Hydrothermally Stable Thioether‐Bridged Mesoporous Materials with Void Defects in the Pore Walls

Hydrothermally stable thioether‐bridged mesoporous materials have been synthesized by one‐step co‐condensation of 1,4‐bis(triethoxysily)propane tetrasulfide (TESPTS) with tetramethoxysilane (TMOS) using cetyltrimethylammonimum bromide (CTAB) as the surfactant in basic conditions. The ordered mesoporous materials can be formed with a wide range of thioether concentrations in the mesoporous framework, as is seen by X‐ray diffraction (XRD) characterization. The results of N₂ sorption and transmission electron microscopy (TEM) reveal that the materials synthesized with TESPTS/TMOS molar ratios in the range 1:8–1:3 have extensive structural defect holes in the nanochannels. All materials exhibit enhanced hydrothermal stability, which is in proportion to the concentration of thioether bridging in the mesoporous framework. The thioether‐functionalized mesoporous materials are efficient adsorbents for removing Hg²⁺ and phenol from waste water. The Hg²⁺‐adsorption capacity of the material can be as high as 1500 mg g^–1.     

Colloidal Suspensions of Nanometer‐Sized Mesoporous Silica

Nanometer‐sized surfactant‐templated materials are prepared in the form of stable suspensions of colloidal mesoporous silica (CMS) consisting of discrete, nonaggregated particles with dimensions smaller than 200 nm. A high‐yield synthesis procedure is reported based on a cationic surfactant and low water content that additionally enables the adjustment of the size range of the individual particles between 50 and 100 nm. Particularly, the use of the base triethanolamine (TEA) and the specific reaction conditions result in long‐lived suspensions. Dynamic light scattering reveals narrow particle size distributions in these suspensions. Smooth spherical particles with pores growing from the center to the periphery are observed by using transmission electron microscopy, suggesting a seed‐growth mechanism. The template molecules could be extracted from the nanoscale mesoporous particles via sonication in acidic media. The resulting nanoparticles give rise to type IV adsorption isotherms revealing typical mesopores and additional textural porosity. High surface areas of over 1000 m² g^–1 and large pore volumes of up to 1 mL g^–1 are obtained for these extracted samples.     

Spin‐Coated Periodic Mesoporous Organosilica Thin Films—Towards a New Generation of Low‐Dielectric‐Constant Materials

Periodic mesoporous organosilica (PMO) thin films have been produced using an evaporation‐induced self‐assembly (EISA) spin‐coating procedure and a cationic surfactant template. The precursors are silsesquioxanes of the type (C₂H₅O)₃Si–R–Si(OC₂H₅)₃ or R′–[Si(OC₂H₅)₃]₃ with R = methene (–CH₂–), ethylene (–C₂H₂–), ethene (–C₂H₄–), 1,4‐phenylene (C₆H₄), and R′ = 1,3,5‐phenylene (C₆H₃). The surfactant is successfully removed by solvent extraction or calcination without any significant Si–C bond cleavage of the organic bridging groups R and R′ within the channel walls. The materials have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD), and ²⁹Si and ¹³C magic‐angle spinning (MAS) NMR spectroscopy. The d‐spacing of the PMOs is found to be a function of R. Nanoindentation measurements reveal increased mechanical strength and stiffness for the PMOs with R = CH₂ and C₂H₄ compared to silica. Films with different organic‐group content have been prepared using mixtures of silsesquioxane and tetramethylorthosilicate (TMOS) precursors. The dielectric constant (k) is found to decrease with organic content, and values as low as 1.8 have been measured for films thermally treated to cause a “self‐hydrophobizing” bridging‐to‐terminal transformation of the methene to methyl groups with concomitant loss of silanols. Increasing the organic content and thermal treatment also increases the resistance to moisture adsorption in 60 and 80 %‐relative‐humidity (RH) environments. Methene PMO films treated at 500 °C are found to be practically unchanged after five days exposure to 80 % RH. These low dielectric constants, plus the good thermal and mechanical stability and the hydrophobicity suggest the potential utility of these films as low‐k layers in microelectronics.     

Combined Surface and Volume Templating of Highly Porous Nanocast Carbon Monoliths

Nanocast carbon monoliths exhibiting a three‐ or four‐modal porosity have been prepared by one‐step impregnation, using silica monoliths containing a bimodal porosity as the scaffold. Combined volume and surface templating, together with the controlled synthesis of the starting silica monoliths used as the scaffold, enables a flexible means of pore‐size control on several length scales simultaneously. The monoliths were characterized by nitrogen sorption, scanning electron microscopy, transmission electron microscopy, and mercury porosimetry. It is shown that the carbon monoliths represent a positive replica of the starting silica monoliths on the micrometer length scale, whereas the volume‐templated mesopores are a negative replica of the silica scaffold. In addition to the meso‐ and macropores, the carbon monoliths also exhibit microporosity. The different modes of porosity are arranged in a hierarchical structure‐within‐structure fashion, which is thought to be optimal for applications requiring a high surface area in combination with a low pressure drop over the material.     

Highly Ordered Mesoporous Silicon Carbide Ceramics with Large Surface Areas and High Stability

Highly ordered mesoporous silicon carbide ceramics have been successfully synthesized with yields higher than 75 % via a one‐step nanocasting process using commercial polycarbosilane (PCS) as a precursor and mesoporous silica as hard templates. Mesoporous SiC nanowires in two‐dimensional (2D) hexagonal arrays (p6m) can be easily replicated from a mesoporous silica SBA‐15 template. Small‐angle X‐ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images show that the SiC nanowires have long‐range regularity over large areas because of the interwire pillar connections. A three‐dimensional (3D) bicontinuous cubic mesoporous SiC structure (Ia3d) can be fabricated using mesoporous silica KIT‐6 as the mother template. The structure shows higher thermal stability than the 2D hexagonal mesoporous SiC, mostly because of the 3D network connections. The major constituent of the products is SiC, with 12 % excess carbon and 14 % oxygen measured by elemental analysis. The obtained mesoporous SiC ceramics are amorphous below 1200 °C and are mainly composed of randomly oriented β‐SiC crystallites after treatment at 1400 °C. N₂‐sorption isotherms reveal that these ordered mesoporous SiC ceramics have high Brunauer–Emmett–Teller (BET) specific surface areas (up to 720 m² g^–1), large pore volumes (～ 0.8 cm³ g^–1), and narrow pore‐size distributions (mean values of 2.0–3.7 nm), even upon calcination at temperatures as high as 1400 °C. The rough surface and high order of the nanowire arrays result from the strong interconnections of the SiC products and are the main reasons for such high surface areas. XRD, N₂‐sorption, and TEM measurements show that the mesoporous SiC ceramics have ultrahigh stability even after re‐treatment at 1400 °C under a N₂ atmosphere. Compared with 2D hexagonal SiC nanowire arrays, 3D cubic mesoporous SiC shows superior thermal stability, as well as higher surface areas (590 m² g^–1) and larger pore volumes (～ 0.71 cm³ g^–1).     

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.     

Preparation of Hollow Silica Nanospheres by Surface‐Initiated Atom Transfer Radical Polymerization on Polymer Latex Templates

Poly(vinylbenzyl chloride), (PVBC) latex particles of about 100 nm in size are prepared by emulsion polymerization. Silyl functional groups are introduced onto the PVBC‐nanoparticle templates via surface‐initiated atom transfer radical polymerization of 3‐(trimethoxysilyl)propyl methacrylate. The silyl groups are then converted into a silica shell, approximately 20 nm thick, via a reaction with tetraethoxysilane in ethanolic ammonia. Hollow silica nanospheres are finally generated by thermal decomposition of the PVBC template cores. Field‐emission scanning electron microscopy and field‐emission transmission electron microscopy are used to characterize the intermediate products and the hollow nanospheres. Fourier‐transform infrared spectroscopy results indicate that the polymer cores are completely decomposed.     

Replication and Coating of Silica Templates by Hydrothermal Carbonization

Hierarchical carbon materials with functional groups residing at the surface are prepared for the first time by using nanostructured silica materials as templates in combination with hydrothermal carbonization at mild temperatures (180 °C). Different carbon morphologies (e.g., macroporous casts, hollow spheres, carbon nanoparticles, and mesoporous microspheres) can be obtained by simply altering the polarity of the silica surface. The surface functionality and hydrophilicity of the resulting materials are assessed by Fourier transform IR spectroscopy, X‐ray photoelectron analysis, and water porosimetry. Raman spectroscopy and X‐ray diffraction measurements show that the materials are of the carbon‐black type, similar to charcoal.     

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.     

Thermally Stable Two‐Dimensional Hexagonal Mesoporous Nanocrystalline Anatase,Meso‐nc‐TiO2: Bulk and Crack‐Free Thin Film Morphologies

Herein a novel synthetic route is described for the production of thermally stable, structurally well‐defined two‐dimensional (2D) hexagonal mesoporous nanocrystalline anatase (meso‐nc‐TiO₂), with a large pore diameter, narrow pore‐size distribution, high surface area, and robust inorganic walls comprised of nanocrystalline anatase. The synthetic approach involves the evaporation‐induced co‐assembly of a non‐ionic amphiphilic triblock‐copolymer template and titanium tetraethoxide, but with a pivotal change in the main solvent of the system, where the commonly used ethanol is replaced with 1‐butanol. This seemingly minor modification in solvent type from ethanol to 1‐butanol turns out to be the key synthetic strategy for achieving a robust, structurally well‐ordered meso‐nc‐TiO₂ material in the form of either thick or thin films. The beneficial “solvent” effect originates from the higher hydrophobicity of 1‐butanol than ethanol, enhancing microphase separation and templating, lower critical micelle concentration of the template in 1‐butanol, and the ability to increase the relative concentration of the inorganic precursor to template in the co‐assembly synthesis. Moreover, thin films with dimensions of several centimeters that are devoid of cracks down to the length scale of the mesostructure itself, having high porosity, well‐defined mesostructural features, and semi‐crystalline pore walls were straightforwardly and reproducibly obtained as a result of the physicochemical property advantages of 1‐butanol over ethanol within our synthesis scheme.     

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.     

Highly Organized Mesoporous TiO2 Films with Controlled Crystallinity: A Li‐Insertion Study

A study of electrochemical Li insertion combined with structural and textural analysis enabled the identification and quantification of individual crystalline and amorphous phases in mesoporous TiO₂ films prepared by the evaporation‐induced self‐assembly procedure. It was found that the properties of the amphiphilic block copolymers used as templates, namely those of a novel poly(ethylene‐co‐butylene)‐b‐poly(ethylene oxide) polymer (KLE) and commercial Pluronic P123 (HO(CH₂CH₂O)₂₀(CH₂CH(CH₃)O)₇₀(CH₂CH₂O)₂₀H), decisively influence the physicochemical properties of the resulting films. The KLE‐templated films possess a 3D cubic mesoporous structure and are practically amorphous when calcined at temperatures below 450 °C, but treatment at 550–700 °C provides a pure‐phase (anatase), fully crystalline material with intact mesoporous architecture. The electrochemically determined fraction of crystalline anatase increases from 85 to 100 % for films calcined at 550 and 700 °C, respectively. In contrast, the films prepared using Pluronic P123, which also show a 3D cubic pore arrangement, exhibit almost 50 % crystallinity even at a calcination temperature of 400 °C, and their transformation into a fully crystalline material is accompanied by collapse of the mesoporous texture. Therefore, our study revealed the significance of using suitable block‐copolymer templates for the generation of mesoporous metal oxide films. Coupling of both electrochemical and X‐ray diffraction methods has shown to be highly advisable for the correct interpretation of structure properties, in particular the crystallinity, of such sol–gel derived films.     

Multiple Functionalization of Mesoporous Silica in One‐Pot: Direct Synthesis of Aluminum‐Containing Plugged SBA‐15 from Aqueous Nitrate Solutions

Aluminum‐containing plugged mesoporous silica has been successfully prepared in an aqueous solution that contains triblock copolymer templates, nitrates, and silica sources but without using mineral acid. The acidity of the solution can be finely tuned from pH 1.4 to 2.8 according to the amount of the introduced aluminum species which ranged from an Al/Si molar ratio of 0.25/1 to 4.0/1. The aluminum nitrate additive in the starting mixture, along with the weak acidity produced by the nitrates, contributes to the formation of plugged hexagonal structures and the introduction of different amounts of aluminum species into the mesostructure. Characterization by X‐ray diffraction, transmission electron microscopy, and N₂ sorption measurements show that the Al‐containing plugged silicas possess well‐ordered hexagonal mesostructures with high surface areas (700–860 m² g^–1), large pore volume (0.77–1.05 cm³ g^–1) and, more importantly, combined micropores and/or small mesopores in the cylindrical channels. Inductively coupled plasma–atomic emission spectrometry results show that 0.7–3.0 wt % aluminum can be introduced into the final samples. ²⁷Al MAS NMR results display that about 43–60% aluminum species are incorporated into the skeleton of the Al‐containing silicas and the amount of the framework aluminum increases as the initial added nitrates rises. Scanning electron microscopy images reveal that the directly synthesized Al‐containing plugged silica has a similar morphology to that of traditional SBA‐15. Furthermore, the Al‐containing plugged samples have excellent performances in the adsorption and the catalytic decomposition of isopropyl alcohol and nitrosamine. Finally, the direct synthesis method is used to produce plugged mesoporous silicas that contain other metals such as chromium and copper, and the resultant samples also show good catalytic activities.     

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.     

Synthesis and Rate Performance of Monolithic Macroporous Carbon Electrodes for Lithium‐Ion Secondary Batteries

Three‐dimensionally ordered macroporous (3DOM) materials are composed of well‐interconnected pore and wall structures with wall thicknesses of a few tens of nanometers. These characteristics can be applied to enhance the rate performance of lithium‐ion secondary batteries. 3DOM monoliths of hard carbon have been synthesized via a resorcinol‐formaldehyde sol–gel process using poly(methyl methacrylate) colloidal‐crystal templates, and the rate performance of 3DOM carbon electrodes for lithium‐ion secondary batteries has been evaluated. The advantages of monolithic 3DOM carbon electrodes are: 1) solid‐state diffusion lengths for lithium ions of the order of a few tens of nanometers, 2) a large number of active sites for charge‐transfer reactions because of the material's high surface area, 3) reasonable electrical conductivity of 3DOM carbon due to a well‐interconnected wall structure, 4) high ionic conductivity of the electrolyte within the 3DOM carbon matrix, and 5) no need for a binder and/or a conducting agent. These factors lead to significantly improved rate performance compared to a similar but non‐templated carbon electrode and compared to an electrode prepared from spherical carbon with binder. To increase the energy density of 3DOM carbon, tin oxide nanoparticles have been coated on the surface of 3DOM carbon by thermal decomposition of tin sulfate, because the specific capacity of tin oxide is larger than that of carbon. The initial specific capacity of SnO₂‐coated 3DOM carbon increases compared to that of 3DOM carbon, resulting in a higher energy density of the modified 3DOM carbon. However, the specific capacity decreases as cycling proceeds, apparently because lithium–tin alloy nanoparticles were detached from the carbon support by volume changes during charge–discharge processes. The rate performance of SnO₂‐coated 3DOM carbon is improved compared to 3DOM carbon.     

Au–Pd Alloy Gradients Prepared by Laterally Controlled Template Synthesis

Lateral control of template synthesis in nanoporous alumina membranes (NAMs) was previously shown by us to enable preparation of graded composite materials. Formation of thickness gradients of Cu was demonstrated using electrodeposition (or electrodissolution) of Cu in the NAM template under a lateral voltage drop applied to the working electrode. This approach is extended here to the formation of compositional gradients. The latter are achieved by electrochemical co‐deposition of two metals (Au and Pd) in the membrane pores from a mixed metal‐ion solution under a lateral potential drop, to form an alloy that shows a continuous lateral change of the Au/Pd ratio. Environmental scanning electron microscopy images of cross sections along the line of the applied voltage gradient show that the deposit height changes gradually, while local elemental analysis by energy dispersive spectrometry and X‐ray diffraction measurements confirm a continuous change of the alloy composition along the membrane matrix.     

Titania and Mixed Titania/Aluminum,Gallium, or Indium Oxide Spheres: Sol–Gel/Template Synthesis and Photocatalytic Properties

Porous polymer beads have been used as templates in which sol–gel chemistry was conducted for the formation of porous titanium dioxide and titania/aluminum, gallium, or indium oxide spheres. The addition of 5, 10, and 15 wt.‐% of the second metal oxide to titania was studied, resulting in little variation in the final porous‐sphere diameter, but in a decreased titania nanocrystal size and an increased specific surface area of the material. The crystallinity of the samples was observed after heating at 550, 750, and 950 °C as anatase to rutile phase transitions became apparent and peaks from the added metal oxide were observed with the increase in temperature. Photocatalytic decomposition of 2‐chlorophenol was monitored in the presence of the titania and titania/metal‐oxide spheres showing that a 5 wt.‐% addition of the second metal oxide gave best photocatalytic results for all the metal oxides studied. At a pH of 6 the pure titania spheres were less photocatalytically active than the Degussa P25 titania, however the mixed titania/5 wt.‐% metal‐oxide samples were more active than the standard in the order In (least active), Ga, then Al (most active). Variation of the solution pH (between pH 2 and 10) had little influence on the photocatalytic activity of the titania/5 wt.‐% aluminum oxide material, more effect on the titanium/5 wt. % gallium oxide, and the most pronounced effect on the titanium/5 wt.‐% indium oxide, with increased activity at higher pH values. The adsorption of pyridine to the titania samples containing the second metal oxide indicated the presence of Lewis‐acid sites.     

Templated Synthesis of Porous Capsules with a Controllable Surface Morphology and their Application as Gas Sensors

Porous capsules composed of hematite, silica, and hematite–silica composites are prepared by a templated synthesis method. Polyelectrolyte multilayer‐coated particles (PEMPs) are used to synthesize goethite nanocrystals and the resulting goethite‐nanocrystal‐embedded PEMPs (PEMP–goethite) are then used as templates to form porous capsules. The surface morphology and surface area of the porous capsules can be controlled by the size of the PEMP–goethite template, which is determined by the extent of growth of the goethite nanocrystals. By controlling the surface morphology and area, it is also possible to tune the sensitivity of the hematite capsules for use as gas‐sensing materials. This surfactant‐free approach is also used to synthesize silica and silica‐based composite capsules with a controllable porous shell thickness. This straightforward approach can also be extended to the synthesis of other porous capsules or particles with a controllable surface morphology.     

Reliable Monolayer‐Template Patterning of SnO2 Thin Films from Aqueous Solution and Their Hydrogen‐Sensing Properties

We demonstrate a novel lithographic technique utilizing a solvent to fabricate a chemically based semiconductor microdevice from an aqueous solution. According to this technique, SnO₂ thin film could be integrated onto predefined sites on a SiO₂/Si wafer. A patterned octadecyltrimethoxysilane self‐assembled monolayer (ODS‐SAM) was prepared by vacuum ultraviolet (VUV) irradiation through a photomask to use as a template for the fabrication of a micropatterned SnO₂ thin film on the SiO₂/Si surface. A Sn‐based thin film was then deposited onto the entire surface of the ODS template from an aqueous solution containing 0.03 mol L^–1 of SnCl₂·2H₂O at 60 °C for 16 h in an ambient atmosphere. The thin film deposited on the methyl‐terminated area of the template was then peeled using an ultrasonic rinse in anhydrous toluene for 30 min, while the film deposited on the silanol area remained intact and undamaged. Rinsing in hydrophilic solvents did not facilitate peeling of the thin film from the methyl‐terminated area. We succeeded by this process in obtaining a high‐resolution, micropatterned Sn‐based thin film on an ODS‐SAM template on Si. The as‐deposited film was composed of fine Sn‐based particles. The sensitivity of this SnO₂ thin film to H₂ gas increases linearly with improving crystallinity. The effectiveness of anhydrous toluene as a rinse in solution lithography is discussed from the viewpoint of the high hydrophobic affinity between the rinse solvent and the terminal groups in the monolayer template.     

Two‐Dimensionally Ordered Copper Grid Patterns Prepared via Electroless Deposition Using a Colloidal‐Crystal Film as the Template

Two‐dimensionally ordered copper grid patterns with different pore sizes and thickness have been fabricated via electroless copper deposition using a colloidal‐crystal film as the template. The pore size of the grid can be adjusted by altering the deposition time. The copper films, with thicknesses of ≈ 100–130 nm and pore sizes of ≈ 100 nm, are flexible and can be peeled off a silicon wafer and rolled up into a reel. Three‐dimensionally ordered porous copper materials have also been prepared using a similar method.