Controllable Synthesis Of One-Dimensional Ultrathin Bismuth Oxybromide Nanotubes And Properties Of CO₂ Photoreduction

The continuous accumulation of atmospheric carbon dioxide（CO₂）seriously destroys the natural carbon balance,exacerbates global warming,and becomes a global challenge and pressing issue.Inspired by the nature photosynthesis,photocatalytic reduction of inert CO₂ into value-added carbon chemicals,which relies on photogenerated electrons and/or holes to trigger the cleaving of many chemical bonds under ambient conditions,has been considered as a sustainable and appealing approach to remit both the energy demands and environmental crisis.As photoabsorption,separation of carriers and interfacial CO₂ catalysis are generally considered to be the crucial steps during the solar CO₂ reduction,it is significant to develop approaches to design advanced architectures and engineer the surface structures of catalysts to optimize these critical processes.Surface defects with abundant local electrons can facilitate the transfer of captured interfacial charges to the adsorbate.The defect site as the reaction center can change the charge density distribution,leading to low coordination edge sites on the surface of the materials and intensifying intermediate bonding,thereby reducing the reaction energy barrier for CO₂ photoreduction.Compared with the defects introduced by high-temperature reducing atmosphere treatment,it will inevitably become the composite center of the carrier,reducing the activity of the reaction.The method of constructing an ultrathin structure is more conducive to the exposed surface atoms in the ultrathin layer tend to escape to form defects.Therefore,a new defect energy level is formed and the light response range is extended.At the same time,the ultrathin structure shortens the bulk carrier diffusion length from the inside to the surface,and can suppress the recombination of electron-hole pairs.Bismuth oxybromide is a layered crystal structure formed by interweaving a[Bi₂O₂]plate with a double halogen plate,which is beneficial to obtain an ultrathin atomic layer structure and a high interlayer charge separation rate.Oxygen defects are easily formed by constructing ultrathin structure of bismuth oxyhalide with high concentration of oxygen atoms.In this thesis,the design and synthesis of ultrathin Bi₅O₇Br and Bi₄O₅Br₂ nanotube structures with oxygen deficiencies are used for the photocatalytic reduction of CO₂activity,and use transmission electron microscopy（TEM）,electron energy spectroscopy（XPS）,X-ray diffraction（XRD）,UV-Vis spectrophotometer（UV-Vis）,photocurrent response and electrochemical impedance spectroscopy and other characterization methods combined with density functional theory calculation to analyze the structural properties of the catalyst.In situ FTIR analysis of the intermediate reaction process,and finally through the characterization of structural properties and activity evaluation results,a comprehensive discussion of the reaction mechanism of photoreduction CO₂,the main research is as follows:（1）Herein,a facile and straightforward hydrothermal process was initially used to one-step fabricate freestanding oxygen-defective ultrathin Bi₅O₇Br nanotubes.The ultrathin-shelled topologies of open tubular scaffolds and abundant surface oxygen vacancies endows the Bi₅O₇Br nanotubes with extended photoadsorption,boosted charge separation and enhanced interfacial CO₂ adsorption and activation.Density functional calculations revealed that the presence of oxygen vacancies on the Bi₅O₇Br surface can not only afford abundant localized electrons and lower the CO₂ reaction energy barriers through stabilizing the reduction intermediates,but also had a stronger covalent interaction and more efficient electron exchange and transfer between CO₂ and oxygen vacancies.Without any co-catalyst or sacrifice reagent,oxygen-defective Bi₅O₇Br nanotubes show superior CO evolution rate of 55.1μmol g^-1h^-1,roughly 85.5times higher than that of bulk Bi₅O₇Br,prevailing over most previously reported outstanding photocatalysts.（2）By using a mixed system of ethylene glycol and water with a surfactant,Bi₄O₅Br₂ nanotubes with different oxygen vacancy concentrations were prepared in a simple and direct hydrothermal step.The prepared nanotube structure can increase the specific surface area of the material.DFT calculations show that the introduction of oxygen vacancies changes the band structure and expands light absorption.Photocurrent and PL spectrum results show that high oxygen vacancy concentrations are conducive to enhanced charge separation and reduce interfacial resistance,in the absence of any cocatalyst or sacrificial agent,Bi₄O₅Br₂ nanotubes with different oxygen vacancy concentrations show different CO release rates,which are 19.56μmol g¹ h^-1and 7.8μmol g^-1 h^-1.Bi₄O₅Br₂ nanotubes with high oxygen vacancy concentration have better photoreduction CO₂ activity.