X-ray absorption spectroscopy of Co(II) sorption complexes on quartz (α-SiO2) and rutile (TiO2)

摘要: Abstract The local molecular structure of Co(II) surface complexes sorbed to two pure mineral substrates, quartz (α-SiO 2 ) and rutile (TiO ), was examined with X-ray absorption spectroscopy (XAS) extended fine (EXAFS) analysis. Absorption spectra were collected for samples equilibrated Co solutions under- over-saturated respect solid Co-hydroxide phases (0.15–3.00 mM) at coverages 0.63–9.51 μmol m −2 equilibration times 23 h 21 days. Quantitative analysis the EXAFS indicates no significant structural differences in atomic environment around quartz, regardless coverage or time. For all Co/quartz samples, is similar (but not identical) that solid, crystalline cobalt hydroxide (Co(OH) (S)), Cobalt octahedrally coordinated by six O atoms 2.06–2.11 A; second-neighbor backscatterers are found 3.11–3.12 A, slightly contracted relative CoCo distance Co(OH) (s)(3.173 A). These results multiple-scattering suggest formation of, primarily, large, multinuclear disordered hydroxide-like precipitates quartz. sorption on rutile, vary changes distinctly different from examined. At low coverages, apparently sorbs directly as mononuclear small complexes. This indicated three Ti distinct distances, 2.95–2.99 A 3.60–3.63 Co. CoTi distances TiTi bulk structure. number has diffused into but rather occupies Ti-equivalent sites surface. high eleven days, average backscattering increases, indicating larger-sized complexes, do resemble those either (s). Analysis these Co/rutile near expected anatase, a TiO polymorph, suggesting geometry octahedra rutile/water interface cation anatase. We may be attributed availability reactive which structurally favorable octahedrally-coordinated 2+ .