Fabrication of hierarchical carbon nanosheet-based networks for physical and chemical adsorption of CO2.

A hierarchical carbon nanosheet-based networks (GPC) with controllable pore structure are developed for physical adsorption and chemical adsorption of CO2. The synthesis employs graphene oxide (GO) nanosheet as the structure-directing agent, cetyltrimethyl ammonium bromide (CTAB) as the soft template and melamine as the bridging molecule. The individual GO nanosheet is uniformly coated with the in-situ chemical polymerization of resorcinol-formaldehyde-melamine (RMF) polymers via electrostatic interaction with melamine. Thus, micropores with high specific surface area is developed from the cross-linked networks of polymers after carbonation and KOH activation, which is beneficial to the physical adsorption of CO2 at low temperature. CTAB as a soft template could induce the assembly of GO to form a "ring-like" stacking three-dimensional structure, producing macropores and mesopores with high pore volume after carbonization which could act as novel reservoirs to host a high loading amount of amine with good dispersion for CO2 chemical adsorption at elevated temperature. After activation with KOH, the specific surface area is up to 1555.7 m2/g, with CO2 physical adsorption capacity of 4.62 mmol/g under 273 K and 1 bar. After loading PEI of 75%, the CO2 chemical adsorption capacity achieves 5.52 mmol/g under 75 °C. The outstanding advantages of hierarchical carbon nanosheet-based networks, including their macro-meso-microporous structures, fast diffusion kinetics, excellent adsorptivity and easy synthesis, endow them with good potential to be used in a wide range of applications.