The bulk heterostructuring of TiO₂via codoping with nonmetals still holds possibilities for the potential development of a visible light photocatalyst and for overcoming the obstacles bracketed with metal ion substitution. In particular, tridoping of C–N–S into TiO₂ was spotlighted with due consideration of its mesmerizing features like simultaneous and relatively low energy substitution of carbon, nitrogen and sulfur from the available precursors (thiourea, L-cystine and L-cysteine), stabilization of the anatase crystal structure, red shift in the band gap response towards the solar spectrum, cooperative interactions with these codopants, and the absence of any impure phase formation even at elevated temperature and with high doping density during the substitution process. Despite these flexibilities, accessible reports on C–N–S-TiO₂ are not extensive and the discussions presented are far from the relevant aspects of the doping mechanism. With the intention of shedding light on the pros and cons of C–N–S-TiO₂, this review is framed with the following viewpoints: (i) underscoring their beneficial effects in photocatalysis; (ii) underlining the doping mode of each dopant in the codoped system with respect to the reaction conditions; (iii) contradictions about the doping states of each dopant in the codoped system with reference to the previous literature; (iv) tentative discussion concepts like modifications of defect structures, dopant distribution, doping mode, mutual interferences among the dopants and crystallization kinetics in the course of codoping. The results emphasize that the codoping process involving carbon, nitrogen and sulfur is quite obfuscated as several doping modes are witnessed for each dopant, which are coupled to other factors like dopant diffusivity and solubility, extent of doping, dopant segregation at the surface, nature of the dopant precursor, unpredictable interactions of the dopant states, and interactive reactions between the dopant and titania precursor together with the annealing conditions. With critical analysis with reference to TiO₂, it is envisaged that thiourea is the best functional precursor to attain diverse doping states for nitrogen, and cationic and anionic doping states for carbon and sulfur, together with the formation of adsorbed sulfate anions. Future research must shed light on the dopant–dopant and dopant–lattice interactions followed by their synergism at the structure-electronic level to uncover the doping mechanism in the codoped systems.

中文翻译：

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C–N–S三掺杂进入TiO ₂基体以进行光催化应用：共掺杂过程中的观察，推测和矛盾

通过与非金属共掺杂进行的TiO ₂整体异质结构化仍为潜在开发可见光光催化剂和克服金属离子取代所带来的障碍提供了可能性。特别是，将C–N–S掺入TiO ₂中引起了人们的关注，特别是考虑到其令人着迷的特性，例如从可用的前体（硫脲，L-胱氨酸和L-半胱氨酸），锐钛矿晶体结构的稳定，带隙响应向太阳光谱的红移，与这些共掺杂物的协同相互作用以及在取代过程中即使在高温和高掺杂密度下也不存在任何不纯相的形成。尽管具有这些灵活性，但有关C–N–S-TiO _2的可获得的报道并不广泛，所讨论的内容与掺杂机制的相关方面相去甚远。旨在阐明C–N–S-TiO _2的优缺点，本综述从以下观点出发：（i）强调其在光催化中的有益作用；（ii）在反应条件下强调共掺杂体系中每种掺杂剂的掺杂方式；（iii）参考先前的文献，关于共掺杂体系中每种掺杂剂的掺杂状态的矛盾；（iv）初步讨论的概念，例如缺陷结构的修改，掺杂剂分布，掺杂模式，掺杂剂之间的相互干扰以及共掺杂过程中的结晶动力学。结果强调，涉及到碳，氮和硫的共掺杂过程非常模糊，因为每种掺杂剂都表现出几种掺杂模式，这与其他因素有关，例如掺杂剂的扩散性和溶解性，掺杂程度，表面的掺杂剂偏析，掺杂剂前驱体的性质，掺杂剂态的不可预测的相互作用以及掺杂剂和二氧化钛前驱体之间的相互作用以及退火条件。通过对TiO的严格分析_{如图2所示}，硫脲是获得氮的各种掺杂状态，碳和硫的阳离子和阴离子掺杂状态以及形成吸附的硫酸根阴离子的最佳功能性前体。未来的研究必须阐明掺杂剂-掺杂剂和掺杂剂-晶格的相互作用，以及它们在结构-电子水平上的协同作用，以揭示共掺杂系统中的掺杂机理。