Adsorption of Phenolic Compounds from Aqueous Solutions, by Activated Carbons, Described by the Dubinin−Astakhov Equation

Abstract

It is shown that the adsorption of phenol and 3-chlorophenol from aqueous solutions, by basic active carbons and at an equilibrium solution pH below that of dissociation of the phenols, can be described by an equation of the DRK type with exponent n ) 4. The principle of temperature invariance is fulfilled between 283 and 313 K, which means that predictions can be made on the basis of a characteristic energy, Es, and of affinity coefficients, βs, relative to phenol. This approach presents an advantage over the traditional Langmuir isotherm. Moreover, the comparison of the limiting amounts adsorbed by the different carbons suggests that phenol and 3-chlorophenol are adsorbed in a monolayer as observed for carbon blacks, except in the case of activated carbons with a low degree of activation in which molecular-sieve effects can take place. Similar conclusions are obtained from the enthalpies of immersion into the aqueous solutions and their comparison with graphitized carbon blacks.

Performance of templated mesoporous carbons in supercapacitors

“…It has been reported [35] that the specific surface areas estimated from the analysis of the nitrogen isotherms by the comparison plot (S comp ) and DFT (S DFT ) were in good agreement with the values obtained from the technique outlined by Stoeckli et al [3,34,35], based on the enthalpy of immer- sion into dilute aqueous solution of phenol (S phenol ). Following an earlier study dealing with exclusively mesoporous carbons [33], where the enthalpy of immersion into benzene (S benzene ) also provides information on the surface area itself, the average surface area obtained from the four different techniques, S total = (S comp + S phenol + S benzene + S DFT )/4, provides a reliable assessment of the surface area.…”

“…Therefore, different techniques were used [3,[33][34][35]. The solids were characterized by the standard techniques based on N 2 adsorption-desorption isotherms at 77 K (Micromeritics ASAP 2010) and immersion calorimetry at 293 K (Tian-Calvet-type calorimeter).…”

“…The analysis of the nitrogen isotherms by different methods such as the BET equation, the comparison plot based on the reference nitrogen isotherm for Vulcan 3G and the DFT method, assuming cylindrical pores, led to independent assessments of the surface of the carbons. This data was further crosschecked with the corresponding enthalpies of immersion of the carbons into benzene and into dilute aqueous solution of phenol (0.4 M) [34]. The latter approach provides the total surface area on the basis of specific enthalpies of immersion of −0.114 J m −2 for benzene and −0.109 J m −2 for phenol adsorbed selectively from an aqueous solution onto the carbon surface, where it forms a monolayer.…”

Heterogeneity of multiwalled carbon nanotubes based on adsorption of simple aromatic compounds from aqueous solutions

“…It can be assumed that in the case of dilute solutions the mechanism of adsorption on the nanotubes is similar to ACs, i.e., the total surface is covered by a monolayer of phenol (Stoeckli et al 2001;Fernandez et al 2003). Water is always adsorbed preferentially by the oxygen-containing surface groups ).…”

Application of the Sips model to the calculation of maximum adsorption capacity and immersion enthalpy of phenol aqueous solutions on activated carbons

“…The adsorption process of phenol from aqueous solution on activated carbon depends on variables such as the activated carbon surface area, the functional groups on its surface and their load, the pH of the solution and the interactions between ions, among other factors [4,5].…”