Studies Of The Synergistically Regulated Photocatalytic Performance Over Lanthanum Titanate By Heterojunction Construction And Plasmon Resonance Effect

Semiconductor photocatalytic technology has attracted extensive attention in the fields of hydrogenn generation from water splitting and reduction of carbon dioxide,which is recognized as an ideal route to solve the current global energy shortage and environmental pollution issues.La₂Ti₂O₇（LTO）,a layer-structured perovskite oxide,has gained much attention in photocatalysis owing to its unique structure,high stability and excellent photocatalytic activity.However,the larger band gap and severe photogenerated carrier recombination restrict its photocatalytic applications.In this paper,to enhance the visible light absorption and carrier separation efficiency,a CN/LTO heterojunction with intimately contacted interfaces was constructed in situ by a molten salt method;Au nanoparticles were then loaded onto the surface of heterojunction to further broaden the light absorption and charge separation through the surface plasmon resonance effect of Au,resulting in efficient photocatalytic hydrogen evolution and CO₂ reduction.The main findings of this thesis are as follows:（1）La₂Ti₂O₇ nanosheets were successfully prepared by the hydrothermal method,and then CN/LTO heterojunctions were synthesized in situ by the molten salt method.The loading amount of LTO was adjusted to tune the composition of heterojunction.The results of X-ray diffraction,scanning electron microscopy,transmission electron microscopy,X-ray photoelectron spectroscopy,Fourier transform infrared spectroscopy,thermogravimetric analysis,UV-vis diffuse reflectance spectra,fluorescence spectroscopy,and photoelectrochemical characterization show that the in situ construction of heterojunctions by molten salt method leads to the nanoscale interfacial contact between CN and LTO,efficient charge separation,and enhanced visible light absorption.As a result,CN/LTO shows significantly improved photocatalytic activity for CO₂ reduction.（2）Plasmonic Au nanoparticles were loaded onto the surface of CN/LTO heterojunction by photodeposition method.The Au nanoparticles exhibit strong SPR absorption in the visible region,and convert the incident photon energy into plasma energy,which is then transferred to the semiconductor to induce fast charge separation,thus enhancing the photocatalytic activity.In the reaction of photocatalytic hydrogen production,Au-CN/LTO-2 shows remarkably improved performance with a hydrogen production rate of 109.6μmol g^-1 h^-1,which is 12 times higher than that of Au-CN;in the reaction of photocatalytic CO₂ reduction,the CO yield of Au-CN/LTO-2 is 2.8 and11.4 times higher than that of Au-CN and Au-LTO,respectively.The results of UV-vis diffuse reflectance spectra,time-resolved fluorescence spectroscopy,and various photoelectrochemical characterization show that the construction of heterojunctions and loading of plasmonic Au nanoparticles promote carrier separation and improve light absorption,which synergistically enhance the photocatalytic performance.