Construction Of Sulfide-Based Hollow Composite System And Study On Regulation Mechanism Of Photocatalytic Properties

Hydrogen energy as an energy carrier has a lot of advantages including cleanliness,high energy density and renewable,which has attracted abundant attention over the world.Moreover,hydrogen energy can effectively alleviate the environmental pollution problems caused by energy shortage and fossil energy combustion.However,hydrogen energy is a primary energy source that cannot be directly obtained.Various forms of hydrogen production methods have been developed up to now.Semiconductor-based photocatalytic hydrogen production has considered to be one of the promising technologies.However,it still faces many problems such as low photocatalytic hydrogen production efficiency、poor stability、ambiguous mechanism of H2 evolution and so on.Therefore,the key to solving these core problems lies in developing efficient photocatalysts and revealing the mechanism of photocatalytic hydrogen production.The development of high-efficiency photocatalysts is the key to solving this issuess.This paper is based on CdS-based semiconductors as the research object.Several approaches have been conducted to optimize its design and improve the photocatalytic H2 evolution activity including decorating co-catalysts,forming solid solution,constructing hollow multi-level structure.Morevoer,the photocatalytic hydrogen production mechanism has been in-depth explored.The research mainly contains the following points:1.Hollow structured NC@Co-NCT/CdS heterojuntion has successfully constructed via the approach of self-templating and ultrasonic with NC@Co-NCT as the reductive cocatalyst.The influence of hollow structure,Co and the concentration of sacrificial agents has been systematically studied.It has been found that the charge transfer channel between NC@Co-NCT polyhedron and CdS nanorods has been successfully built,which is benficial for the fast charge cariers’ migration and separation.The photocatalytic H2 mechanism has been deeply investigated through density functional theory calculations and experiment data.It has been demonstrated that the photogenerated electrons on the conduction band of CdS have achieved quick transfer and separation.Co naoclusters as the active sites effectively promote the reductive reaction,resulting in the improved photocatalytic H2 evlution activity.The rate of H2 evoution over NC@Co-NCT/CdS composite is up to 3.8 mmol·g-1·h-1,which is about 5.8 times of pristine CdS.2.Hollow structured Co9S8/Zn0.5Cd0.5S composite has been successfully fabricated through the method of self-templating,buliding solid solution and in-suit chemical deposition with Co9S8 as the oxidative cocatalyst.Hollow structured Co9S8 polyhedron can not only provide a plateform to deposite Zn0.5Cd0.5S nanospheres,but also avoid the self-aggreation of Zn0.5Cd0.5S.The photocatalytic H2 ecolution mechanism over Co9S8/Zn0.5Cd0.5S hybrid have been investigated through the technolohies of surface photo surface photovoltage spectroscopy(SPV),electron spin resonance(ESR),surface work function and son on.An intimate interface has been formed between Co9S8 and Zn0.5Cd0.5S.In the influence of built-in electric field,the photgenerated holes on the valence band of Zn0.5Cd0.5S are captured by Co9S8,which can effectively relieve the self-photocorrision,promote the photogenerated electron-holes separation,resulting in the improvement of photocatalytic H2 evolution activity.Compared with pristine Zn0.5Cd0.5S sample,the H2 evolution performance of 10Co9S8/Zn0.5Cd0.5S hybrid has been promoted into 10.9 mmol·g-1·h-1 and the apparent quantum efficiency achieves 8.96%.3.Hollow structured decorated Au@HCS@PdS photocatalytic system with spatially separated dual cocatalysts has been successfully constructed using hard templating approach.The species of Au as the reductive cocatalyst and PdS as the oxidative cocatalyst are separately loaded on the inner and outer surfaces of hollow CdS(HCS).The transfer paths of photogenerated electron-holes have been demonstrated through the technologies of ESR and SPV:the electrons tend to transfer to inner Au active aites while the photogenerated holes incline to the outter PdS species,resulting in the oriented separatinon and migration.It has been found that compared with HCS,the activion energy has been obviously reduced,resulting in the improvement of H2 evolution activity over Au@HCS@PdS hybrid up to 16.35 mmol·h-1·g-1,which is about 112 times of HCS.