Effect of electrochemical treatments on the surface chemistry of activated carbon

The effect of the electrochemical treatment (galvanostatic electrolysis in a filter-press electrochemical cell) on the surface chemistry and porous structure of a granular activated carbon (GAC) has been analyzed by means of temperature-programmed desorption and N-2 (at 77 K) and CO2 (at 273 K) adsorption isotherms. The anodic and cathodic treatments, the applied current (between 0.2 and 2.0 A) and the type of electrolyte (NaOH, H2SO4 and NaCl) have been studied as electrochemical variables. Both anodic and cathodic treatments lead to an increase in the surface oxygen groups. A suitable choice of the electrochemical variables allows a selective modification of the amount and the nature of the surface oxygen groups of the GAC. In general, the electrochemical treatment does not modify significantly the textural properties of the GAC. However, an increase in the porosity of the activated carbon occurs during the cathodic treatment in oxygen-saturated solutions. This result is interpreted as a consequence of carbon gasification driven by reaction with peroxide species generated by electroreduction of oxygen. The anodic treatment in NaCl produces oxidation degrees comparable to those achieved by classical chemical oxidations. (C) 2008 Elsevier Ltd. All rights reserved.