CO2 adsorption fitting models using biochar

https://doi.org/10.1016/j.seppur.2022.121131

“Table 4 illustrates the parameters of two fitting models. Coefficient of determinations from Freundlich shows a good correlation (R₂ greater than 0.99) of describing CO₂ uptake performance under different relative pressures, which follows the similar rule that the Freundlich equation implies a perfect fit to carbonous materials on carbon capture [50]. Moreover, thermodynamics analysis is also explored in terms of the change in enthalpy (ΔH⁰) and entropy (ΔS⁰) of the adsorption process under different temperatures. Moreover, it is estimated according to Van’t Hoff’s equation:”

“Fig. 5. Influences of temperatures on coefficients.” https://doi.org/10.1016/j.seppur.2022.121131

“As illustrated in Table 4 and Fig. 5, the negative sign of ΔH⁰ (-35.876 kJ·mol⁻¹) suggests the exothermic process of CO₂ adsorption, whilst the entropy (−11.155 J·mol⁻¹·K⁻¹) expresses the orderliness of the adsorption system. It is noted that the value of ΔH⁰ is lower than 80 kJ·mol⁻¹ [51], which is recognized as a standard to distinguish physical or chemical CO₂ adsorption; BBC-KOH mainly follows physical sorption to capture CO₂. Besides, the turbidity would be reduced according to the value of ΔS⁰, proving the atmospheric CO₂ would be captured by adsorbents and remain on the surface or in the pore textural to achieve the negative sign of ΔH⁰ [52].”