Wettability of Magnetite Nanoparticles Guides Growth from Stabilized Amorphous Ferrihydrite.

Lucas Kuhrts,Péter Pekker,Jens Baumgartner,Damien Faivre,Sylvain Prévost,Oliver Spaeker,Mihály Pósfai,Daniel M Chevrier,Mathias Egglseder

doi:10.1021/jacs.1c02687

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.

Highlights

The theory of nonclassical nucleation conceptualizes the formation of solids via condensed, noncrystalline transient particles
While pure magnetite is notoriously difficult to synthesize in a controlled manner under ambient aqueous conditions due to the low-concentration supersaturation limits of ferrous and ferric chloride, our results indicate that an uncommon but well-defined nanocrystal morphology forms by the surface-wetting properties of a polymer-stabilized precursor phase in the presence of poly(arginine)
Magnetite nanoparticles formed in the presence of poly(arginine) exhibit a morphological transition from compact to substructured single crystals, visible in TEM micrographs (Figure 1A−C)

Summary

Introduction

The theory of nonclassical nucleation conceptualizes the formation of solids via condensed, noncrystalline transient particles It has been demonstrated in numerous examples that such prenucleation cluster-driven processes can produce a variety of complex synthetic crystal architectures.[1] Similar strategies are employed in biomineralizing organisms, where hybrid materials with tailored properties[2,3] are realized by a spatially controlled mineralization process directed through additive-stabilized amorphous precursors.[4−7] Such biomineralization pathways are the benchmark for the preparation of synthetic systems with refined properties at ambient conditions.[8,9] Magnetotactic bacteria, for example, produce magnetite (Fe3O4) nanoparticles precisely defined in size and morphology.[10] Intrigued by the biomimetic effect of poly-. Biomineralized magnetite crystals are formed under environmental conditions via a transient, protein-stabilized ferric (oxyhydr)oxide[12,13] and similar amorphous precursors have been observed in synthetic magnetite,[14] no approach to rationalize and direct their crystallization has yet emerged

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