Wettability of Magnetite Nanoparticles Guides Growth from Stabilized Amorphous Ferrihydrite

Abstract

Crystal formation via amorphous precursors is a long-sought-after gateway to engineer nanoparticles with well-controlled size and morphology. Biomineralizing organisms, like magnetotactic bacteria, follow such a nonclassical crystallization pathway to produce magnetite nanoparticles with sophistication unmatched by synthetic efforts at ambient conditions. Here, using in situ small-angle X-ray scattering, we demonstrate how the addition of poly(arginine) in the synthetic formation of magnetite nanoparticles induces a biomineralization-reminiscent pathway. The addition of poly(arginine) stabilizes an amorphous ferrihydrite precursor, shifting the magnetite formation pathway from thermodynamic to kinetic control. Altering the energetic landscape of magnetite formation by catalyzing the pH-dependent precursor attachment, we tune magnetite nanoparticle size continuously, exceeding sizes observed in magnetotactic bacteria. This mechanistic shift we uncover here further allows for crystal morphology control by adjusting the pH-dependent interfacial interaction between liquidlike ferrihydrite and nascent magnetite nanoparticles, establishing a new strategy to control nanoparticle morphology. Synthesizing compact single crystals at wetting conditions and unique semicontinuous single-crystalline nanoparticles at dewetting conditions in combination with an improved control over magnetite crystallite size, we demonstrate the versatility of bio-inspired, kinetically controlled nanoparticle formation pathways.

Minimizing Fe-Bearing Waste Guided by Modulating the Precipitation Pathway: A Novel Magnetite Precipitation Approach for Zinc Hydrometallurgy

“…Previous studies investigated the formation process of magnetite and suggested that the process pathway largely depends on the stability of Fe­(III)-bearing intermediates. Intermediates were only detectable when they were stabilized (mainly by additives − ), as magnetite was favored when intermediates are unstable . This discrepancy of the magnetite formation pathway coincides with the formation process in this study.…”

“…When the alkali was insufficient, intermediate phases (including GR and Fe­(OH) 3 ) would first form and transform to magnetite gradually within 1 h, approximately, By contrast, magnetite directly precipitates without formation of intermediate phase in the presence of sufficient alkali. A higher concentration of alkali will increase the surface tension and consequently gives rise to the lower free energy barrier. , In addition, surface site blocking is another factor to stabilize these coprecipitated intermediates, given that these nanoparticles had large surface energy and were easily aggregated, inhibiting the subsequent interfacial reaction. Consequently, the coprecipitates of ZnO and Fe-bearing intermediate phase accumulated at the early stage, facilitating Zn 2+ ions diffusion from ZnO to Fe-bearing intermediate phase and consequently enhanced the retention of Zn in magnetite (Figure a,4).…”

“…Hence, we expect that co-precipitation of Zn may have the potential to be inhibited by promoting the rapid and direct precipitation of magnetite and avoiding the formation of Fe-bearing intermediates. Organic additives are the most commonly studied factors in modulating the magnetite formation pathway. − However, these additives are undesirable in hydrometallurgy, as they will have a negative influence on the subsequent process (e.g., electrowinning). Instead, previous studies also found that slowly adding alkali into Fe-bearing solution easily induced the formation of intermediates such as green rust (GR), whereas direct formation of magnetite was observed when the Fe-bearing solution was slowly added into the alkali .…”

Crystal–Chemical and Biological Controls of Elemental Incorporation into Magnetite Nanocrystals

“…To ensure that these observations are real and were not generated by specific precipitation conditions or bacterial strain, we performed additional magnetite syntheses with a mixture of Co, Mn, and Zn using distinct protocols and bacterial strain. The choice of metals is made by their frequent use as dopants to tune the magnetic properties of magnetite. ,, First, abiotic magnetite nanoparticles were synthesized using a titration device (see Materials and Methods) following a well-established protocol to produce highly pure magnetite. − Using this device, the pH of the precipitation solution is kept constant during magnetite precipitation by adding NaOH solution, and the Fe, Co, Mn, and Zn mixture is progressively added to the precipitation solution. In addition, the magnetotactic strain Magnetospirillum gryphiswaldense MSR-1 was cultivated with a mixture of Co, Mn, and Zn at the same concentration (see Materials and Methods).…”

Phase Separation of Oppositely Charged Polymers Regulates Bioinspired Silicification

“…[21][22][23] In chemical syntheses, coacervate-directed crystallization was achieved. [24][25][26][27][28] In this work, we used synthetic polycations and polyanions, as well as an aqueous silica source, to investigate bioinspired polymer-induced silicification under mild conditions. We show that each polymer alone stabilizes soluble silicon, whereas polymer mixtures induce silica precipitation.…”