Preparation Of Triazine-based Framework Materials And The Synergistic Effect In Photocatalytic CO₂ Reduction

The importance of energy to modern society is obvious.Nowadays,due to the rapid development of industrial level,the problem of energy shortage has become increasingly serious.So as to meet the daily needs of human beings,the excessive use of traditional fossil fuels not only causes the scarcity of resources,but also produces a large amount of"greenhouse gases"（CO₂）,which leads to the rise of sea level and serious imbalance of ecosystem.In view of this,many countries have put forward the concept of"carbon neutrality",in which photocatalysis to reduce CO₂ into sustainable clean energy is one of the main strategies to achieve such goals.As the new crystal materials,triazine-based frameworks（COFs and CTFs）are widely used in the field of photocatalysis because of their large accumulation layers,adjustable pore size and high specific surface area.However,these porous materials still face serious problems such as photoelectron-hole recombination in the photocatalysis process,so it is necessary to improve their reactivity effectively through post modification.Currently,many inorganic semiconductors（such as Ti O₂,Bi₂WO₆,Cu₂S,etc.）and some organic molecules（OMs）with special structures have been proven to have high efficiency electron transport in photocatalytic processes.On this basis,the functional combination of these substances with triazine frame materials is a feasible strategy to improve the efficiency of light-driven CO₂ conversion.In this paper,the triazine-based frameworks were taken as the research object,two different hybrid materials were constructed by simple synthesis method,and the synergistic effect of photocatalytic carbon dioxide reduction was investigated by regulating the defect structure and intramolecular charge transfer.The concrete research contents are as follows:（1）Cu S_x/TP-TA heterostructure is used for photocatalytic CO₂ reduction:Cu₂S nanospheres and defect-rich Cu₂S（Cu S_x）nanosheets were prepared by solvothermal method.And the triazine-containing covalent framework（TP-TA COF）was grown in situ on the surface of inorganic materials by one-step hydrothermal method,resulting in Cu S_x/TP-TA and Cu₂S/TP-TA.The structure characterization and photoelectrochemical tests of the related materials were carried out.The results show that,due to the inhibition of photogenic carrier recombination by heterostructure formation.Compared with the corresponding sulfide and TP-TA COF components,the two hybrid structures show significantly enhanced charge transport.It is worth emphasizing that Cu S_x/TP-TA provides a greater photocurrent than Cu₂S/TP-TA,and the subsequent photocatalytic CO₂reduction reaction also shows a CO precipitation rate about 2.8 times higher than Cu₂S/TP-TA photocatalyst.In order to further verify the influence of the establishment of heterogeneous structure between Cu S_x and TP-TA COF on catalytic activity,we prepared Cu S_x+TP-TA composite by simple physical mixing.The experimental results were almost consistent with the above results,which were attributed to the reasonable construction of heterogeneous structure between organic and inorganic photocatalysts,as well as the synergistic effect provided by the defect center can improve the separation efficiency of photogenerated carrier and further enhance its photocatalytic activity effectively.In addition,we also proposed the possible electron direction during the catalytic process by in situ FT-IR test.（2）CTF/TAPT molecule heterojunction photocatalyst is used for photocatalytic CO₂reduction:three kinds of metal-free molecule heterojunction photocatalysts were designed using a green and pollution-free method.Organic molecules（OMs）with different structural units were anchored and dispersed on covalent triazine framework（CTFs）via strong intermolecularπ-πstacking.CTFs were modified by OMs to improve the interfacial charge transfer rate.Under the simulated sunlight irradiation,the molecular heterostructure catalyst formed by Donor-π-Acceptor structured（D-π-A）organic molecule（TAPT）and AA stacking mode covalent triazine framework（AA-CTF）can produce 7.32μmol·g^-1·h^-1 CO after optimization.It is much higher than that of the hybrid materials constructed by organic molecules without D-π-A structure（AA-TAPB）and AB stacking mode hybrid material（AB-TAPT）.The improved photocatalytic performance was attributed to the efficient intramolecular charge transfer（ICT）in D-π-A organic molecules and the synergistic effect provided by the strongπ-πinteraction with AA-CTF.In particular,efficient electron transfer in the molecular structure after the formation of heterojunction can achieve effective charge separation at the interface,thus extending the photogenerated carrier lifetime.Finally,the possible reaction mechanism in the photocatalytic process was proposed by in situ FT-IR test and simple simulation calculation.