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Interaction of Cr3+ with Silica Gel at the Aqueous Interface Using Fluorescence in Sodium Dodecyl Sulfate Micelles and Confocal Fluorescence Microscopy

2012    Idrees, Muhammad; Silva, Marcelo; Silva, Alessandra F.; Zimmermann, Lizandra M.; Bruch, Jociane; Mendonca, Caio O.; Almerindo, Gizelle I.; Nome, Rene A.; Atvars, Teresa D. Z.; Fiedler, Haidi D.; Nome, Faruk

Chemical composition and species distribution in clay surfaces are key factors which control sorption and desorption processes of Cr3+ between sediment and water. Adsorption of Cr3+ on silica gel has been studied by following the quenching of naphthalene fluorescence in aqueous sodium dodecyl sulfate (SDS) micelles, which concentrate naphthalene and Cr3+ in the micellar surface. Adsorption for pH <= 5 follows a Langmuir model, and experimental data fitting is successfully described by a model based on discrete sites on the surface with variable charge as a function of pH. Probably the mechanism of Cr3+ adsorption at the silica gel surface is predominantly electrostatic, with outer-sphere complexation and ion exchange with adsorbed H+ ions. Confocal laser-scanning fluorescence microscopy measurements reveal the Cr3+ spatial distribution in three dimensions. Specifically, both images and spectra measured with confocal microscopy indicate that Cr3+ is distributed across the entire particle, not just adsorption at the surface.