Achieving Functionality and Multifunctionality through Bulk and Interfacial Structuring of Colloidal-Crystal-Templated Materials

Over the past 25 years, the field of colloidal crystal templating of inverse opal or three-dimensionally ordered macroporous (3DOM) structures has made tremendous progress. The degree of structural control over multiple length scales, understanding of mechanical properties, and complexity of systems in which 3DOM materials are a component have increased substantially. In addition, we are now seeing applications of 3DOM materials that make use of multiple features of their architecture at the same time. This Feature Article focuses on the different properties of 3DOM materials that provide functionality, including a relatively large surface area, the interconnectedness of the pores and the resulting good accessibility of the internal surface, the nanostructured features of the walls, the structural hierarchy and periodicity, well-defined surface roughness, and relative mechanical robustness at low density. It provides representative examples that illustrate the properties of interest related to applications including energy storage and conversion systems, sensors, catalysts, sorbents, photonics, actuators, and biomedical materials or devices

Morphology Control of Carbon, Silica, and Carbon/Silica Nanocomposites: From 3D Ordered Macro-/Mesoporous Monoliths to Shaped Mesoporous Particles

We demonstrate that confinement of a concentrated triconstituent precursor solution (a soluble phenol-formaldehyde prepolymer, tetraethylorthosilicate, and the nonionic triblock copolymer F127) in a poly(methyl methacrylate) (PMMA) colloidal crystal template permits control over the external morphology of mesostructured products. It is possible to produce either monoliths with hierarchical porosity (ordered macropores from PMMA spheres and large mesopores from F127) or cubic and spherical mesoporous nanoparticles. The specific morphology depends on the concentration of F127 and on the presence of 1,3,5-trimethyl benzene (TMB) as an additive. At lower F127 content and without TMB, macroporous monoliths of the carbon/silica composite are obtained, which can be converted to carbon monoliths with dual porosity after the extraction of silica with hydrofluoric acid or to silica monoliths after calcination in air. Large worm-like mesopores are present in macropore walls. An increase in the F127 concentration leads to disassembly of the macroporous skeleton during pyrolysis and produces a bimodal mixture of uniformly sized cubic nanoparticles (ca. 120 nm edge lengths) and smaller spherical nanoparticles (ca. 55 nm diameters) (MSP-1). These nanoparticles are derived from the octahedral and tetrahedral holes in the colloidal crystal template through the solid-state disassembly of the inorganic skeleton. The addition of TMB changes the mechanism of nanoparticle formation. In this case, solvent-induced phase separation between the polymer template and the inorganic precursors occurs below 100 °C, which results in spherical nanoparticles (MSP-2), whose product diameters depend more critically on sample composition. Both MSP-1 and MSP-2 nanoparticles are mesoporous, but their textural properties vary significantly with type and composition. The MSP-1 particles keep their cubic shapes even after being heated at 1000 °C in an inert atmosphere

Multiconstituent Synthesis of LiFePO₄/C Composites with Hierarchical Porosity as Cathode Materials for Lithium Ion Batteries

Monolithic, three-dimensionally ordered macroporous and meso-/microporous (3DOM/m) LiFePO4/C composite cathodes for lithium ion batteries were synthesized by a multiconstituent, dual templating method. Precursors containing sources for lithium, iron, and phosphate, as well as a phenol-formaldehyde sol and a nonionic surfactant were infiltrated into a colloidal crystal template. Millimeter-sized monolithic composite pieces were obtained, in which LiFePO4 was dispersed in a carbon phase around an interconnected network of ordered macropores. The composite walls themselves contained micropores or small mesopores. The carbon phase enhanced the electrical conductivity of the cathode and maintained LiFePO4 as a highly dispersed phase during the synthesis and during electrochemical cycling. Monoliths containing 30 wt % C were electrochemically cycled in a 3-electrode cell with lithium foil as counter and reference electrodes. No additional binder or conductive agent was used. The capacity was as high as 150 mA h g–1 at a rate of C/5, 123 mA h g–1 at C, 78 mA h g–1 at 8C, and 64 mA h g–1 at 16C, showing no capacity fading over 100 cycles. In spite of the low electronic conductivity of bulk LiFePO4 (10–9–10–10 S cm–1), the monolithic LiFePO4/C composite was able to support current densities as high as 2720 mA g–1

Conjugation of Colloidal Clusters and Chains by Capillary Condensation

Conjugation of Colloidal Clusters and Chains by Capillary Condensatio

Solvent Effects on Morphologies of Mesoporous Silica Spheres Prepared by Pseudomorphic Transformations

In surfactant-induced, pseudomorphic transformations of submicrometer-sized nonporous spheres to mesoporous silica spheres, the surface morphologies of the products depend on the solvent used during the initial Stöber synthesis. After hydrothermal transformations employing cetyltrimethylammonium bromide (CTAB) as a surfactant, pseudomorphic products of parent silica spheres synthesized in ethanol (HT-SiO2-EtOH) are mesoporous throughout and have smooth surfaces. In contrast, products from spheres synthesized in isopropanol (HT-SiO2-iPrOH) or butanol (HT-SiO2-BuOH) possess highly corrugated shells surrounding a nonporous core. On the basis of 29Si solid-state magic angle spinning (MAS) NMR spectra, this significant change in surface morphology after the hydrothermal transformation is related to small differences in the degree of condensation of the parent silica spheres. In the case of HT-SiO2-EtOH, the higher degree of condensation of the parent spheres limits sphere dissolution, and the transformation is mostly pseudomorphic. For the other two systems, parent spheres are more reactive and release more silica into solution. Porous shells are therefore formed on the surface of the remaining spheres. Morphological changes were investigated by scanning and transmission electron microscopy. The porosity of the mesoporous silica spheres produced by these reactions was determined by nitrogen sorption measurements and small-angle X-ray scattering. The diffusion depth of CTAB was revealed by nanocasting carbon into the mesoporous silica spheres via phenol-paraformaldehyde gas-phase polymerization and subsequently removing the silica structure. As a result of limited surfactant penetration into the cores of HT-SiO2-iPrOH spheres, replicated mesoporous carbon spheres possess a corrugated mesoporous shell and a hollow core

Dual Templating of Macroporous Silicates with Zeolitic Microporous Frameworks

Dual Templating of Macroporous Silicates with Zeolitic Microporous Framework

Template-Directed Synthesis and Organization of Shaped Oxide/Phosphate Nanoparticles

Oxide nanoparticles (NPs) are typically synthesized from the assembly of atoms, ions or other species by bottom-up methods. Here we report an alternative, top-down approach as a general route to synthesize porous and nonporous oxide/phosphate nanocubes. The method is based on the construction of three-dimensionally ordered macroporous (3DOM) structures via colloidal crystal templating, followed by the spontaneous disassembly of these structures into particulate building blocks assisted by the introduction of amphiphilic surfactants. Syntheses and analyses of nanocubes composed of d-block transition metal (Cr, Mn, Fe, Co, Ni, Cu and Zn) oxides and several mixed oxides are presented to exemplify the generality of the method. Because the NP morphology is defined by the rigid colloidal crystal template, particle composition and characteristics can be readily tuned, leaving much freedom for the development of NP functionality. In addition, the shaped particles retained their geometric relation, namely the face-centered cubic arrangement dictated by the colloidal crystal template, but they could self-reassemble into ordered simple cubic arrays, which provides a unique approach for in situ particle organization. In this paper, the self-reassembly process is also discussed in detail

Colloidal Photonic Crystal Pigments with Low Angle Dependence

Poly(methyl methacrylate) (PMMA)-based colloidal photonic crystals have an incomplete photonic band gap (PBG) and typically appear iridescent in the visible range. As powders, synthetic PMMA opals are white, but when infiltrated with carbon black nanoparticles, they exhibit a well-defined color that shows little dependence on the viewing angle. The quantity of black pigment determines the lightness of the color by controlling scattering. The combined effects of internal order within each particle and random orientation among the particles in the powder are responsible for this behavior. These pigments were employed as paints, using a mixture of polyvinyl acetate as a binder and deionized water as the solvent, and were applied to wood and paper surfaces for color analysis

Synthesis and Characterization of a Reactive Vinyl-Functionalized MCM-41: Probing the Internal Pore Structure by a Bromination Reaction

Synthesis and Characterization of a Reactive Vinyl-Functionalized MCM-41:  Probing the Internal Pore Structure by a Bromination Reactio

Effects of Hierarchical Architecture on Electronic and Mechanical Properties of Nanocast Monolithic Porous Carbons and Carbon−Carbon Nanocomposites

This study compares the effects of meso- and macroporosity and the influence of nanocomposite structure on textural, electronic, and mechanical properties of monolithic carbon samples. Glassy carbon monoliths with three-dimensionally ordered macropores and walls containing mesopores (3DOM/m C) were synthesized by nanocasting from monolithic silica with hierarchical pore structure. The porous silica monoliths (3DOM/m SiO2) were prepared by combining colloidal crystal templating with surfactant templating. These preforms were infiltrated with a phenolic resin through a gas-phase process. After carbonization and HF extraction of silica, the resulting carbon monoliths maintained the open, interconnected macropore structure of the preform and the mesoporosity of the skeleton, which provided a high surface area >1200 m2/g to the material. Subsequent introduction of more graphitic, nitrogen-doped carbon into the mesopores by chemical vapor deposition produced a monolithic nanocomposite material (3DOM/m C/C). The materials were characterized in detail by powder X-ray diffraction, Raman spectroscopy, small-angle X-ray scattering, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, nitrogen-adsorption measurements, depth-sensing indentation, and electrochemical measurements. The mechanical strength, electronic conductivity, and capacity for lithiation of 3DOM/m C, 3DOM/m C/C, and a 3DOM carbon prepared from resorcinol-formaldehyde precursors without templated mesopores (3DOM RFC) were compared to evaluate the effects of the wall nanostructure and composition on these properties. The mechanical strength and electronic conductivity of the nanocomposite were significantly higher than those before addition of the second carbon phase. The nanocomposite suppressed formation of a solid-electrolyte interface layer during lithiation and had higher lithiation capacity than 3DOM RFC at high discharge rates, but not at low rates