Ionic Liquids And Single-atom Co-modified GC₃N₄ Photocatalysts For Efficient CO₂ Reduction

Photocatalytic CO₂ reduction can convert CO₂ and H₂O into high calorific value fuels such as CO and CH₄,and is one of the effective means to solve the environmental problems caused by excessive CO₂ emissions.The key to this process is the development of efficient,stable and economical semiconductor photocatalytic materials.Polymer semiconductor graphitic carbon nitride(g-C₃N₄)has the advantages of visible light response,strong stability and simple preparation,but its electron kinetic process is slow and lack of catalytic sites,resulting in its photocatalytic efficiency and selectivity are not ideal.Aiming at the above problems,this paper develops a dual-regulatory strategy based on the introduction of single atomic sites,that is,the introduction of ionic liquids or single atoms on the surface of g-C₃N₄ as an electron trapper and the promotion of CO₂ reduction catalytic sites,while the introduction of single atoms as hole capture and promotion of H₂O oxidation catalytic phenolic sites,the two synergistic to achieve efficient and highly selective photocatalytic CO₂ reduction conversion process.This paper mainly consists of two parts:(1)Diatomic Ni and Co co-modified g-C₃N₄ for photocatalytic CO₂ reduction.Firstly,boron oxygen species were modified on the surface of ultra-thin porous g-C3N4nanosheets(CN)treated with secondary high temperature calcination and nitric acid treatment,and the single atom Ni and Co of oxygen coordination were anchored by ion exchange method.A single-atom Ni and Co-modified g-C₃N₄ nanocomposite was constructed.The photocatalytic performance of the best Ni and Co co-modified samples was 17 times that of CN,and the CO₂ reduction selectivity was 100%.Transient absorption spectroscopy and electrochemical test results show that this performance improvement is due to the ability of single atom Ni to regulate photogenerated electrons and promote catalytic CO₂ reduction,and single atom Co can regulate photogenerated holes and promote catalytic H₂O oxidation.(2)Ionic liquid(IL)and single-atom Co co-modified g-C₃N₄ are used for photocatalytic CO₂ reduction.The ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborat(emim[BF₄])was used to replace the single atom Ni,and the new ionic liquid and single atom co-modified photocatalyst(IL/Co-b CN)were obtained by hydrogen bonding induction assembly modification on the surface of g-C₃N₄.Experimental results show that the photocatalytic CO₂ activity of the best IL/Co-b CN samples reaches 42 times that of CN,there is basically no H₂ generation,and the selectivity of CO and CH₄ production reaches 100%.The dynamics of carriers was studied by in-situ technique.By in situ transient absorption technology,the mechanism of improving photocatalytic activity can be seen that the efficiency of CN electron transfer is increased by 107 times compared with single-atom Co co-modification.It was demonstrated that IL regulates electrons at the reducing reaction end and catalyzes CO₂reduction;single-atom Co regulates holes at the oxidation reaction end,catalyzing H₂O oxidation.In addition,the intermediates of the CO₂ reduction reaction process were deeply explored by in situ infrared technology,and the mechanism of the entire reaction process was speculated.This paper provides an effective modulation strategy for efficient and selective reduction of CO₂ into a valuable chemical and an in situ exploration of electron dynamics methods to achieve efficient photocatalytic carbon dioxide reduction.