Study on the decarbonization mechanism of composite adsorbent by Mg-MOF-74-based modified biochar

• The composite adsorbent is prepared from MOFs and biochar by in-situ growth method. • The adsorption mechanism is innovatively investigated by Gaussian09 based on DFT. • Biochar causes lattice defects in MOFs and increases chemisorption properties. • The surface of the composite adsorbent contains four kinds of adsorption sites. • Four adsorption sites are coupled to the adsorption and produce two pathways. In this paper, the composite adsorbent by MOFs-based modified biochar was prepared by in-situ growth method based on the structural design of modified biochar and Mg-MOF-74, both of which contained unsaturated metal centers and oxygen-containing functional groups. The coupling mechanism between MOFs and biochar was investigated by CO 2 adsorption properties and various characterizations. Based on the density functional theory (DFT), the three-dimensional model of composite adsorbent was constructed by combining the characterization of various microscopic properties to reveal CO 2 adsorption mechanism of the composite adsorbent. Finally, the correctness of the microscopic mechanism of the composite adsorbent was verified by using surface element analysis. The results reveal that biochar causes lattice defects in MOFs, improving the pore structure, and the composite of biochar and MOFs increases the CO 2 adsorption performance. Biochar is connected with Mg-MOF-74 through oxygen-containing functional groups and unsaturated metal centers to form a composite adsorbent. The four adsorption sites constructed with electron-bearing oxygen vacancies, metal ions, lattice oxygen, and chemisorbed oxygen are coupled to act on CO 2 adsorption, chemisorption properties of the composite adsorbent are enhanced. MOFs are affected by the spatial site resistance effect brought by the biochar to produce oxygen defects, which couples with the unsaturated metal adsorption sites to realize the composite adsorption of metals. There is electron transfer during CO 2 adsorption by the composite adsorbent and the stable carbonate is generated.