| Solar energy conversion is considered to be an ideal approach to resolve the energy shortage and environmental pollution problems. Semiconductor-based photocatalytic water splitting is one of attractive routes for solar energy conversion. Although great progresses have been made in recent years, the conversion efficiency of solar energy to hydrogen over semiconductor photocatalysts is still too low, which has been an obstacle for the development of photocatalytic water splitting. The present thesis was focused on improving the separation and transformation efficiency of photogenerated charges through designing the semiconductor photocatalysts. Two kinds of metal sulfides composite photocatalysts with novel structures were prepared and achieved the improvement of photocatalytic hydrogen evolution activity and stability under visible light irradiation. Even under the cocatalyst-free condition, both photocatalysts exhibit high efficiency photocatalytic hydrogen evolution. The main results were as following:(1) Embedding plasmonic Au nanoparticles into Cd S semiconductor(Au@Cd S) was aiming to take full advantage of electromagnetic fields at the surface of the Au nanoparticles to improve the separation and transformation efficiency of photogenerated charges. Au@Cd S was prepared using a hydrothermal approach. Au nanoparticles with the diameter about 10-15 nm uniformly dispersed inside Cd S semiconductor. It should be noted that the Au nanoparticles were coated with non-conducting insulation layer. The insulation layer could block the interface electron transfer, but not affect the transformation of electromagnetic fields. PL spectra show that both the formation rate and lifetime of photoexcited electron-hole pairs in Au@Cd S were dramatically increased, comparing with that of pure Cd S. Au@Cd S photocatalysts exhibit high visible-light-driven H2 evolution activity with Na2SO3 and Na2 S as sacrificial reagent. Without the use of any cocatalysts, the quantum efficiency of 0.5%Au@Cd S is around 12.1% under 420 nm irradiation. This result is much higher than that of pure Cd S and Au/Cd S composite with Au nanoparticles attaching on the surface of Cd S. When using additional 0.1% Pt as a cocatalyst, the quantum efficiency of Au@Cd S could be further improved to 45.6% and the stability could be significantly improved. The high catalytic activity is well maintained without notable decrease during the entire reaction time investigated.(2) Controllable growing Cd S nanoparticles on the surface of mesoporous Si O2(denoted as Cd S/Si O2). Firstly, Cd O/Si O2 precurser was prepared by a sol-gel method in the presence of citric acid. Then Cd S nanoparticles were formed inside the channel of mesoporous Si O2 through anion exchange method in a Na2 S aqueous solution. TEM results show that Cd S nanoparticles are present about 8-10 nm. The photocatalytic H2 evolution performance shows that the quantum efficiency of Cd S/Si O2 at 420 nm can reach up to 42.0% without use of any cocatalysts, which is much higher than that of bulk Cd S and other cocatalyst-free Cd S composite photocatalysts reported in the literature. PL spectra show that a specific defect configuration is formed on the surface of Cd S nanoparticle, which facilitates trapping photoexcited electrons. These surface defects could serve as the active sites of photocatalytic reaction and play the role of cocatalysts. Besides, this strategy is also applicable to prepare other supported metal–sulfide composites.In summary, metal sulfide semiconductor photocatalysts with high photocatalytic hydrogen evolution efficiency were prepared based on two strategies. This work might provide some reference and guidance for further designing highly efficient photocatalysts for water splitting. |
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