Constructing CdS/Cd/doped TiO2 Z-scheme type visible light photocatalyst for H2 production

Constructing Z-scheme type photocatalyst is an efficient way to improve the charge separation efficiency and enhance the photocatalytic activity. In this report, the Cd:TiO2 nanoparticles are prepared via the sol-gel route and employed as a starting material. When it was reduced by NaBH4 at 300 degrees C, the surface oxygen vacancies were produced and Cd2+ was reduced into metal Cd-0 nanoparticle (denoted as R-Cd:TiO2). Subsequently, the formed R-Cd:TiO2 was treated with thioureain the hydrothermal reaction. Through the decomposition of thiourea, the oxygen vacancies were refilled by S(2-)from thiourea to form S:TiO2/TiO2 (d-TiO2) and Cd was partially converted into CdS to form CdS/Cd/d-TiO2 composite. The formed CdS/Cd/d-TiO2 composite exhibits improved photocatalytic activity. Under visible light irradiation (lambda>400 nm), the H-2 production rate of CdS/Cd/d-TiO2 reaches 119 mu mol h(-1) with 50 mg of photocatalyst without any cocatalyst, which is about 200 and 60 times higher than that of S:TiO2/TiO2 (0.57 mu mol h(-1)), CdS (2.03 mu mol h(-1)) and heterojunction CdS/d-TiO2 (2.17 mu mol h(-1)) materials, respectively. The results illustrate that metal Cd greatly promotes the charge separation efficiency due to the formation of Z-scheme type composite. In addition, the photocatalytic activity in the visible light region was dramatically enhanced due to the contribution of both CdS and d-TiO2. The method could be easily extended to other wide bandgap semiconductors for constructing visible light responsive Z-scheme type photocatalysts.