Proton Adsorption on a Titanium Oxide in the Presence of Bicarbonate

Abstract

AbstractThe very high concentration of aqueous CO2 species below ground highlights a need to fully characterize the physicochemical behavior of this compound in the soil environment. This study focused on the adsorption of bicarbonates by a Ti oxide, and on its effects on the adsorption of protons, which was measured by the backtitration technique. The inorganic C adsorbed on the Ti oxide from pH 1.5 to 10 with a broad maximum at pH 4 to 6. For every molecule of inorganic C adsorbed (expressed as HCO3 adsorbed), an average of 2.3 protons were removed from the liquid phase (either by coadsorption or neutralization of the proton). The point of zero salt effect (PZSE) also increased from pH 5.7 to 6.2. The high stoichiometry of 2.3 suggests that the bicarbonate will also affect the desorption of cationic impurities; higher levels of Na, Ca, and Mg were measured in the liquid phase in the presence of inorganic C at pH 4. This study indirectly highlights that modeling the adsorption of protons by an oxide (even a “simple” one like Ti oxide) can be easily complicated by the presence of low levels of inorganic C or the presence of adsorbed cationic impurities.