Abstract Titanium dioxide-based nanocomposite materials are the most widely used materials to enhance the photocatalytic activity of titanium dioxide (TiO2) due to their excellent light absorbing properties. However, the wide use of TiO2 is restricted by its large band gap. Doping TiO2 with iron (Fe) is one of the strategies that have been employed in order to narrow the band gap of TiO2, thus promoting its photocatalytic activity to the visible light region. In this work, new energy levels between the valence band and the conduction band were introduced by incorporating Fe in the TiO2 lattice resulting to an effective shift of the light absorption to the visible light region. On the other hand, the incorporation of NaF in the TiO2 lattice led to significant changes on its crystal phases from brookite-anatase to anatase-rutile phases. In this study, the hydrothermal synthesis route was combined with microwave heating as a smart pathway of reducing the synthesis cost by reducing synthesis temperature and time while achieving an efficient photocatalytic activity of the TiO2 nano-photocatalysts. XRD diffraction patterns demonstrated that a mixture of brookite-anatase was obtained, which was transformed to the anatase-rutile phases after doping TiO2 with Fe in the presence of NaF. Microscopic investigations further showed that the doped TiO2 nano-photocatalyts exhibited a spherical shape with an average particle size in the range of 10–20 nm. UV–Vis analysis showed that the indirect and direct band gap of Fe-doped TiO2 in the presence of NaF was significantly narrowed to 1.67–1.83 eV and 2.05–2.17 eV, respectively. The synergistic effect of NaF on the crystallinity of Fe-doped TiO2 calcined at 400 °C in air was demonstrated to form an anatase-rutile phase.

中文翻译：

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氟化钠 (NaF) 对通过微波辅助水热处理开发的 Fe 掺杂 TiO2 的结晶度和带隙的协同作用

摘要 二氧化钛基纳米复合材料由于其优异的吸光性能，是增强二氧化钛（TiO2）光催化活性的最广泛使用的材料。然而，TiO2 的广泛应用受到其大带隙的限制。用铁 (Fe) 掺杂 TiO2 是为了缩小 TiO2 的带隙，从而将其光催化活性提高到可见光区域而采用的策略之一。在这项工作中，通过在 TiO2 晶格中加入 Fe 来引入价带和导带之间的新能级，从而有效地将光吸收转移到可见光区域。另一方面，在 TiO2 晶格中掺入 NaF 导致其晶相从板钛矿-锐钛矿相到锐钛矿-金红石相发生显着变化。在这项研究中，水热合成路线与微波加热相结合，作为一种智能途径，通过降低合成温度和时间来降低合成成本，同时实现 TiO2 纳米光催化剂的有效光催化活性。XRD 衍射图表明，获得了板钛矿-锐钛矿的混合物，在 NaF 存在下用 Fe 掺杂 TiO2 后，该混合物转变为锐钛矿-金红石相。显微研究进一步表明，掺杂的 TiO2 纳米光催化剂呈球形，平均粒径在 10-20 nm 范围内。UV-Vis 分析表明，在 NaF 存在下，Fe 掺杂的 TiO2 的间接带隙和直接带隙分别显着缩小至 1.67-1.83 eV 和 2.05-2.17 eV。