With the aim of improving the visible-light photocatalytic activity of TiO₂, the structural, electronic and optical properties of bare and sulfur-doped g-C₃N₄/TiO₂ composites have been investigated as potential candidate materials. Both periodic DFT calculations for all structural and electronic properties and TD-DFT calculations which are carried out on finite clusters extracted from the periodic structures and embedded in an array of point charges devised to reproduce the periodic electrostatic environment have been performed. Two dopant positions were considered, and a systematic comparison of key properties of the composites and their isolated components was carried out to clarify the effect of S dopant and TiO₂ substrate. Overall, we find that both g-C₃N₄ and S-g-C₃N₄ can significantly modify TiO₂ properties. In particular, compared to TiO₂, the composites present an overall improved generation of electron–hole pairs and a decrease of their recombination rates, as well as an enhanced absorption in the visible region, but with distinct photocatalytic mechanisms for non-doped and doped composites. Although this suggests that all investigated composites appear in principle as good candidates to enhance solar light-driven photocatalytic activity of TiO₂, the dependence of the results on the doping position that we observed, which is difficult to control experimentally, indicates that S doping of g-C₃N₄ could be a delicate approach to producing g-C₃N₄/TiO₂-based composites with improved properties in an experimentally controlled and systematic way.

中文翻译：

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用于光催化应用的硫掺杂 g-C3N4/TiO2 锐钛矿 （101） 复合材料：基于 DFT 的计算研究


为了提高 TiO2 的可见光光催化活性，研究了裸露和硫掺杂 g-C3N4/TiO2 复合材料的结构、电子和光学性能，作为潜在的候选材料。已经执行了所有结构和电子特性的周期性 DFT 计算和 TD-DFT 计算，这些计算是在从周期性结构中提取的有限簇上进行的，并嵌入到旨在再现周期性静电环境的点电荷阵列中。考虑了两个掺杂剂位置，并对复合材料及其分离成分的关键性能进行了系统比较，以阐明 S 掺杂剂和 TiO2 基材的影响。总体而言，我们发现 g-C3N4 和 S-g-C3N4 都可以显着改变 TiO2 的性质。特别是，与 TiO2 相比，复合材料总体上提高了电子-空穴对的产生并降低了它们的复合速率，并在可见光区域增强了吸收，但对于非掺杂和掺杂复合材料具有不同的光催化机制。尽管这表明所有研究的复合材料原则上都是增强太阳光驱动光催化 TiO2 活性的良好候选者，但结果对我们观察到的掺杂位置的依赖性，这在实验上很难控制，这表明 g-C3N4 的 S 掺杂可能是一种微妙的方法，以实验控制和系统的方式生产具有改进性能的 g-C3N4/TiO2 基复合材料。