Template‐Assisted Synthesis of Mesoporous Magnetic Nanocomposite Particles

A new concept is proposed to synthesize mesoporous magnetic nanocomposite particles of great scientific and technological importance. Mesoporous silica coatings were created on micrometer‐sized magnetite (Fe₃O₄) particles using cetyltrimethylammonium chloride micelles as molecular templates. The characterization by transmission electron microscopy (TEM), nitrogen adsorption–desorption, diffuse‐reflectance Fourier‐transform infrared spectroscopy, and zeta‐potential measurements confirmed the deposition of mesoporous silica thin layers on the magnetite particles. The synthesized particles showed a drastic increase in specific surface area with an average pore size of 2.5 nm. The coating material showed a negligible effect on the saturation magnetization of the original particles that were fully protected by silica coatings. The synthesized mesoporous magnetic nanocomposite particles have a wide range of applications in toxin removal, waste remediation, catalysis, reactive sorbents, and biological cell separations.     

Morphology‐Controlled Growth of Large‐Area Two‐Dimensional Ordered Pore Arrays

A solution‐dipping template strategy for large‐area synthesis of morphology‐controlled, ordered pore arrays is reported. The morphology of the pore array can easily be controlled by concentration of the precursor solution and treatment conditions. With decrease of the concentration from a high level to a very low level nanostructured complex (pore–hole, and pore–particle) arrays, through‐pore arrays, and even ring arrays can, in turn, be obtained. The pore size is adjustable over a large range by changing the diameter of the template's latex spheres. This synthesis route is universal and can be used for various metals, semiconductors and compounds on any substrate. Such structures may be useful in applications such as energy storage or conversion, especially in integrated next‐generation nanophotonics devices, and biomolecular labeling and identification.     

Template Deformation‐Tailored ZnO Nanorod/Nanowire Arrays: Full Growth Control and Optimization of Field‐Emission

Here, a facile and effective route toward full control of vertical ZnO nanorod (NR)/nanowire (NW) arrays in centimeter‐scale areas and considerable improvement of field‐emission (FE) performance is reported. Controlled deformation of colloidal crystal monolayer templates is introduced by heating near glass‐transition temperature. The NR/NW density, uniformity, and tapering were all adjusted through selection of template size and deformation, and electrolyte composition. In line with the adjustments, the field‐emission performance of the arrays is significantly improved. A low turn‐on electric field of 1.8 V µm^?1, a field‐enhancement factor of up to 5 750, and an emitting current density of up to 2.5 mA cm^?2 were obtained. These improved parameters would benefit their potential application in cold‐cathode‐based electronics.     

Systematic Study of the Growth of Aligned Arrays of α‐Fe2O3 and Fe3O4 Nanowires by a Vapor–Solid Process

Growth of aligned and uniform α‐Fe₂O₃ nanowire (NW) arrays has been achieved by a vapor–solid process. The experimental conditions, such as type of substrate, local growth and geometrical environment, gas‐flow rate, and growth temperature, under which the high density α‐Fe₂O₃ NW arrays can be grown by a vapor–solid route via the tip‐growth mechanism have been systematically investigated. The density of the α‐Fe₂O₃ NWs can be enhanced by increasing the concentration of Ni atoms inside the alloy substrate. The synthesized temperature can be as low as 400 °C. Fe₃O₄ NWs can be produced by converting α‐Fe₂O₃ NWs in a reducing atmosphere at 450 °C. The transformation of phase and structure have been observed by in situ transmission electron microscopy. The magnetic and field‐emission properties of the NWs indicate their potential applications in nanodevices.     

A Facile Sol–Gel Strategy for the Synthesis of Rod‐Shaped Nanocrystalline High‐Surface‐Area Lanthanum Phosphate Powders and Nanocoatings

Synthesis of rod‐shaped nanocrystalline lanthanum phosphate with an average length of 40 nm even after calcination at 400 °C has been realized through a room‐temperature aqueous sol–gel process. The sol is characterized by particle‐size, zeta‐potential, and viscosity measurements. Gelation of the sol is induced by ammonia. The lanthanum phosphate phase‐formation process is followed by thermal, Fourier‐transform IR, and X‐ray diffraction analysis. Transmission electron microscopy shows that the sol and gel particles have a rod‐shaped morphology and comparable particle sizes. Using the Scherrer equation a crystallite size of 11 nm is obtained for the gel powder calcined at 400 °C and Brunauer–Emmett–Teller (BET) nitrogen‐adsorption analysis showed a high specific surface area of 100 m² g^–1. Ammonia temperature‐programmed desorption measurements show that the density of Lewis acid sites is four times higher than ever reported in the case of lanthanum phosphates. The catalytic activity of the above sample is demonstrated by using it as a Lewis‐acid catalyst in an acetal‐formation reaction with a very good yield of 85 %. The sol is used to develop nanocoatings on a glass surface and the morphology of the coatings is investigated using atomic force microscopy and scanning electron microscopy. The microstructure of the coating confirmed the rod‐shaped nature of the sol particles. The coating was uniform with a thickness of about 55 nm.     

Sono‐ and Photochemical Routes for the Formation of Highly Dispersed Gold Nanoclusters in Mesoporous Titania Films

A sono‐ and photochemical approach has been developed to incorporate highly dispersed gold nanoclusters into mesoporous TiO₂ films. The first step involves the sonication of a TiO₂ film immersed in a gold chloride solution. This effectively removes the air trapped in the porous film matrix and drives the gold chloride into the pore channels, leading to a homogeneous adsorption of ionic Au in the TiO₂ mesoporous matrix. The second step takes advantage of the photocatalytic property of TiO₂ to reduce the adsorbed Au ions to Au⁰. As the gold nanoclusters thus produced are stabilized by the TiO₂ mesonetwork, no organic capping molecules are required. Highly dispersed Au/TiO₂ nanoheterojunction arrays can be obtained using this interesting approach.     

Nanocrystalline Metal Oxides from the Injection of Metal Oxide Sols in Coordinating Solutions: Synthesis,Characterization, Thermal Stabilization,Device Processing,and Gas‐Sensing Properties

Metal oxide (SnO₂, TiO₂, In₂O₃, ZnO) sols are prepared by various sol–gel processes in such a way as to hinder the condensation reactions. The obtained sols are injected at 160 °C into a solution of tetradecene and dodecylamine, and kept under heating for different periods of time. Depending on the starting sol, variously crystallized oxide nanoparticles are obtained, whose phase compositions and chemical structure have been studied by X‐ray diffraction (XRD) and Fourier transform IR spectroscopy. The elimination of the organic residuals has been carried out by thermal treatment, and the thermal evolution of the nanoparticles has been studied by thermal analyses and Raman spectroscopy. High‐resolution transmission electron microscopy studies coupled with XRD measurements show that the thermal treatment does not markedly affect the particle size, which remains in the nanometer‐sized regime (from 3.5 to 8.5 nm, depending on the system), except in the case of ZnO. The thermally purified and stabilized powders, drop‐coated onto alumina substrates with pre‐deposited electrical contacts, have been tested as gas‐sensing devices, displaying outstanding sensing properties even at room temperature.     

Promoting Active Sites in Core–Shell Nanowire Array as Mott–Schottky Electrocatalysts for Efficient and Stable Overall Water Splitting

Developing earth‐abundant, active, and robust electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a vital challenge for efficient conversion of sustainable energy sources. Herein, metal–semiconductor hybrids are reported with metallic nanoalloys on various defective oxide nanowire arrays (Cu/CuO_x, Co/CoO_x, and CuCo/CuCoO_x) as typical Mott–Schottky electrocatalysts. To build the highway of continuous electron transport between metals and semiconductors, nitrogen‐doped carbon (NC) has been implanted on metal–semiconductor nanowire array as core–shell conductive architecture. As expected, NC/CuCo/CuCoO_x nanowires arrays, as integrated Mott–Schottky electrocatalysts, present an overpotential of 112 mV at 10 mA cm^?2 and a low Tafel slope of 55 mV dec^?1 for HER, simultaneously delivering an overpotential of 190 mV at 10 mA cm^?2 for OER. Most importantly, NC/CuCo/CuCoO_x architectures, as both the anode and the cathode for overall water splitting, exhibit a current density of 10 mA cm^?2 at a cell voltage of 1.53 V with excellent stability due to high conductivity, large active surface area, abundant active sites, and the continuous electron transport from prominent synergetic effect among metal, semiconductor, and nitrogen‐doped carbon. This work represents an avenue to design and develop efficient and stable Mott–Schottky bifunctional electrocatalysts for promising energy conversion.     

CO2 Capture by As‐Prepared SBA‐15 with an Occluded Organic Template

A novel CO₂ capture phenomenon is observed by modifying as‐prepared mesoporous silica SBA‐15 (SBA(P)) with tetraethylenepentamine (TEPA), not only conserving the energy and time required for removing the template, but also opening the way to utilizing the micelle for dispersing guest species. The TEPA species dispersed within the channels of SBA(P) are highly accessible to CO₂ molecules; moreover, the hydroxyl group of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (Pluronic P123) template is able to modify the interactions between CO₂ and the amine to enhance the adsorptive capacity of this system. The remarkably high adsorption capacity (173 mg g^–1) of this mesoporous silica–amine composite suggests potential CO₂ trapping applications, especially at low CO₂ concentrations during prolonged cyclic operations.     

Synthesis and characterisation of the thallium‐substituted superconducting cuprate Hg1−xTlxBa2Ca2Cu3O8+δ

The objective of this research is the development of chemical routes for the preparation of high‐temperature superconducting powders. A simple sol–gel synthesis technique for preparing the superconducting compound Hg_1−xTl_xBa₂Ca₂Cu₃O_8+δ (Hg,Tl‐1223) has been refined. A systematic study of the influence of synthesis conditions on the phase purity of the obtained superconducting material is described. We have demonstrated that superconducting Hg_1−xTl_xBa₂Ca₂Cu₃O_8+δ phase of good quality can be obtained by this sol–gel synthesis method. Replacing Hg by Tl in the bulk material significantly increased the superconducting transition temperature. An as‐prepared sample showed T_C(onset)=136 K, but after oxygen treatment the critical temperature of Hg_1−xTl_xBa₂Ca₂Cu₃O_8+δ superconductor increased to 140 K. Copyright © 1999 John Wiley & Sons, Ltd.     

Size and Shape Dependence of Organo‐Interconnected Silsesquioxanes through Hydrolysis‐Condensation Reaction Conditions: Nanotubes,Spheres and Films

A tris‐silylated urea‐based compound, 1,3,5‐tris(triethoxysilylpropylureido)benzene has been synthesized. Hybrids materials with different shapes (films, spheres and tubes) are obtained upon base‐catalyzed hydrolytic condensation of this compound. A self‐templating process is demonstrated using electron microscopy (SEM and TEM) and X‐ray diffraction (SAXS and WAXS) techniques. We show the formation of nanometer size hollow tubes according to the size of the self‐templating crystalline precursor. The possibility for this self‐templating to occur is due to a favored dissolution of the self‐assembled molecules of the precursor in a preferential direction parallel to the cross‐section of the crystals.     

A New Sol–Gel Material Doped with an Erbium Complex and Its Potential Optical‐Amplification Application

The crystal structure of a ternary Er(DBM)₃phen complex (DBM = dibenzoylmethane; phen = 1,10‐phenanthroline) and its in‐situ synthesis via a sol–gel process are reported. The infrared (IR), diffuse reflectance (DR), and fluorescence spectra of the pure complex and the Er³⁺/DBM/phen co‐doped luminescent hybrid gel, formed via an in‐situ method (ErDP gel), have been investigated. The results reveal that the erbium complex is successfully synthesized in situ in the ErDP gel. Excitation at the maximum absorption wavelength of the ligands resulted in the typical near‐IR luminescence (centered at around 1.54 μm) resulting from the ⁴I_13/2 → ⁴I_15/2 transition of the Er³⁺ ion, which contributes to the efficient energy transfer from the ligands to the Er³⁺ ion in both the Er(DBM)₃phen complex and the ErDP gel (an antenna effect). The full width at half maximum (FWHM) centered at 1541 nm in the emission spectrum of the ErDP gel is 72 nm, which has potential for optical‐amplification applications. Further theoretical analysis on the Er³⁺ ion in the ErDP gel shows that it appears to be a promising candidate for tunable lasers and planar optical amplifiers.     

Electric‐Field‐Assisted Growth of Vertical Graphene Arrays and the Application in Thermal Interface Materials

Owing to the development of electronic devices moving toward high power density, miniaturization, and multifunction, research on thermal interface materials (TIMs) is become increasingly significant. Graphene is regarded as the most promising thermal management material owing to its ultrahigh in‐plane thermal conductivity. However, the fabrication of high‐quality vertical graphene (VG) arrays and their utilization in TIMs still remains a big challenge. In this study, a rational approach is developed for growing VG arrays using an alcohol‐based electric‐field‐assisted plasma enhanced chemical vapor deposition. Alcohol‐based carbon sources are used to produce hydroxyl radicals to increase the growth rate and reduce the formation of defects. A vertical electric field is used to align the graphene sheets. Using this method, high‐quality and vertically aligned graphene with a height of 18.7 µm is obtained under an electric field of 30 V cm^?1. TIMs constructed with the VG arrays exhibit a high vertical thermal conductivity of 53.5 W m^?1 K^?1 and a low contact thermal resistance of 11.8 K mm² W^?1, indicating their significant potential for applications in heat dissipation technologies.     

Fabrication and Optical Characteristics of Position‐Controlled ZnO Nanotubes and ZnO/Zn0.8Mg0.2O Coaxial Nanotube Quantum Structure Arrays

The position‐controlled growth and structural and optical characteristics of ZnO nanotubes and their coaxial heterostructures are reported. To control both the shape and position of ZnO nanotubes, hole‐patterned SiO₂ growth‐mask layers on Si(111) substrates with GaN/AlN intermediate layers using conventional lithography are prepared. ZnO nanotubes are grown only on the hole patterns at 600 °C by catalyst‐free metal–organic vapor‐phase epitaxy. Furthermore, the position‐controlled nanotube growth method allows the fabrication of artificial arrays of ZnO‐based coaxial nanotube single‐quantum‐well structures (SQWs) on Si substrates. In situ heteroepitaxial growth of ZnO and Zn_0.8Mg_0.2O layers along the circumference of the ZnO nanotube enable an artificial formation of quantum‐well arrays in a designed fashion. The structural and optical characteristics of the ZnO nanotubes and SQW arrays are also investigated using synchrotron radiation X‐ray diffractometry and photoluminescence and cathodoluminescence spectroscopy.     

Organic–Inorganic Hybrid Nanocomposites Prepared by Means of Sol–Gel Condensation of Bismethacrylatesilanes in Reactive Diluents

A bismethacrylatesilane monomer (BMS) was prepared via selective Michael addition of aminopropyltrimethoxysilane (APTMS) to the acrylate groups of 2‐methacryloyloxyethyl acrylate (ethyleneglycol acrylatemethacrylate, EGAMA). Sol–gel condensation of BMS in triethyleneglycoldimethacrylate (TGDMA) afforded in situ stable methacrylate‐functional nanoparticle dispersions, with average nanoparticle diameter of 3–4 nm, as determined by means of element‐specific transmission electron microscopy (TEM). Condensation in the absence of TGDMA could be achieved without gelation. Viscosities of the resulting nanoparticle dispersions were low, ranging from 12 to 1969 mPa s, shear‐rate‐independent and increased with the nanoparticle fraction, exhibiting hard‐sphere behavior. The nanoparticle dispersions in TGDMA were employed as matrix for the preparation of photocurable acrylic nanocomposites. Mechanical properties such as compressive and flexural strength as well as Young’s moduli (6000 to 8700 MPa) have been determined. Low volume shrinkage was observed upon polymerization. The volume shrinkage depended on the nanofiller fraction.     

Synthesis of Nanofiber‐Based Silica Networks Mediated by Organized Poly(ethylene imine): Structure,Properties, and Mechanism

Linear poly(ethylene imine) (PEI) can self‐organize into fibrous aggregates with a crystalline core and a brushlike shell of ethyleneimine (EI) segments. Silicification from alkoxysilane mediated by PEI aggregates easily produces silica nanofibers (20–23 nm in diameter) with a core of axial, crystalline PEI filaments (5–7 nm in width) and a shell of silica (6–8 nm in thickness). Removing the axial filament of PEI from the silica nanofiber by calcination produces silica nanotubes. More interestingly, a nanowire‐like platinum lining is formed in the silica nanofiber—a result of the PEI filament's ability to reduce PtCl₄^2–. The degree of polycondensation, composition, and surface area of the resulting silica are investigated by ²⁹Si magic angle spinning NMR spectroscopy, elemental analysis, and N₂/He adsorption–desorption measurements. The time course of the reaction and the amount of silica source needed for silica‐fiber formation confirm that silica deposition occurs exclusively and site selectively on the surface of the organized, fibrous PEI. Thus, the fibrous aggregates of PEI appear to be highly suitable for depositing silica fibers from both tetramethoxysilane and tetraethoxysilane.     

“Black” Titania Coatings Composed of Sol–Gel Imprinted Mie Resonators Arrays

Optical technologies and devices rely on the controlled manipulation of light propagation through a medium. This is generally governed by the inherent effective refractive index of the material as well as by its structure and dimensionality. Although a precise control over light propagation with sub‐wavelength size objects is a crucial issue for a plethora of applications, the widely used fabrication methods remain cumbersome and expensive. Here, a sol–gel dip‐coating method combined with nanoimprinting lithography on arbitrary glass and silicon substrates is implemented for the fabrication of TiO₂‐based dielectric Mie resonators. The technique allows obtaining sub‐micrometric pillars featuring unprecedented vertical aspect ratios (>1) with relatively high fidelity and precision. Spectroscopic characterization at visible and near‐infrared frequencies demonstrate that the resonant properties of these dielectric pillar arrays allow for a drastic reduction of light transmission (cutting more than 50% on glass) and reduced reflection (reflecting less than 3% on glass and 16% on bulk silicon), accounting for an efficient light trapping. These results provide a guideline for the fabrication of Mie resonators using a fast, versatile, low‐cost, low‐temperature technique for efficient light manipulation at the nanoscale.     

The effect of heat treatment process on structure and properties of ZnO nano layer produced by sol–gel method

ZnO nano layer was prepared by sol–gel method using zinc acetate dihydrate, methanol and diethanolamine as precursor, solvent and stabilizer, respectively. According to the thermal analysis results, the heat treatment process after producing ZnO nano layer can be divided into three stages. The structure of the nano layer showed a significant dependency on heat treatment temperature in the low temperature heat treatment stage, which is performed to evaporate the organic components. The high temperature heat treatment stage has no significant effect on the structure of the films. The temperature employed in the first stage of heat treatment process during the initial 10 min of heat treatment was found to be important in determining the structure of the films. The results determined that the elimination condition of the organic components is very important for achieving high crystallinity.     

Highly Dispersed Mixed Zirconia and Hafnia Nanoparticles in a Silica Matrix: First Example of a ZrO2–HfO2–SiO2 Ternary Oxide System

ZrO₂ and HfO₂ nanoparticles are homogeneously dispersed in SiO₂ matrices (supported film and bulk powders) by copolymerization of two oxozirconium and oxohafnium clusters (M₄O₂(OMc)₁₂, M = Zr, Hf; OMc = OC(O)–C(CH₃)?CH₂) with (methacryloxypropyl)trimethoxysilane (MAPTMS, (CH2?C(CH₃)C(O)O)–(CH₂)₃Si(OCH₃)₃). After calcination (at a temperature ≥800 °C), a silica matrix with homogeneously distributed MO₂ nanocrystallites is obtained. This route yields a spatially homogeneous dispersion of the metal precursors inside the silica matrix, which is maintained during calcination. The composition of the films and the powders is studied before and after calcination by using Fourier transform infrared (FTIR) analysis, X‐ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS). The local environment of the metal atoms in one of the calcined samples is investigated by using X‐ray Absorption Fine Structure (XAFS) spectroscopy. Through X‐ray diffraction (XRD) the crystallization of Hf and Zr oxides is seen at temperatures higher than those expected for the pure oxides, and transmission electron microscopy (TEM) shows the presence of well‐distributed and isolated crystalline oxide nanoparticles (5–10 nm).     

Polyaniline–Silica Composite Conductive Capsules and Hollow Spheres

In this paper, we report on the preparation of monodisperse polyaniline (PANi)–silica composite capsules and hollow spheres on monodisperse core–gel‐shell template particles. An extension of the previously reported inward growth method was used. The samples were self‐stabilized without external additives. The core–gel‐shell particles were prepared by the inward sulfonation of monodisperse polystyrene particles. The introduced sulfonic acid and sulfone groups are responsible for the gel properties. The gel‐shell thickness and core size were synchronously controlled over the whole particle radius range. After aniline (ANi) monomer was preferentially absorbed in the sulfonated polystyrene shell, PANi was formed by polymerization. PANi was doped in situ with a sulfonic acid group to give the capsules a high conductivity. PANi hollow spheres were derived after the polystyrene cores were dissolved: their cavity size and shell thickness were synchronously controlled by using different core–gel‐shell particles. The PANi–silica composite capsules and hollow spheres were therefore prepared by a sol–gel process using tetraethylorthosilicate in the conducting shell. The PANi shell became more robust while maintaining the same conductivity level. Morphological results indicate that the PANi and silica formed a bicontinuous network. Fourier‐transform infrared (FTIR) spectra revealed that the hydrogen bonding in the PANi–gel shell was enhanced after the silica phase was incorporated, which could explain the high conductivity level after the silica phase was added. In a converse procedure, silica capsules and hollow spheres were prepared by a sol–gel process that incorporated tetraethylorthosilicate into the core–gel‐shell templates, which was followed by the absorption and polymerization of aniline in the silica shell thus forming PANi–silica composite capsules and hollow spheres. The silica capsules and hollow spheres thereby became conductive.