Comparative study of the adsorption from aqueous solutions and the desorption of phenol and nonylphenol substrates on activated carbons

Adsorption of phenol and nonylphenol from aqueous solutions on microporous activated carbons has been studied. The phenol isotherm changes from L-shap ed for surface oxygen group free carbon (I sample) to a two-stepped isother m for oxidized carbon (IN sample, HNO3 treated) Furthermore, the adsorbed a mounts diminish in about 25% on IN carbon. It is proposed that a change in the adsorption mechanism take place; i.e., weak interaction forces between the rr electrons in phenol and the pi electron in carbon are present on the original I carbon, while a donor-acceptor complex on the oxidized IN carbo n is operating between basic surface oxygen groups and phenol aromatic ring s. The shape of nonylphenol isotherms is two-stepped for both carbons. The introduction of acidic oxygen surface groups on the carbon enhances the spe cific nonylphenol adsorption by about 40%. This may be interpreted as being due to the fact that nonylphenol is hydrogen-bonded to the oxidized carbon surface by means of acidic groups. Thermal desorption experiments indicate that phenol is mainly physisorbed. Thermal desorption further confirms tha t nonylphenol is possibly bonded to oxygen surface groups by hydrogen bonds . (C) 2001 Academic Press.