SiC空穴迁移率和光催化性能调控研究

Effective regulation of photogenerated charge's separation efficiency and migration rate remains a key scientific problem that has not yet been solved in photocatalytic science. Based on new idea improving the photocatalytic efficiency by regulating electron and hole's migration rate and direction, we take SiC as example to establish the theoretical model and calculation method of electron and hole's migration rate of simple semiconductor materials. Research contents include to study regulating law of electron and hole's migration rate in SiC influenced by doping metal and nonmetallic and different doping methods, to design and prepare the doped SiC with high hole migration rate, to evaluate its photocatalytic reduction of CO2 in water, and to establish basic principles regulating photocatalytic performance of semiconductor materials on expressing the relevance between relative migration rate of electrons and holes and its photocatalytic performance. In addition, we also explore the principle and method of regulating the efficiency of photoelectrons and holes separation by compounding SiC with another semiconductor material. This second semiconductor would be selected using theoretical calculation, so we could design and prepare high active heterogeneous structure, in which photogenerated electrons and holes are regulated to disperse respectively along the semiconductor with high mobility ratio. Under this study, we would reveal the relationship between material properties and migration rate, establish the theoretical model and clarify the mechanism of action. It would has important scientific and practical value for enriching the basic theory of photocatalysis, understanding the mechanism of photocatalysis, innovating the structure of photocatalytic materials, and obtaining high efficient photocatalytic materials.

有效调控光生电荷分离效率和迁移速率是光催化科学尚未解决的关键科学问题。项目基于调控电子和空穴迁移率和迁移方向提高光催化效率的新思路，拟以SiC为模型，建立简单半导体材料电子和空穴迁移率的理论模型和计算方法；研究金属和非金属掺杂及其掺杂方式对SiC电子和空穴迁移率的调控规律；设计制备高空穴迁移率的掺杂SiC；评价其对水中CO2光催化还原的性能；阐明电子和空穴迁移率相对大小与光催化性能的关系，确立据此调控半导体材料光催化性能的基本原理。此外，初步探索通过SiC与第二种半导体的复合来调控光生电子和空穴分离效率的原理和方法。结合理论计算选择第二半导体，设计和制备高活性异质结构，控制光生电子和空穴分别向高迁移率半导体方向分离；揭示材料性能与迁移率的关系；建立理论模型；阐明作用机理。本研究对于丰富光催化基础理论，理解光催化作用机理，创新光催化材料结构，获得高效光催化材料具有重要科学意义和实际价值。

以SiC和TiO2载流子迁移方向和速率调控为目标，通过表面改性、界面修饰及与其它半导体复合等方法，设计和制备出2类高活性异质结构光催化剂，并发现如下重要规律。（1）通过静电自组装技术用三维纳米晶碳化硅(3D-SiC)和二维纳米片硫化钼(2D-MoS2)构筑出一种万寿菊型纳米花。发现该3D-SiC/2D-MoS2复合物在可见光照射下表现高的甲烷和计量比氧气释放活性。优良的光催化性能是因为3D-SiC和2D-MoS2的Z-scheme复合是电子结构和迁移率的强强结合。CO2到CH4的还原发生在SiC组元上，而H2O到O2的氧化发生在MoS2组元上；SiC比MoS2有更负的导带和更快的电子迁移率，而MoS2比SiC有更正的价带和更快的空穴迁移率。进而，以SiC为主光催化剂，采用分步复合方法构筑了一种直接异质结和间接异质结复合串联的Z-scheme结构光催化剂Cu2O-Pt/SiC/IrOx，显著提高了CO2到HCOOH和H2O到O2的光催化效率。（2）在金红石基底(R)上光沉积金属Pt，然后用钛酸丁酯水解法沉积TiO2层，再经适当热处理将TiO2层转变为锐钛矿(A)，使纳米Pt颗粒内嵌于A/R异相结界面，构建出新型A/Pt/R结构光催化剂。发现该复合光催化剂表现出比纯A/R、Pt/A/R高27.2和2.5倍的光催化产氢活性，这归因于形成的反向串联肖特基结有效促进了光生电荷的分离与转移。这个新策略和原理进一步用准金属化合物Ni12P5代替Pt形成的A/Ni12P5/R所证实。另外，采用形变势能理论和密度泛函微扰+瓦尼尔插值方法建立了载流子迁移率计算模型；采用熔融盐法合成了对CO2还原具有高光催化活性的新型固溶体Zn2Ti1-xGexO4；项目在J. Am. Chem. Soc.、Nat. Commun、J. Catal.等学术期刊发表学术论文10篇，培养研究生3名。