Fabrication Of High Active G-C₃N₄ And ZnIn₂S₄ For Photocatalytic Reduction Of CO₂ And Water-splitting To Produce H₂

The drastic depletion of non-renewable fossil fuel has caused severe greenhouse effect and energy crisis problems.Therefore,it is of great importance to search method for resource utilization of CO₂ or to seek a cleaner energy alternative to fossil fuel.In the last several decades,much attention has been paid to semiconductor photocatalytic technology as it can use sunlight to initiate the redox reaction under mild reaction conditions,which is regarded as a promising and valid approach for addressing environment and energy problems.Semiconductor photocatalysts such as graphite carbon nitride（g-C₃N₄）and zinc indium sulfide（ZnIn₂S₄）have been used for CO₂ reduction and water-splitting for H₂ production due to their suitable band structure and visible-light responsive property.However,they can not be widely used in practical applications due to the poor photoreactivity caused by quick recombination of photo-generated carriers.In this thesis,we tried to improve the photoreactivity by modification of g-C₃N₄ and ZnIn₂S₄.The stratagies are summarized as follows:Section Ⅰ:Ti₃C₂/g-C₃N₄ hybrid for photocatalytic reduction of CO₂.As Ti₃C₂ can act as an electron reservior,we prepared Ti₃C₂/g-C₃N₄ hybrid to efficient separation of the charge carriers of g-C₃N₄.Urea can intercalate into the interlayer of multi-layered Ti₃C₂ by sonicating the mixed solutiom of Ti₃C₂ and urea.After evaporation,the mixed powders of Ti₃C₂-urea were calcinated to obtain ultrathin 2D/2D Ti₃C₂/g-C₃N₄ hybrid.Here,urea not only was used as the precursor of g-C₃N₄,but also acted as the gas template to exfoliate muti-layered Ti₃C₂ into Ti₃C₂ nanosheets.Ultrathin Ti₃C₂/g-C₃N₄ hybrid exhibited enhanced photocatalytic CO₂ reduction property by exceeding the pristine g-C₃N₄ by a factor of 8.1 times,which is due to the intimate interface contact between Ti₃C₂ with g-C₃N₄ that stimulated the separation of photo-generated charge carriers and improved chemisorption and activation of CO₂.Section Ⅱ:S-doped g-C₃N₄ for water-splitting to produce H₂.The doped S atom will preferentially replace the sp²-hybridized edge N atom in heptazine of g-C₃N₄,which will result in the breaking of hydrogen bond within layer,improving the photoreactivity by reducing the potential barriers.Here S-doped g-C₃N₄ was prepared by calcination the mixture of thioacetamide（TAA）and dicyandiamide,where TAA is used as the sulfur source.It was found that doping g-C₃N₄ with S can（1）adjust the band structure of g-C₃N₄ to improve the visible-light absorption and reduction ability of conduction band electrons;（2）be conducive to the delocalization of charge in heptazine to boost the migration through the surface and separation efficiency of charge;and（3）make samples exhibit hierarchical porous structure to provide more reduced active sites.When compared with that of pristine g-C₃N₄,the photocatalytic H₂ production activity of the optimal S-doped g-C₃N₄ sharply increased 7.7 times.Section Ⅲ:CeO₂/ZnIn₂S₄ hybrid for photocatalytic reduction of CO₂: CeO₂ can be used to migrate photo-generated carriers of ZnIn₂S₄,enhancing its photoreactivity.Here The CeO₂/ZnIn₂S₄ hybrid ws prepared by microwave-assisted hydrothermal treatment the mixed solution of CeO₂ cubes,zinc chloride,indium chloride trihydrate,and TAA in ethanol solution.The prepared CeO₂/ZnIn₂S₄ hybrid exhibited overwhelming superior photoreactivity toward CO₂ reduction,exceeding pristine ZnIn₂S₄ and CeO₂ by a factor of 3.9 and 7.4 times,respectively.The enhanced photoreactivity is ascribed to the promoted charge separation,augmented the charge density and enlarged specific surface area of the photocatalyst.