多元量子点能级有序异质结构敏化改性石墨相氮化碳光催化性能研究

Semiconductor photocatalysis techinique can transform the low density solar energy into the chemical energy of a high density by utilizing solar light to drive chemical reaction, and thus is believed one promissing route to resolving the world-wide energy and enviromental crisis. As a photocatalyst of polymeric semiconductor, metal-free graphitic carbon nitride (g-C3N4) possess advantageous in visible-light-active, turntable semiconductor band structure, good stability, and relatively low-cost. Nevertheless, bare g-C3N4 suffers from high exciton binding energy, high electron–hole recombination rate, low quantum efficiency, and insufficient visible light absorption. These drawbacks seriously limit its photocatalytic performance. In this proposal, we proposed a new route to modify the photocatalytic activity of g-C3N4 by using multivariate quantum dot heterojunctions with aligned energy level. We first design and prepare graphene and Nd2X3(X=S,Se,Te) quantum dots having a more narrow band gap and lower band-edge position than those of g-C3N4, and then use them as photosensitizer to construct g-C3N4 based heterojunction photocatalyst by using a layer-by-layer techinique. based on the well-arranged energy level alignment and well maching of each component energy level, it is hoped a combination of much more efficient separation of photo electrons, lower fraction of the photon energy loss, improved quantum efficiency and a more widen solar energy absorption could be achived. The expected achievement will offer a new route to develop a high performance g-C3N4 photocatalyst

半导体光催化技术利用太阳光驱动化学反应，将低密度太阳能转化为高密度化学能, 被认为是解决当前能源和环境危机的有效途径。石墨相氮化碳（g-C3N4）光催化剂不含金属组分，具有可见光催化活性，能带结构易于调控、化学稳定性好、成本低廉，但其激子结合能高、电子-空穴复合严重、量子效率低，对太阳光利用不够充分。本项目提出“采用能级有序的多元量子点异质结构敏化改性g-C3N4光催化性能”的新思路。拟合成石墨烯量子点（GQDs）和Nd2X3(X=S, Se, Te) 型半导体量子点作为敏化剂，按照其带边能级高低次序与g-C3N4逐层复合，构建能级有序的异质结复合光催化剂，基于各组分间的能级匹配和能级排列以期实现催化剂光生电子快速转移、降低光生电荷在传输过程中的损耗、提高量子效率，拓宽对太阳光谱的响应范围，增强g-C3N4光催化活性，为g-C3N4的光催化性能改性提供新的方法和思路。

当前，环境污染和能源短缺问题日益严峻。半导体光催化技术利用太阳能驱动化学反应，为解决能源危机和环境污染问题提供了有效途径。g-C3N4不含贵金属元素，成本低廉、化学及热稳定性好，具有良好的光吸收性能及可见光活性。然而，g-C3N4比表面积小、电子转移和输送能力差、光生电子-空穴复合率高，对太阳光利用不够充分，限制其在光催化领域中的应用。针对以上问题，本项目围绕g-C3N4 纳米化剥离、异质原子掺杂与敏化改性等开展了多方面研究工作。主要研究内容及成果有：（1）利用98% H2SO4强的质子化作用与水合放热效应，实现了g-C3N4快速剥离，发现不但可将其剥离成纳米片还可得到纳米带，质子化剥离后的g-C3N4禁带宽度增大、紫外吸收增强，电子-空穴复合受到抑制，纳米带2h内对水溶液中的亚甲基蓝（MB）的降解率可接近100%，紫外光催化性能明显优于体相g-C3N4。 该成果实现了对体相g-C3N4的快速高效剥离，丰富了对g-C3N4 化学性质和光吸收性能的认识。（2）采用球磨法将不同g-C3N4前驱物与金属银复合，制备了具有不同比表面积的Ag掺杂g-C3N4复合光催化剂，引入了C-Ag键，拓宽了光吸收范围，降低了光生电子-空穴对的复合率，有效提高了g-C3N4可见光降解水体中有机染料的光催化活性，为金属掺杂g-C3N4复合光催化剂的制备提供了新的方法和思路。（3）将金属掺杂与超分子自组装相结合，制备Ag掺杂g-C3N4多孔微球， 提高了复合光催化剂的比表面积，同时引入C-Ag键增强的可见光吸收能力，促进了光生电子和空穴快速分离，使光催化性能得到进一步提升。（4）将尿素和对氨基苯甲酸进行共结晶，通过高温煅烧制备C掺杂g-C3N4复合光催化剂，增强对可见光的吸收，提高了导电性，促进了对光生电荷的转移和分离，有效提高了对水溶液中的亚甲基蓝的可见光催化降解活性。（5）分将酞菁铜(CuPc)、酞菁钴(CoPc)和酞菁锌（ZnPc）等作为光敏化剂，采用水热法与g-C3N4复合，制备了g-C3N4/酞菁复合光催化剂，拓宽了g-C3N4对可见光的吸收范围， g-C3N4/ZnPc对燃油中噻吩的氧化脱除率可达到84.4% ，对水溶液中甲基橙的降解率大于93%, 显著优于纯的g-C3N4。