Effects of Surface Functionalities on Adsorption

Aqueous solution of phenol is the most studied solution on the effects of functionalities on adsorption. As mentioned above, in light of the results of Grant and King (1990), the effects of functionalities on adsorption of phenols should be studied separately for reversible and irreversible adsorption. The results summarized below are for the total adsorption at equiUbilum. 

Dramatic effects of oxidation and reduction of the carbon surface on the adsorption of phenol and nitrobenzene were first shown by CoughUn and Ezra (1968). Surface oxygen functionalities were increased by oxidation with arruno-nium thiosulfate solution, and reduction was performed with zinc amalgam in HCl solution. The isotherms of phenol on three carbon samples are shown in 

Contrary to the effects of surface carboxyl and hydroxyl groups, the surface quinone (or carbonyl) groups acmally increased the adsorption of aromatics. Epstein et al. (1971) observed these effects with the adsorption of p-nitrophenol. Their explanation was that the carbonyl groups aid the adsorption of aromatics by involving the formation of an electron donor-acceptor complex of the aromatic ring with the surface carbonyl groups, as proposed earlier by Mattson et al. (1969). 

Simple experimental procedures are known for generating the two different types of acid oxygen groups on carbon (Cookson, 1978). Surface oxides developed by chemical treatment and dry oxidation at temperatures 400 °C are mainly the carboxyl and hydroxyl types. At temperatures 400 °C, the dry oxidation treatment yields mainly carbonyl groups (in the form of quinone and hydroquinone). 

The effects of oxygen functionalities on the adsorption of aliphatic compounds from their aqueous solutions have also been studied (Cookson, 1978 Jankowska et al., 1991 Radovic, 1996). The adsorption capacities of butyl disulfide and decane were both decreased by surface oxides (Cookson, 1978). Hence it was concluded that surface oxides hindered adsorption of nonpolar aliphatic compounds. 

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