The isosteric enthalpy of adsorption (${\Delta }_{ads}\dot{h}$) of CO₂ in three different micro and mesoporous materials was evaluated in this work. These materials were a microporous material with functional groups of nitrogen and oxygen (CMFs, carbon microfibers), a mesoporous material with silanol groups (SBA-15, Santa Barbara Amorphous), and a mesoporous material with amine groups (SBA-15_APTES, SBA-15 amine-functionalized with (3-Aminopropyl)-triethoxysilane). The temperature interval explored was between 263 K and 303 K, with a separation of 5 K between each one, so a total of nine CO₂ isotherms were obtained. Using the nine isotherms and the Clausius–Clapeyron equation, the reference value for ${\Delta }_{ads}\dot{h}$ was found. The reference value was compared with those ${\Delta }_{ads}\dot{h}$ obtained, considering some arrangement of three or five CO₂ isotherms. Finally, it was found that at 298 K and 1 bar, the total amount of CO₂ adsorbed is 2.32, 0.53, and 1.37 mmol g⁻¹ for CMF, SBA-15, and SBA-15_APTES, respectively. However, at a coverage of 0.38 mmol g⁻¹, ${\Delta }_{ads}\dot{h}$ is worth 38, 30, and 29 KJ mol⁻¹ for SBA-15_APTES, CMFs, and SBA-15, respectively. So, physisorption predominates in the case of CMF and SBA-15 materials, and the ${\Delta }_{ads}\dot{h}$ values significantly coincide regardless of whether the isotherms arrangement used was three or five. Meanwhile, in SBA-15_APTES, chemisorption predominates as a consequence of the arrangements used to obtain ${\Delta }_{ads}\dot{h}$. This happens in such a way that the use of low temperatures (263–283 K) tends to produce higher ${\Delta }_{ads}\dot{h}$ values, while the use of high temperatures (283–303 K) decreases the ${\Delta }_{ads}\dot{h}$ values.

SBA-15 materials were functionalized with amino groups, APTES. The functionalization was carried out with ethanol or toluene, in air or nitrogen atmosphere. Texture and silanol ratio of functionalized materials were characterized by CO2 adsorption, N2 adsorption, SEM, TEM, and NMR. The results of this work indicates that functionalization in toluene is better than functionalization in ethanol, in order to anchor the largest number of APTES molecules on SBA-15 surface. For the same purpose, during functionalization process, the use of nitrogen atmosphere is better than the use of air atmosphere.