Facile Synthesis of Fluorinated Microporous Polyaminals for Adsorption of Carbon Dioxide and Selectivities over Nitrogen and Methane

Abstract

Monoaldehyde compounds, benzaldehyde, 4-methyl­benzaldehyde, 4-fluoro­benzaldehyde, and 4-trifluoro­methyl­benzaldehyde, were utilized to react with melamine respectively to yield four hyper-cross-linked microporous polyaminal networks, PAN-P, PAN-MP, PAN-FP, and PAN-FMP, via a facile “one-step” polycondensation without adding any catalyst. It is found that relative to non-fluorinated polymers the fluorinated ones show the increased BET specific surface areas from 615 to 907 m² g^–1. Moreover, the incorporations of methyl and trifluoromethyl on the phenyl rings can effectively tailor the pore sizes from 0.9 to 0.6 nm. The polar C–F bond and nitrogen-rich polyaminal skeleton result in high CO₂ adsorption enthalpies (38.7 kJ mol^–1) and thereby raise the CO₂ uptake up to 14.6 wt % (273 K, 1 bar) as well as large CO₂/N₂ and CO₂/CH₄ selectivities of 78.1 and 13.4 by the ideal adsorbed solution theory, respectively. The facile and scalable preparation method, low cost, and large CO₂ adsorption and selectivities over N₂ and CH₄ endow the resultant microporous polyaminals with promising applications in CO₂-capture from flue gas and natural gas