构建窄禁带低价带TiO2光催化体系用于煤化工酚类水污染物的降解

The vast emission of highly toxic and hardly degradable phenolic wastewater from numerous coal chemical industrial enterprises in Inner Mongolia leads to an enormous environmental stress. The TiO2-based visible-light photocatalytic degradation of phenolic water contaminants driven by solar energy provides an effective solution for this problem. However, the wide bandgap of TiO2 is unfavorable for the high efficient use of solar energy. A reliable method to narrow the bandgap of TiO2 is raising the valence band via nonmetal doping or self-structural modification. However, the major drawback of valence band rising is the loss of oxidizing and degradative capacity of the photogenerated holes. This project proposes to tune the electronic structure of TiO2 by using electron-withdrawing ligands, which is capable of narrowing the bandgap and enhancing the oxidization capacity of the photogenerated holes by pulling the valence band down. Therefore, the visible-light photocatalytic degradative capacity of modified TiO2 for phenolic contaminants is enhanced, and the recombination of photogenerated charge carriers is inhibited by the electron-withdrawing effect. This research applies theoretical calculation to assist the catalyst design, structure simulation and energy band structure analyses. Meanwhile, a variety of experiments and characterization are employed to investigate the bond structures of different electron-withdrawing ligands with TiO2, as well as the consequent influences on the energy band structure, quantum efficiency, and photocatalytic performance. Based on the combined theoretical and experimental study, the mechanism and fundamental understanding of electron-withdrawing ligands for the energy band structure tuning of TiO2 are systematically elucidated. The outcomes of this research are expected to provide theoretical reference for the practical application of photocatalysis.

内蒙地区众多煤化工企业产生的大量高毒性难降解含酚废水带来了巨大的环境压力，太阳能驱动TiO2可见光催化降解酚类污染物是解决这一问题的有效途径。但TiO2禁带较宽不利于太阳能的高效利用，通过非金属掺杂或自结构修饰提升价带是一个缩减TiO2禁带的可靠方法，但价带提升的主要缺点是光生空穴氧化、降解能力的损失。本项目提出利用吸电子配体调控TiO2电子结构，在缩减禁带的同时诱导价带降低以增强光生空穴的氧化性，强化修饰后TiO2对酚类污染物的可见光催化降解性能，同时利用吸电子配体的吸电子效应促进光生载流子分离。研究拟采用理论计算辅助进行催化剂设计、结构模拟和能带结构分析，同时采用多种实验和表征方法，研究不同吸电子配体与TiO2的键合结构，及其对能带结构、量子效率和光催化性能的影响。通过理论与实验结合，系统揭示吸电子配体对TiO2能带结构的调控机制和基本规律，研究结果可为光催化技术的实用化提供理论参考。

TiO2光催化技术在环境污染治理领域有着广阔的应用前景，但TiO2的宽带隙不利于光能的高效利用。因此，发展易操作的、低成本的能带调控策略是TiO2光催化技术产业化的关键。本项目提出采用吸电子配体调控TiO2的能带结构，构建窄禁带、低价带TiO2光催化体系用于酚类水污染物的降解，研究能带调控机制和光催化机理。主要研究进展如下：. （1）发现吸电子基团（如羧基、硫酸根）配位可引起价带边下降，并诱导带隙中的缺陷态（如氧空位、碳掺杂）形成价带尾态，导致窄禁带、低价带TiO2的形成。同时，吸电子基团的配位还可有效促进光生载流子的分离。. （2）发现溶解的O2分子能够化学吸附在富含氧空位缺陷的TiO2表面，引起表面氢键增强和共吸附H2O分子和-OH基团的大量增加。共吸附使O2分子的化学吸附更加稳定，并显著促进了光生载流子的分离和光生空穴的表面积累，这有效地增强了光生空穴对酚类的直接氧化降解。. （3）发展了一种利用羧基化碳物种与氧空位缺陷的协同效应，构建窄禁带、低价带TiO2光催化体系的方法。所制备的光催化剂具有良好的宽光谱响应性能，在660 nm光照下对苯酚仍有近30%的降解率，在740 nm光照下对苯酚仍有降解活性。并且，该光催化剂可以高效降解和矿化煤化工废水中的多种酚类污染物。在450 nm LED光照下降解120 min后，各种酚类的降解率接近100%，矿化率均在75%以上。采用多类型碳物种掺杂、修饰可显著增强该光催化体系的稳定性。粉煤灰负载可进一步增强该光催化剂的降解性能和可分离回收性能。. （4）发展了一种“熏烟法”一步制备“纳米硫/硫酸根-P25”Ⅱ型异质结光催化剂的方法，该异质结在可见光下具有良好的光催化降解活性和大肠杆菌灭菌性能。. 本项目研究结果可为窄禁带、低价带TiO2光催化体系的构建和煤化工酚类水污染物的高效光催化降解提供科学依据，具有显著的科学意义。.