Labile Fe(III) from sorbed Fe(II) oxidation is the key intermediate in Fe(II)-catalyzed ferrihydrite transformation

Further insights into the Fe(ii) reduction of 2-line ferrihydrite: a semi in situ and in situ TEM study

“…S7 †). This is in agreement with recent work by Sheng et al 29 who also indicated that Fe(II) (aq) oxidation is negligible at similar concentrations and reaction times without the presence of 2-line FH. Some recent reports 47,48 have indicated that high energy electrons generated by the TEM in liquids can create hydrated electrons (e H ), and a rich amount of radicals species such as Hc and OHc.…”

“…The presence of these nanoparticles from only Fe(II) (aq) solutions under our experimental conditions was rather unexpected as they have never been reported in the literature. [20][21][22][23][26][27][28][29][30] Fe(II) (aq) solutions were carefully protected from oxygen oxidation to avoid precipitation of Fe(III) oxy/hydroxides. As such we do not believe the nano-particles observed were a product of oxidation from O 2(g) and/or air.…”

“…The reductive dissolution of 2-line FH by Fe(II) (aq) has been indirectly inferred from various analytical methods of the nal reaction products. 13,20,21,28,29 This inference has been done based on the fact that traces of the 2-line FH signals are detected at the end of the reaction period.…”

“…Meanwhile, surface nucleation, solid-state conversion, and growth favours MG precipitation. 13,20,21,29 Though more detailed research has indicated that the major reaction steps in current proposed conceptual models comprise of (1) the adsorption of Fe(II) (aq) onto 2-line FH, (2) immediate oxidation of Fe(II)-2-line FH to Fe(III) with electron exchange to other Fe(III) lattice atoms, (3) atom exchange at the interface of the redox couple in step 2, (4) electron conduction through the solid, (5) the production of a "reactive surface FH/labile Fe(III)", (6) reductive release of Fe(II) (aq) , (7) continuing cycle of 1-6 until LP, GT, MG or HT are precipitated on the surface of the "reactive-FH/labile Fe(III) phase" and nally (8) complete bulk transformation of the initial 2-line FH to LP, GT, MG or HT that depends upon the experimental conditions. 20,21,23,29,30 Evidence for these more detailed steps in conceptual models have come from decades of research via the use of solution (e.g.…”

“…EPR, XPS, XAS, Mössbauer, XRD, X-ray reectivity, STM, STXM, AFM, ex situ TEM, IR/Raman) and computational analysis. 20,21,23,[29][30][31] Development of LC TEM and the environmental TEM, as well as their use over the last couple of decades, has revolutionized the way we have understood nucleation pathways of nanoparticles; their coalescence; nano-crystal growth and dissolution; shape and crystal face evolution; nano-particle solution dynamics; electrochemical reactions and some biological processes. [32][33][34][35][36][37][38][39] However, to the best of the author's knowledge, the biotic or abiotic reduction of FH (or other iron(III) oxyhydroxides) with Fe(II) (aq) via the use of LC TEM has not yet been investigated.…”