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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 PtCl4 2-, 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.
Highlights
The platinum group metals (PGM), (Pd, Pt, and Rh), are of great interest as catalysts in various industries, in particular, their obligatory utilization in automotive catalytic converters, which is necessary to effectively reduce the hydrocarbons, CO, and NOx emitted in exhaust gas [1]
We have demonstrated that Pt sorbed on a bacterial cell surface is present as a Pt(II) chloro-complex, possibly PtCl42, using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) (Figs 3, 4, and 5)
The results of our X-ray absorption fine structure (XAFS) analysis are consistent with the fact that Pt biosorption is favored at lower pH in NaCl solutions (Fig 1), where anionic species of the Pt chloro-complex are possibly sorbed onto protonated amine groups on the cell wall [15,17]
Summary
The platinum group metals (PGM), (Pd, Pt, and Rh), are of great interest as catalysts in various industries, in particular, their obligatory utilization in automotive catalytic converters, which is necessary to effectively reduce the hydrocarbons, CO, and NOx emitted in exhaust gas [1]. Coordination Structure of Pt Sorbed on Bacterial Cells merit of being relatively inexpensive and is scalable to large volumes; the application of microbial activity and biomass techniques, such as biosorption and bioreduction, can satisfy such requirement. Bioreduction, such as Pd(II) to Pd(0) and Pt(IV) to Pt(0), is well known as a useful technique for the recovery of PGM from aqueous solutions using sulfate-reducing bacteria [4,5]. 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 including PGM using biosorbent materials
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