ζ-potential on carbons and carbides

Abstract A ζ-potential behavior of close to zero in high pH solutions is observed when carbons and carbides are treated with acetone and ultra-pure water in turn in order to improve the wetting of samples. The abnormal ζ-potential behavior can not be explained by the view of the dissociation of acidic functional groups, but could be accounted for by the effect of H2O and atmospheric CO2. The H2O effect contributes to the difference of ζ-potential between boiled and vacuum-dried carbons at pH 11. In addition, the rate of approaching zero for ζ-potential is relatively faster in the CO2-free aqueous solution than in an ambient aqueous solution. According to the complementary effect of H2O and atmospheric CO2, it allows us to postulate that atmospheric CO2 is adsorbed onto surface and ζ-potential is dependent on the dissociation of CO2. However, CO2 is replaced by H2O when H2O diffuses into the surface which causes the ζ-potential to approach zero. In addition, the atmospheric CO2 peak is detected in API-MS. The API-MS patterns exhibit no more than the broad CO2 peak at around 533 K for either active carbon or SiC, with a negligible number of carboxylic groups. An idea regarding the mechanism of the abnormal ζ-potential behavior is discussed.