Professor LAN Yaqian group of Nanjing Normal University: inorganic semiconductor crystal covalent organic framework Z-scheme heterojunction for artificial light synthesis

In the field of artificial light synthesis, it is one of the most challenging photocatalytic reactions to realize the photoreduction of CO2 with water as sacrificial agent driven by visible light Therefore, it is very important to design and synthesize effective photocatalysts to realize the reaction Recently, a series of COFS (COFS) - inorganic semiconductor heterojunction materials were designed and synthesized by Professor LAN Yaqian of Nanjing Normal University to realize the reduction of CO2 under the condition of solid gas These composite materials can realize efficient CO 2 photoreduction with water as electron donor without additional photosensitizers and sacrificial agents Driven by visible light, the Z-scheme heterojunction catalyst realizes efficient electron hole separation and transfer between COF and oxide semiconductor under light excitation (Fig 1), and effectively links the reduction of CO2 on COF with the water oxidation reaction on oxide semiconductor through covalent bond This is the first report on the application of COF semiconductor heterojunction with stable covalent bond in the synthesis of artificial light Figure 1 Introduction of Professor LAN Yaqian's research group on the use of COF semiconductor Z-scheme in artificial light synthesis (source: angelw Chem Int ed.) Since its establishment at the end of 2012, it has been mainly engaged in the research direction of cluster chemistry and coordination chemistry, and has designed and synthesized crystal materials with novel and stable structure for conversion and application in the fields of light, electricity, chemical energy and other related clean energy The research content involves the synthesis and application of POMs, MOCs, MOFs and COFs At present, the research group has made a series of important progress in the field of photocatalysis, including photodegradation of water, CO 2 photoreduction, electrochemical hydrogen production (her), oxygen evolution reaction (OER), oxygen reduction reaction (ORR) and CO 2 electroreduction reaction More than 100 papers have been published in NAT Commun., J am Chem SOC., angelw Chem Int ed., adv mater., chem SOC Rev And other internationally renowned journals At present, the research group has 4 postdoctors, 12 doctors and 16 masters Professor LAN Yaqian's cutting-edge scientific research achievements: inorganic semiconductor crystal covalent organic framework Z-scheme heterojunction is used in artificial light synthesis In the field of artificial light synthesis, it is still very challenging to realize the photocatalytic CO 2 photoreduction and water oxidation (i.e water as sacrificial agent) reaction driven by visible light Recently, a series of Z-scheme heterojunction catalysts (Fig 2) composed of crystalline covalent organic framework (cof-318, cof-316) and inorganic semiconductors (TiO2, Bi2WO6 and α - Fe2O3) were designed and synthesized by Professor LAN Yaqian's research group of Nanjing Normal University, and these reactions were completed under the condition of solid gas reaction Fig 2 Synthesis and structure diagram of COF oxide semiconductor heterojunction (source: angelw Chem Int ed.) Fig 2 is the diagram of synthesis of COF semiconductor heterojunction material with cof-318 and oxide semiconductor TiO 2, Bi 2WO 6 and α - Fe 2O 3 This material was synthesized under solvothermal conditions Take cof-318-tio2 as an example: in the mixed solution of hhtp and Tfpc, a certain amount of pre synthesized microcrystalline TiO2 was added in situ and then mixed uniformly by ultrasonic assisted Degassing the system and keeping the system in vacuum After that, the heterojunction cof-318-tio2 was obtained by reaction in a constant temperature oven at 120 ℃ for three days Fig 3 Structure and morphology characterization of COF oxide semiconductor heterojunction (source: angelw Chem Int ed.) The structure and morphology characterization of the synthesized COF oxide semiconductor heterojunction material were tested by the author (Fig 3) Firstly, the successful synthesis of crystalline cof-318 and cof-318-tio2 was confirmed by powder diffraction The covalent bond between cof-318 and TiO2 was proved by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations It can be seen from the transmission electron micrograph of cof-318-tio2 that TiO2 in the composite is completely coated by cof-318, which also indicates that there is a strong interaction between TiO2 and COF from the side Figure 4 CO2 adsorption and optical performance test of COF oxide semiconductor heterojunction (source: angelw Chem Int ed.) After that, the author tested the CO 2 adsorption and optical performance characterization of the synthesized COF oxide semiconductor heterojunction material (Figure 4) Thanks to the efficient CO 2 adsorption of the COF crystalline porous materials, the adsorption capacity of the cof-318-tio 2 composite is still 27.5cm 3/g, which fully meets the needs of the CO 2 reduction reaction The results show that LUMO energy level of cof-318 can meet the requirements of CO 2 reduction potential, while the valence band energy of TiO 2, Bi 2WO 6 and α - Fe 2O 3 are higher than that of water oxidation to oxygen Therefore, it is theoretically believed that the COF semiconductor heterojunction can be reduced by CO2 and oxidized to oxygen by water Figure 5 Photo catalytic performance of COF oxide semiconductor heterojunction catalyst under the condition of solid gas reaction (source: angelw Chem Int ed.) with COF oxide semiconductor heterojunction material as catalyst, under visible light, the photo catalytic test is conducted under saturated CO 2 and water vapor (gas-solid reaction, no Add additional photosensitizers and electron sacrificing agents) Fig 5 shows the photo reduction performance of CO2 of the COF oxide semiconductor heterojunction material Under the experimental conditions, CO2 can be converted into CO by high efficiency photocatalysis, with nearly 100% selectivity After 4 hours, the co output reaches 278.7 μ mol g − 1 At the same time, water as electron donor produces oxygen by water oxidation The author also studied the circulation stability of the catalyst, and the results showed that the performance of the catalyst decreased only about 5% under five circulation tests The author also confirmed that CO in the product originated from CO 2 and O 2 from H 2O by means of isotope calibration and GC-MS Fig 6 Mechanism of CO 2 photoreduction (source: angelw Chem Int ed.) in addition, the photocatalytic mechanism of COF oxide semiconductor heterojunction composite is also discussed in this paper Firstly, it is proved that the electron transport direction is from TiO2 to cof-318 by the combination of dos and in-situ XPS, and the Z-scheme heterojunction is formed on the macro level It is suggested that the efficient electron transfer from TiO2 to cof-318 is the main reason for the efficient reduction of CO2 The author thinks that after charge redistribution on COF, it is preferentially enriched on pyridine and cyano group, so that CO2 reduction reaction takes place at this position, while water oxidation reaction takes place on TiO 2 with a large number of positive holes Moreover, the density functional theory (DFT) calculation results based on the connectome structure model of the author confirm the above theory (Fig 6) To sum up, this work has developed an innovative strategy to covalently connect crystal covalent organic framework (COF) with inorganic semiconductors Stable organic-inorganic Z-type heterojunction has been obtained and successfully used in artificial photosynthesis This work provides an important case study and a new strategy for the development of efficient and stable crystalline photocatalysts for artificial photosynthesis This work was published in Angewandte Chemie International Edition (DOI: 10.1002 / anie 202000929) under the title of "semiconductor covalent organic framework Z-scheme heterojunctions for artistic Photosynthesis" The corresponding author is Professor LAN Yaqian of Nanjing Normal University Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information website, chembeangoapp, chembeango official micro blog, CBG information wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the representative research groups in China, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.