Designation And Photocatalytic Mechanism Study Of Ceria-Based Composite Materials

Semiconductor photocatalysis technology has been widely studied in the photocatalytic degradation,water splitting for hydrogen production,carbon dioxide reduction reaction,and methane oxidation etc.It is considered to be one of the important means to solve environmental pollution and energy crisis.Compared with bulk semiconductors,one-dimensional nanorod-like structures have physical properties such as high aspect ratios and large specific surface area,which enable the rapid transfer of photogenerated carriers to the surface for chemical reactions.However,a single semiconductor has a narrow visible light response range,easy and rapid recombination of photogenerated carriers.In this paper,ceria nanorods are selected as the matrix material to study the light absorption and the transferation and separation of photogenerated electron-holes by constructing a heterocomposite structure,and to explore the photocatalytic performance and mechanism.The major research of this paper are as follows:（1）In this work,n-type ceria nanorods were modified by p-type Mn₃O₄ to construct p-n heterostructures.Firstly,the Mn₃O₄/CeO₂heterojunction were characterized by various means;and then the photocatalytic degradation of Rh B was carried out.The results showed that the Mn₃O₄/CeO₂ heterojunction had stronger photocatalytic activity than Mn₃O₄ and CeO₂,and the optimal ratio of Mn₃O₄/CeO₂（Mn₃O₄/CeO₂-2）composite material is more than 95%in photocatalytic degradation of Rh B（10m M）in 3 hours.The kinetic constants of Mn₃O₄/CeO₂-2 are 28.6 times and 36.6 times higher than those of Mn₃O₄ and CeO₂,respectively.In addition,the activity of the optimal composite remains stable after four degradation cycles.The results of optical analysis and electrochemical analysis show that the composite structure has a larger photoresponse range and stronger light absorption ability,faster separation of photogenerated carriers and longer existence lifetime of photogenerated carriers,Smaller charge transport resistance at the solid-liquid interface,and thus the composite structure has enhanced photocatalytic performance.Finally,the Z-type mechanism of photocatalytic reaction of Mn₃O₄/CeO₂heterojunction is proposed based on trapping experiments and electron spin tests（ESR）.（2）The Cd S QDs/CeO₂ composite was constructed by a simple one-step hydrothermal reaction.The Cd S QDs/CeO₂ composite material forms an intimate contact interface between Cd S quantum dots and CeO₂nanorods.The optimal molar content of Cd S quantum dots is 3 at%,and the optimal photocatalytic hydrogen production rate of the Cd S QDs/CeO₂is 101.12μmol h^-1g^-1,its photocatalytic H₂ release amount is 45 times that of pure CeO₂ nanorods.Through UV-Vis diffuse reflectance spectroscopy,it is known that the composite structure has a larger photoresponse range and stronger light absorption capacity.Photoluminescence and transient fluorescence indicate that the composite structure has faster separation of photogenerated carriers and longer photogenerated carriers.The electrochemical test shows that the transfer resistance of the charge at the solid-liquid interface is smaller.The capture experiment of the photocatalytic reaction and electron spin test（ESR）suggest that the Cd S QDs/CeO₂ nanorod composite structure is the Z-type photocatalytic reaction mechanism.（3）Cd Se QDs/CeO₂ nanorod composites were prepared by thermally assisted liquid phase chemical synthesis in a water bath.The performance of Cd Se QDs/CeO₂ nanorod composites is significantly improved.The optimal photocatalytic hydrogen production rate of Cd Se QDs/CeO₂-0.075nanorods composite is 283μmol h-1g-1,which is 126 times that of CeO₂nanorods.The enhanced photocatalytic performance is mainly due to the fact that the Cd Se QDs/CeO₂ nanorod composite has a larger photoresponse range,suitable energy band structure and 0D/1D morphology advantages,which can effectively promote the separation and transfer of photogenerated carriers.In addition,the first-principles calculations based on density functional theory（DFT）show that the Cd Se QDs/CeO₂ composite has stronger water adsorption and active hydrogen desorption capacity,which is beneficial to the photocatalytic hydrogen production reaction.（4）One-dimensional rod-like Cd Se+Cd S QDs/CeO₂ composites decorated with double quantum dots were prepared by a two-step synthesis method of hydrothermal and liquid deposition.In the Cd Se+Cd S QDs/CeO₂ nanorod composite material,double quantum dots are distributed on the surface of CeO₂ nanorods,which expands the photoresponse range and improves the light absorption ability;the appropriate energy band and the 0D/1D morphology advantage effectively promotes the separation and transfer of photogenerated carriers.The hydrogen production rate of the optimal 0.1Cd S+0.1Cd S QDs/CeO₂composite is 639μmol h^-1g^-1,which is 232.5,12.1 and 2.7 times higher than that of CeO₂,0.1Cd S QDs/CeO₂,and 0.1Cd Se QDs/CeO₂ composites,respectively.And the activity of the Cd Se+Cd S QDs/CeO₂ nanorod composites remained stable after five cycles of photocatalytic hydrogen production.72 Figures,2 Tables,222 Refernces...