Isosteric Enthalpy Behavior of CO2 Adsorption on Micro-Mesoporous Materials: Carbon Microfibers (CMFs), SBA-15, and Amine-Functionalized SBA-15

The isosteric enthalpy of adsorption (Delta(ads)(h)over dot) 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)(h)over dot was found. The reference value was compared with those Delta(ads)(h)over dot 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)(h)over dot 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)(h)over dot 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)(h)over dot. This happens in such a way that the use of low temperatures (263-283 K) tends to produce higher Delta(ads)(h)over dot values, while the use of high temperatures (283-303 K) decreases the Delta(ads)(h)over dot values.