The effect of the physical and chemical characteristics of activated carbons on the adsorption energy and affinity coefficient of Dubinin equation

The dependency of adsorption energy (E) and affinity coefficient (β) of Dubinin equations (Dubinin-Radushkevich (DR) or Dubinin-Astakhov (DA)) on surface chemistry and porosity of activated carbons was investigated by analyzing adsorption of nitrogen, benzene, trichloroethylene (TCE), and water vapor by several surface-modified activated carbons and carbon fibers. For all studied nonpolar adsorbates, carbons with smaller average micropores showed higher adsorption energies independent of their surface chemistry. For water vapor, carbons with higher surface polarities showed higher adsorption energies due to specific adsorbate-adsorbent interactions. Adsorption energies increased with decreasing average micropore widths. βN2,DR for different carbons were observed to vary in the 0.292-0.539 range. Carbons with higher degrees of mesoporosity had higher βN2,DR values, while no dependency was observed between βN2,DR and surface chemistry. A comparison of DR and DA cases indicates that: (1) the average value of βN2,DA is considerably above the classical value of this parameter; and (2) the range of βN2,DA values were smaller compared to βN2,DR, despite a wide range of mesoporosity of carbons examined. Obtained βTCE,DR values varied in the 0.952-1.243 range, with an average value of 1.085±0.083, independent of surface chemistry or porosity of activated carbons. A similar result was observed for βTCE,DA. βH2O,DR values of different granular and fibrous activated carbons changed in the range of 0.081-0.271. They depended more on the carbon surface chemistry and less on the porosity. A similar result was obtained when DA equation was considered.