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将光化学辅酶再生与氧化还原酶的催化过程相偶联，构建生物催化的人工光合作体系，合成人类所需的燃料或化学品，对于解决环境和能源问题具有重要意义。其中，制备和应用高效的可见光活性催化剂是实现这一过程的关键。石墨相氮化碳(g-C3N4)是一种具有可见光响应活性的聚合物半导体材料，可以作为光催化剂应用于辅酶再生及其他领域。但是存在光生电子-空穴易复合、量子产率较低等问题。为了解决上述问题，本文采用超声辅助水热法将WS2负载在g-C3N4上，制备一种WS2/g-C3N4复合催化剂，并通过与甲酸脱氢酶、甲醛脱氢酶和乙醇脱氢酶三种酶催化的级联反应相偶联，构建人工光合体系，实现CO2到甲醇的转化。主要研究内容和结果如下：1）通过超声辅助水热法制备了一系列含不同比例WS2的WS2/g-C3N4复合材料，并通过不同的光催化实验检测了它们的光催化性能。实验结果表明，5 wt% WS2/g-C3N4的光催化性能最高，4小时内催化辅酶再生产率可以达到35%左右，大约是单独的g-C3N4的3-4倍。通过与甲酸脱氢酶、甲醛脱氢酶和乙醇脱氢酶三种酶催化的级联反应相偶联，10小时内甲醇产率为372.1 μmolh-1gcat-1，达到了单纯g-C3N4的7.5倍的效率。此外，罗丹明降解试验也表明5 wt% WS2/g-C3N4的光催化性能最高，可以在1小时内完全降解10 mg/L的RhB溶液，降解速率是单独g-C3N4的2.6倍。从这些实验证明了WS2掺杂可以显著提升g-C3N4的光催化性能。2）通过XRD、FT-IR、TEM、EDS、XPS、BET、TGA、PL等多项表征手段对WS2，g-C3N4以及所制备的WS2/g-C3N4复合催化剂的理化性质进行了系统的表征，并对复合催化剂活性提高的机理进行了分析。推测WS2与g-C3N4之间形成一种异质结结构，由于g-C3N4的价带和导带均高于WS2，而WS2的导带高于g-C3N4的价带，因此在光催化反应过程中，g-C3N4导带上的激发电子将会迁移到WS2的导带，而WS2价带上的空穴会移动到g-C3N4的价带，从而促进了光生电子和空穴的有效分离，使光催化的效率得到提高。;Construction of biocatalayzed artificial photosynthetic system by incorporating the photochemical regeneration of coenzyme NADH with the redox enzymatic process to produce various fuels and chemical has an important significance for solving environmental and energy problems. To achieve this, fabricating and employing catalysts with high visible light activity was the key point. Graphite phase carbon nitride (g-C3N4) is a kind of polymeric semiconductor material with excellent visible light response, which enable g-C3N4 a wide range application as photocatalyst in photocatalytic coenzyme regeneration and other fields. However, due to the problems such as easy electron-hole recombination and low quantum yield of g-C3N4, the further application of the material is limited. In order to solve these problems, WS2/g-C3N4 composites were prepared by load WS2 on g-C3N4 through a simple ultrasonic-assisted hydrothermal method. The WS2/g-C3N4 composites was then used for photocatalytic regeneration of NAD+ to NADH, which were then coupled with dehydrogenases for sustainable bioconversion of CO2 to methanol under visible light irradiation. The main research work is as follows:1) A series of WS2/g-C3N4 composites with different ratios of WS2 were prepared by simple ultrasonic-assisted hydrothermal method. Their photocatalytic performance was evaluated by NADH photoregeneration and rhodamine B degradation experiments. The experimental results show that the photocatalytic performance of 5 wt% WS2/g-C3N4 is the highest, and the NADH regeneration yield reached about 35% within 4 hours, which was about 3-4 times higher that of pure g-C3N4. By coupling this NADH photoregeneration process with the cascade enzymatic CO2 reduction reaction catalyzed by formic acid dehydrogenase, formaldehyde dehydrogenase and alcohol dehydrogenase, a methanol productivity reached to 372.1 μmolh-1 gcat-1, which is 7.5 times that obtained using pure g-C3N4. For further application demonstration, the activity of WS2/g-C3N4 composite catalyst toward photodegradation of Rhodamine B (RhB) was evaluated. RhB removal ratio approaching 100% was achieved in 1 hour by using the WS2/g-C3N4 composite catalyst with 5 wt% of WS2, at an apparent degradation rate approximately 2.6 times higher than that of pure g-C3N4.2) To explore the mechanism accounting for the enhancement in the activity of the WS2/g-C3N4 composites, the morphological characteristics and physicochemical properties of g-C3N4, WS2, and the WS2/g-C3N4 composites were fully characterized by XRD, FT-IR, TEM, EDS, XPS, BET, TGA, PL, etc. It was speculated that a heterojunction structure was formed between WS2 and the g-C3N4. Considering the both the valence band and conduction band of g-C3N4 are higher than that of WS2, while the conduction band of WS2 is higher than the valence band of g-C3N4, upon light irradiation, the excited electrons on the conduction band of g-C3N4 will migrate to the conduction band of WS2, and the holes in the valence band of WS2 will move to the valence band of g-C3N4; thus recombination of electrons and holes was decreased and the photo-harvesting efficiency was enhanced.
|曾鹏. WS2/g-C3N4复合光催化剂的制备及在人工光合作用体系中的应用[D]. 中国科学院大学,2018.|
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