CaCl₂-Activated Carbon Nitride: Hierarchically Nanoporous Carbons with Ultrahigh Nitrogen Content for Selective CO₂ Adsorption

Abstract

Bulk carbon nitride (C3N4) was transformed into hierarchically nanoporous, nitrogen-rich (N-rich) carbons via calcium chloride (CaCl2)-mediated thermal activation. By systematically varying the annealing time and CaCl2:C3N4 weight ratio, we describe the fragmentation-recombination porogen mechanism and show that Ca2+ effectively stabilizes pyridinic N species through high-temperature solvent–solute interactions. The resulting N-rich nanocarbons were applied as CO2 sorbents over the pressure range of 0–1.0 bar. For these relatively low surface area materials, surface chemistry has the dominant impact on the affinity for CO2 adsorption, primarily at low pressures relevant for carbon capture. An optimal sample with a gravimetric CO2 uptake of 1.9 mmol/g at 25 °C and 0.1 bar and large associated isosteric heat of adsorption (Q st > 45 kJ/mol) resulted in incredible CO2/N2 selectivity (S IAST = 105) for a simulated binary gas feed of 10% CO2 (1.0 bar, 25 °C). We attribute these attractive properties to a unique combination of dipole-rich surface chemistry (43 at % N), moderate porosity (V pore = 0.6 cc/g), and relatively small N2 accessible surface area (180 m2/g).

Porphyrin-Based Nanoporous Organic Polymers for Adsorption of Carbon Dioxide, Ethane, and Methane

“…Moreover, as shown in Table S3, the affinity parameters of K H and A 0 for C 2 H 6 and CO 2 gases in PNOP-2 is higher than those in PNOP-1, indicating that C 2 H 6 /CH 4 and CO 2 /CH 4 selectivities of PNOP-2 are obviously higher than PNOP-1. Second, compared to PNOP-1, the smaller pore sizes of 0.93, 1.00, and 1.49 nm in PNOP-2 are very close to the kinetic diameter of the C 2 H 6 and CO 2 gas molecules (0.33–0.44 nm), resulting in the increased gas selectivity by way of the pore-trapping effect …”

“…Second, compared to PNOP-1, the smaller pore sizes of 0.93, 1.00, and 1.49 nm in PNOP-2 are very close to the kinetic diameter of the C 2 H 6 and CO 2 gas molecules (0.33−0.44 nm), resulting in the increased gas selectivity by way of the poretrapping effect. 58…”

Calcium Poly(Heptazine Imide): A Covalent Heptazine Framework for Selective CO2 Adsorption

“…Recently, our group reported the synthesis of N-rich nanoporous carbons for selective CO 2 adsorption by calcium chloride (CaCl 2 ) mediated ionothermal treatment of melon-based carbon nitride . In doing so, we discovered the conversion toward a semicrystalline intermediate just before the onset of carbonization.…”

“…10 Recently, our group reported the synthesis of N-rich nanoporous carbons for selective CO 2 adsorption by calcium chloride (CaCl 2 ) mediated ionothermal treatment of melonbased carbon nitride. 11 In doing so, we discovered the conversion toward a semicrystalline intermediate just before the onset of carbonization. In the current work, we report an optimized salt melt synthetic process for isolating this crystalline framework, a Ca-complexed analogue of PHI with altered crystalline structure as compared to KPHI.…”

Ab Initio Investigation of the Elastic Properties of CaxSn1−x Alloys for Use As Battery Anodes

“…Due to the reactive nature of Ca, various materials have been proposed and investigated for use as anodes (i.e., Al, Li, Na, Si, Sn, Zn) [24][25][26][27]. The reactive nature of Ca permits the formation of a wide range of intermetallic compounds (IMCs) with each of these materials (except Na) over a wide range of Ca concentrations [28][29][30]. Because of the large number of IMCs that are formed, there is significant variation in capacity associated with each unique material [24][25][26][27].…”