Sulfides Photocatalysts With Visible-light Response: Synthesis And Properties On Water Splitting H₂ Evolution

Searching for highly active photocatalysts for solar H2 evolution from water, which is considered as an ideal clean energy source, has been a challenging and very important research topic due to the growing environmental concerns and increasing energy demand. Since the report of water splitting to produce hydrogen using solar energy with Ti O2 as semiconductor photocatalyst by Fujishima and Honda, photocatalytic water splitting has become a clean, sustainable and economic method to produce hydrogen, and lots of attentions have been focused on developing new methods and/or photocatalysts to produce hydrogen through water splitting.On one hand, the mechnism of the water splitting and the influenced factors to enhance the photocatalytic activities have been researched and discussed. Up to now, it has been reported that more than 150 kinds of novel photocatalysts have been developed. On the other hand, relatively low solar absorption ability and H2 evolution efficiency limited the application and further development of the water splitting to a large extent. Deep understanding of the water splitting mechnism and full discussion on the approches to obtain enhanced photocatalytic properties are key factors to break through the bottleneck period. Last but not least, we can make full use of these factors to develop novel highly efficient photocatalysts.Basing on the above reviews, four different sulfides photocatalysts are systematically investigated. The research abstract are sumarrized as following::1. Band gap-tunable(Cu In)xZn2(1-x)S2 solid solutions.Gap-tunable(C u In)x Zn2(1-x)S2 solid solutions have been successfully prepared via a solvothermal approach, and they possessed high activity for hydrogen production from water under visible light irradiation.(Cu In)0.2Zn1.6S2 solid solution exhibits the highest photocatalytic activity for water splitting, and its average H2 evolution rate is 0.984 mmol h-1 g-1 under visible light irradiation(λ> 420 nm) even without a noble metal cocatalyst. Further studies revealed that the compositions as well as the photophysical properties, particle size and surface areas also play important roles on their photocatalytic activity for water splitting.2. Cube-in-cube hollow Cu9S5 nanostructures. Cube- in-cube hollow Cu9S5 nanostructures have been synthesized through hydrothermal method with C u2 O nanocubes as templates, and a plausible formation mechanism of these unique structures has been proposed based on an outward gas bubble-assisted assembly process. Single shell hollow Cu9S5 nanocubes could also been synthesized in the similar reaction procedure by changing the sulfur source. Further studies reveal that the cube- in-cube nanostructures can greatly enhance the photocatalytic activity in solar H2 evolution compared with the single shell cube structure, because of its multi-reflections of light. 3. Cu Fe S2 nanocrystals with NIR light response. A ternary type of closed-cage fullerene-like structure of Cu Fe S2 was prepared via a facile solvothermal method, and it has absorption in NIR- light region. The average rate of H2 evolution over the non-loaded fullerene- like C u Fe S2 catalyst is about 0.35 mmol h-1 g-1 and 0.095 mmol h-1 g-1 under the simulated sunlight irradiation and near- infrared light irradiation, respectively. Further comparing the morphologies, surface area, light absorption ability with those of the natural chalcopyrite powder revealed that the unique structure of the fullerene- like Cu Fe S2 nanoparticles can promote the separate of the photo- induced carriers. 4. Rationally designed n-n heterojunction. A novel n-n heterojunction photocatalyst Cd S-Zn WO4 was researched, in whichZn WO4 possess a more negative C B while a more positive VB compared with that of the Cd S. The energetic diagramof the Cd S-Zn WO4 heterojunctions has been proposed based on the photoelectrochemical characterizations. The water splitting results illustrate that this kind of n-n heterojunctions is suitable and highly efficient for solar hydrogen evolution. The photocatalytic activity of Cd S-30 mol%-Zn WO4 reaches 31.5 mmol h-1 g-1 under visible light with an A.Q.Y. of 20.4% at 420 nm, which is ca. 6.8 and 755 times higher than that of pure Cd S and Zn WO4 under the similar condition, respectively.