Self-activated, urea modified microporous carbon cryogels for high-performance CO2 capture and separation

Conventionally, porous carbons were synthesized using corrosive chemical activating agents. On contrary, we designed a single-step synthesis method for the preparation of a series of self-activated heteroatom (N)-doped carbon cryogels from potassium hydrogen phthalate (KHP) and urea at various temperatures (700-1000 degrees C), in the absence of any activating agent. To highlight the effectiveness of N-doping in porosity generation and CO2 adsorption/separation, a comparative analysis was drawn with a series of undoped carbon cryogels. Notably, the N-doped cryogels exhibit a highly porous structure with remarkable specific surface area (SSA; 2084 m(2) g(-1)), micropore volume (1.1806 cm(3) g(-1)), well-defined pore size distribution, and abundant narrow micropores (<1.04 nm). Additionally, a considerable mechanical strength (compressive strength = 0.621 MPa and compressive modulus = 8.86 MPa) was also observed. Moreover, the porous cryogel endowed with sufficient pyrrolic nitrogen content (approximate to 51.4 at %) lead to high CO2 adsorption (280.57 mg/g at 273 K and 171.31 mg/g at 298 K at 1 bar) and an excellent ideal adsorbed solution theory (IAST)-based CO2/N-2 selectivity (approximate to 115) at 273 K, surpassing the CO2 adsorption/separation performance of previously reported N-doped carbons and resorcinol-based carbon gels. Furthermore, the moderate heat of adsorption (36.109 kJ mol(-1)) and stable cyclic behavior of CO2 adsorption-desorption under flue gas conditions (i.e., 15% CO2/85% N-2) unveils the physisorption nature of adsorption which governs the energy-effective regeneration process. Summarizing, the present work demonstrates the successful fabrication of highly porous carbon cryogels as efficient CO2 adsorbents, thereby opening new synthetic avenues for self-activating porous carbon formation. (C) 2022 Elsevier Ltd. All rights reserved.