Confocal microscopy and femtosecond-based second-harmonic generation characterization of the interaction of chromium ions with environmental surfaces

Investigating the interaction of silicon and aluminum oxides with aqueous solutions containing chromium ions is important for environmental studies and technological applications. We review bulk thermodynamic adsorption experiments of trivalent and hexavalent chromium with various natural and synthetic surfaces. Subsequently, we review two optical probes aimed at characterizing sub-surface and molecular interactions associated with the adsorption process. Laser-scanning confocal fluorescence microscopy has been used to investigated silica gel/chromium interactions and particle morphology. Surface second-harmonic generation spectroscopy has been explored to study chromium adsorption at the quartz/water interface.

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► Sorption of chromium in silica and quartz has been optically probed.
► Confocal microscopy probes sorption sites inside silica doped with pyranine.
► The same approach is used to study Cr(III) uptake and distribution in silica.
► Second-harmonic generation (SHG) probes Cr(VI) at the quartz–water interface.
► SHG measurements inform on kinetics, binding, and orientation of Cr(VI).