Three‐Dimensional Assemblies of Zirconia Nanocrystals Via Shape‐Preserving Reactive Conversion of Diatom Microshells

Abstract

The synthesis of three-dimensional (3-D) assemblies of zirconia nanocrystals via the shape-preserving reactive conversion of biologically reproducible, silica-based microtemplates (diatom microshells) is demonstrated for the first time. Silica diatom microshells were first converted into magnesia replicas via an oxidation-reduction displacement reaction with magnesium gas. The magnesia replicas were then converted into zirconia replicas via a metathetic displacement reaction with zirconium tetrachloride gas. By utilizing both types of shape-preserving displacement reactions, bioclastic silica microtemplates may be converted into functional nanocrystalline assemblies with a variety of complex, but well-controlled 3-D shapes and chemistries for catalytic/chemical, biological, electrical, thermal, mechanical, and other applications. J ournal

Template‐Directed Control of Crystal Morphologies

“…[37] A small number of inorganic templates have also been employed to template polycrystalline inorganic solids, such as porous alumina membranes, [38,39] colloidal crystals of silica spheres [40][41][42] and CaCO 3 sea urchin skeletal plates [43,44] Direct chemical reaction of silicaceous diatom frustrules has yielded ceramics including TiO 2 , ZrO 2 and BaTiO 3 . [45][46][47] Descriptions of synthetic routes to single crystals with complex morphologies, however, remain extremely limited, and in common with the biogenic strategy, have all relied upon templating. Crystallisation of ACC within the cylindrical pores of track-etch membranes generated rod-shaped single crystals of calcite, [18,19] while precipitation of ACC within a mould comprising a regular array of pillars, and controlled nucleation at a single, defined site yielded millimetre-sized crystals, when the pillar separation was less than 15 mm.…”

Manganese‐Doped Zinc Orthosilicate‐Bearing Phosphor Microparticles with Controlled Three‐Dimensional Shapes Derived from Diatom Frustules

“…Work over the past several years has demonstrated how the silica‐based chemistry of diatom frustules can be modified, while preserving the starting 3‐D frustule shape, through the use of gas/solid and liquid/solid reactions (i.e., via the now‐patented Bioclastic and Shape‐preserving Inorganic Conversion, or BaSIC, process) 38–43 . Coating‐based approaches, or combined coating and reaction approaches, have also been used to alter the frustule chemistry 43–48 .…”

Layer‐By‐Layer Dendritic Growth of Hyperbranched Thin Films for Surface Sol–Gel Syntheses of Conformal, Functional, Nanocrystalline Oxide Coatings on Complex 3D (Bio)silica Templates

“…[28] The chemical surface modification of complex, 3D, nanostructured templates derived from biological sources enables the attractive characteristics of biological self-assembly to be merged with those of synthetic chemistry to yield functional inorganic materials with a wide range of selectable compositions and structures. [32][33][34][35][36][37][38][39] Consider, for example, the intricate microshells (frustules) assembled by diatoms (aquatic microalgae). [40] Each of the tens of thousands of extant diatom species assembles a silicabased frustule with a particular 3D shape and patterned, nanoscale features (e.g., pores, channels, protuberances) that are replicated with fidelity upon biological reproduction.…”

“…Recent work has shown how gas/silica displacement reactions (e.g., with Mg(g), TiF 4 (g), or ZrCl 4 (g) reactants) may be used to alter the chemistry of diatom frustules (e.g., into MgO, Si, TiO 2 , or ZrO 2 ) while preserving the starting frustule morphology. [33][34][35][36][37][38][39] Unfortunately, the relative thermodynamic stability of SiO 2 limits the range of compositions that may be accessed by such gas/silica displacement reactions. The solution-based sol-gel coating process [43,44] can provide an alternative, chemically versatile route for the modification of silica-based diatom frustules or other complex nanostructured silica assemblies.…”