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Experimental and theoretical approaches for the surface interaction between copper and activated sludge microorganisms at molecular scale.

Luo HW, Chen JJ, Sheng GP, Su JH, Wei SQ, Yu HQ - Sci Rep (2014)

Bottom Line: The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis.XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds.To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes.

View Article: PubMed Central - PubMed

Affiliation: CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry.

ABSTRACT
Interactions between metals and activated sludge microorganisms substantially affect the speciation, immobilization, transport, and bioavailability of trace heavy metals in biological wastewater treatment plants. In this study, the interaction of Cu(II), a typical heavy metal, onto activated sludge microorganisms was studied in-depth using a multi-technique approach. The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis. EPR spectra indicated that Cu(II) was held in inner-sphere surface complexes of octahedral coordination with tetragonal distortion of axial elongation. XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds. To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes. These results are useful to better understand the speciation, immobilization, transport, and bioavailability of metals in biological wastewater treatment plants.

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X-ray absorption near-edge structure of reference compounds and Cu- activated sludge under different conditions.
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f3: X-ray absorption near-edge structure of reference compounds and Cu- activated sludge under different conditions.

Mentions: The K-edge X-ray absorption spectra of Cu(II) complexing with the activated sludge before and after EPS extraction at various pH values were collected. The Cu K-edge XANES spectra of samples and various standards are shown in Fig. 3. The pre-edge peak at 8976 eV (Arrow 1) was assigned to the 1s to 3d dipole-forbidden electronic transition (probably hybridized by p orbitals of the ligands)23. Another peak at 8981 eV (Arrow 2) was resulted from reduced Cu(I) signal. However, the presence of a shoulder at 8981 eV in the Cu absorption edge spectra and the absence of a pre-edge from 8976 eV indicate the presence of Cu(I) in the samples. This peak showed a slightly increase after sequential scans, suggesting a radiation-induced reduction of Cu(II)24. The other two peaks in the Cu K-edge XANES spectra (Arrows 3 and 4) were attributed to the 1s to 4p main edge electron transitions. The splitting of the derivative XANES spectra might result from anisotropic square planar symmetry of Cu(II) compounds, or could be referred to the tetragonal distortion of the CuO6 octahedron due to Jahn-Teller effect. These inflections provided information about the three dimensional geometry and coordination environment of Cu in the Cu complexes. The Peak 3 and Peak 4 corresponded respectively to the 1s → 4p and 1s → continuum transitions for Cu(II) compounds in octahedral symmetry2526. The energy gap between the two peaks was 5.0 eV (Fig. 3), attributed to the distortion of 4pz orbit in metalic center. This obtained value was of a similar level to those for other Cu(II) compounds in slightly tetragonally distorted octahedral environments, and was also in accordance with the EPR analytical results. Moreover, the sample spectra in our work had a distinct shoulder peak, which might be due to the degree of axial distortion and the covalence of the equatorial ligands bonded to Cu(II).


Experimental and theoretical approaches for the surface interaction between copper and activated sludge microorganisms at molecular scale.

Luo HW, Chen JJ, Sheng GP, Su JH, Wei SQ, Yu HQ - Sci Rep (2014)

X-ray absorption near-edge structure of reference compounds and Cu- activated sludge under different conditions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4233339&req=5

f3: X-ray absorption near-edge structure of reference compounds and Cu- activated sludge under different conditions.
Mentions: The K-edge X-ray absorption spectra of Cu(II) complexing with the activated sludge before and after EPS extraction at various pH values were collected. The Cu K-edge XANES spectra of samples and various standards are shown in Fig. 3. The pre-edge peak at 8976 eV (Arrow 1) was assigned to the 1s to 3d dipole-forbidden electronic transition (probably hybridized by p orbitals of the ligands)23. Another peak at 8981 eV (Arrow 2) was resulted from reduced Cu(I) signal. However, the presence of a shoulder at 8981 eV in the Cu absorption edge spectra and the absence of a pre-edge from 8976 eV indicate the presence of Cu(I) in the samples. This peak showed a slightly increase after sequential scans, suggesting a radiation-induced reduction of Cu(II)24. The other two peaks in the Cu K-edge XANES spectra (Arrows 3 and 4) were attributed to the 1s to 4p main edge electron transitions. The splitting of the derivative XANES spectra might result from anisotropic square planar symmetry of Cu(II) compounds, or could be referred to the tetragonal distortion of the CuO6 octahedron due to Jahn-Teller effect. These inflections provided information about the three dimensional geometry and coordination environment of Cu in the Cu complexes. The Peak 3 and Peak 4 corresponded respectively to the 1s → 4p and 1s → continuum transitions for Cu(II) compounds in octahedral symmetry2526. The energy gap between the two peaks was 5.0 eV (Fig. 3), attributed to the distortion of 4pz orbit in metalic center. This obtained value was of a similar level to those for other Cu(II) compounds in slightly tetragonally distorted octahedral environments, and was also in accordance with the EPR analytical results. Moreover, the sample spectra in our work had a distinct shoulder peak, which might be due to the degree of axial distortion and the covalence of the equatorial ligands bonded to Cu(II).

Bottom Line: The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis.XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds.To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes.

View Article: PubMed Central - PubMed

Affiliation: CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry.

ABSTRACT
Interactions between metals and activated sludge microorganisms substantially affect the speciation, immobilization, transport, and bioavailability of trace heavy metals in biological wastewater treatment plants. In this study, the interaction of Cu(II), a typical heavy metal, onto activated sludge microorganisms was studied in-depth using a multi-technique approach. The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis. EPR spectra indicated that Cu(II) was held in inner-sphere surface complexes of octahedral coordination with tetragonal distortion of axial elongation. XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds. To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes. These results are useful to better understand the speciation, immobilization, transport, and bioavailability of metals in biological wastewater treatment plants.

Show MeSH
Related in: MedlinePlus