Yiwen Chen1,Mario Gomez2,Miao Song3,Dongsheng Li3,Alan Lea3,Yihang Duan4,Yongfeng Jia4
Shenyang University of Chemical Technology1,Guangzhou University2,Pacific Northwest National Laboratory3,Chinese Academy of Sciences4
Yiwen Chen1,Mario Gomez2,Miao Song3,Dongsheng Li3,Alan Lea3,Yihang Duan4,Yongfeng Jia4
Shenyang University of Chemical Technology1,Guangzhou University2,Pacific Northwest National Laboratory3,Chinese Academy of Sciences4
Lepidocrocite (γ-FeOOH) is a key metastable Iron (III)-oxy/hydroxide that is commonly encountered in natural environments such as reductomorphic and hydromorphic soils. Its presence in anthropogenic environments such as those found in mining industries of resource minerals, coal liquefaction, and oxidized alloy steel radioactive waste containers is also widespread. Unfortunately, despite its importance, the catalytic behaviour induced by Fe(II)<sub>(aq)</sub>, commonly found in those environments and the underlying transformation mechanisms to more thermodynamically stable phases (e.g. Goethite, Magnetite) remains unclear after decades of scattered research. As such, we conducted a detailed research program via the use of XRD, ATR-FTIR/Raman, and semi <i>in-situ</i> environmental TEM to further probe its catalytic behaviour and underlying transformation mechanisms when it is present under the influence of Fe(II)<sub>(aq)</sub>. Based on this work and our reaction conditions, we found that Goethite and Lepidocrocite were the dominant products throughout and at the end of our reaction time (12 days). Furthermore, we found that there were 4 intermediate steps along the mineralization pathways of the end products which were initiated by a dissolution type of reaction. Fascinatingly, 2 of the intermediate steps along its reaction pathway presented novel types of non-classical mechanisms of crystallization via some type of guided oriented type of particle attachment. Moreover, one of these intermediate steps resembled a bio-mimetic-like mechanism similar to what is observed during bacterial particle attachment. Such bio-mimetic-like behavior has never yet been documented for an inorganic type of Iron (III)-oxy/hydroxide catalytic reaction with Fe(II)<sub>(aq)</sub>. Our work also gives possible insights into how Goethite particles with particular morphologies (e.g. Christmas trees or start shaped) frequently observed in nature or laboratory may evolve from Lepidocrocite under its catalytic transformation with Fe(II)<sub>(aq)</sub>. Finally, we propose the first unified conceptual model mechanism under our reaction conditions on the catalytic transformation of LP under the influence of Fe(II)<sub>(aq).</sub>