单质硫、硼光催化材料表面反应活性的理论研究

As a new class of wide visible-light-absorption elemental photocatalysts, alpha-sulfur and beta-boron are impractical for solar energy conversion due to their low photocatalytic activities. Normally, the exposed surfaces of elemental sulfur and boron are inert facets with extremely low surface energies, resulting in weak adsorption for the reactant molecules and difficult charge transfer between photocatalytsts and the reactant molecules, which is one of the key factors for the observed low photocatalytic activities in experiments. Considering the surface properties of elemental photocatalysts, we propose a novel approach to promote the photocatalytic activiy of elemental photocatalysts by surface modification (including heteroatom modification or interface composition with functionalized graphene or hexagonal boron nitride) based on our previous understanding, while keeping their intrinsic and highly efficient visible-light-absorption unchanged. Surface modification can induce surface polarization to increase the surface energy and the adsorption energy of reactant molecules, promoting the separation and transfer of the photo-excited carriers. By using the first-principles calculations, we intend to study the effects of surface modification on the atomic and electronic structures of elemental photocatalysts, aiming to explore the general rules of surface polarization and surface energy modulation induced by surface modification, and the mechanism of photocatalytic activity enhancement resulted from surface modification. This approach could help to design and develop high performance photocatalysts with efficient visible-light-response.

硫和硼是具有宽谱可见光吸收的新型单质光催化材料，但是目前其光催化活性低，难以真正应用于太阳能转化。单质硫和硼晶体的表面通常是低表面能的惰性面，因此反应物分子在其表面吸附弱，使得光催化剂与反应物分子之间的电荷转移困难，这是导致单质光催化材料活性低的关键因素之一。以本课题组前期相关研究为基础，结合单质硫和硼的表面性质分析，本项目拟通过表面改性（异质原子表面修饰,或者与功能化石墨烯或氮化硼进行界面复合）提高单质硫和硼的表面能、诱导表面极化，增强反应物分子的表面吸附，促进光生载流子的分离和转移，在保持宽谱可见光吸收的前提下提高其光催化反应活性。拟采用第一性原理计算研究表面改性对硫和硼等单质光催化材料表面原子/电子结构的影响，探索表面改性调变表面能、诱导表面极化的规律，揭示表面改性提高光催化反应活性的微观机制，为发展具有优异可见光响应特性的高性能新型光催化材料提供理论指导和科学依据。

单质硼、硫等半导体材料是一类新型的廉价光催化材料，但是由于其暴露的通常是低表面能的惰性晶面，使得光生载流子难以转移至目标反应物分子上，导致此类单质光催化材料的光催化活性低下，难以真正应用。针对这一关键问题，采用基于密度泛函理论的第一性原理计算，本项目系统研究了不同异质原子（如硼、氟、溴、磷、氮和氧等）在单质硼和硫低指数晶面的表面掺杂,发现只有弱氧化性的磷进行表面掺杂才能保证单质硼、硫表面原子结构的完整性，并在一定程度上诱导硼、硫低指数面的表面极化，提高其表面能和反应物分子在相关晶面的吸附强度，从而促进光生载流子向目标反应物分子（如光解水反应中的H2O分子和光还原二氧化碳反应中的CO2分子）的转移。此外，在本项目的资助下还深入研究了硼、氮、磷等非金属元素掺杂对低维纳米碳材料（包括石墨烯、石墨相氮化碳等）的表面电子结构和表面极性的影响，发现非金属元素表面掺杂可显著引起低维纳米碳材料的表面极化。上述相关研究结果为基于非金属元素表面掺杂或表面修饰来发展单质半导体及低维纳米碳基高性能能量转化材料和器件提供了科学依据。