Synthesis of Particulate Hierarchical Tandem Heterojunctions toward Optimized Photocatalytic Hydrogen Production

Abstract

Photocatalytic hydrogen production using semiconductors is identified as one of the most promising routes for sustainable energy; however, it is challenging to harvest the full solar spectrum in a particulate photocatalyst for high activity. Herein, a hierarchical hollow black TiO₂ /MoS₂ /CdS tandem heterojunction photocatalyst, which allows broad-spectrum absorption, thus delivering enhanced hydrogen evolution performance is designed and synthesized. The MoS₂ nanosheets not only function as a cost-effective cocatalyst but also act as a bridge to connect two light-harvesting semiconductors into a tandem heterojunction where the CdS nanoparticles and black TiO₂ spheres absorb UV and visible light on both sides efficiently, coupling with the MoS₂ cocatalyst into a particulate photocatalyst system. Consequently, the photocatalytic hydrogen rate of the black TiO₂ /MoS₂ /CdS tandem heterojunction is as high as 179 µmol h^-1 per 20 mg photocatalyst under visible-light irradiation, which is almost 3 times higher than that of black TiO₂ /MoS₂ heterojunctions (57.2 µmol h^-1 ). Most importantly, the stability of CdS nanoparticles in the black TiO₂ /MoS₂ /CdS tandem heterojunction is greatly improved compared to MoS₂ /CdS because of the formation of tandem heterojunctions and the strong UV-absorbing effect of black TiO₂ . Such a tandem architectural design provides new ways for synthesizing particulate photocatalysts with high efficiencies.

Keywords: CdS; TiO2; cocatalyst; photocatalytic hydrogen evolution; tandem heterojunction.