Mechanism of Adsorption of Phenols by Carbon Black from Aqueous Solution

Abstract

The adsorption of phenols by carbon black from aqueous solution was investigated. to discuss the mechanism of interaction on the adsorbent surface, referring to the partition coefficient in n-octanol/water system, Px.The shape of adsorption isotherm was discussed with respect to the position of substituents and also the degree of dissociation.There was found a linear relationship between Langmuir constant a and log Px. This result was explained thermodynamically on the assumption of a surface layer on the carbon black, concluding that the surface layer is considered to play the similar role to n-octanol layer in the partition experiment.Free energy of adsorption calculated from Langmuir constant b seemed to be an apparent one and to be influenced predominantly by the free energy of binding.Regarding the relationship between the adsorbed amount at an identical equilibrium concentration, Mc, and the equilibrium concentration at an identical adsorbed amount, Cm, the following equation was derived:log Mc=(1/λ)log (1/Cm)+κwhere λ and κ are constant.Plotting log Mc against log Px the derivatives were classified into groups I and II, suggesting the increase in adsorption of group I may be predominantly due to the tendency of the hydrophobic bonding, while that of group II may be influenced by the free energy of binding in addition to the tendency of the hydrophobic bonding.