Thin, Conformal, and Continuous SnO₂ Coatings on Three‐Dimensional Biosilica Templates through Hydroxy‐Group Amplification and Layer‐By‐Layer Alkoxide Deposition

Abstract

Appreciable effort is underway to develop robust protocols for synthesizing functional nanostructured assemblies. Desired characteristics for such protocols include precise control of structure (down to the nanoscale), versatile control of chemistry (for tailored functionality), and massively parallel assembly (for large-scale manufacturing). The precise, versatile, and scalable fabrication of functional nanostructured assemblies, particularly those with intricate 3D morphologies, remains a significant challenge for nanotechnology.Nature provides spectacular examples of precise and highly replicable 3D self-assembly of inorganic materials on the micrometer to nanometer scales.[1] Diatoms, for example, generate nanostructured silica microshells (frustules) with thousands of species-specific morphologies.[1d] Sustained reproduction of a particular diatom species can yield enormous numbers of frustules with similar 3D morphologies.[1e]Such intricate, genetically precise, and massively parallel 3D self-assembly under ambient conditions lies well beyond the current capabilities of synthetic micro-and nanofabrication. However, to utilize the precision and massive parallelism of such biological assembly for a variety of nanostructured devices, the silica-frustule chemistry needs to be altered for desired electronic, optical, chemical, or other properties.While gas-solid reactions [2a-c] and gas-phase deposition [2d,e] have been used to alter the chemistries of bioclastic structures, these approaches require volatile reactants orprecursors. An alternate range of chemistries may be accessed with liquid-phase deposition methods. For example, Kunitake, et al. [3] have used a layer-by-layer surface sol-gel process to deposit conformal oxide-bearing coatings on hydroxy-or carboxy-bearing surfaces (for example, latex spheres [3b,c] or cellulose [3d,e] ). However, this surface sol-gel process has not been used to generate thin, conformal, and continuous functional oxide coatings on intricate 3D biomineral structures.Herein, we demonstrate, for the first time, how the intricate nanostructured silica valves of diatom frustules may be coated with a thin (50 nm), conformal, and continuous layer of a functional oxide (SnO 2 ) through dendritic amplification of hydroxy groups on the silica surfaces and then use of an automated surface sol-gel process. A device built from such SnO 2 -coated diatom frustule valves acts as a sensitive detector for NO gas.Initial experiments produced patchy, discontinuous oxide coatings, which we attribute to a low density of surface hydroxy groups available to initiate the sol-gel reaction on the silica valves. Therefore, it was necessary to increase the number of accessible hydroxy functionalities through a series of chemical reactions (Scheme 1). The diatom silica was first subjected to an oxidizing RCA-1 cleaning solution and then treated with (3-aminopropyl)triethoxysilane to functionalize the surfaces with amine groups. The surfaces were then exposed, in alternating fashion, to solutions of po...

Biotemplated Materials for Sustainable Energy and Environment: Current Status and Challenges

“…Other metal oxide replicas, such as ZrO 2 and MgO, have been produced by using methods such as gas/solid displacement reactions [146] or wet chemical processes. [147,148] Apart from metal oxides, other materials, such as Ge-Si oxides and metal chalcogenides, that may have potential applications for solar cells have also been synthesized. Rorrer et al achieved the biological fabrication of Ge-doped biosilica frustules by employing a two-stage cell culture of the diatom Pinnularia, and the incorporation of these diatom frustules into an electroluminescent device.…”

“…[190] More than 30 % of the pore volume in the biogenically derived silicon material was found in pores with diameters less than 2 nm, which gave the silicon an open crystal structure highly amenable to the intercalation of lithium ions. Some important materials for LIBs, such as TiO 2 [141][142][143][144][145] and SnO 2 , [148] with diatom structures have also been synthesized by reprinted from reference [195] with permission from Elsevier; parts c) and d) reprinted from reference [196]; part e) reprinted from reference [197] with permission from Elsevier; and part f) reprinted from reference [198]. using various methods, although the properties have not been tested and reported yet.…”

“…Furthermore, Sandhage and co-workers reported the successful coating of a thin (50 nm), conformal, and continuous layer of a functional oxide (SnO 2 ) onto the intricate nanostructured silica valves of diatom frustules through dendritic amplification of hydroxyl groups on the silica surfaces and then use of an automated surface sol-gel processes. [148] A device built from such SnO 2 -coated diatom frustule valves acts as a sensitive detector for NO gas. They also prepared free-standing (silica free) microscale titania structures with morphologies inherited from complex-shaped, 3D biosilica templates (diatom frustules) by using a simple protein-mediated approach.…”

3D imaging of diatoms with ion-abrasion scanning electron microscopy

“…Because the complexity of diatom silica structures can exceed that possible using synthetic material production approaches, and diatoms reproduce these structures faithfully, in enormous numbers, and inexpensively, diatoms are being developed as a source of nanostructured materials (Sandhage et al, 2005). Facilitating this are techniques that either use diatoms as templates for functionalized coatings (Payne et al, 2005; Rosi et al, 2004; Weatherspoon et al, 2007), or convert their silica entirely to other chemistries while maintaining nanoscale features (Bao et al, 2007; Kusari et al, 2007; Sandhage K.H. et al, 2002; Sandhage et al, 2005; Unocic R.R.…”

Hierarchical, Titania‐Coated, Carbon Nanofibrous Material Derived from a Natural Cellulosic Substance

“…[11][12][13] Apart from being used as templates, it would be an ideal opportunity to employ natural substances as scaffolds for materials fabrication, namely, composite materials formed by guest thin-film coatings of host natural substances would possess unique properties due to the combination of the functional and structural features of both sides. [9,14] Moreover, further carbonization of the organic natural substances under proper conditions could yield unique nanostructured carbon materials with inherited fine morphologies. In the present work, a promising hierarchical, titania-coated, carbon nanofibrous material with enhanced photocatalytic activity was fabricated by employing a cellulosic material (common commercial filter paper) as both the scaffold and carbon precursor.…”