Development of in situ polymerized amines into mesoporous silica for direct air CO2 capture

Direct air CO2 capture (DAC) is inevitable to achieve negative emissions and lower CO2 concentration in the atmosphere. The use of class III supported amine materials has shown great potential as effective materials for CO2 capture from both flue gas and low concentrations of CO2. In this work, a linear polyethylene amine tethered to mesoporous silica foam was synthesized by controlled in situ cationic ring opening polymerization of 2-methyl-2-oxazoline. The sorbent was characterized based on porosity, FTIR, elemental analysis, and surface morphology. The CO2 capture performance at different temperatures was measured using a volumetric method, whereas the dynamic breakthrough analysis (DBA) technique was evaluated using simulated air of 400 ppm CO2 at different temperatures and relative humidities. The CO2 adsorption isotherms were studied in the temperature range from 5 to 80 °C and were fitted using different isotherm models. To evaluate the effects of moisture on the CO2 capture performance, breakthrough experiments were performed using 400 ppm CO2 at various relative humidities (0–65%). It was found that the CO2 uptake calculated from the breakthrough experiment is enhanced at higher moisture contents and decreases at higher temperatures. The maximum CO2 uptake was 1.50 mmol/g at 25 °C and 65% RH. The CO2 adsorption kinetics of the sorbent was found to follow the Avrami model, whereas the dual site Langmuir model was found to be the best fit for the adsorption isotherms. The developed sorbent exhibited a stable cyclic performance and retained its initial CO2 uptake during 10 consecutive cycles. This study demonstrates that in situ polymerization of amines into porous supports is a viable route for designing sorbents with high CO2 adsorption performance for DAC applications.