Synthesis of novel and tunable Micro-Mesoporous carbon nitrides for Ultra-High CO2 and H2S capture

Carbon nitride (CN) materials with intrinsic high nitrogen content are potential candidates for acidic gas adsorption. However, these nanomaterials should be further treated to achieve tunable textural properties for ultra-high gas adsorption. Herein, we synthesized dual-pore carbon nitride materials (DP-CN) with a series of ethylenediamine to carbon tetrachloride ratios with different amounts of potassium hydroxide (KOH) as a chemical activator using nanosilica (SiO2) as a hard template to tune the physicochemical properties of the materials. The prepared DP-CN adsorbents had a large surface area (up to 2036.9 m2/g), great pore volume (up to 1.15 cm3/g), and high nitrogen content (10.6 to 15.1 wt%). The best DP-CN displayed ultra-high CO2 and H2S adsorption capacity at 1 bar (8.3 and 13.8 mmol/g, respectively), 10 bar (16.9 and 23.1 mmol/g, respectively), and 30 bar (22.9 mmol/g for CO2) at 25 °C, which was significantly higher than those of other pure mesoporous carbon nitrides (M-CN) and carbon-based adsorbents. Moreover, the best adsorbent exhibited good CO2/N2, CO2/CH4, H2S/N2, and H2S/CH4 selectivity, suitable heat of adsorption, and excellent cyclic stability. According to density functional theory calculations, H2S adsorbs more strongly than CO2 on carbon nitride surfaces, and the adsorption energies of CO2 and H2S are related to charge-transfer values from the surface to the adsorbed species. The results revealed that the exceptional textural properties and high nitrogen content of the materials could play the main role in the superior adsorption of CO2 and H2S. This generation of CN materials is expected to be practical for a various range of separation processes, catalysis, capacitors, and energy storage.