Adsorption of anionic and cationic dyes on activated carbons with different surface chemistries

The influence of the surface chemical groups of an activated carbon on the removal of different classes of dyes is evaluated. Starting from the same material (NORIT GAC 1240 PLUS), the following treatments were carried out in order to produce a series of samples with different surface chemical properties but with no major differences in their textural properties: oxidation in the liquid phase with 6 M HNO3 and 10 M H2O2 (acid materials) and heat treatment at 700degreesC in H-2 or N-2 flow (basic materials). The specific micropores volume and mesopores surface area of the materials were obtained from N-2 adsorption equilibrium isotherms at 77 K. The surface chemistry was characterised by temperature programmed desorption, by the determination of the point of zero charge (pH(pzc)) and by the evaluation of the acidity/basicity of the samples. Elemental and proximate analyses were also carried out. Equilibrium isotherms of selected dyes (an acid, a basic and a reactive dye) on the mentioned samples were obtained and the results discussed in relation to their surface chemistry. In general, the Langmuir model provided the best fit for the adsorption data. It is shown that the surface chemistry of the activated carbon plays a key role in dye adsorption performance. The basic sample obtained by thermal treatment under H-2 flow at 700degreesC is the best material for the adsorption of all the tested dyes. (C) 2004 Elsevier Ltd. All rights reserved.