Imine-Linked Polymer-Derived Nitrogen-Doped Microporous Carbons with Excellent CO₂ Capture Properties

Abstract

A series of nitrogen-doped microporous carbons (NCs) was successfully prepared by direct pyrolysis of high-surface-area microporous imine-linked polymer (ILP, 744 m²/g) which was formed using commercial starting materials based on the Schiff base condensation under catalyst-free conditions. These NCs have moderate specific surface areas of up to 366 m²/g, pore volumes of 0.43 cm³/g, narrow micropore size distributions, and a high density of nitrogen functional groups (5.58–8.74%). The resulting NCs are highly suitable for CO₂ capture adsorbents because of their microporous textural properties and large amount of Lewis basic sites. At 1 bar, NC-800 prepared by the pyrolysis of ILP at 800 °C showed the highest CO₂ uptakes of 1.95 and 2.65 mmol/g at 25 and 0 °C, respectively. The calculated adsorption capacity for CO₂ per m² (μmol of CO₂/m²) of NC-800 is 7.41 μmol of CO₂/m² at 1 bar and 25 °C, the highest ever reported for porous carbon adsorbents. The isosteric heats of CO₂ adsorption (<i>Q</i>_st) for these NCs are as high as 49 kJ/mol at low CO₂ surface coverage, and still ∼25 kJ/mol even at high CO₂ uptake (2.0 mmol/g), respectively. Furthermore, these NCs also exhibit high stability, excellent adsorption selectivity for CO₂ over N₂, and easy regeneration and reuse without any evident loss of CO₂ adsorption capacity