Posts Tagged ‘XAS’

As a last post today, I want to draw your attention to a talk showcasing a very interesting use of X-ray spectroscopy to monitor redox changes in solution. It was one of those talks that you choose to go at the last minute out of pure curiosity andĀ ends up having an impact on your future experimental plans …

We know that the toxicity of arsenic (As) and chromium (Cr) depends, in part, on their redox state. Arsenic is more toxic in its reduced form, while Cr is more toxic in its oxidized form. Ginder-Vogel, from the U. of Delaware, showed that it is possible to monitor changes in As and Cr speciation over time in a batch experiment using quick-scanning X-ray absorption spectroscopy (Q-XAS). He said that their good-old synchrotron is perfect for the job since these older instruments are not powerful enough to oxidize the samples. Unfortunately, because the sensitivity is low, they need fairly high As (5 mM) and Cr (100 mM) concentrations; much higher than in natural environments. Ginder-Vogel concluded his interesting talk by showing that the rates of As redox reactions they measured are faster than those reported from batch experiments in other lab studies. He argued that this is due to XANES being able to “see” the whole bulk material, while in other laboratory studies only dissolved species are removed from the batch reactor for speciation measurements. Overall this seems to be a very promising method to study redox changes during precipitation/dissolution and adsorption experiments.


Update on sept. 11 2009 : The article related to this talk is now available on PNAS as open access (Ginder-Vogel et al., 2009)

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