Preparation And Photocatalytic Properties Of Metal Sulfide Composite Photocatalyst

Global energy shortages, intensified environmental pollution and climate problems are already the most challenging problems facing mankind in this century. As human society is increasingly dependent on nonrenewable fossil fuels, safe and clean renewable energy is increasingly needed. Solar energy is the most abundant,inexhaustible clean energy and can be converted into chemcial energy through efficient catalysts. It is of great potential in catalytic water splitting, catalytic degradation of pollutants and other prospects. But now commonly used photocatalysts are nobel metals,which are hard to generalize for their high cost. Non-noble metal-based photocatalysts,with merits of low cost, abundant reserves and comparable properties to Pt, Pd after reasonable design and optimization, have received extensive attention from catalytic industry researchers. Transition metal sulfides have unique advantages in electron transport due to their outstanding electrochemical properties, but the visible light absorption of ordinary transition metal sulfides is confined, the photogenerated electron-hole pairs easily recombine and the quantum yield is quite low. Therefore, how to overcome the shortcomings through the selection, design and regulation of materials is the key problem for photocatalytic application. CdS is an excellent semiconductor photocatalyst of great value with a band gap of 2.5 eV, but its combination of electron-hole pairs makes its catalytic properties extremely limited. Therefore in our work, the structure design of transition metal M (Fe, Co, Ni) chalcogenide compounds are combined with CdS to form CdS/MxSy composite photocatalysts, and their photocatalytic properties can be achieved or beyond the level of Pt and other precious metals. The main contents of this paper are as follows:1. A one-dimensional FexSy precursor was prepared by ternary solvent hydrothermal method using ammonium ferrous sulfate and thiourea as raw materials, and then annealed at high temperature in an inert gas atmosphere to obtain one-dimensional Fe7S8. The composite photocatalyst was obtained after integrated with CdS QDs,follwed with it's photocatalytic water splitting test. The molar ratio of iron source to sulfur source, annealing temperature, product morphology and the mass ratio of CdS QDs in the preparation process have a great influence on the hydrogen production performance of the composite photocatalyst. The optimum catalytic properties after optimization of experimental conditions are 519.6 ?mol h-1, which is better than that of Pt under the same conditions.2. Ni3S2 nanomaterial was prepared by simple high pressure hydrothermal method using nickel acetate as raw material, and then Ni3S2@C nobel-metal-free cocatalyst was prepared by secondary hydrothermal method utilizing glucose. The composite material and CdS were combined to form a new type of efficient photocatalyst. The maximum activity of CdS/Ni3S2@C catalyst was 1164.7 ?mol h-1,and the stability was almost the same as that of CdS/Pt catalyst. After 12 h reaction, only 9.7% of the generated hydrogen was lost, since the loss on CdS/Pt was 9.4%. Considering the photocorrosion on CdS QDs can not be avoided, we can conclude that the CdS/Ni3S2@C composite catalyst has high stability while achieving or even surpassing the photocatalytic hydrogen production activity of nobel-metal catalyst.