Computational Investigation of the Interaction of Multifunctionalized Porous Aromatic Frameworks with SO₂

The adsorption of pure SO₂, a sulfur-containing acid gas, by porous aromatic frameworks (PAFs) was investigated with a range of computational methods including first-principles density functional theory and grand canonical Monte Carlo calculations. We found that the presence of combinations of functional groups, including the electron-donating groups −CH₃, −OH, and −NH₂, and the electron-withdrawing groups −CN, −COOH, and −NO₂, within the PAF structures was predicted to enhance SO₂ uptake at low pressure. In particular, the simulations predicted that the functionalized PAFs, especially double-functionalized PAFs, PAF-(OH)₂ and PAF-(COOH)₂, as well as mixed-functionalized PAFs, PAF-2-CN-3-NO₂ and PAF-3-OH-5-NH₂, were able to capture high loadings of SO₂ pure gas under a very low pressure at 298 K. The additional functional groups were able to strengthen the interactions between the PAF frameworks and the acid gas molecules. At the same time, introducing two functional groups to PAFs generally decreases the maximum adsorption limit, due to the smaller pore volume available to the gases. In this work, we created a library of various functionalized PAFs, as well as simulated their adsorption isotherms. The results of this work can be used as a guideline for other combinations of functionalized PAFs and their experimental synthesis for maximal acid gas adsorption.