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Gert Bernhard - One of the best experts on this subject based on the ideXlab platform.
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An EXAFS and TRLFS investigation on uranium(VI) sorption to pristine and leached albite surface
2020Co-Authors: Marcus Walter, Thuro Arnold, Andreas C Scheinost, Gerhard Geipel, Gert BernhardAbstract:Abstract Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0-6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10 −6 M U(VI) showed one silicon atom at a U-Si distance of 3.09 Å, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, =Si(O) 2 =UO 2 , on the Silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO 4 , resulting in surface material similar to Amorphous Silica Gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 Å. This indicates the formation of an inner-sphere surface complex. 2004 Elsevier Inc. All rights reserved
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an exafs and trlfs investigation on uranium vi sorption to pristine and leached albite surfaces
Journal of Colloid and Interface Science, 2005Co-Authors: Marcus Walter, Thuro Arnold, Andreas C Scheinost, Gerhard Geipel, Gert BernhardAbstract:Abstract Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0–6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10 −6 M U(VI) showed one silicon atom at a U Si distance of 3.09 A, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, Si(O) 2 UO 2 , on the Silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO 4 , resulting in surface material similar to Amorphous Silica Gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 A. This indicates the formation of an inner-sphere surface complex.
Marcus Walter - One of the best experts on this subject based on the ideXlab platform.
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An EXAFS and TRLFS investigation on uranium(VI) sorption to pristine and leached albite surface
2020Co-Authors: Marcus Walter, Thuro Arnold, Andreas C Scheinost, Gerhard Geipel, Gert BernhardAbstract:Abstract Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0-6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10 −6 M U(VI) showed one silicon atom at a U-Si distance of 3.09 Å, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, =Si(O) 2 =UO 2 , on the Silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO 4 , resulting in surface material similar to Amorphous Silica Gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 Å. This indicates the formation of an inner-sphere surface complex. 2004 Elsevier Inc. All rights reserved
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an exafs and trlfs investigation on uranium vi sorption to pristine and leached albite surfaces
Journal of Colloid and Interface Science, 2005Co-Authors: Marcus Walter, Thuro Arnold, Andreas C Scheinost, Gerhard Geipel, Gert BernhardAbstract:Abstract Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0–6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10 −6 M U(VI) showed one silicon atom at a U Si distance of 3.09 A, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, Si(O) 2 UO 2 , on the Silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO 4 , resulting in surface material similar to Amorphous Silica Gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 A. This indicates the formation of an inner-sphere surface complex.
Alain Walcarius - One of the best experts on this subject based on the ideXlab platform.
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factors affecting copper ii binding to multiarmed cyclam grafted mesoporous Silica in aqueous solution
Langmuir, 2009Co-Authors: Stephanie Goubertrenaudin, Mathieu Etienne, Stephane Brandes, Michel Meyer, Franck Denat, Benedicte Lebeau, Alain WalcariusAbstract:Single- as well as multi-anchored cyclam-functionalized Silica samples have been prepared by grafting Amorphous Silica Gel (K60) and mesostructured Silica (SBA-15) with silylated cyclam precursors bearing one, two, or four triethoxysilyl groups, respectively ascribed to cyclam-mono, cyclam-di, and cyclam-tetra. Their reactivity toward copper(II) has been thoroughly investigated in aqueous solution and discussed with respect to the number of arms tethering the ligand to the Silica surface and the structural ordering of the adsorbent in terms of capacity, long-term stability, and speed of access to the binding sites. Less-than-complete metal ion uptake was always observed, even in excess of cyclam groups with respect to solution-phase Cu(II), suggesting lower stability of immobilized complexes relative to those in solution. Therefore, the number of arms attaching cyclam moieties to the Silica walls (one, two, or four) was found to dramatically affect the binding properties of these hybrids toward copper(II), revealing significantly larger capacities when reducing the number of arms (less rigidity constraints in the macrocycle). In parallel, multiarm tethering resulted in better chemical resistance toward degradation as evidenced by UV-visible monitoring of Cu-cyclam complexes in solution (i.e., more ligand leaching from the adsorbent for singly tethered cyclam). On the other hand, electron spin resonance (ESR) experiments did not evidence significant differences between complexes bearing one, two, or four alkyl arms, since all Cu(II)-cyclam surface complexes were found to be hexacoordinated with a strong equatorial ligand field. Comparison of Amorphous Gels and mesostructured materials indicates that the binding properties of the adsorbents were hardly influenced by their level of ordering, suggesting that accessibility to the binding sites was not the limiting factor. Some advantage belonging to mesostructured adsorbents was however observed with respect to the rate of access to the active centers at pH values close to neutrality (due to faster mass transport), but this was no more the case when operating at lower pH values where the formation of the Cu-cyclam complex became the rate-determining step, as pointed out by electrochemistry.
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rate of access to the binding sites in organically modified Silicates 2 ordered mesoporous Silicas grafted with amine or thiol groups
Chemistry of Materials, 2003Co-Authors: Alain Walcarius, Mathieu Etienne, Benedicte LebeauAbstract:Five different ordered mesoporous Silica samples displaying various pore sizes and structures (two small-pore MCM-41, two large-pore MCM-41, and one small-pore MCM-48) and one Amorphous Silica Gel have been grafted with either aminopropyl or mercaptopropyl groups. The resulting aminopropyl-grafted Silicas (APS) and mercaptopropyl-grafted Silicas (MPS) have been studied in solution via protonation of APS and metal ion binding on both APS and MPS. Special attention was given to characterize the accessibility to the binding sites and to the speed at which the reactants are reaching these reactive centers inside the mesoporous materials. Results have been obtained from batch experiments, by monitoring the reactant depletion in suspensions containing APS or MPS particles, and discussed with respect to the structure and porosity of the organic−inorganic hybrids. As a general trend, both accessibility and rate of access to the reactive sites were higher with ordered mesoporous solids than with Amorphous material...
Gerhard Geipel - One of the best experts on this subject based on the ideXlab platform.
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An EXAFS and TRLFS investigation on uranium(VI) sorption to pristine and leached albite surface
2020Co-Authors: Marcus Walter, Thuro Arnold, Andreas C Scheinost, Gerhard Geipel, Gert BernhardAbstract:Abstract Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0-6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10 −6 M U(VI) showed one silicon atom at a U-Si distance of 3.09 Å, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, =Si(O) 2 =UO 2 , on the Silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO 4 , resulting in surface material similar to Amorphous Silica Gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 Å. This indicates the formation of an inner-sphere surface complex. 2004 Elsevier Inc. All rights reserved
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an exafs and trlfs investigation on uranium vi sorption to pristine and leached albite surfaces
Journal of Colloid and Interface Science, 2005Co-Authors: Marcus Walter, Thuro Arnold, Andreas C Scheinost, Gerhard Geipel, Gert BernhardAbstract:Abstract Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0–6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10 −6 M U(VI) showed one silicon atom at a U Si distance of 3.09 A, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, Si(O) 2 UO 2 , on the Silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO 4 , resulting in surface material similar to Amorphous Silica Gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 A. This indicates the formation of an inner-sphere surface complex.
Thuro Arnold - One of the best experts on this subject based on the ideXlab platform.
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An EXAFS and TRLFS investigation on uranium(VI) sorption to pristine and leached albite surface
2020Co-Authors: Marcus Walter, Thuro Arnold, Andreas C Scheinost, Gerhard Geipel, Gert BernhardAbstract:Abstract Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0-6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10 −6 M U(VI) showed one silicon atom at a U-Si distance of 3.09 Å, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, =Si(O) 2 =UO 2 , on the Silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO 4 , resulting in surface material similar to Amorphous Silica Gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 Å. This indicates the formation of an inner-sphere surface complex. 2004 Elsevier Inc. All rights reserved
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an exafs and trlfs investigation on uranium vi sorption to pristine and leached albite surfaces
Journal of Colloid and Interface Science, 2005Co-Authors: Marcus Walter, Thuro Arnold, Andreas C Scheinost, Gerhard Geipel, Gert BernhardAbstract:Abstract Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0–6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10 −6 M U(VI) showed one silicon atom at a U Si distance of 3.09 A, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, Si(O) 2 UO 2 , on the Silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO 4 , resulting in surface material similar to Amorphous Silica Gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 A. This indicates the formation of an inner-sphere surface complex.