THE EFFECT OF ZETA-POTENTIAL OF ACTIVATED CARBON ON THE ADSORPTION OFDYES FROM AQUEOUS-SOLUTION .1. THE ADSORPTION OF CATIONIC DYES - METHYL GREEN AND METHYL VIOLET

The effect of the zeta (zeta) potential of activated carbon on the ads orption of cationic dyes from aqueous solution has been studied. The p H(zpc) of the zero-point charge of activated carbon has been measured by microelectrophoresis. Plots of saturated amount adsorbed for methyl green and methyl violet on activated carbon versus zeta potential hav e also been determined. The results show that the electrostatic intera ction between cationic dyes and the surface of activated carbon has a great effect on adsorption capacity. When the zeta potential of activa ted carbon is lower than -30 mV, the electrostatic attraction between cationic dyes and the carbon surface greatly increases the adsorption capacity. However, when the potential of activated carbon is between - 30 and +60 mV the electrostatic force between dyes and the carbon surf ace is diminished and the adsorption capacity of activated carbon is a pproximately unchanged. The capacity is significantly reduced due to t he electrostatic repulsion between cationic dyes and the carbon surfac e when the zeta potential is higher than +60 mV. The adsorption kineti c and thermodynamic parameters as functions of pH have been determined . The mechanism for adsorption of cationic dyes on activated carbon ha s also been studied. (C) 1994 Academic Press. Inc.