Reduced graphene oxide -MnO₂ nanocomposite for CO₂ capture from flue gases at elevated temperatures

The newly prepared reduced graphene oxide-MnO₂ (rGO-MnO₂) nanocomposite has exhibited highly selective CO₂ adsorption from gaseous mixtures at elevated temperatures. The Mn²⁺ basic sites are scattered over the rGO-MnO₂ nanocomposite which produce an effective BET surface area of 710 m² g^-1 for selective CO₂ capture. The selective adsorption of CO₂ (5.87 mmol g^-1) over N₂ (0.36 mmol g^-1) and CH₄ (0.41 mmol g^-1) at 298 K/1 bar was achieved by the nanocomposite. The heat of adsorption followed a unique correlation with the quantity of CO₂ adsorbed and fits well to the Fowler-Guggenheim equation. The mechanism of CO₂ adsorption on the nanocomposite was complemented with molecular modelling and simulations. The rGO-MnO₂ have shown better CO₂ adsorption capacity of 28.5 mmol g^-1 at 323 K/20 bar as compared to zeolite derivatives, MOFs, and carbons as reported in the literature. The formation of inert frameworks with 3-6 nm porous structure in the nanocomposite thermally stabilizes to capture CO₂ repeatedly. The nanocomposite with adsorption capacity of 3.69 mmol g^-1 at 373 K/1 bar is quite close to real-life conditions for flue gas treatment.