CO₂ Activation By Oxygen Vacancies And Frustrated Lewis Pairs On Photocatalyst Surface

With the acceleration of global industrialization,the demand for energy has increased dramatically.However,the global energy structure is still dominated by fossil fuels,as a result,the rapid consumption of this kind of non-renewable energy has been accelerated and led the increased emission of CO2.Developing a technology about new clean energy sources and reducing CO2 content in the atmosphere are of great significance to solve the global energy crisis and environmental problems.Solar energy-driven CO2 energy conversion is an ideal new technology to solve energy shortage and reduce greenhouse effect.However,the linear CO2 molecule structure faces a great challenge in direct photoreduction because its stable C=O bond in normal condition.Defect structure can effectively capture and activate CO2 molecules,reduce the energy barrier of the reaction process,and thus improve the efficiency of photocatalytic reduction of CO2.In this paper,by constructing oxygen vacancies defect and frustrated Lewis acid pairs active sites in amorphous oxide semiconductors and ternary hydroxide photocatalysts respectively,CO2 molecule can be effectively activated by oxygen vacancies and frustrated Lewis acid pairs,thus direct splitting to produce carbon and oxygen or photoreduction to CH4.The details are as follows:(1)Photoinduced oxygen vacancies assisted CO2 splitting.In this paper,amorphous oxide semiconductor α-Zn-Ge-O was synthesized by liquid-phase reduction method.Oxygen vacancies(OVs)in amorphous oxide semiconductor α-Zn-Ge-O can be generated by photo-corrosion reaction in semiconductor materials,it can effectively capture oxygen atoms in CO2 molecule and activate them,thus reducing the energy barrier of photocatalytic reduction of CO2.At the same time,oxygen is released due to the persistent oxidation by the photogenerated hole,and the photogenerated electrons reduced CO2 to the substances C and release O2.This reaction path needs low energy consumption and can achieve a sustained light splitting of gaseous molecules to produce O2.It is an ideal oxygen supply technology for removing gaseous oxide molecules in closed space and has potential application prospects in space exploration(such as manned spacecraft),ocean exploration(such as underwater manned exploration),civil defense engineering and ecosystem construction in large public confined space.(2)Photoreduction of activated CO2 by frustrated Lewis pairs.In this paper,ternary metal hydroxide CoGeO2(OH)2 was synthesized by hydrothermal method.On the basis of oxygen vacancies activated CO2,the oxygen vacancies were introduced into CoGeO2(OH)2 to form unsaturated metal ions as Lewis acid sites and surface lattice hydroxyl groups of material as Lewis base sites,both of them could form frustrated Lewis acid-base pairs(FLPs),which can accelerate the activation of CO2 so that achieved an efficient photocatalytic reduction of CO2.In the other hand,due to the hydroxyl group contained on the catalyst surface can directly participate in the catalytic reaction as a proton source,there is no need to add additional proton sources such as H2O or H2,which reduces the activation energy of the reaction.At the same time,the oxygen vacancies on the catalyst surface can be used as the adsorption and dissociation site of water molecule,so that the hydroxyl consumed during the reaction can be regenerated in the water vapor environment,thus realizing a self-breathing photocatalytic CO2 reduction with surface lattice hydroxyl as the proton source.