Synthesis,Photocatalysis And Structure-property Relationship Of Cr-Ti-and Mo-Ti-oxide Clusters

Using sunlight to catalyze the cycloaddition reaction between CO2 and epoxy compounds is a highly effective approach to achieve CO2 resource utilization and reduce carbon emissions.However,CO2 molecule is inherently inert,making the reaction conditions relatively harsh,which calls for the need to identify catalysts that can operate under mild conditions with high efficiency.Recently,titanium oxide clusters have emerged as promising candidates due to their precise molecular structure and exceptional photocatalytic properties.These clusters have demonstrated significant potential in the field of sunlight capture,utilization,and structureactivity relationship studies.To achieve efficient photocatalytic CO2 conversion,two fundamental methods,ligand modification,and metal doping,which enhance the visible light response of titanium oxide clusters.Among them,transition metal doping is a technique that has several benefits for titanium oxide clusters.Firstly,it can introduce impurity levels and expand the absorption band edge to the visible region.Secondly,it can introduce Lewis acid active sites that enhance the performance of CO2 activation.The transition metals,specifically chromium,and molybdenum before VIB,have several features that make them suitable for doping titanium oxide clusters.These features include rich valence changes(Cr has+3 and+6 valence,Mo has+5 and+6 valence),oxygen coordination properties(forming M-O-M and M=O bonds with oxygen),strong Lewis acidity,and similar ionic radii to Ti4+.Consequently,Cr and Mo can form heterometallic doped titanium oxide clusters with Ti,which have novel structures,strong visible light absorption,and abundant surface Lewis acid catalytic sites.These clusters can efficiently capture sunlight and catalyze CO2 conversion.However,mixed metallic oxygen clusters of IVB and VIB group are rare,and this dissertation aims to fill this gap.In this study,we synthesized four Cr-Ti-and Mo-Ti-polymetallic oxide clusters and studied their structures,photoresponse properties,photocatalytic CO2 conversion performance,and structure-activity relationship.The following three chapters provide detailed information on these topics.The first chapter of this dissertation provides a concise overview of semiconductor photocatalysis,focusing on its various types and mechanisms,as well as the research significance of CO2 cycloaddition reaction.Subsequently,the paper delves into the progress made in the field of ligand modification and hetero-metal doping of titanium oxide clusters.Finally,the paper concludes by highlighting the importance of the topic and presenting a summary of the research content.Chapter second chapter of this report,two chromium-doped titanium oxide clusters surface functionalized with benzoic acid using a one-pot solvothermal method.To understand their properties,various techniques were employed,including XRD,ESI-MS,and 133Cs-NMR,to examine their structure and solution properties.The band structure was determined by UV-vis diffuse reflection spectrum and Mott-Schottky plot.These clusters were also tested for photoresponse and photocatalytic activity,and their performance was compared to similar compounds.The study revealed a higher charge separation efficiency and catalytic activity after light exposure,and the clusters were used in photocatalytic dye degradation and cycloaddition reaction of CO2 with epoxide.The structure-activity relationship was analyzed,and it was found that Cs@Ti7Cr14 had a higher photocatalytic activity compared to(H3O)@Ti7Cr14.Furthermore,the reaction rate varied with light and heating temperature,suggesting the presence of photothermal synergistic effect.Overall,this study provides new insights into improving the optical absorption performance of titanium oxide clusters.In the third chapter of this study,two Mo-doped titanium oxide clusters,namely Ti6Mo4 and Ti4Mo4,were synthesized using a solvothermal method.Various analytical techniques,such as single crystal X-ray diffraction,powder XRD,infrared spectroscopy,and Raman spectroscopy,were employed to investigate their structure and composition.Both clusters contained Mo2O4 units,with Mo exhibiting valence states of+5 and+6.Theoretical calculations determined the electron structure and photogenerated charge separation type,revealing that the valence band was composed of the electron orbital of the Mo=O unit.In contrast,the conduction band was composed of Ti 3d.Additionally,both clusters exhibited remarkable synergistic catalytic properties of photocatalysis and Lewis acid catalysis,as they could capture the cycloaddition reaction of CO2 catalyzed by visible light.The two clusters also showed outstanding performance in the visible photocatalytic degradation of organic dyes,displaying high activity,stability,and recyclability.Notably,Ti6Mo4 was found to be more catalytically active than Ti4Mo4,and both Ti and Mo were found to be active sites.In conclusion,doping Mo into TOCs as a heterometal can create a new class of bi-functional molecular materials with visible light response and Lewis acid sites.This exciting discovery presents a new direction for constructing heterogeneous metal TOCs and enriching the structure and function of the metaloxygen cluster(MOCs)family.