A comparison between oxidation of activated carbon by electrochemical and chemical treatments

The anodic oxidation of a granular activated carbon (GAC) in NaCl solution has been studied. The influence of the electrocatalyst-anode material, applied current and time of treatment on both the surface chemistry and porous texture properties of the GAC has been analyzed. For comparison purposes, the same GAC has been treated with three of the classical chemical oxidants: HNO3, H2O2 and (NH4)2S2O8 at different concentrations and for different times. Results show that the anodic treatment in NaCl causes a remarkable oxidation of the AC without modifying significantly its textural properties. TPD profiles and the linear dependence of the amount of CO- and CO2-evolution against the oxidation level denotes that surface oxygen groups of similar nature and composition are formed anodically, regardless of the anode material. The achieved oxidation degree depends on the different ability of each anode for the electrochemical generation of highly oxidizing chlorine species, and it increases progressively with the applied current and the time of treatment. In general, for similar treatment times, the anodic treatment in NaCl can produce oxidation degrees much higher than the chemical treatment with (NH4)2S2O8, which has been found to be the most oxidative chemical studied in this work.