Al₂O₃-Based Photocatalyst For Photocatalytic CO₂ Reduction

With the excessive consumption of fossil fuels,humanities are facing a major crisis of energy shortage.Meanwhile quantities of environmental pollution problems and greenhouse effects have become apparent increasingly.Photocatalytic technology has shown application potential in solving energy and environmental problems,in which photocatalytic reduction of carbon dioxide features great prospect.However,the poor performance of some photocatalytic materials limits their industrial application to reality.Currently,surface/interface structure regulation of catalysts is considered to be the most effective method for improving catalyst activity.Aluminum is the most earth abundant metal element,and the preparation of aluminum oxide features the characteristic of cost-effective.Moreover,large specific surface area,oxidation resistance,and good stability of aluminum oxide leads to wide utilization as substrate in the field of catalysis.However,there are few reports of alumina as an independent photocatalyst,owing to the wide band gap of the crystalline structure of alumina,making it unable to possess the light response.If alumina can be developed as an independent photocatalyst,it will provide further practical significance for industrial production or realistic application to find cost-effective and efficient photocatalysts.In this paper,Al₂O₃containing pentacoordinated aluminum species（Al ^V）and oxygen vacancies were synthesized by solvethermal method afterwards Pt were introduced in photocatalysts.The loading 1wt%Pt sample shows the greatest improvment performance,5-fold enhancement in comparison of pristine Al₂O₃.HADDF-STEM demonstrates the existence of Pt are single atoms and clusters.The CO₂-TPD analysis shows that chemical adsorption on CO₂molecules gradually strengthen with increase of the content of Pt introduced.The signal corresponding to the intermediate active species has a relatively significant improvement in situ-DRIFTS test,meaning the further promotion of the reaction.Based on the performance results,the mechanism that Pt clusters take for adsorption and activation of CO₂molecules,and Pt single atoms act as electron transport channels to improve charge separation is proposed.Moreover,Al₂O₃containing Al ^Vand oxygen vacancies were synthesized by solvethermal method afterwards Au single atoms were anchored by Al ^Vsites.The HADDF-STEM and XAFS analysis proved the existence of Au is single atom.ESR and NMR test confirmed that Au single atoms occupying the oxygen vacancies were anchored by Al ^Vsites.CO₂-TPD experiment showed the introduction of Au single atoms greatly improves the adsorption and activation of CO₂molecules.In situ DRIFTS and DFT showed that the electronic structure of Al₂O₃was adjusted by the anchored Au single atom,so that CO₂molecules were in an electron rich environment during surface reactions.DFT also revealed that Au single atoms reduced the energy barrier at each step of the CO generation path,by up to 36%.Furthermore,amorphous components were also introduced into pristine Al₂O₃by hydrothermal method.Inducing amorphous components into Al₂O₃leads to elongation of the Al–O bond and the formation of oxygen vacancies,which makes Al₂O₃an independent photocatalyst for CO₂adsorption and reduction.The generation rate of CO can reach 36.5μmol g^-1h^-1,which is 6.5 times that of P25 Ti O₂.On one hand,longer bond length leads to narrower band gap and the UV response.On the other hand,DFT results demonstrate that the energy of oxygen vacancy formation in the Al₂O₃catalyst containing amorphous components is 0.93 lower than that in crystalline Al₂O₃.The effects of oxygen vacancies can be attributed to:（1）leading to narrower band gap further.（2）A significant effffect for the activation of the CO₂molecules.（3）The appropriate oxygen vacancy concentration promoting the charge separation efficiency...