a successful attempt to selectively dope lanthanide ions into the {101} facets of ultrathin TiO_2 nanosheets with coexposed {001}/{101} facets through a facile one-step solvothermal method. The lanthanide doping slightly extended the light-harvesting region and markedly improved the charge-separated states of the TiO_2 nanosheets as evidenced by UV-vis absorption and steady-state/transient photoluminescence spectra. Upon simulated sunlight irradiation, we observed a 4.2-fold enhancement in the photocatalytic H_2 evolution activity of optimal Yb~(3+)-doped TiO_2 nanosheets compared to that of their undoped counterparts. Furthermore, when Pt nanoparticles were used as cocatalysts to reduce the H_2 overpotential in this system, the photocatalytic activity enhancement factor increased to 8.5. By combining these results with those of control experiments, we confirmed that the extended charge-separated states play the main role in the enhancement of the photocatalytic H_2 evolution activity of lanthanide-doped TiO_2 nanosheets with coexposed {001}/{101} facets.
引文
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[49]Z. Y. Zhang, Y. Z. Huang, K. C. Liu, L. J. Guo, Q. Yuan, B. Dong, Adv.Mater., 2015, 27, 5906–5914.
[50]Z.Y. Zhang, X. Y. Jiang, B. K. Liu, L. J. Guo, N. Lu, L. Wang, J. D. Huang,K. C. Liu, B. Dong, Adv. Mater., 2018, 30, 1705221.
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