Preparation And Properties Of Cadmium Sulfide-Metal Sulfide Composite Photocatalysts

Solar photocatalytic hydrocarbon fuel production technology has the potential to solve the global energy shortage and environmental pollution,and is one of the main ways to implement the sustainable development strategy and the goal of"Carbon emissions peak,Carbon neutrality".As a typical II-VI semiconductor with an intrinsic band gap of about 2.4 e V,CdS is a narrow-band gap visible light photocatalyst with good absorption performance to visible light.However,single CdS is prone to the phenomena of photogenerated electron pairs recombination and photocorrosion in the photoreaction process.Mn S,Ag₂S and other metal sulfides can promote the photogenerated carrier separation of CdS by morphology design and energy band modification,which has a great application prospect.Thus,CdS-metal sulfides photocatalysts are synthesized to carry out the performance of photocatalytic hydrogen production and CO₂reduction.（1）One-dimensional CdS nanorods-Mn S S-scheme heterostructure（named CM）was prepared by solvothermal method under high temperature and pressure.Mn S were loaded on CdS nanorods with an average diameter of 45 nm and a length of 275 nm.The photocatalytic hydrogen production rate of CM composites can reach 866μmol·g^-1·h^-1with sacrificial agent,which is 2.04 times that of pure CdS nanorods.This performance improvement can be attributed to these factors:（1）photogenerated electron transport rapidly in rod structure,enhancing the reaction effiency.（2）the formation of S-scheme heterojunction structure preserves the redox capacity and prevent the recombination of photogenerated carriers.（3）the amount of hydroxyl radical and other active substances increased sharply during the photoreaction.Finally,the hydrogen generation mechanism of S-scheme heterojunction of one-dimensional CdS nanorods-Mn S was proposed by means of electron paramagnetic resonance,electrochemical impedance and transient photocurrent response.（2）CdS nanosheet-assemble flowers were prepared by a simple self-assemble strategy using hydrothermal method,with Ag₂S quantum dots loaded on the CdS nanosheet.Ag₂S quantum dots with an average diameter of 6 nm were distributed on the CdS nanosheet assemble flowers,which accelerated electron transfer,prevented the recombination of photogenerated electron pairs,reduced the reaction overpotential,thus improving CO₂reduction photocatalytic performance of CdS.The quantum size effect of Ag₂S quantum dots widens the band width of Ag₂S QDs/CdS nanosheets-assemble flowers.Meanwhile,the large specific surface area of CdS nanosheets-assemble flowers provides more reactive sites,which further improves the reaction efficiency.The CdS-Ag₂S QDs composite with 5 wt%Ag₂S QDs loaded achieves CO evolution rate of16.6μmol·g^-1·h^-1without noble-metal cocatalysts,which is 2.10 times that of pure CdS nanosheet.This experiment provides a new perspective for the design of quantum dot assisted catalyst and a feasible method to improve the photocatalytic CO₂reduction.