ABSTRACT
In heterojunction photocatalytic materials, the size of the nanoparticles and electron-hole separation efficiency have a great influence on the photocatalytic hydrogen production activity. In this work, for the first time, a strategy of combining sulfur vacancy engineering and quantum size control for constructing CdS (MOF)/PI heterojunctions was reported. Sulfur-deficient CdS (MOF) nanoparticles with a size of 5-10 nm were derived from in situ sulfurization of Cd-MOF precursors and highly dispersed on the surface of 2D polyimide (PI). The experimental and characterization results demonstrated that CdS (MOF)/PI heterojunctions possess broader and stronger light absorption towards the visible region than pristine PI. More importantly, a considerable amount of sulfur vacancies were introduced into CdS (MOF) nanoparticles. The presence of abundant surface and bulk sulfur vacancies created more unsaturated coordinated Cd 3c atoms, which increased the proportion of the (002) crystal planes that act as highly active crystal planes of CdS (MOF), providing more active reaction sites. The surface sulfur vacancy level located near the Fermi level serves as the photogenerated electron trap level, thereby increasing the efficiency of electron-hole separation and further prolonging the lifetime of photogenerated electrons. As a result, the 18%CdS(MOF)/PI heterojunction exhibited a higher hydrogen evolution rate of 8640 µmol g-o after 4 hours of illumination, which was 20 times higher than that of 18%CdS/PI under visible light irradiation. This work highlights the role of sulfur defects in the modification of the CdS (MOF)/PI heterojunction as a feasible strategy for improving charge separation and photocatalytic performance.
