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| - Kinetic Studies of Chromium (VI) Binding to Carboxylic Acid- and MethylEster-Functionalized Silica/Water Interfaces Important in Geochemistry
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| - Real-time kinetic measurements of hexavalent chromium binding to fused silica surfaces functionalized withcarboxylic acid and methyl ester terminal groups are performed in situ using resonantly enhanced surfacesecond harmonic generation (SHG) at pH 7 and 300 K. These functional groups were chosen because of theirhigh abundance in humic acids and related biopolymers. Kinetic measurements are conducted in thesubmonolayer regime using chromate solution concentrations ranging from 1 × 10-6 to 2 × 10-5 M. Theadsorption rates were analyzed using the standard Langmuir model and the Frumkin−Fowler−Guggenheimmodel. The desorption kinetics are consistent with a first-order process. These results indicate that hexavalentchromium mobility in carboxylic acid- and ester-rich soil environments increases with decreasing chromateconcentrations. Based on the measured half-lives of the adsorbed Cr(VI) species, remobilization of boundhexavalent chromium due to natural or anthropogenic events that lower the chromate concentration in theaqueous phase can occur within minutes.
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