Molecular-scale study of Cr(vi) adsorption onto lepidocrocite facets by EXAFS, in situ ATR-FTIR, theoretical frequency calculations and DFT+U techniques

Abstract

Lepidocrocite, as a ubiquitous iron mineral, is widely detected as different morphologies in natural environments, controlling the mobility and availability of heavy metal ions (HMIs). These different morphologies of lepidocrocite...

Facet-Dependent Competitive Adsorption Mechanisms of Chromate and Oxalic Acid on γ-FeO(OH) Nanocrystals

“…Hereafter, the higher thickness of R-LEP also indicated a relatively high ratio of {001}/{010}-exposed lepidocrocite facets (Figures d,e). According to our previous estimation, the proportion of {010} and {001} facets on P-LEP was about 89.5% and 8.1%, while these on R-LEP reached at 67.6 and 30.0%, respectively (Figure f). Moreover, the surface reactivity of lepidocrocite was determined by the type of active sites.…”

“…The adsorption capacity for Cr(VI) could be expressed by the normalization of the specific surface area (P-LEP: 177 m 2 •g −1 , R-LEP: 61 m 2 • g −1 ). 13 As shown in Figure 2a, the Cr(VI) adsorption amount decreased with increasing OA concentration as the reactions reached equilibrium, indicating that competitive adsorption occurred between these two anions. Herein, R-LEP exhibited more efficient adsorption performance than P-LEP.…”

“…To further resolve Cr(VI) adsorption speciation, the theoretical frequencies of the interfacial coordination config- urations (Figure 5c,d) were calculated with the cluster models according to our previous study. 13 The corresponding theoretical vibrational frequencies of the protonated monodentate binuclear (HMB) structure on the {010} facet were at 989, 956, 886, and 845 cm −1 , while the bidentate binuclear (BB) complex on the {001} facet possessed four peaks at 952, 929, 834, and 807 cm −1 . 13 These peaks could be well fitted to those of experimental frequencies (Figure 5e), indicating that the two Cr(VI) surface coordination modes were the dominant configurations on lepidocrocite, which were consistent with Cr K-edge EXAFS fitting analysis.…”

“…Combined with the optimal fitting results of the first shell (Cr–O), the energy shift values were then fixed for the higher shell fitting. In addition, the FEFF model was used for calculating the reference amplitude functions and the scattering paths of phase shifts …”

Chemical speciation and distribution of adsorbed Cd(ii) on goethite: influence of pH and sulfate

“…[1][2][3] Cadmium in soil systems is strongly sequestrated by the soil solid-phase component, including oxide minerals, clay minerals, soil organic matter, etc. Iron (oxyhydr)oxides are omnipresent in soil systems, whose size often ranges from the nanometer scale to the micrometer scale, considerably contribute to the specific surface areas of soils, and possess a significant number of reactive surface hydroxyl sites, [4][5][6][7] and thus they are considered as important geosorbents and carriers that severely influence the bioavailability and migration of cadmium elements in soil. 8,9 Because of the importance of soil iron (oxyhydr)oxidewater interface reactions, the retention/bonding mechanism of cadmium on iron (oxyhydr)oxide minerals has been discussed extensively.…”