Theoretical Simulation Of Carbon Dioxide Adsorption On Functionalized 3D-COF And Defective Uio-66

Crystalline porous materials including metal organic frameworks（MOFs）and covalent organic frameworks（COFs）have been widely applied in various fields,such as gas storage and separation,sensors,catalysis,and energy storage.With the growing demand for the synthesis of more kinds of materials with different functionalization,we can use the adjustable pores and surface functionalization to design and prepare new porous materials.In this thesis,a series of new adsorbent materials were designed through functional group modification and defect construction.Computational simulation methods were used to evaluate the adsorption and selectivity of CO₂,which provided a theoretical support for the design and synthesis of new CO₂ adsorption materials.Specific research contents include:1.Three kinds of three-dimensional covalent organic frameworks（3D-COF-1,3D-COF-2 and 3D-COF-3）materials that have been synthesized by experimenters were selected as the parent COF.Based on grand canonical Monte Carlo（GCMC）simulations and density functional theory（DFT）calculations,the CO₂ adsorption and separation of pure components and binary mixtures in functionalized COFs were investigated.The functional groups include –OH,-CH₃,-OCH₃,-NH₂,-CH₂NH₂,-CHO,-NCO,-COOH,-SO₃ H,-E-COOH and-c-COOH.The calculations indicated that the COFs modified with the concerned functional groups enhanced gas uptake at low pressures owing to stronger interaction energy between the gas molecule and the framework,while reduced gas uptake at high pressures as a result of a decrease in pore size and pore volume.CO₂ uptake monotonously increases with the increase of the binding energy according to DFT calculations,suggesting the functional groups play a key role in CO₂ capture on micro porous COFs.The GCMC simulations further showed that any of the functional groups we considered increased the selectivity relative to their parent materials.Functional groups such as-CH₂NH₂,-COOH,-SO₃ H,and-E-COOH are more effective in enhancing adsorption at 1 bar.The sulfonic acid group functionalized COF have shown promise in significantly enhancing the adsorption and separation of CO₂.2.Porous materials with defective structures have good performance in many aspects such as gas adsorption,catalysis,and sensing.We selected Uio-66 which is a representative and has known exact defect structure for CO₂ adsorption and separation simulation.Molecular simulations were used to study the differences in CO₂ adsorption capacity and selectivity between the defective Uio-66 and the perfect Uio-66.DFT calculations were performed on the inorganic clusters of defective Uio-66 to design stable and reasonable configuration at defect vacancy.The results show that the defective Uio-66 can increase the amount of CO₂ adsorption under high pressure due to the larger pore size,but decreases the amount of adsorption due to the reduction of interaction sites at low pressure.The cluster configuration formed by formic acid and water coordinated with zirconium atoms respectively is more stable and has higher adsorption capacity than the formate coordinated configuration proposed in the experiment.Defective Uio-66 also had a lower selectivity because of the smaller difference in adsorption enthalpy between CO₂ and N₂.