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Origin of magnetism in hydrothermally aged 2-line ferrihydrite suspensions Liang Cao, Zhaoxia Jiang, Yonghua Du, Xinmao Yin, Shibo Xi, Wen Wen, Andrew Roberts, Andrew Thye Shen Wee, Yimin Xiong, Qingsong Liu, and Xingyu Gao Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04716 • Publication Date (Web): 26 Jan 2017 Downloaded from http://pubs.acs.org on January 31, 2017
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Environmental Science & Technology
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Origin of magnetism in hydrothermally aged 2-line
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ferrihydrite suspensions
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Liang Cao,†,‡ Zhao-Xia Jiang,# Yong-Hua Du,§ Xin-Mao Yin,||, & Shi-Bo Xi,§ Wen Wen,† Andrew
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P. Roberts,┴ Andrew T. S. Wee,|| Yi-Min Xiong,‡ Qing-Song Liu,ξ,‼,* Xing-Yu Gao†,*
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† Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P. O. Box 800–204,
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Shanghai, 201800, P. R. China
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‡ High Magnetic Field Laboratory, Chinese Academy of Sciences, 350 Shushanhu Road, Hefei,
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230031, Anhui, P. R. China
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# State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese
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Academy of Sciences, 19 Beitucheng Western Road, Beijing, 100029, P. R. China
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§ Institute of Chemical and Engineering Sciences, A*STAR (Agency for Science, Technology
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and Research), 1 Pesek Road, Jurong Island, 627833, Singapore
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|| Department of Physics, National University of Singapore, 2 Science Drive 3, 117542,
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Singapore
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& SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key
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Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong
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Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen, 518060, P. R.
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China
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┴ Research School of Earth Sciences, The Australian National University, 142 Mills Road,
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Canberra, ACT 2601, Australia
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ξ Department of Marine Science and Engineering, Southern University of Science and
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Technology of China, Shenzhen, 518055, P. R. China
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!! Laboratory for Marine Geology, Qingdao National Oceanography Laboratory for Science and
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Technology, Qingdao, 266071, P. R. China
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KEYWORDS.
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Ferrihydrite, Magnetism, Chemical structure, Synchrotron, XMCD, XAS
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ABSTRACT.
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As an iron oxyhydroxide, nano-sized ferrihydrite (Fh) is important in Earth science, biology, and
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industrial applications. However, its basic structure and origin of its magnetism have long been
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debated. We integrate synchrotron-based techniques to explore the chemical structures of 2-line
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ferrihydrite and to determine the origin of its magnetism during hydrothermal aging in air. Our
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results demonstrate that both the magnetism and X-ray magnetic circular dichroism (XMCD)
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signal of 2-line ferrihydrite are enhanced with aging time, and that XMCD spectral patterns
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resemble that of maghemite (γ-Fe2O3) rather than magnetite (Fe3O4). Fe L-edge and K-edge X-
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ray absorption spectroscopy (XAS) further indicate formation of both maghemite and hematite
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(α-Fe2O3) with increasing concentrations with longer hydrothermal aging time. Thus, magnetic
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enhancement with longer hydrothermal aging time is attributed to increasing maghemite
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concentration instead of a magnetically ordered ferrihydrite as previously reported. Moreover, L-
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edge and K-edge XAS spectra with different probing depths yield different ratios of these Fe
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oxides, which suggest the formation of a core (ferrihydrite-rich)-shell (with a mixture of both
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allotropes; α-Fe2O3 and γ-Fe2O3) structure during hydrothermal aging. Our results provide
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insights into the chemical evolution of 2-line ferrihydrite that reveal unambiguously the origin of
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its magnetism.
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TEXT.
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Introduction
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Nano-sized ferrihydrite (typically
