Prediction of the capture and utilization of atmospheric acidic gases by azo-based square-pillared fluorinated MOFs

Abstract

More than the permissible limit of acidic gases like CO₂, SO₂, and NO₂ in the atmosphere are responsible for the formation of acid rain, the greenhouse effect and many other undesirable environmental hazards. So, the capture and utilization of these gases are essential for mankind. Herein, we proposed an azo-based square pillared MOF, [Ni(MF₅)(1,2-bis(4-pyridy)diazene)₂]_n, with the CUS metal site, i.e. M = Al/Fe, for the selective capture and conversion of acidic gas molecules into commodity chemicals such as cyclic carbonate, sulphite and nitrite. With the aid of Density Functional Theory (DFT), [Ni(MF₅)(1,2-bis(4-pyridy)diazene)₂]_n has been optimized, and the specific force field is derived via guest–host interaction. The Grand Canonical Monte Carlo (GCMC) simulation has been used to explore the guest–host interactions over a wide range of pressures, and their respective stability under pre-humidification is evaluated. The adsorption prediction reveals that MFFIVE-Ni-apy have a higher adsorptive capacity (37.1 mmol g⁻¹), and especially ALFFIVE-Ni-apy possesses a higher affinity towards guest molecules (CO₂, SO₂) rather than FEFFIVE-Ni-apy. Additionally, the adsorption of gases in the presence of humidity reveals that ALFFIVE-Ni-apy has an optimal adsorption capacity for all investigated acidic gases even at 38.5 RH%. The absorbed acidic gases on MFFIVE-Ni-apy were used for the theoretical investigations on cycloaddition with the aid of DFT as an application perspective of the toxic gases instead of expelling into atmosphere. The Climbing Image Nudged Elastic Band (CI-NEB) approach was used to discover the transition state in this scenario, in which the cycloaddition of adsorbed CO₂, SO₂, and NO₂ gases with epoxides leads to the formation of cyclic carbonates, sulphites, and nitrates, respectively.