Enhanced CO₂ Adsorption and CO₂/N₂/CH₄ Selectivity of Novel Carbon Composites CPDA@A-Cs

Abstract

New carbon composites (CPDA@A-Cs) were successfully prepared by carbonizing and activating the polydopamine (CPDA) and asphalt-based carbons (A-Cs) for CO2 capture and separation. The resulting CPDA@A-Cs were characterized, and the CO2, N2, and CH4 adsorption separation performances of CPDA@A-Cs were investigated systematically. Results showed that CPDA@A-Cs exhibit a high Brunauer–Emmett–Teller specific surface area of 2031 m2/g and a high total pore volume of 0.81 cm3/g, respectively. Boehm titration showed that the introduction of CPDA made the basic site concentration of CPDA@A-Cs increase in comparison with that of the parent A-C, and X-ray photoelectron spectroscopy analysis indicated that the N-containing groups mainly consisted of pyridinic N and pyridonic N. At the ambient pressure, the CO2 uptakes of CPDA@A-Cs amounted up to 6.89 mmol/g at 273 K and 4.05 mmol/g at 298 K, increasing by 34% compared with the parent A-C, and much higher than that of the most reported carbonaceous materials under the same adsorption conditions. Meanwhile, the CO2/N2 and CO2/CH4 adsorptive separation selectivities were significantly enhanced. For the CO2/N2 (0.15/0.85) mixture, its ideal adsorbed solution theory (IAST)-predicted selectivity at normal pressure and temperature was found to be 25.1, whereas for the CO2/CH4 (0.5/0.5) mixture, its IAST-predicted selectivity under the same conditions was calculated to be 5.1. Fixed-bed experiments showed that the CO2/N2 mixture and CO2/CH4 mixture can be well separated at room temperature. Density functional theory calculations revealed that surface pyridinic N and pyridonic N of the composites make a significant contribution to the enhanced CO2 capture capacity and CO2/N2 or CO2/CH4 selectivity.