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Study on the coordination structure of pt sorbed on bacterial cells using x-ray absorption fine structure spectroscopy.

Tanaka K, Watanabe N - PLoS ONE (2015)

Bottom Line: EXAFS spectra demonstrated that Pt sorbed on bacterial cells has a fourfold coordination of chlorine ions, similar to PtCl42-, which indicated that sorption on the protonated amine groups of the bacterial cells.This work clearly demonstrated the coordination structure of Pt sorbed on bacterial cells.The findings of this study will contribute to the understanding of Pt biosorption on biomass, and facilitate the development of recovery methods for rare metals using biosorbent materials.

View Article: PubMed Central - PubMed

Affiliation: Institute for Sustainable Sciences and Development, Hiroshima University, Higashi-Hiroshima, Japan.

ABSTRACT
Biosorption has been intensively investigated as a promising technology for the recovery of precious metals from solution. However, the detailed mechanism responsible for the biosorption of Pt on a biomass is not fully understood because of a lack of spectroscopic studies. We applied X-ray absorption fine structure spectroscopy to elucidate the coordination structure of Pt sorbed on bacterial cells. We examined the sorption of Pt(II) and Pt(IV) species on bacterial cells of Bacillus subtilis and Shewanella putrefaciens in NaCl solutions. X-ray absorption near-edge structure and extended X-ray absorption fine structure (EXAFS) of Pt-sorbed bacteria suggested that Pt(IV) was reduced to Pt(II) on the cell's surface, even in the absence of an organic material as an exogenous electron donor. EXAFS spectra demonstrated that Pt sorbed on bacterial cells has a fourfold coordination of chlorine ions, similar to PtCl42-, which indicated that sorption on the protonated amine groups of the bacterial cells. This work clearly demonstrated the coordination structure of Pt sorbed on bacterial cells. The findings of this study will contribute to the understanding of Pt biosorption on biomass, and facilitate the development of recovery methods for rare metals using biosorbent materials.

No MeSH data available.


Related in: MedlinePlus

Platinum LIII-edge XANES spectra of reference materials and Pt-sorbed bacterial cells at pH 2.(a) B. subtilis and (b) S. putrefaciens. The dotted lines indicate the maximum peak energy of K2PtCl4.
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pone.0127417.g003: Platinum LIII-edge XANES spectra of reference materials and Pt-sorbed bacterial cells at pH 2.(a) B. subtilis and (b) S. putrefaciens. The dotted lines indicate the maximum peak energy of K2PtCl4.

Mentions: Platinum LIII-edge XANES spectra are shown in Fig 3. The absorption increase occurring at the Pt LIII-edge corresponds to the 2p3/2→5d electronic transitions [27,28]. XANES spectra reflect the oxidation state of a target element. For example, the shift in the peak maximum energy depends on the oxidation state, and this has been successfully applied to distinguish the oxidation state of redox-sensitive elements, such as As, Co, and Mn [19, 29–31]. XANES spectra of Pt metal foil and K2PtCl4 with Pt in the divalent state indicate a lower energy position of the peak maximum than K2PtCl6 with Pt in the tetravalent state, but the energy shift is only ~ 1 eV (Fig 3). The ~ 1 eV energy shift observed in the Pt LIII-edge XANES spectra is not sufficiently large to distinguish between the oxidation states of Pt(0), Pt(II), and Pt(IV). Therefore, we focused on another observable difference between the divalent and tetravalent species, which is seen in the intensity of the white line peaks. The K2PtCl6 tetravalent Pt compound has a higher peak in the Pt LIII-edge XANES spectra than has the K2PtCl4 divalent Pt compound. The intensity of the white line reflects the unoccupied Pt(5d) orbital because the absorption edge corresponds to an electron transition from the 2p3/2 to 5d orbitals in the Pt atom [27,28]. The electron configurations of the zero valent, divalent, and tetravalent species are [Xe]4f145d96s1, [Xe]4f145d8, and [Xe]4f145d6, respectively, and the respective number of unoccupied 5d orbitals is 1, 2, and 4. The intensity of the peak maximum is expected to correlate positively with the number of unoccupied 5d orbitals in the reference compound. The K2PtCl6 tetravalent compound indeed showed a higher peak maximum than the zero valent Pt metal foil and the K2PtCl4 divalent species (Fig 3).


Study on the coordination structure of pt sorbed on bacterial cells using x-ray absorption fine structure spectroscopy.

Tanaka K, Watanabe N - PLoS ONE (2015)

Platinum LIII-edge XANES spectra of reference materials and Pt-sorbed bacterial cells at pH 2.(a) B. subtilis and (b) S. putrefaciens. The dotted lines indicate the maximum peak energy of K2PtCl4.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4440633&req=5

pone.0127417.g003: Platinum LIII-edge XANES spectra of reference materials and Pt-sorbed bacterial cells at pH 2.(a) B. subtilis and (b) S. putrefaciens. The dotted lines indicate the maximum peak energy of K2PtCl4.
Mentions: Platinum LIII-edge XANES spectra are shown in Fig 3. The absorption increase occurring at the Pt LIII-edge corresponds to the 2p3/2→5d electronic transitions [27,28]. XANES spectra reflect the oxidation state of a target element. For example, the shift in the peak maximum energy depends on the oxidation state, and this has been successfully applied to distinguish the oxidation state of redox-sensitive elements, such as As, Co, and Mn [19, 29–31]. XANES spectra of Pt metal foil and K2PtCl4 with Pt in the divalent state indicate a lower energy position of the peak maximum than K2PtCl6 with Pt in the tetravalent state, but the energy shift is only ~ 1 eV (Fig 3). The ~ 1 eV energy shift observed in the Pt LIII-edge XANES spectra is not sufficiently large to distinguish between the oxidation states of Pt(0), Pt(II), and Pt(IV). Therefore, we focused on another observable difference between the divalent and tetravalent species, which is seen in the intensity of the white line peaks. The K2PtCl6 tetravalent Pt compound has a higher peak in the Pt LIII-edge XANES spectra than has the K2PtCl4 divalent Pt compound. The intensity of the white line reflects the unoccupied Pt(5d) orbital because the absorption edge corresponds to an electron transition from the 2p3/2 to 5d orbitals in the Pt atom [27,28]. The electron configurations of the zero valent, divalent, and tetravalent species are [Xe]4f145d96s1, [Xe]4f145d8, and [Xe]4f145d6, respectively, and the respective number of unoccupied 5d orbitals is 1, 2, and 4. The intensity of the peak maximum is expected to correlate positively with the number of unoccupied 5d orbitals in the reference compound. The K2PtCl6 tetravalent compound indeed showed a higher peak maximum than the zero valent Pt metal foil and the K2PtCl4 divalent species (Fig 3).

Bottom Line: EXAFS spectra demonstrated that Pt sorbed on bacterial cells has a fourfold coordination of chlorine ions, similar to PtCl42-, which indicated that sorption on the protonated amine groups of the bacterial cells.This work clearly demonstrated the coordination structure of Pt sorbed on bacterial cells.The findings of this study will contribute to the understanding of Pt biosorption on biomass, and facilitate the development of recovery methods for rare metals using biosorbent materials.

View Article: PubMed Central - PubMed

Affiliation: Institute for Sustainable Sciences and Development, Hiroshima University, Higashi-Hiroshima, Japan.

ABSTRACT
Biosorption has been intensively investigated as a promising technology for the recovery of precious metals from solution. However, the detailed mechanism responsible for the biosorption of Pt on a biomass is not fully understood because of a lack of spectroscopic studies. We applied X-ray absorption fine structure spectroscopy to elucidate the coordination structure of Pt sorbed on bacterial cells. We examined the sorption of Pt(II) and Pt(IV) species on bacterial cells of Bacillus subtilis and Shewanella putrefaciens in NaCl solutions. X-ray absorption near-edge structure and extended X-ray absorption fine structure (EXAFS) of Pt-sorbed bacteria suggested that Pt(IV) was reduced to Pt(II) on the cell's surface, even in the absence of an organic material as an exogenous electron donor. EXAFS spectra demonstrated that Pt sorbed on bacterial cells has a fourfold coordination of chlorine ions, similar to PtCl42-, which indicated that sorption on the protonated amine groups of the bacterial cells. This work clearly demonstrated the coordination structure of Pt sorbed on bacterial cells. The findings of this study will contribute to the understanding of Pt biosorption on biomass, and facilitate the development of recovery methods for rare metals using biosorbent materials.

No MeSH data available.


Related in: MedlinePlus