Adsorption of CO₂ on Activated Carbons Prepared by Chemical Activation with Cupric Nitrate

Activated carbons were prepared from a lignocellulosic material, African palm shells (Elaeis guineensis), by chemical impregnation of the precursor with solutions of 1-7% w/v Cu(NO₃)₂ at five different concentrations. These were carbonized in a carbon dioxide atmosphere at 1073 K to obtain different carbons. Their textural properties were characterized by nitrogen and carbon dioxide adsorption isotherms in order to evaluate the pore-size distribution. The immersion enthalpies of the activated carbons in benzene, dichloromethane, and water were determined. The CO₂ adsorption capacities of the materials at 273 K under low-pressure conditions were also determined. Chemical characterization was performed by mass spectrometry, Fourier transform infrared spectroscopy, and temperature-programmed reduction. With this method of preparation under the concentrations described, activated micro-mesoporous carbons were obtained, with the formation of highly mesoporous solids that favored the process of diffusion of molecules of CO₂ into the material. Here, we show that activated carbons were obtained with different textural characteristics: surface Brunauer-Emmett-Teller areas varied between 473 and 1361 m² g^-1 and micropore volume between 0.18 and 0.51 cm³ g^-1. The activated carbon with the highest values of textural parameters was ACCu5-1073. Micro-mesoporous solids were obtained with the methodology used. This is important as it may help the entry of CO₂ molecules into the pores. The adsorption of CO₂ in the materials prepared presented values between 103 and 217 mg CO₂ g^-1; the values of volume of narrow microporosity obtained were between 0.16 and 0.45 cm³ g^-1. The solid with the greatest capacity for adsorption of CO₂ and volume of narrow microporosity was ACCu3-1073. The use of these solids is of importance for future practical and industrial applications. The adsorption kinetic of CO₂ in the activated carbons prepared with metallic salt of copper is in good accordance with the intraparticle diffusion model, for which diffusion is the rate-limiting step. The adsorption of CO₂ in the prepared activated carbons is favorable from the energy and kinetic point of view, as these accompanied by the presence of wide micro-mesoporosity favor the entry of CO₂ into the micropores.