摘要/Abstract

采用以太阳光为能源、半导体材料为催化剂的催化体系将胺类化合物转化为相应的亚胺类化合物的方法是一种理想的有机合成手段.为了探索这类反应更温和的反应条件及更清晰的反应机理，本工作以NH₂-MIL-68（In）和硫脲为前驱体制备了In₂S₃分级纳米管，并进一步采用热离子交换的方法制备了In₂S₃/CdIn₂S₄纳米管复合材料.采用粉末X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、高分辨透射电子显微镜（HRTEM）、紫外-可见漫反射光谱（UV-vis DRS）、荧光光谱（PL）和电化学阻抗谱（EIS）等分析手段对催化剂的结构、形貌、光电性质等进行了表征.实验结果显示，In₂S₃和CdIn₂S₄间有效异质结降低了In₂S₃/CdIn₂S₄复合材料的光生载流子的复合效率，使In₂S₃/CdIn₂S₄具有较高的催化活性.催化剂的活性测试实验结果证明，In₂S₃和CdIn₂S₄间有效异质结和分级结构间的协同作用使In₂S₃/CdIn₂S₄纳米复合材料可作为一种有效的光催化剂催化氧化苯甲胺的偶联反应.活性物种捕获实验证明该反应是由光生空穴（h⁺）引发的.此外，此研究发现苯甲胺的氧化偶联反应同时可以在氧气或氮气条件下发生，打破了该反应必须要有氧气参与的束缚，拓展了苯甲胺氧化偶联反应的适用范围.循环实验结果显示，催化剂可循环使用五次，证明该催化剂具有较好的稳定性.
关键词: NH₂-MIL-68(In), 分级纳米结构, 可见光催化, 苯甲胺偶联反应, 异质结
It is a more attractive strategy that the selective oxidation of amines to the corresponding imines driven by visible light and photocatalyst. However, it is still necessary to look further into the mechanism of the transformation. In order to advance a new green photocatalysts system under milder conditions, hierarchical In₂S₃ nanotubes, which maintained the mother skeleton of NH₂-MIL-68(In), was prepared from NH₂-MIL-68(In) and thiourea, and a cation exchange method was used to synthesize hierarchical In₂S₃/CdIn₂S₄ heterostructured composites. The structure, morphology and photoelectric properties of the catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), fluorescence spectroscopy (PL) and electrochemical impedance spectra (EIS) analysis. The results showed that the existence of heterojunction between In₂S₃ and CdIn₂S₄ could minimize the recombination rate of photogenerated electron-hole pairs, which made the In₂S₃/CdIn₂S₄ show superior catalytic activity. The results of the evaluated experiments under visible light illumination showed that lots of synergy existed between the hierarchical structure, and the heterostructure could help to enhance the efficiency of carriers transfer and separation, which resulting in a high photocatalytic efficiency of In₂S₃/CdIn₂S₄ nanohybrids for the oxidation coupling of benzyl amines to imines under visible light irradiation. Interestingly, the further investigation concerned to the reaction condition revealed that the product could be detected not only in air but also in N₂ conditions, which burst out of the restriction of the reported reaction conditions and made the condition of the conversion become milder. The possible photocatalytic mechanism for the transformation was investigated by a series of experiments which concerned to the catching of the active species. The results showed that the reason for the occurring of the reaction was initiated by the presence of the nitrogen-centered radical cations and the carbon-centered radicals which were induced by the photogenerated hole (h⁺) in the photocatalyst. As for these situations, the conditions for the conversion of benzyl amines to imines were milder than the reported ones ever. What's more, from our experiments, the catalysts can be recycled five times at least, which indicated good reusability of hierarchical In₂S₃/CdIn₂S₄ nanohybrids.
Key words: NH₂-MIL-68(In), hierarchical structure, visible-light photocatalysis, coupling of benzyl amines, heterostructure


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