The maximum levels of Cr VI removal

Upon analysis of the reacted Cr(III) phase on the Pd-BnM, the Cr K edge XANES spectra bear more resemblance to those previously reported for Cr(OH)3 and CrOOH [65] and [66], lacking the edge feature of the spinel FeCr2O4 standard presented here. Further to this, EXAFS analyses and subsequent fitting of data from the samples of Pd-BnM formate and H2 reacted with model Cr(VI) solutions, indicated that the same Cr phase forms irrespective of the GF109203X donor used. The fitted Cr-O shell (1.97–1.98 Å) is consistent with a Cr(III) octahedral co-ordination, where Cr(VI) typically forms a tetrahedral co-ordination at shorter interatomic distances of 1.67–1.69 Å [54], [58] and [67]. Considering the TEM-EDX maps which indicate overgrowth of the Fe surface with a discreet Cr phase, the two outer shells (3.01 and 3.60–3.61 Å) are likely to be Cr-Cr. The first Cr-Cr/Fe shell (3.01 Å) is consistent with the edge sharing distances reported for polymeric CrOOH polymorphs at 3.00–3.06 Å [57], [68], [69] and [70]. Significantly the fitted spectra lack the corner sharing Cr-Cr shell, at ∼3.98 Å [54] and [68], common to ?-CrOOH. The second fitted Cr-Cr/Fe shell (3.60–3.61 Å) has been interpreted previously as a double corner sharing path between adsorbed Cr(III) and Fe(III) hydroxides [70] and [71]. It is also pertinent capsid the fitted spectra lack the larger Cr-Cr atomic distance shells associated with chromite [58]. This supports TEM observations and previous studies [17], which suggest that the majority of Cr in such systems is in a non-magnetic surface phase, as opposed to incorporated into a spinel structure [72].