摘要/Abstract
近年来, 多孔有机光催化材料因其结构和能带易调控、比表面积大和密度小等优点而备受关注. 本工作以Horner-Wadsworth-Emmons (HWE)反应为基础, 使用有机碱(t-BuOK)作为催化剂, 在室温下制备了两例C=C连接的三嗪共轭多孔聚合物, 分别是由双取代的苯环和三甲基三嗪通过C=C键连接的结构(TB-CPN)和由三苯胺和三甲基三嗪通过C=C键连接的结构(TT-CPN）, 将其用于光降解水产氢. 通过固体核磁和红外等结构表征, 证明C=C的存在, 说明结构的正确性. 然后, 在300 W氙灯光源下分别将两个聚合物作为光催化剂进行裂解水产氢研究, 其中, TT-CPN的产氢速率达到了913.3 μmol•h -1•g-1, 相同条件下, TB-CPN的产氢速率为TT-CPN的86%. 此外, TT-CPN在连续照射反应25 h后, 其光催化活性几乎没有降低, 表现出良好的光化学稳定性和可重复性. 本工作采用了一种低温、短反应时间的方法来合成C=C连接的共轭多孔聚合物, 用于可见光照射下光催化分解水制氢, 期望为多孔聚合物的设计合成提供新的方案.
关键词: 低温合成, 烯烃连接, 多孔聚合物, 光催化, 析氢
Global energy storage and environmental pollution have received increasing attention, and finding sustainable clean energy to replace fossil fuels has become an urgent issue. Visible-light-driven photocatalytic water splitting can not only obtain clean hydrogen energy, but also can store solar energy. Therefore, great efforts have been put into research and it has consequently developed rapidly. In recent years, different types of photocatalysts, such as inorganic materials, metal complexes, organic dyes and porous organic networks, have been extensively explored. Among these photocatalysts, conjugated porous networks (CPNs) have attracted much attention due to their adjustable structures, high specific surface area and high structural stability. The band gap and the specific surface area of materials is significant to photocatalytic performance. Hence, exploring appropriate band gap and porosity of materials is the main challenge, which can be achieved by changing the reaction methods and reactants to adjust the materials structure. In this article, unsubstituted olefin-linked (C=C) CPNs through Horner-Wadsworth-Emmons (HWE) reaction have been designed, which are the structure of disubstituted benzene and trimethyltriazine connected by C=C bond (TB-CPN) and the structure of triphenylamine and trimethyltriazine connected by C=C bond (TT-CPN) respectively. In this method, organic base (t-BuOK) was used as a catalyst, and finished the reaction at room temperature, which cost less energy. The entire synthesis procedure takes relatively short time, compared with other polymeric means costing 72 h or 48 h. Firstly, the formation of olefin (C=C) bonds was characterized by Fourier transform infrared (FT-IR) spectroscopy. Next, the structure of the polymers was further confirmed by solid-state nuclear magnetic resonance. Nitrogen adsorption-desorption measurement was applied to examine the porosity of the polymers, it showed that TT-CPN has a larger specific surface area than TB-CPN. The band gap of TT-CPN and TB-CPN obtained by UV-Vis diffuse reflection spectra is 2.22 and 2.30 eV, respectively. After that, the two polymers were used as photocatalysts to investigate the visible-light-driven hydrogen evolution by water splitting. Of these, the porous polymer TT-CPN reveals a better photocatalytic behavior with a hydrogen evolution rate of 913.3 μmol•h -1•g-1. Under the same testing condition, the hydrogen evolution rate of TB-CPN was only 86% of TT-CPN. Besides, after TT-CPN was continuously irradiated under visible light for 25 h, its photocatalytic activity barely decreased, showing good photochemical stability and repeatability. In a word, in this article, a method with low-temperature and short reaction time was developed to synthesize C=C bond connected conjugated porous networks, and the polymers were used for efficient photocatalytic water splitting to produce hydrogen under visible light irradiation. This method may provide a new choice for the design and synthesis of porous polymers as photocatalysts.
Key words: low-temperature synthesis, olefin-linkage, conjugated porous networks, photocatalysis, hydrogen evolution
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