The Important Role Of Excited State Hydrogen Bond In Photocatalytic Reduction Of CO₂

The two biggest problems that mankind needs to solve today are the environment and energy.Although CO₂ is the most important greenhouse gas,it is also the most abundant C1resource in nature.There are many CO₂ conversion technologies,but among them,photocatalytic reduction of CO₂ into valuable hydrocarbon fuel is the most promising technology,because solar energy is inexhaustible.Although researchers have studied photoreduction of CO₂ for a long time and achieved a lot of results,the biggest bottleneck--low catalytic efficiency has not been solved.The reason is that there are few studies on the mechanism of photoreduction of CO₂.First,few people have studied the electron hole recombination by studying the transition process in the photophysical process.Secondly,most of the photochemical processes studied before are in the ground state,but the photochemical process actually occurs in the excited state.The photophysical and photochemical processes in the excited state are the most important to understand the mechanism of photoreduction of CO₂.It is worth paying attention to H₂O,which is both the reactant and the solvent in the system,because it exists in the system with abundant hydrogen bonds,so the hydrogen bonds in the excited state are very important.In this paper,combining the theory of molecular photochemistry,catalyst selection of known structure model:the calcein and 6-carboxyl fluorescein,currently popular quantum dots:phthalocyanine iron quantum dots of three kinds of photocatalytic reduction of CO₂ system,experiment and theory method to study the excited state of combining hydrogen bond in the light of the photocatalytic reduction of CO₂ important role in the process of physics and chemistry.Calcein,a pure substance with known structure,was selected as the model catalyst to successfully reduce CO₂ to CO without sacrificing agent and photosensitizer.We put on computing as a whole-hydrogen bond and the reactants complex model,light limiting step of physical process for CO₂ activation,CO₂ bond Angle,bond length and spin density changes showed that CO₂ activation,CO₂ activation occurred in the system between the process,it causes excited electron transfer induced by hydrogen bonding,The reduction of CO₂ and the oxidation of H₂O occur in the photochemical process.These two steps are REDOX reactions,in which the oxidation of H₂O is the rate-limiting step of the whole reaction,and they are closely related to the electron transfer and hydrogen transfer induced by the excited hydrogen bond.Pure 6-carboxyl fluorescein was selected as the model catalyst under the conditions of no sacrificial agent,no photosensitizer and homogeneous phase.The successful reduction of CO₂to CO makes the combination of experiment and calculation possible.In order to discuss electron and hydrogen transfer of excited state hydrogen bonds,the catalyst and reactant are considered as a whole in calculation--hydrogen bond complex model,rate-limiting step of photophysical process,fluorescence process,and the introduction of hydrogen bonds can reduce electron-hole recombination.The generation of COOH·and OH·occurs in photochemical processes,and these two steps are REDOX reactions,in which COOH·is the rate-limiting step of the whole reaction.The O atom in 6-FAM hydroxyl functional group is the active center of COOH·formation,and they are closely related to electron transfer and hydrogen transfer induced by excited hydrogen bond.Iron phthalocyanine quantum dots（Fe PC-CQDs）were prepared by chemical oxidation with pure material of known molecules.CO₂ was successfully reduced to CH₄without sacrificing agent and photosensitizer.In this paper,the catalytic conditions and reaction mechanism of photocatalytic reduction of CO₂ by iron phthalocyanine quantum dots have been studied,and the key influence of excited hydrogen bond on photophysical and photochemical process in photocatalysis has been studied.The photochemical process of photocatalytic reduction of CO₂was calculated.It was found that the bottleneck of the reaction was the formation of·CH₃ radical from CH₃OH.The excited hydrogen bond induced the photocatalytic reduction of CO₂,which enriched and improved the mechanism of photoreduction of CO₂.