A Better Understanding of the SBA-15 Pores Filling through Textural Changes in CMK-3 Carbon Synthesis and Its CO₂:CH₄ Adsorption Selectivity

This text reports the morphological and textural behavior of the synthesis stages of a CMK-3 carbon type using a silicon matrix of the SBA-15 type calcined at 823 K as a template. During the synthesis, three intermediate materials were obtained because of (i) the addition of sucrose to the SBA-15 template (CCMK3-1st), (ii) the addition of sucrose to the CCMK3-1st material (CCMK3-2nd), and (iii) the carbonization by pyrolysis of the by-product CCMK3-2nd (CCMK3-F). The texture of the above materials was found by analyzing the N₂ adsorption isotherms, applying the classical adsorption theories to obtain the BET-specific surface and the meso- and micropore distributions by the BJH and Dubinin–Astakhov (DA) methods, respectively, in addition to the non-localized density functional theory (NLDFT). Similarly, with high resolution, the samples were analyzed morphologically by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Finally, the adsorption isotherms of CO₂ and CH₄ of the CMK-3 sample were obtained at six different temperatures in the interval of 243 to 303 K to evaluate the behavior of the isosteric enthalpy of adsorption (q_st) and its CO₂:CH₄ ideal selectivity. The final CMK-3 carbon presented two families of micro- and mesopores of 1.5 and 3.2 nm, nanopipe diameters of 3.5 nm, and a specific surface area of 1350 m²/g. It also presented values of 6.0 and 2.4 mmol/g adsorbed CO₂ and CH₄ at 243 K, respectively, and strong intermolecular interactions, with q_st values higher than 22 kJ/mol reflected in high selectivity values for an ideal mixture of CO₂:CH₄ (30:70%).