A novel approach for the preparation of phase-tunable TiO2 nanocomposite crystals with superior visible-light-driven photocatalytic activity

Abstract

A series of novel TiO 2 nanocomposite crystals with superior visible-light-driven photocatalytic activity were successfully prepared using a soft chemical solution process involving direct reaction of aqueous H 2 O 2 with a 2-ethoxyethanol solution of tetraisopropyl titanate before calcination of the resulting peroxo-titanium complexes at 500 °C for 4 h. The synthesized TiO 2 samples are composed of anatase and rutile phases, and the ratio of rutile could be continuously tuned from 0 to 96% by altering the 2-ethoxyethanol volume. There are clear red-shifts in the UV-Vis absorption spectra and apparent band gap narrowing for the synthesized TiO 2 in comparison with Evonik P-25. The synthesized TiO 2 samples are found to be much more efficient for methylene blue degradation under visible-light irradiation. The optimized sample (2-ethoxyethanol: 5 ml; rutile in bulk: 46%) exhibits 5-fold higher adsorption capacity and 3-fold higher photocatalytic activity than those of Evonik P-25 (λ ≥ 400 nm). Characterizations including X-ray diffraction and Raman spectroscopy reveal that the surface of the optimized TiO 2 sample only contains a small quantity of rutile. It is concluded that the surface phase composition and distribution of the TiO 2 nanocomposite crystals are essential to their greatly enhanced photocatalytic activities and strong adsorption capacities. In addition, the concentration of defects existing in the synthesized TiO 2 is also regarded to account for these enhanced properties. 采用新的化学溶液法, 通过不同体积的钛酸四异丙酯的2-乙二醇单乙醚溶液与一定浓度的H 2 O 2 水溶液直接反应并对生成的钛过氧化配合物进行焙烧, 制备了一系列TiO 2 光催化剂. 表征发现, 所得TiO 2 样品为金红石和锐钛矿的纳米复合晶体, 改变2-乙二醇单乙醚的体积可实现金红石相比例在0–96%广范围的调变.与商业二氧化钛P-25相比, 所得的TiO 2 紫外-可见光吸收谱出现明显红移, 间隙能降低, 在可见光照射下, 该样品对亚甲基蓝有良好的降解活性. 当2-乙二醇单乙醚的添加量为5 ml时, 所得样品体相中金红石相比例接近50%, 其光催化活性和吸附性能最好, 可分别是P-25的3倍和5倍. 拉曼光谱结合X射线衍射等表征结果表明, 该样品的表面仅含少量的金红石相. TiO 2 纳米复合晶表面晶相的组成和分布对其光催化降解亚甲基蓝的活性及其吸附能力有直接的影响. 另外, TiO 2 纳米复合晶的缺陷浓度也是增强其光吸收能力, 提高其可见光光催化活性的原因之一. A novel approach for synthesis of phase-tunable TiO 2 is provided. The phase composition, distribution, and amount of oxygen vacancies are regarded as critical to the obtained superior visible-light-driven photocatalytic activity.