A TIME-RESOLVED XANES STUDY OF AN ORGANO-CLAY REDOX SYSTEM

In situ, time-resolved X-ray absorption near edge structure (XANES) sp ectroscopic measurements of tetraphenylboron (TPB)-treated Fe-bearing clay minerals were conducted to investigate whether smectite structura l Fe was reduced during surface-enhanced oxidative degradation of TPB. Reference samples were prepared by reducing varying amounts of struct ural Fe with Na-dithionite in an inert atmosphere. Analysis of the Fe K-alpha X-ray fluorescence near edge structure of reference and TPB-tr eated samples was accomplished by comparing the ratios of edge crest i ntensities at energies corresponding to oxidized and dithionite-reduce d samples following intensity normalization and energy calibration. Ab out 15% of nontronite structural Fe was reduced during the course of t he reaction with TPB, whereas more than 50% of the structural Fe in mo ntmorillonite was reduced. XANES spectroscopy provided additional spec troscopic evidence for differences in the reactivity of crystallograph ic sites of Fe within montmorillonites (both cis and trans Fe) and non tronites (predominantly cis Fe) and suggests that TPB reacted preferen tially with trans Fe.