Nitridation Of Cobalt Tungstate Modified Cadmium Sulfide Nanocomposites For Photocatalytic Water Splitting Hydrogen Production

The extensive use of fossil fuels and the concomitant environmental pollution are evidently serious challenges around the world.Therefore,it is urgent for human to develop renewable and green energy sources.Hydrogen?H2?is a clean fuel with a high enthalpy of combustion,which is considered to be one of the ideal substitutes for fossil fuels.Photocatalytic water splitting technology using semiconductors is one of an effective way to convert solar energy to hydrogen energy.As a typical semiconductor,CdS is widely used in the field of photocatalytic H2 production due to its suitable band gap of 2.4 e V.However,pure CdS has low performance in practical photocatalytic water splitting due to the fast electron-hole recombination.Therefore,how to effectively suppress the charge recombination has become the key to improve the H2 production activity of CdS.In this paper,CdS is modified by loading another semiconductor or cocatalyst to improve the photocatalytic H2 production activity.The main research contents are as follows:1.CoWO₄/CdS nanocomposite photocatalysts are prepared by the in-situ synthesis method for the study of photocatalytic H2 production.The experiment results show that the blank CoWO₄ nanoparticles can produce hydrogen under visible light irradiation.The CoWO₄-0.5-CdS sample exhibits an optimal photocatalytic H2 evolution rate of 1224mmol·g-1·h-1,which is 35 times than blank CdS and 15 times than CoWO₄.The p-n heterojunction formed between CoWO₄ and CdS can improve the separation and transfer efficiency of photo-generated carriers,which effectively inhibit the charge recombination and further increase the H2 production activity of CdS.2.CoWO₄/CdS-N nanocomposite photocatalysts are synthesized by the one-step nitridation method for the study of photocatalytic H2 production.The experiment results show that CoWO₄ is destroyed by the nitriding process and formed metal nitrides on the surface of CdS nanowires.The optimal sample CoWO₄-0.5-CdS-N exhibits the highest H2 evolution rate of 3650 mmol·g-1·h-1,which is 104 times higher than CdS,2.98 times than non-nitrided samples CoWO₄/CdS,and even 1.24 times of Pt/CdS sample.The presence of metal nitrides on the CdS surface not only enhance the light absorption and separation of photo-generated electron-hole pairs,but also accelerate the reaction kinetics of hydrogen,thereby increasing the H2 production activity of CdS.3.A novel Co₄N-WNx/CdS nanocomposite photocatalysts are synthesized by the electrostatic self-assembly method for the study of photocatalytic H2 production.The experiment results show that when the loading is 10 wt%,the photocatalytic H2 production rate of Co₄N-WNx/CdS composites achieve 14.42 mmol·g-1·h-1,which is 8.1 times higher than Pt/CdS and 528 times than blank CdS nanowires.In addition,the optimal sample still exhibits a photocatalytic activity of 0.938 mmol·g-1·h-1 even at the condition of normal temperature and pressure without adding sacrificial agents.The two-phase metal nitrides Co₄N-WNx as cocatalysts could improve the separation and transfer rate of photo-generated carriers,thereby enhancing the photocatalytic H2 production activity of CdS.