Study Of Long Afterglow Materials For The Application In Round-the-Clock Photocatalytic Reduction Of CO₂

The solar-driven photocatalytic reduction of carbon dioxide(CO2)is an ideal way to convert solar energy into high-value chemical fuels,providing a possible solution to the issues of greenhouse gas emissions and the fossil fuel energy crisis.However,almost all photocatalysts rely on sunlight,which is intermittent and unstable due to factors such as day/night cycles,geography,and seasonality.This results in the photocatalytic CO2 reduction technology being unable to work continuously in environments without light,such as rainy or foggy days,or at night,and its efficiency falls far short of practical applications.Giving the unique ability of long afterglow materials,they can store externally received light energy in traps within the material,and gradually release the stored energy in the form of light after the external illumination has ceased.Inspired by this concept,we propose using long afterglow materials as photocatalysts to effectively absorb photons for driving catalytic reactions under light irradiation,while simultaneously storing excess photo-generated charges in traps.Under dark conditions,the stored charges can be gradually released to the surface of the material through the afterglow effect,potentially extending the duration of photocatalytic reactions and even enabling all-weather photocatalytic reactions.This dissertation focuses on the unique charge storage mechanism of long afterglow materials,and discusses the role of defect-engineered long afterglow materials in catalysis from both the perspective of catalytic active sites and charge storage centers.Specifically,we discuss defect engineering in terms of broadening the photoreaction spectrum,promoting CO2 adsorption activation,and enhancing charge storage capabilities,with the aim of designing and developing economically viable,stable,highly selective photocatalytic materials for CO2 reduction that can continuously work in the dark.The specific research contents are as follows:(1)Long afterglow material Sr2MgSi2O7:Eu2+,Dy3+is used for the first time in photocatalytic CO2 reduction.As a representative of silicate long afterglow materials,Sr2MgSi2O7 has attracted great attention in the fields of luminescence and biomedicine due to its long afterglow time and moisture resistance.In this dissertation,Sr2MgSi2O7:Eu2+,Dy3+long afterglow material was synthesized by solid-state sintering method and first applied in photocatalytic CO2 reduction.The results show that the material not only has good visible light absorption,but also has suitable band positions to meet the thermodynamic requirements of photocatalytic CO2 reduction.Photocatalytic CO2 reduction test shows that the material can achieve high selective photocatalytic reduction of CO2 to CO under sunlight without using any sacrificial or co-catalysts,and can still exhibit weak photocatalytic CO2 reduction activity after the light is turned off.The above research results indicate that Sr2MgSi2O7:Eu2+,Dy3+long afterglow material has good application prospects in all-weather photocatalysis.(2)Oxygen vacancy engineering enhances the round-the-clock photocatalytic CO2 reduction of Sr2MgSi2O7:Eu2+,Dy3+.Introducing defects into the material and constructing surface unsaturated sites through defect engineering can not only increase the charge storage capacity of the long persistent luminescence material,but also regulate light absorption and promote CO2 adsorption and activation.In order to further prolong the photocatalytic activity of Sr2MgSi2O7:Eu2+,Dy3+in the dark,this dissertation designs and prepares oxygen vacancy-rich Sr2MgSi2O7:Eu2+,Dy3+.The research shows that the long persistent luminescence material can achieve nearly 100%selectivity for CO2 reduction to CO under visible light drive,with an average yield of 1.15 μmol g-1 h-1.Even after the light is stopped,the photocatalytic CO2 reduction activity of this persistent luminescence material can continue for more than 3 hours.Furthermore,the ADF-STEM,XAFS,TL and EPR were carried out to reveal the defect sites and relative quantities of long afterglow materials,further expounding the changes in electronic structure of oxygen vacancy-rich Sr2MgSi2O7:Eu2+,Dy3+and facilitation of oxygen vacancy for afterglow performance.Meanwhile,the in-situ DRIFT and in-situ XPS were combined with DFT to explore CO2 activation mechanism,illustrating that the coordinately unsaturated Sr sites near Vo,as the high active sites,can induce localized electrons accumulation,which not only assists the adsorption of CO2 molecules,but also promotes the reduction of the formation barrier energy of COOH*intermediates "rate-limiting step",resulting in highly selective conversion of CO2 into CO.