| Summary: | The isosteric enthalpy of adsorption (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mo>Δ</mo><mrow><mi>a</mi><mi>d</mi><mi>s</mi></mrow></msub><mover accent="true"><mi>h</mi><mo>˙</mo></mover></mrow></semantics></math></inline-formula>) of CO<sub>2</sub> 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 CO<sub>2</sub> isotherms were obtained. Using the nine isotherms and the Clausius–Clapeyron equation, the reference value for <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mo>Δ</mo><mrow><mi>a</mi><mi>d</mi><mi>s</mi></mrow></msub><mover accent="true"><mi>h</mi><mo>˙</mo></mover></mrow></semantics></math></inline-formula> was found. The reference value was compared with those <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mo>Δ</mo><mrow><mi>a</mi><mi>d</mi><mi>s</mi></mrow></msub><mover accent="true"><mi>h</mi><mo>˙</mo></mover></mrow></semantics></math></inline-formula> obtained, considering some arrangement of three or five CO<sub>2</sub> isotherms. Finally, it was found that at 298 K and 1 bar, the total amount of CO<sub>2</sub> adsorbed is 2.32, 0.53, and 1.37 mmol g<sup>−1</sup> for CMF, SBA-15, and SBA-15_APTES, respectively. However, at a coverage of 0.38 mmol g<sup>−1</sup>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mo>Δ</mo><mrow><mi>a</mi><mi>d</mi><mi>s</mi></mrow></msub><mover accent="true"><mi>h</mi><mo>˙</mo></mover></mrow></semantics></math></inline-formula> is worth 38, 30, and 29 KJ mol<sup>−1</sup> for SBA-15_APTES, CMFs, and SBA-15, respectively. So, physisorption predominates in the case of CMF and SBA-15 materials, and the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mo>Δ</mo><mrow><mi>a</mi><mi>d</mi><mi>s</mi></mrow></msub><mover accent="true"><mi>h</mi><mo>˙</mo></mover></mrow></semantics></math></inline-formula> 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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mo>Δ</mo><mrow><mi>a</mi><mi>d</mi><mi>s</mi></mrow></msub><mover accent="true"><mi>h</mi><mo>˙</mo></mover></mrow></semantics></math></inline-formula>. This happens in such a way that the use of low temperatures (263–283 K) tends to produce higher <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mo>Δ</mo><mrow><mi>a</mi><mi>d</mi><mi>s</mi></mrow></msub><mover accent="true"><mi>h</mi><mo>˙</mo></mover></mrow></semantics></math></inline-formula> values, while the use of high temperatures (283–303 K) decreases the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mo>Δ</mo><mrow><mi>a</mi><mi>d</mi><mi>s</mi></mrow></msub><mover accent="true"><mi>h</mi><mo>˙</mo></mover></mrow></semantics></math></inline-formula> values.
|
|---|