XAFS Spectroscopy Study of Cu(II) Sorption on Amorphous SiO2and γ-Al2O3: Effect of Substrate and Time on Sorption Complexes

Grazing-incidence XAFS investigations of Cu(II) sorption products at α-Al2O3–water and α-SiO2–water interfaces

“…Cu sorbs to the ct-SiO2 (0001) surface as monodentate or bridging bidentate surface complexes, with the former being more likely. In general, the proposed structure of Cu complexes sorbed on a-A1203 and ec-SiO2 substrates investigated in this study are consistent with the observation that Cu sorption complexes are more tightly bound to the surface of cx-A1203 powders than Cu sorption complexes on am-SiO2 (Cheah, et al, 1998). Highresolution AFM or TEM images of the single crystal surfaces are required to determine if surface morphology is consistent with the proposed structure and distribution of Cu sorption species.…”

“…However, the relatively low uptake of Cu on the o~-SiO2 (0001) surface, and the absence of backscattering from neighboring atoms beyond the 2 nd shell Si atoms suggests that Cu forms a weakly bound monodentate surface complex. These observations are consistent with the bonding proposed for Cu(II) species sorbed on am-SiO2 colloids (Cheah, et al, 1998). …”

“…Distances to near-neighbor A1 atoms (2.78-2.93A) are consistent with edge-sharing bidentate Cu(II) complexes on both ct-A1203 (1-102) and (0001) surfaces. The orientation of the equatorial oxygen atoms relative to the surface and the Cu-A1 1 st shell distances, which are slightly longer than previously observed for edgesharing bidentate Cu complexes (Cheah, et al, 1998), suggest that the Cu complex is attached to the surface through an equatorial and an axial oxygen when bonded to a terrace site (see below). If a monodentate complex bonded to the surface through an axial oxygen did dominate Cu sorption on the two cc-A1203 surfaces, then we would not expect to observe structural order beyond the 1 st shell of A1 atoms.…”

Coordination variation of hydrated Cu2+/Br1− ions traversing the interfacial water in mesopores

“…The appearance of Cu-Si bonds indicates that the hydrated Cu 2+ ions are now directly attached to the pore surface, and R Cu-Si = 3.15 Å (with phase shift correction) together with N Cu-Si =1 support the view that monodentate binding of Cu 2+ ion to the SiO 4 tetrahedron is more favorable. 25 Now, a fact becomes clear: Cu 2+ ions will retain their bulk-like coordination structure until inner-sphere complexes are formed. Starting at φ de = 20%, the peak accentuated by the dashed line α on the dμ/dE curve for Cu K-edge (Figure 1(b)) shifts steadily towards lower energy.…”

Kinetics and Mechanism of Metal Retention/Release in Geochemical Processes in Soil - Final Report

“…Multinuclear metal hydroxides of Pb (II), Co (II), Cu (II), Ni (II) and Cr(III) on clay mineral oxides and aluminosilicates have been discerned with EXAFS (Papelis and Hayes, 1996;, Scheidegger, et al, 1996, Cheah, et al 1998, Elzinga and Sparks, 1999 and electron spin resonance (ESR) spectroscopy McBride et al,1984). The EPR studies of Cu(II) adsorption on titanium dioxide by Bleam and McBride (1986) suggests that Cu(II) forms hydrous clusters when the adsorption of Cu(II) exceeded a critical surface concentration (4% of monolayer coverage).…”