Self-activated, urea modified microporous carbon cryogels for high-performance CO2 capture and separation. (15th June 2022)

• Record Type: Journal Article
• Authors: Nazir, Ghazanfar; Rehman, Adeela; Park, Soo-Jin
• Is Part Of: Carbon. Volume 192(2022)
• Page Start: 14
• Page End: 29
• Publication Date: 2022-06-15
• Subjects: Carbon cryogels -- CO2 adsorption -- Heteroatom doping -- IAST selectivity -- Kinetics -- Thermodynamics; Carbon -- Periodicals; Carbone -- Périodiques; Koolstof; Toepassingen; Electronic journals; 546.681
• DOI: 10.1016/j.carbon.2022.02.040
• Languages: English
• ISSNs: 0008-6223

Abstract

Abstract: 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 °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 (≈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 /N2 selectivity (≈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% N2 ) 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. Graphical abstract: Image 1 Highlights: A facile, solvent-free, and self-activated synthesis of highly porous carbon cryogels. A high specific surface area (2084 m 2 g −1 ) and large micropore volume (1.1806 cm 3 g −1 ) was observed. Urea plays a dual role in carbon cryogel porous framework i.e., as a porogen and as a heteroatom dopant. A sufficient population of narrow micropores <1.04 nm results in high CO2 uptake of 280.57 mg/g at 273 K/1 bar. An excellent CO2 /N2 selectivity (up to 115) was determined by IAST method.