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Cu(II) sorption by biogenic birnessite produced by Pseudomonas putida strain MnB1: Structural differences from abiotic birnessite and its environmental implications

Abstract

Biogenic birnessite is the most prevalent form of Mn-oxides in nature, and plays important roles in controlling the mobility of heavy metals such as Cu(II). This study focuses on the fine mineralogical characteristics of Cu(II)-incorporated biogenic (bio-) birnessite produced by Pseudomonas putida strain MnB1, and discussing the structural stability of Cu-binding birnessite. Compared to a structural analog hexagonal (abio-) birnessite, the X-ray diffraction (XRD) patterns of bio-birnessite showed an enlarged interlayer space from 7.33 to ~9.17 Å; besides, the reduced in-plane crystallinity and increased lattice parameter b were indicated after Cu(II) adsorption. The linear combination fitting of Mn K-edge X-ray absorption near-edge structure (XANES) indicated ~13% Mn(II) while few Mn(III) was present in bio-birnessite. The saturated sorption amount of Cu(II) was 0.17 and 0.25 mol Cu/mol Mn for bio- and abio-birnessite, respectively. By conducting extended X-ray absorption fine structure (EXAFS) spectroscopic analysis, multiple coordination paths as Cu-Mn ~2.85 Å, Cu-Cu ~3.00 Å and Cu-Mn ~3.43 Å were indicated to exist in both bio- and abio-birnessite, showing the diversity of Cu coordination structure. The fitted coordination numbers of these three paths were much larger (with identical Debye-Waller factor) in bio-birnessite (1.9, 1.9 and 2.5 respectively) than in abio-birnessite (1.1, 1.1, 1.6), indicating Cu had more surrounding atoms in bio-birnessite. The results indicated that in bio-birnessite, Cu sorption by vacant sites, i.e. incorporation into vacancy (INC species) or adsorbing on vacancy (TCS species), was more dominant, which may benefit from the larger interlayer space for accommodation of Cu inner-sphere complex and few content of structural Mn(III) competing for vacant sites. In turn, the Cu inner-sphere complex modified both layer and interlayer structures of bio-birnessite. In abio-birnessite, Cu favorably bind at abundant edge sites as dimers or multinuclear clusters, which contributed to a larger sorption amount. Whereas, this binding style was depressed in bio-birnessite, because the organic ligands released by microbial activity may block layer edges. Theoretically, the structural stability of Cu clusters at edges should be weaker than TCS and INC species. This work also gives insights into the geochemical behaviors of Cu(II) controlled by widespread biogenic birnessite.

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Publication details

The article was received on 15 Dec 2017, accepted on 03 Feb 2018 and first published on 05 Feb 2018


Article type: Paper
DOI: 10.1039/C7CE02168B
Citation: CrystEngComm, 2018, Accepted Manuscript
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    Cu(II) sorption by biogenic birnessite produced by Pseudomonas putida strain MnB1: Structural differences from abiotic birnessite and its environmental implications

    Y. Liu, Y. Li, N. Chen, H. Ding, H. Zhang, F. Liu, H. Yin, S. Chu, C. Wang and A. Lu, CrystEngComm, 2018, Accepted Manuscript , DOI: 10.1039/C7CE02168B

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