Rational design of silicas with meso-macroporosity as supports for high-performance solid amine CO2 adsorbents

Silica-supported amine adsorbents are extensively studied for CO2 capture. However, rational design of silica materials with specific pore structures as amine supports for large CO2 adsorption capacity, fast adsorption-desorption kinetics, easy regeneration, and good cyclic performance, still remains a challenge. Herein, we synthesize a series of ordered silicas with either bimodal or trimodal meso-macro porosities through a single- or double-templating route as supports for polyethylenimines (PEI) to make solid amine CO2 adsorbents. Bimodal silicas with textural mesopores and interconnected macropores are ideal supports at medium amine loading, illustrated by significantly high amine efficiencies, e.g., 50BPEI (800)/PS-80-00 achieves a CO2 uptake of 350 mg g−1 PEI at 75 °C, 1 bar, which is the one of the highest values among PEI/silica composites reported so far; however, further increase of amine loading leads to severe amine efficiency fading. In comparison, trimodal silicas with internal mesopores, textural mesopores, and interconnected macropores show outstanding performance at high amine loading, e.g., 70BPEI (800)/PS-80-187 exhibits a CO2 adsorption capacity of 215 mg g−1 adsorbent at 75 °C, 1 bar, which is one of the highest values among reported PEI/silica composites. Moreover, we also study the correlations of the CO2 adsorption capacity and kinetics, regeneration of adsorbent, and cyclic CO2 adsorption-desorption performance with the PEI type, PEI loading amount, and operation temperatures. This work brings insight into factors affecting the CO2 capture performance for amine-impregnated silica composites, providing an important guidance to design high-performance solid amine CO2 adsorbents in the near future.