苝酰亚胺（PDI）是一类光吸收范围宽、化学稳定性和热稳定性强、光电转换效率高、可修饰性丰富的有机材料，在光催化应用方面也得到迅速发展。但也存在载流子复合率高、催化位点缺乏、物质利用效率低等问题。本文围绕PDI高分子光催化剂的光生电荷分离传输与能带结构调控，展开一系列原创性研究。以污染物净化、有机物高产率高选择性氧化反应为应用模型，系统阐释了催化剂结构与催化性能的关系。制备了全光谱吸收三嗪-PDI高分子光催化剂。偶极增大与结晶性提高，增强了内建电场，促进了光生载流子的产生和分离，为光生电荷的快速传输提供了通道。三嗪-PDI的可见光催化苯酚降解速率0.191 h-1，分别是g-C3N4和自组装超分子PDI的12.7和2.2倍。同时，三嗪-PDI深入的价带位置（1.66 V相对于RHE）提高了矿化率，24小时总有机碳去除率达到79%，比自组装超分子PDI高38%。另外，三嗪-PDI还可将吲哚转化为吲哚-3-硫氰酸酯，条件温和产率较高，避免了贵金属催化剂与高温高压等极端条件的使用。此工作给出了PDI光催化剂的内建电场调控的手段。光催化剂的氧化能力强，并不意味着可以满足一切需求。制备了具有中等氧化能力的超薄三苯胺-PDI高分子可见光催化剂。在室温，环境空气和420nm可见光照射下，三苯胺-PDI将1,2,3,4-四氢异喹啉氧化为3,4-二氢异喹啉，转化率为90%，选择性为92%。选择性远高于传统N-溴代丁二酰亚胺氧化方法的60%，并且光催化剂可回收利用。高选择性归因于给电子结构三苯胺的引入，改变了催化剂的价带位置，减弱氧化性，从而提高选择性。价带电势1.10V（相对于RHE）与四氢异喹啉氧化成二氢异喹啉的电位相匹配，避免了过度氧化并提高了选择性。此外，该催化体系以空气为绿色氧化剂、适度的氧化能力的特点，避免了副产物的形成以及分离和纯化的困难。纯的PDI对活泼底物表现良好的氧化性能，但对醇类底物效果不佳。将NiO助催化剂负载到尿素-PDI（UPDI）表面，构筑复合光催化剂。可见光催化苯甲醇氧化到苯甲醛的产率为87%，远高于UPDI的5%。NiO助催化剂的作用在于：促进光生空穴传输到催化剂表面以氧化醇类底物；NiO可促进醇α-H攫取反应，使醇类底物生成碳自由基，参与反应过程。富电子醇类衍生物的产率高于缺电子醇类衍生物。该工作为现有的有机光催化剂的性能突破提供了可行的途径。
Perylene diimide (PDI) is a seiries of organic materials with wide light-absorption range, strong chemical and thermal stability, high photoelectric conversion efficiency, and rich modifiable properties. It has also been rapidly developed in photocatalytic applications. However, there are also problems such as high carrier recombination rate, lack of catalytic sites, and low reactant utilization efficiency. In this paper, a series of original researches are carried out on the photo-generated charge separation, transport and band structure regulation of PDI polymer photocatalysts. Taking the purification of pollutants and the high-yield and high-selective oxidation reaction of organics as application models, the relationship between structure and performance of photocatalysts is systematically disclosed. A full-spectrum triazine-PDI polymer photocatalyst was prepared. Enlarged dipole and increased crystallinity strengthen the built-in electric field, promote the generation and separation of photo-generated carriers, and provide a channel for the fast transfer of photo-generated charges. Under visible-light irradiation, degradation rate of phenol by triazine-PDI was 0.191 h-1, 12.7 and 2.2 times that of g-C3N4 and self-assembled supramolecular PDI, respectively. Meanwhile, deep position of valence band of triazine-PDI (1.66 V vs RHE) improves the mineralization rate, and TOC removal rate reaches 79% in 24 h, 38% higher than self-assembled supramolecular PDI. In addition, triazine-PDI can also convert indole into indole-3-thiocyanate, with mild conditions and higher yield, avoiding the use of precious metal catalysts and extreme conditions such as high temperature and high pressure. This work provides a feasible way of controlling the built-in electric field of the PDI photocatalysts. Strong oxidation ability of photocatalyst does not indicate that it can meet all needs. An ultra-thin triphenylamine-PDI polymer photocatalyst with moderate oxidation ability was prepared. At room temperature, ambient air and 420 nm visible light irradiation, triphenylamine-PDI oxidizes 1,2,3,4-tetrahydroisoquinoline to 3,4-dihydroisoquinoline, the conversion rate is 90%, and the selectivity is 92%. The selectivity is much higher than 60% of the traditional N-bromosuccinimide oxidation method, the photocatalyst can be recycled as well. High selectivity is attributed to the introduction of the electron-donating structure of triphenylamine, which changes the position of the valence band of PDI photocatalyst, weakens the oxidation ability, thus improves the selectivity. Potential of valence band of 1.10V (vs RHE) matches the potential for oxidation of tetrahydroisoquinoline to dihydroisoquinoline, avoiding excessive oxidation and improving selectivity. In addition, the catalytic system uses air as a green oxidant and has a moderate oxidation ability, which avoids the formation of byproducts and the difficulty of separation and purification. Pure PDI shows good oxidation performance on active substrates, but has poor effect on alcoholic substrates. Cocatalyst NiO was loaded on the surface of urea-PDI (UPDI) to construct a composite photocatalyst. The yield of visible-light-driven oxidation of benzyl alcohol to benzaldehyde was 87%, much higher than the 5% of UPDI. The role of caocatalyst NiO is to promote the transport of photo-generated holes to the surface of photocatalyst so as to oxidize the alcohol substrate; NiO can promote the alcohol α-H abstraction, so that the alcohol substrate generates carbon-centered free radicals and participates in reaction process. Yields of electron-rich alcohol derivatives are higher than that of electron-deficient ones. This work provides a feasible way for the performance breakthrough of the existing organic photocatalysts.
