Synthesis And Photocatalytic Performance Of The Complex Sulfides

The potential use of solar energy to produce H₂ and degrade pollutants based on photocatalytic technology has provided a novel direction to solve the current energy and environment problems.As a key material to make high-efficiency use of solar energy,photocatalyst has attracted much attention.Sulphides have received great attention due to its proper bandgap and well photoresponse.However,the low photocatalyst activity and easy photocorrosion limit the further application when it was used as photocatalyst individually,such as ZnS and CdS.The problem can be solved by elements doping,semiconductors coupling and precious metal deposits.When two different semiconductors combine with each other,heterojunction will be formed between their surfaces.There is a potential difference on both sides of the heterojunction,which can effectively separate the photoelectrons and prevent its combination with holes,thus promoting the photocatalytic activity.We have prepared three kinds of photocatalysts of ZnS/NiS,CdS/NiS and CdS/WS₂ and their photocatalytic activity were investigated in the water splitting experiment under the light illumination.Followed by three conclusions:?1?ZnS nanoparticles with good crystallinity and band gap of 3.22 eV were obtained by hydrothermal method.Nevertheless,the ZnS is not stable when it is used as photocatalyst.To solve the problem,NiS was introduced in the system.The gained ZnS/NiS particle not only improve the stability of ZnS but also enhance the photocatalyst activity.The ZnS/NiS sample with optimum ratio of Zn/?Zn+Ni?demonstrates a H₂ generation rate of 42.47 mmol h-1 g-1 in the aqueous solution of Na₂SO₃,which is 5.3 times than that of pure ZnS.Furthermore,the adding of NaYF₄,Er?NO₃?₃ in ZnS/NiS can lead to a response to visible light.?2?The uniform CdS/NiS nanoparticles with average size of 45 nm were obtained with one-step hydrothermal method.The influences of hydrothermal temperature and time,the molar ratio of Cd and Ni,the adding amount of KOH on the photocatalyst activity were investigated.Results indicate that the samples of CdS/NiS have excellent photocatalyst H₂ evolution in the 10 vol%lactic acid.The CdS/NiS sample,which was obtained with the adding of 10 mmol KOH and the Ni/?Cd+Ni?= 10 mol%by hydrothermal 24 h at 200 ?,has a H₂ production rate of 24.37 mmol h-1 g-1.The corresponding apparent quantum efficiency?AQE?is 12.78%at 420 nm.The rate of H₂ production maintaining well in 12 h indicates that the CdS/NiS photocatalyst is stable.?3?The CdS/WS₂ compound was synthesized by two-step hydrothermal method,calcination method and one-pot hydrothermal method.The CdS/WS₂ sample gained by the alkaline hydrothermal method has the best photocatalyst H₂ production,and the particle size of WS₂ has little influence on its photocatalyst activity.The new prepared CdS/WS₂ can keep stable through a period of time of heat treatment.When the molar ratio of W and Cd is equal to 3 vs 7,the largest H₂ evolution rate of CdS/WS₂ is 27.45 mmol h-1 g-1.