利用太阳能和半导体光催化剂将温室气体CO₂还原成有价值的化工原料，在缓解温室效应的同时实现CO₂的资源化利用，是当前众多研究者关注的热点课题之一。石墨相氮化碳(g-C₃N₄)作为一种新型的非金属半导体光催化剂，备受关注。然而，光生载流子容易复合、光吸收性能和活性位点有限等缺点限制了其光催化还原二氧化碳的效率。针对上述缺点，本文开发一种高活性、稳定、经济的复合催化剂，有效提高了g-C₃N₄光催化还原CO₂的性能，为设计和开发高效还原CO₂的光催化剂做出了有益的探索。

由于传统方法制备的无定形g-C₃N₄结构中存在表面缺陷和氢键，光生载流子的分离效率较低，导致其光催化活性较弱。目前，提高无定形g-C₃N₄的结晶度是解决这一问题的理想途径之一。本文首先针对无定型碳氮严重制约其高效光催化还原CO₂的局限，首先采用熔融盐法对无定型碳氮进行结晶化处理，然后在此基础上，采用三聚氰胺固相缩聚法制备非金属S元素掺杂的石墨相氮化碳(SCN)，对能带结构进行掺杂。并结合催化性能，探索最佳掺S比例。实验证明掺杂硫元素的催化性能相比晶体g-C₃N₄显著提高，在反应8 h内产物CO的平均产率达到6.415 μmol g^-1 h^-1，是未掺杂的5.4倍。

其次在制备过程中，发现CCN粉末在水中易形成胶体，经过冷冻干燥处理后，形成碳氮气凝胶的层状结构，比表面积大幅度增加，孔隙结构增多，而多孔结构具有优异的气体吸附储藏优势，继而针对g-C₃N₄晶体材料结合催化性能，探索用最少比例的石墨相碳氮制备稳定的气凝胶。实验证明气凝胶的催化性能显著提高，CO平均产率达到25.7 μmol g^-1 h^-1，是CCN粉末的21.7倍。

最后设计高催化活性的CN_X/Ru@Cu-HHTP异质结复合半导体光催化剂。构筑g-C₃N₄基typeⅡ型异质结复合半导体不仅有助于光生载流子的分离和迁移，而且可以保留各自较强的氧化能力或还原能力，能显著提高g-C₃N₄光催化还原CO₂产物的产量。实验证明掺复合后CN_X/Ru@Cu-HHTP催化性能显著提高，CO平均产率达到41.12 μmol g^-1 h^-1，是未复合材料BDCNN的34.2倍。

Using solar energy and semiconductor photocatalysts to reduce the greenhouse gas CO₂ into valuable chemical raw materials and realize the resource utilization of CO₂ while alleviating the greenhouse effect is one of the hot topics that many researchers are currently paying attention to. g-C₃N₄(CCN), as a new type of metal-free semiconductor photocatalyst, has attracted much attention. However, the shortcomings of photogenerated carriers such as easy recombination, light absorption performance, and limited active sites limit their photocatalytic carbon dioxide reduction efficiency. Given the above shortcomings, this paper develops a highly active, stable, and economical composite catalyst, which effectively improves the performance of g-C₃N₄ photocatalytic reduction of CO₂, and makes useful explorations for the design and development of photocatalysts for efficient CO₂ reduction.

Due to the surface defects and hydrogen bonds in the amorphous g-C₃N₄ structure prepared by traditional methods, the separation efficiency of photogenerated carriers is low, resulting in weak photocatalytic activity. At present, improving the crystallinity of amorphous g-C₃N₄ is one of the ideal ways to solve this problem. In this paper, in view of the limitations of amorphous carbon and nitrogen that seriously restrict its efficient photocatalytic reduction of CO₂, the amorphous carbon and nitrogen method is first crystallized by molten salt, and then on this basis, non-metallic S element doped graphitic carbon nitride (SCN) is prepared by melamine solid phase polycondensation method, and the band structure is doped. Combined with catalytic performance, the optimal doping ratio was explored. Experiments show that the catalytic performance of doped sulfur is significantly improved compared with crystal g-C₃N₄, and the average yield of CO within 8 h of the reaction reaches 6.415 μmol g^-1 h^-1, which is 5.4 times that of undoped.

Secondly, in the preparation process, it was found that CCN powder was easy to form colloids in water, and after freeze-drying treatment, the layered structure of carbon nitrogen aerogels was formed, the specific surface area was greatly increased, the pore structure increased, and the porous structure had excellent advantages of gas adsorption storage, and then the preparation of stable aerogels with the least proportion of graphite phase carbon and nitrogen was explored for the combined catalytic performance of g-C₃N₄ crystal materials. Experiments show that the catalytic performance of aerogels is significantly improved, and the average CO yield reaches 25.7 μmol g^-1 h^-1, which is 21.7 times that of CCN powder.

Finally, a CN_X/Ru@Cu-HHTP heterojunction composite semiconductor photocatalyst with high catalytic activity was designed. The construction of g-C₃N₄-based typeⅡ heterojunction compound semiconductor not only helps the separation and migration of photogenerated carriers but also can retain their strong oxidation or reduction ability, which can significantly improve the efficiency of g-C₃N₄ photocatalytic reduction of CO₂ products. Yield. Experiments show that the catalytic performance of CN_X/Ru@Cu-HHTP is significantly improved after compounding, and the average CO yield reaches 41.12 μmol g^-1 h^-1, which is 34.2 times that of uncomposites BDCNN_X.