Templated Synthesis and Structural Study of Densely Packed Metal Nanostructures in MCM‐41 and MCM‐48

A template synthetic method to prepare densely packed metal nanostructures in functionalized (MCM)‐41 and MCM‐48 is described. The intrachannel surface of host silica has been functionalized to carry positive charges for the accommodation of highly concentrated and negatively charged metal complexes. After reduction, Au and Pt nanowire bundles in MCM‐41 as well as Pd nanowire networks in MCM‐48 are formed. The Pt nanowire bundles in MCM‐41 are observed to grow along a preferred direction and stack along Pt {111} planes relative to the pore wall of the host. Furthermore, bimetallic AuPt alloy nanowire bundles in MCM‐41 have also been prepared and characterized.     

Spherical MSU‐1 Mesoporous Silica Particles Tuned for HPLC

Among the mesoporous silica micellar templated structures (MTSs), MSU‐X silica, obtained through an N⁰I⁰ assembly between non‐ionic polyethyleneoxide‐based surfactants (N⁰) and silica neutral inorganic precursors (I⁰), exhibits a regular ordered structure with a 3D wormhole porous framework and an easily controlled pore size. These materials have been tested for applications requiring both a narrow mesopore size distribution and isotropic properties. A specific double‐step synthesis that we developed recently for MSU‐X materials has allowed us to prepare mesoporous silica particles with the required shape, size, and properties. Both the particles’ synthesis and comparative HPLC separation tests with a commercial ungrafted silica HPLC powder of identical shape and size are reported.     

Fabrication and Size‐Selective Bioseparation of Magnetic Silica Nanospheres with Highly Ordered Periodic Mesostructure

In this paper, we report a novel synthesis and selective bioseparation of the composite of Fe₃O₄ magnetic nanocrystals and highly ordered MCM‐41 type periodic mesoporous silica nanospheres. Monodisperse superparamagnetic Fe₃O₄ nanocrystals were synthesized by thermal decomposition of iron stearate in diol in an autoclave at low temperature. The synthesized nanocrystals were encapsulated in mesoporous silica nanospheres through the packing and self‐assembly of composite nanocrystal–surfactant micelles and surfactant/silica complex. Different from previous studies, the produced magnetic silica nanospheres (MSNs) possess not only uniform nanosize (90 ～ 140 nm) but also a highly ordered mesostructure. More importantly, the pore size and the saturation magnetization values can be controlled by using different alkyltrimethylammonium bromide surfactants and changing the amount of Fe₃O₄ magnetic nanocrystals encapsulated, respectively. Binary adsorption and desorption of proteins cytochrome c (cyt c) and bovine serum albumin (BSA) demonstrate that MSNs are an effective and highly selective adsorbent for proteins with different molecular sizes. Small particle size, high surface area, narrow pore size distribution, and straight pores of MSNs are responsible for the high selective adsorption capacity and fast adsorption rates. High magnetization values and superparamagnetic property of MSNs provide a convenient means to remove nanoparticles from solution and make the re‐dispersion in solution quick following the withdrawal of an external magnetic field.     

Generation of Monodisperse Mesoporous Silica Microspheres with Controllable Size and Surface Morphology in a Microfluidic Device

A one‐step in situ method, termed microfluidic diffusion‐induced self‐assembly, for the synthesis of monodisperse ordered mesoporous silica microspheres, is reported. The method combines microfluidic generation of uniform droplets and subsequent in situ rapid solvent diffusion‐induced self‐assembly within the microfluidic channel. The mesoporous silica microspheres prepared in this way reveal well‐ordered 2D hexagonal mesostructures with unprecedented corrugated surface morphology of disordered mesopores that are larger than 15 nm. It is speculated that the formation of an interfacial subphase and rapid diffusion of solvent to oil are attributed to the formation of the unique surface morphology. It is also shown that the surface morphology and the particle size of the mesoporous silica microspheres can be systematically controlled by adjusting fluidic conditions.     

Cover Picture: Generation of Monodisperse Mesoporous Silica Microspheres with Controllable Size and Surface Morphology in a Microfluidic Device (Adv. Funct. Mater. 24/2008)

A one‐step in situ method, termed microfluidic diffusion‐induced self‐assembly, for the synthesis of monodisperse ordered mesoporous silica microspheres, is reported. The method combines microfluidic generation of uniform droplets and subsequent in situ rapid solvent diffusion‐induced self‐assembly within the microfluidic channel. The mesoporous silica microspheres prepared in this way reveal well‐ordered 2D hexagonal mesostructures with unprecedented corrugated surface morphology of disordered mesopores that are larger than 15 nm. It is speculated that the formation of an interfacial subphase and rapid diffusion of solvent to oil are attributed to the formation of the unique surface morphology. It is also shown that the surface morphology and the particle size of the mesoporous silica microspheres can be systematically controlled by adjusting fluidic conditions.     

Template‐Assisted Self‐Assembly of Spherical Colloids into Complex and Controllable Structures

Colloidal aggregates with well‐controlled sizes, shapes, and structures have been fabricated by dewetting aqueous dispersions of monodispersed spherical colloids across surfaces patterned with two‐dimensional arrays of relief structures (or templates). The capability and feasibility of this approach have been demonstrated with the organization of polymer latex or silica beads into homo‐aggregates, including circular rings; polygonal and polyhedral clusters; and linear, zigzag, and spiral chains. It was also possible to generate hetero‐aggregates in the configuration of HF and H₂O molecules that contained spherical colloids of different sizes, compositions, densities, functions, or a combination of these features. These uniform, well‐defined aggregates of spherical colloids are ideal model systems to investigate the aerodynamic, hydrodynamic, and optical properties of colloidal particles characterized by non‐spherical shapes and/or complex topologies. They can also serve as a new class of building blocks to generate hierarchically self‐assembled structures that are expected to exhibit interesting features valuable to areas ranging from condensed matter physics to photonics.     

Fine‐Tuning of Superhydrophobicity Based on Monolayers of Well‐defined Raspberry Nanoparticles with Variable Dual‐roughness Size and Ratio

Superhydrophobic surfaces have been extensively investigated for self‐cleaning, low‐adhesion, anti‐corrosion or reduced‐drag applications. Roughness and its characteristics, i.e., morphology, overall roughness and individual feature size, is an essential factor for superhydrophobicity. Several experimental methods and theoretical models strived to predict how the surface wettability is affected by the surface roughness. However, due to the difficulty of making practical surfaces with well‐defined roughness profiles, only limited and arbitrary experimental studies focused on practical superhydrophobic films. Here, the roughness factors which determine the wetting properties of films are reported, based on monolayers of well‐defined raspberry silica‐silica nanoparticles, exhibiting a wide‐range and systematic variation of individual features sizes and ratios (large over small features). The advancing water contact angle does not depend on the feature size or ratio, while the contact angle hysteresis (CAH) is strongly dependent on both. The minimum size and size ratio to reach superhydrophobicity were determined. These new insights into the wetting of rough surfaces can be used to direct the design of practical superhydrophobic materials for advanced applications such as solar panels, microelectronics or microfluidic devices.     

Sub‐20 nm Magnetic Dots with Perpendicular Magnetic Anisotropy

A new and simple method for the preparation of magnetic dot arrays is introduced. Diblock copolymer micelles with a silica core are used as template for the generation of nanostructure arrays. The silica cores are utilized as mask for ion milling preparation. The morphology and size of the silica and magnetic dot arrays are discussed. The magnetic dots are made from Co/Pt multilayer films. Ferromagnetic dots with a diameter well below 20 nm and perpendicular easy axis of magnetization are created. The switching behavior changes from domain wall motion, dominant in the film, to single domain particle switching in the dots. The magneto‐optic saturation signals and the evolution of magnetic anisotropy are discussed.     

Tracking the direction-of-arrival of multiple moving targets bypassive arrays: algorithm

We propose a maximum likelihood (ML) approach for tracking the direction-of-arrival (DOA) of multiple moving targets by a passive array. A locally linear model is assumed for the target motion, and the multiple target states (MTSs) are defined to describe the states of the target motion, The locally linear model is shown to be strongly locally observable almost everywhere. The approach is to estimate the initial MTS by maximizing the likelihood function of the array data. The tracking is implemented by prediction through the target motion dynamics using the initial MTS estimate. By incorporating the target motion dynamics, the algorithm is able to eliminate the spread spectrum effects due to target motion. A modified Newton-type algorithm is also presented, which ensures fast convergence of the algorithm. Finally, numerical simulations are included to show the effectiveness of the proposed algorithm     

Polyamidoamine Dendrimers Prepared Inside the Channels of Pore‐Expanded Periodic Mesoporous Silica

Polyamidoamine dendrimers up to the fourth generation have been grown with unprecedentedly high loading within the channels of pore‐expanded (10.6 nm) MCM‐41 silica. In‐depth characterization using nitrogen adsorption, solid‐state NMR, FTIR, thermogravimetry, and elemental analysis showed that the dendrimers grow inside the channels with an average yield better than 99 %. The pore size and structure of the support have been found to be determining factors as to how much dendrimer growth can be achieved.     

Amorphous and Crystalline GeTe Nanocrystals

A facile method for the synthesis of crystalline and amorphous GeTe nanoparticles (NPs) using bis((trimethylsilyl)amido)germanium(II), Ge[N(SiMe₃)₂]₂, and elemental tellurium dispersed in tri‐n‐octylphosphine (TOP) is reported. As synthesized, crystalline particles exhibit narrow dispersity at smaller sizes and tend to grow into anisotropic shapes with increasing reaction time (growth). Furthermore, crystalline GeTe NPs possess rhombohedral symmetry with absorption band energies in near IR region (0.76–0.86 eV). Amorphous GeTe particles prepared at low temperatures are nearly spherical in morphology and display amorphous‐to‐crystalline phase transition at 209–237 °C depending on their primary particle size. Detailed investigation of the local structure of the amorphous GeTe using pair distribution function (PDF) method reveals that it is closely related to that of the pressure‐ and temperature‐stabilized orthorhombic GeTe.     

Direct Heating Amino Acids with Silica: A Universal Solvent‐Free Assembly Approach to Highly Nitrogen‐Doped Mesoporous Carbon Materials

A general solvent‐free assembly approach via directly heating amino acid and mesoporous silica mixtures is developed for the synthesis of a family of highly nitrogen‐doped mesoporous carbons. Amino acids have been used as the sole precursors for templating synthesis of a series of ordered mesoporous carbons. During heating, amino acids are melted and strongly interact with silica, leading to effective loading and improved carbon yields (up to ≈25 wt%), thus to successful structure replication and nitrogen‐doping. Unique solvent‐free structure assembly mechanisms are proposed and elucidated semi‐quantitatively by using two affinity scales. Significantly high nitrogen‐doping levels are achieved, up to 9.4 (16.0) wt% via carbonization at 900 (700) °C. The diverse types of amino acids, their variable interactions with silica and different pyrolytic behaviors lead to nitrogen‐doped mesoporous carbons with tunable surface areas (700–1400 m² g^?1), pore volumes (0.9–2.5 cm³ g^?1), pore sizes (4.3–10 nm), and particle sizes from a single template. As demonstrations, the typical nitrogen‐doped carbons show good performance in CO₂ capture with high CO₂/N₂ selectivities up to ≈48. Moreover, they show attractive performance for oxygen reduction reaction, with an onset and a half‐wave potential of ≈?0.06 and ?0.14 V (vs Ag/AgCl).     

Synthesis of Monodisperse Ag?Au Alloy Nanoparticles with Independently Tunable Morphology,Composition, Size,and Surface Chemistry and Their 3‐D Superlattices

Here, a strategy for synthesizing monodisperse Ag? Au alloy nanoparticles whereby particle attributes such as morphology, composition, size, and surface chemistry may be independently controlled, varied, and customized is presented. The synthesis uses a multi‐step procedure to deliver control of morphology, size, and composition in discrete and independent steps. Specifically Ag nanoparticles with the same morphology but different sizes are first prepared by the chemical reduction of Ag ions. A digestive ripening post‐treatment followed by seed‐mediated growth is then applied to narrow the size distribution and to vary the particle size. Monodisperse Ag? Au alloy nanoparticles are then formed by a replacement reaction with HAuCl₄. Both single‐crystalline truncated octahedral (TO) Ag? Au alloy nanoparticles and icosahedral multiply twinned particles can be easily prepared by this procedure. By using truncated octahedrons as the model morphology, the syntheses of nanoparticles with the same size but different compositions, of nanoparticles with the same composition but variable sizes, and of nanoparticles with different surface chemistry are demonstrated and discussed in detail. Because of the shape and size monodispersity, all of the as‐synthesized Ag? Au alloy nanoparticles easily form superlattices on a solid substrate upon slow evaporation of the solvent. The packing pattern of the nanoparticles is strongly dependent on the native morphology of the nanoparticles.     

Carbon Vesicles: A Symmetry‐Breaking Strategy for Wide‐Band and Solvent‐Processable Ultrablack Coating Materials

Solvent‐processable ultrablack materials have obvious application convenience in many situations, such as absorbing coatings on large and complex surfaces. However, developing solvent‐processable ultrablack materials with high light‐absorption performance and wide absorption band remains a great challenge. In this article, carbon vesicles (CVs) are fabricated for solvent‐processable ultrablack coating. The fabrication process involves a templated co‐condensation of silica and resorcinol formaldehyde resin (RF resin), followed by carbonization and template removal. The resultant structure shows a very thin inner layer, a rough outer layer, as well as a nano‐porous interlayer. This structure introduces randomness and breaks the spherical symmetry of the common carbon hollow spheres. As a result, structural color due to inner‐particle interference is avoided. In addition, the as‐fabricated CVs show a wide‐band low reflectance because of its low carbon filling ratio and nanoscale scatterer size. The lowest reflectance reaches ≈0.10% at 360 nm, making it the darkest solvent‐processable ultrablack material ever reported. The symmetry‐breaking strategy presented here provides an efficient way for the design of solvent‐processable ultrablack materials.     

Surface‐Confined Atom Transfer Radical Polymerization from Sacrificial Mesoporous Silica Nanospheres for Preparing Mesoporous Polymer/Carbon Nanospheres with Faithful Shape Replication: Functional Mesoporous Materials

A facile approach for the preparation of mesoporous polymer nanospheres (MPN) and mesoporous carbon nanospheres (MCN) with complete shape retention based on surface‐confined atom transfer radical polymerization of various methacrylate monomers from in situ generated initiator‐modified hard silica nanospheres template is developed. This approach yields mesoporous silica‐polymer hybrid nanospheres (MSPN) with mesopores that are uniformly filled with covalently attached well‐defined poly(methacrylate)s. The silica frameworks are subsequently etched, resulting in MPN. Pyrolysis of MSPN and subsequent removal of silica template resulted in the production of MCN. They retain the size, shape, and mesoporous ordering of the silica template nanospheres. Gel permeation chromatography analysis of the silica free polymers reveals that they have controlled molecular weights and low polydispersities (PDIs). Kinetics studies reveal that the molecular weight of the grafted polymer increases linearly with time, maintaining low PDIs, indicating the living nature of the polymerization. The mesoporous polymer material is found to have low dielectric constant, which paves the way for their use as low‐dielectric constant materials in microelectronics. This approach allows fabrication of functional MPN using functional comonomers, which are successfully used for the synthesis of “clickable” mesoporous polymer nanospheres, removal of ionic contaminates through anion exchange, and glucose sensing.     

Ordered Mesoporous In2O3: Synthesis by Structure Replication and Application as a Methane Gas Sensor

The synthesis and characterization of ordered mesoporous In₂O₃ materials by structure replication from hexagonal mesoporous SBA‐15 silica and cubic KIT‐6 silica is presented. Variation of the synthesis parameters allows for different pore sizes and pore wall thicknesses in the products. The In₂O₃ samples turn out to be stable up to temperatures between 450 °C and 650 °C; such high thermal stability is necessary for their application as gas sensors. Test measurements show a high sensitivity to methane gas in concentrations relevant for explosion prevention. The sensitivity is shown to be correlated not only with the surface‐to‐volume ratio, but also with the nanoscopic structural properties of the materials.     

Evaporation‐Induced Coating and Self‐Assembly of Ordered Mesoporous Carbon‐Silica Composite Monoliths with Macroporous Architecture on Polyurethane Foams

A facile approach of solvent‐evaporation‐induced coating and self‐assembly is demonstrated for the mass preparation of ordered mesoporous carbon‐silica composite monoliths by using a polyether polyol‐based polyurethane (PU) foam as a sacrificial scaffold. The preparation is carried out using resol as a carbon precursor, tetraethyl orthosilicate (TEOS) as a silica source and Pluronic F127 triblock copolymer as a template. The PU foam with its macrostructure provides a large, 3D, interconnecting interface for evaporation‐induced coating of the phenolic resin‐silica block‐copolymer composites and self‐assembly of the mesostructure, and endows the composite monoliths with a diversity of macroporous architectures. Small‐angle X‐ray scattering, X‐ray diffraction and transmission electron microscopy results indicate that the obtained composite monoliths have an ordered mesostructure with 2D hexagonal symmetry (p6m) and good thermal stability. By simply changing the mass ratio of the resol to TEOS over a wide range (10–90%), a series of ordered, mesoporous composite foams with different compositions can be obtained. The composite monoliths with hierarchical macro/mesopores exhibit large pore volumes (0.3–0.8 cm³ g^?1), uniform pore sizes (4.2–9.0 nm), and surface areas (230–610 m² g^?1). A formation process for the hierarchical porous composite monoliths on the struts of the PU foam through the evaporation‐induced coating and self‐assembly method is described in detail. This simple strategy performed on commercial PU foam is a good candidate for mass production of interface‐assembly materials.     

Novel Cathode Materials for Na‐Ion Batteries Composed of Spoke‐Like Nanorods of Na[Ni0.61Co0.12Mn0.27]O2 Assembled in Spherical Secondary Particles

The development of high‐energy and high‐power density sodium‐ion batteries is a great challenge for modern electrochemistry. The main hurdle to wide acceptance of sodium‐ion batteries lies in identifying and developing suitable new electrode materials. This study presents a composition‐graded cathode with average composition Na[Ni_0.61Co_0.12Mn_0.27]O₂, which exhibits excellent performance and stability. In addition to the concentration gradients of the transition metal ions, the cathode is composed of spoke‐like nanorods assembled into a spherical superstructure. Individual nanorod particles also possess strong crystallographic texture with respect to the center of the spherical particle. Such morphology allows the spoke‐like nanorods to assemble into a compact structure that minimizes its porosity and maximizes its mechanical strength while facilitating Na⁺‐ion transport into the particle interior. Microcompression tests have explicitly verified the mechanical robustness of the composition‐graded cathode and single particle electrochemical measurements have demonstrated the electrochemical stability during Na⁺‐ion insertion and extraction at high rates. These structural and morphological features contribute to the delivery of high discharge capacities of 160 mAh (g oxide)^?1 at 15 mA g^?1 (0.1 C rate) and 130 mAh g^?1 at 1500 mA g^?1 (10 C rate). The work is a pronounced step forward in the development of new Na ion insertion cathodes with a concentration gradient.     

Fabrication of dry-etched mirrors in GaAs-based and InP-based lasers using chemically assisted ion-beam etching at low temperatures

We have fabricated dry-etched mirrors in high-speed InGaAs/GaAs/AlGaAs pseudomorphic multiple quantum well ridge-waveguide lasers at 60°C and in InGaAs/InP bulk lasers at 5°C using enhanced chemically assisted ion-beam etching (CAIBE) technique. The technique allows the etching of laser structures with good surface morphology and excellent anisotropy without cold traps in the etching system. Characteristics of the dry-etched facet lasers match those of cleaved devices. The low sample temperatures for etching allowed the use of standard photoresists as etch masks.