One‐Pot Aqueous Solution Syntheses of Iron Oxide Nanostructures with Controlled Crystal Phases through a Microbial‐Mineralization‐Inspired Approach

Abstract

Iron-oxidizing bacteria produce trivalent iron oxides with the controlled crystal phases outside of their cells. Herein we have synthesized iron oxides with controlled oxidation states and crystal phases through a microbial-mineralization-inspired approach in an aqueous solution at low temperature. Trivalent iron oxides, such as lepidocrocite, ferrihydrite, goethite, and hematite, are selectively obtained from an aqueous solution containing divalent iron ions below 90 °C. The presence of a chelating agent facilitates the control of the oxidation states through the ligand-controlled approach because the precipitation of the divalent iron species is inhibited by the complexation between divalent iron ion and a chelating agent. The control of the crystal phases is achieved by the tuning of the synthetic conditions, such as the initial pH, the concentration of a chelating agent, and the reaction temperature. Furthermore, the resultant iron oxides have hierarchically organized structures consisting of nanoscale objects. The microbial-mineralization-inspired approach by using a chelating agent has potentials for the further morphological control of iron oxides and the further application to aqueous-solution syntheses of other metal oxides.

Magnetite Nanostructured Porous Hollow Helical Microswimmers for Targeted Delivery

“…To resolve these issues, we explored substitutes for materials used in the aforementioned methods to conduct the synthesis. FeCl 2 , FeCl 3 solutions, and their mixture, all of which are safe media that have been applied to prepare various magnetite precursors, were chosen as ideal substitutes . Through parametric experiments (Figure S2, Supporting Information), we were able to identify the optimum conditions for the biotemplated synthesis: in a mixture of FeCl 2 –FeCl 3 (ratio of molar concentration, 2:1) at 65 °C with the protection of ultrahigh‐purity N 2 ; no addictive is needed.…”

Effects of organic polymer addition in magnetite synthesis on the crystalline structure

“…15,16 The in situ precipitation of Fe 3 O 4 with 13 mm average diameter particles in cationic chitosan hydrogels 17 and the crystal phase control of the iron oxide were attempted in an aqueous solution with ethylenediaminetetraacetic acid. 18 Also, preparation of Fe 3 O 4 nanoparticles modied with poly-(diallyldimethylammonium chloride) (PDDAC) has been also reported. 19 These studies suggest that organic-inorganic interaction affects the nanostructure and properties of Fe 3 O 4 -polymer hybrids.…”

Controlled radical polymerization of styrene with magnetic iron oxides prepared through hydrothermal, bioinspired, and bacterial processes

“…Bioinspired process. 31 An aqueous solution of disodiumdihydrogen ethylenediamine tetraacetate (EDTA, Kanto, 99.5%) was prepared in a polypropylene vessel using puried water.…”

“…In addition, radical polymerization has only been examined with commercial materials. Specially prepared iron oxides, such as Fe 3 O 4 , obtained through a hydrothermal synthesis, 30 synthesized via a bioinspired process, 31 synthesized by bacteria, [32][33][34] or coated with oleate, 35 are expected to exhibit activity superior to that of commercial iron oxides.…”