Surface Diffusion on Active Carbon in Adsorption From Solutions

Effective surface diffusivities (Ds ) for the adsorption process: of p-nitrophenol (PNF) on 14 types of carbon were determined. The carbons used differed in both their pore structure and the chemical character of the surface. On the basis of analysis of the most frequently used adsorption isotherms, the B-parameter of the Dubinin-Raduszkiewicz equation and the standard change of free energy of activation were suggested, as the values that can determine the Ds variability. The number of acidic and basic oxygen functional groups to be found on the carbon surface can be used for the same purpose. The increase of the Ds value with the increase of basicity of the surface is due to the loss of aromatic character by the n electron system of the planar surfaces of the microcrystalliles and the simultaneous decrease of proportional covering the surface with oxygen. The decrease of the Ds value with the increase of acidity is due to higher specific interactions which results from the increase of the degree of covering of the surface with oxygen and from the ability to form hydrogen bonds with the —OH group of the PNF molecule.