Nanocrystalline Precursors for the Co‐Assembly of Crack‐Free Metal Oxide Inverse Opals

Abstract

Inorganic microstructured materials are ubiquitous in nature. However, their formation in artificial self-assembly systems is challenging as it involves a complex interplay of competing forces during and after assembly. For example, colloidal assembly requires fine-tuning of factors such as the size and surface charge of the particles and electrolyte strength of the solvent to enable successful self-assembly and minimize crack formation. Co-assembly of templating colloidal particles together with a sol-gel matrix precursor material helps to release stresses that accumulate during drying and solidification, as previously shown for the formation of high-quality inverse opal (IO) films out of amorphous silica. Expanding this methodology to crystalline materials would result in microscale architectures with enhanced photonic, electronic, and catalytic properties. This work describes tailoring the crystallinity of metal oxide precursors that enable the formation of highly ordered, large-area (mm ) crack-free titania, zirconia, and alumina IO films. The same bioinspired approach can be applied to other crystalline materials as well as structures beyond IOs.

Modular Design of Advanced Catalytic Materials Using Hybrid Organic–Inorganic Raspberry Particles

“…Formation of Titania IO Films : TiO 2 nanocrystals were synthesized by hydrolysis and polycondensation of titanium isopropoxide (TIP) in the presence of tetramethylammonium hydroxide (TMAH, CAUTION TMAH is highly toxic) …”

“…A constant amount of TIP in isopropanol was typically added dropwise to the aqueous solution of TMAH at room temperature under stirring; the TMAH concentration was varied to achieve different ratios of TIP to TMAH ( R TIP/TMAH ). The reaction mixture was then heated and refluxed for ≈6 h. These nanocrystals were used directly in the colloidal assembly solution as the matrix precursor, without purification …”

“…In the case of coassembly, as the colloids are pulled toward the substrate and each other by capillary and depletion forces, they template the formation of the background matrix within their interstices. At the same time, the matrix precursor in the assembly mixture serves as an amorphous viscoelastic medium that accommodates stresses and prevents cracking, so that long‐range (millimeters) defect‐free colloidal lattices can be obtained . Once the templating colloids are removed by calcination or dissolution, a highly interconnected porous inverse opal (IO) network remains (Figure C,D).…”

“…The formation of high‐quality IOs employing sol–gel‐based transition metal oxides precursors is generally challenging, as densification during hydrolysis, drying, and calcination produces cracked structures . Our synthetic approach uses precursors with both nanocrystalline and amorphous phases, which achieve a balance of viscoelastic forces and minimal volume shrinkage during EISA, as discussed in a forthcoming paper . We have developed methods to assemble high quality IO materials in both film and PB formats using a variety of transition metal oxides; representative examples of such titania, alumina, and zirconia structures are shown in Figure .…”

Gas sensors using ordered macroporous oxide nanostructures

“…[70][71][72] When compared with a monolayer 2D counterpart, 3DOM thin lms tend to be endowed with strengthened continuous connection channels, as well as improved avenues for conducting electrical signals. 73 The preparation of 3DOM metal oxides is oen based on the metal precursor solution impregnation. [74][75][76] Miyake et al recently reported a novel epitaxial growth process of single-crystal 3DOM…”