CO(2) Adsorption Behaviors of Biomass-Based Activated Carbons Prepared by a Microwave/Steam Activation Technique for Molecular Sieve

In this study, the activated carbon was prepared with superior CO(2) selective adsorption properties using walnut shells, a biomass waste, as a precursor. The activations were conducted at various times using the microwave heating technique in a steam atmosphere. The surface morphology and chemical composition of activated carbon were analyzed using a scanning electron microscope and energy-dispersive X-ray spectroscopy. The textural properties were investigated using the N(2)/77K isothermal method, and the structural characteristics were examined using X-ray diffraction analysis. The CO(2) and H(2) adsorption properties of activated carbon were analyzed using a thermogravimetric analyzer and a high-pressure isothermal adsorption apparatus, respectively, under atmospheric and high-pressure conditions. Depending on the activation time, the specific surface area and total pore volume of the activated carbon were 570–690 m(2)/g and 0.26–0.34 cm(3)/g, respectively. The adsorption behaviors of CO(2) of the activated carbon were different under atmospheric and high-pressure conditions. At atmospheric pressure, a significant dependence on micropores with diameters less than 0.8 nm was observed, whereas, at high pressure, the micropores and mesopores in the range of 1.6–2.4 nm exhibited a significant dependence. However, H(2) adsorption did not occur at relatively low pressures. Consequently, the prepared activated carbon exhibited superior selective adsorption properties for CO(2).