A time resolved XANES study of an organo-clay redox system

In situ, time-resolved X-ray absorption near edge structure (XANES) spectroscopic measurements of tetraphenylboron (TPB)-treated Fe-bearing clay minerals were conducted to investigate whether smectite structural Fe was reduced during surface-enhanced oxidative degradation of TPB. Reference samples were prepared by reducing varying amounts of structural Fe with Na-dithionite in an inert atmosphere. Analysis of the Fe K α X-ray fluorescence near edge structure of reference and TPB-treated samples was accomplished by comparing the ratios of edge crest intensities at energies corresponding to oxidized and dithionite-reduced samples following intensity normalization and energy calibration. About 15% of nontronite structural Fe was reduced during the course of the reaction with TPB, whereas more than 50% of the structural Fe in montmorillonite was reduced. XANES spectroscopy provided additional spectroscopic evidence for differences in the reactivity of crystallographic sites of Fe within montmorillonites (both cis and trans Fe) and nontronites (predominantly cis Fe) and suggests that TPB reacted preferentially with trans Fe.