Photocatalyst systems containing earth abundant elements for photocatalytic H2 or O2 production from water.

• Main Author: Wang, Yabo.
• Other Authors: Xu Rong
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Materials::Nanostructured materials; DRNTU::Engineering::Nanotechnology; DRNTU::Engineering::Chemical engineering
• Online Access: http://hdl.handle.net/10356/51191
• Institution: Nanyang Technological University

H2 production from photocatalytic water splitting using sunlight and photocatalysts is a clean and carbon neutral process to meet the energy and environmental requirements in the future. In this study, research was focused on the design and synthesis of visible light-active photocatalyst systems composed of earth-abundant elements for H2 production from water. Besides the H2 production catalyst for the half reaction of water reduction, an O2 production catalyst was also attempted to understand the other half reaction of water oxidation in water splitting. Firstly, a series of Zn-Cu-Cd sulfide nanocomposite photocatalysts were synthesized using a solvothermal method. Due to the different solubility product constant of ZnS and CdS, the as-prepared samples exhibited CdS-rich core and ZnS-rich surface characteristics. By varying the stage for the addition of copper precursor, Zn-Cu-Cd sulfide nanosphere photocatalysts with controlled copper location and content were obtained. The incorporation of copper remarkably enhanced the activity for H2 production. And sample with copper on the surface is more active than sample with copper in the core. The best sample was found to be with copper both in the core and on the surface, which showed a quantum efficiency of 14.7% at 420 nm. Due to the difference in material properties of ZnS and CdS, it is still a challenging work to synthesize ZnxCd1-xS solid solutions. A facile solvothermal method was applied to prepare ZnxCd1-xS photocatalysts to improve their performance for H2 production. It was found that homogeneous solid solution of ZnxCd1-xS can be formed when x ≤ 0.5. At optimized conditions, a H2 production rate of 1.1 mmol h-1 was obtained under visible light irradiation even without cocatalyst, and the corresponding quantum efficiency is 30.4% at 420 nm. Further work was carried out to dope Ni2+ into ZnxCd1-xS solid solution. A single-source precursor method was developed to synthesize homogeneously doped photocatalysts. Single-source precursors were firstly formed between metal cations and diethyldithiocarbamate anions. The subsequent solvothermal treatment of as-prepared single-source precursors led to the formation of Ni2+-doped ZnxCd1-xS solid solutions. Ni2+ doped samples showed higher activity for H2 production than undoped samples. Due to the accommodation centers for photo-generated charge carriers provided by Ni2+ doping sites, enhanced charge separation efficiency was obtained in Ni2+-doped ZnxCd1-xS, which led to their high activities. A quantum efficiency of 22.8% was obtained at 420 nm.