Synthesis of carbon tubes with mesoporous wall structure using designed silica tubes as templates

Hollow silica tubes with mesoporous wall structure were synthesized through the sol-gel reactions of tetraethoxysilane and n-octadecyltrimethoxysilane (TEOS/C18-TMS) on the surface of ammonium dl-tartrate crystals. Novel hollow carbon tubes with mesoporous walls and rectangular-shaped channels were fabricated using the silica tubes as templates.     

Microfluidization-assisted synthesis of hollow mesoporous silica nanoparticles

Hollow mesoporous silica nanoparticles (HMSNs) with the diameter in range of 100–500 nm and the wall thickness of about 50 nm were synthesized by templates of cetyltrimethylammonium bromide under the assistant of microfluidization technique. These HMSNs were demonstrated effective drug loading and a pH-responsive drug release.     

Nanostructured gold hollow microspheres prepared on dissolvable ceramic hollow sphere templates

Fifty and one-hundred micrometer diameter nanostructured gold hollow microspheres (GHSs), in >98% purity, have been prepared by using ceramic hollow spheres, CHSs, as templates. Tennanometer diameter gold nanoparticles were covalently linked to the thiol moiety of (3-mercaptopropyl)trimethoxysilane, which had been self-assembled onto the CHSs. Greater structural strength was obtained by the generation of additional gold nanoparticles, in situ on the gold nanoparticle coated CHSs (by immersing the gold nanoparticle coated CHSs into an aqueous mixture of hydroxylamine and gold chloride). GHSs were obtained by dissolving the CHSs templates. The sizes, shapes, surface areas (185.3 m2/g for CHSs and 182.9 m2/g for GHSs), pore diameters (7.7 nm for CHSs and 7.8 nm for GHSs), and pore volumes (0.41 cm3/g for CHSs and 0.36 cm3/g for GHSs) of GHSs were quite similar to their CHSs counterparts. Significantly, GHSs showed surface plasmon bands whose maximum (644 nm) shifted from that observed for the parent 10-nm gold nanoparticles (522 nm).     

Synthesis of lamellar mesoporous silica materials using LCs as templates

The study focuses on the synthesis of mesoporous silica materials using liquid crystals (LCs) formed in an aqueous mixture of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) as templates and tetrathoxysilane (TEOS) as precursor. For this purpose, the phase behavior and range of LC areas were determined at different temperatures, concentrations, and ratios of CTAB/SDS. It was found that LCs became denser with the increased of concentration of surfactants. The mesoporous materials were synthesized using LCs as templates at various temperatures, surfactant concentrations, and pH values. The mesoporous samples were characterized using SEM and nitrogen sorption analysis. The research results showed that the structure of synthesized samples were lamellar and their surface areas increased significantly with the increase of temperature in the temperature range of LCs, reaching about 900?m²/g at 60°C. The surfactant concentrations affect the thickness of pore wall and thereby the specific surface area of products. The specific surface area and the order of mesoporous sample increased gradually with the decrease of pH.     

Fabrication of hollow silica spheres using droplet templates derived from a miniemulsion technique

Hollow silica spheres have been successfully fabricated by means of a miniemulsion technique, in which miniemulsion droplets of tetraethoxysilane (TEOS) and octane were prepared with cetyltrimethylammonium bromide as a surfactant and hexadecane as a costabilizer and used as templates. As the TEOS diffused out from the droplets, it was hydrolyzed and condensed to form a silica shell at the oil/water interface. In this way, hollow silica spheres could be obtained directly since the miniemulsion droplets of octane could be evaporated very easily during the reaction process or the drying process; neither an additional dissolution nor a calcination process or additional surface modification of the templates were needed.     

ZSM-5 monolith of uniform mesoporous channels

A ZSM-5 monolith of uniform mesopores(meso-ZSM-5) was synthesized with the template method using carbon aerogel of uniform mesopores of great pore volume. The pore size distribution determined by N2 adsorption showed the presence of mesopores with an average pore width of 11 nm and micropores with an average pore width of 0.51 nm. Field emission scanning electron micrograph observation revealed the presence of uniform mesopores. X-ray diffraction and FT-IR provided evidence that the synthesized meso-ZSM-5 monolith has a highly crystalline ZSM-5 structure.     

Electrosynthesis of polythiophene nanowires via mesoporous silica thin film templates

Early electrosynthesized polythiophene nanowires were prepared employing a mesoporous silica template, which was also electrochemically produced. A cathodic potential step was applied to a fluorine doped tin oxide conducting glass electrode in a cationic surfactant and silicate reagent medium to deposit highly ordered mesoporous silica films. To evaluate the pores order and, consequently, optimal deposition potential, the electrochemical response of the electrodes was studied using ferrocene as redox probe. The modified electrodes were used to accomplish polythiophene electrodeposits employing 0.6 mM thiophene and 0.1 M tetrabutylammonium hexafluorophosphate in anhydrous CH₃CN as working solution. Transmission electron microscope images of the deposits revealed the presence of polythiophene nanowires of about 6 nm in diameter arranged normal to the electrode surface. The unprecedented small size and arrangement of the obtained nanowires place this work as the first study that successfully accomplished the formation of nanoscale electrochemically synthesized conducting polymer nanowires.     

Synthesis of thermally stable mesoporous cerium oxide with nanocrystalline frameworks using mesoporous silica templates

Highly ordered mesoporous cerium oxides, composed of nanocrystalline pore walls and exhibiting high thermal stability even at 973 K, were synthesized using mesoporous silica templates with hexagonal p6mm and cubic Ia3d symmetries.     

Fabrication and thermal analysis of submicron silver tubes prepared from electrospun fiber templates

Submicron silver tubes have been synthesized by a polymer-based template approach. Two different approaches to metallization, electroless deposition and exchange plating, were evaluated within the template approach. Silver films with average thickness approximately 50-100 nm were deposited on polycarbonate fibers approximately 400 nm in diameter by each technique, resulting in tubes with a diameter between 450 and 500 nm after thermal degradation of core fibers. These nanomaterials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and scanning thermal microscopy. The thermal conductivity of the silver submicron tubes was found to differ depending on the method of preparation, with tubes from electroless plating possessing relative thermal conductivity values that were 1 order of magnitude higher than that from exchange plating, 3000 W/m x K and 660 W/m x K, respectively. Interestingly, these results indicate that silver submicron tubes possess higher thermal conductivity than the bulk metal. This observation is discussed in the context of the continuous conduction path of the tubes and their high surface area-to-volume ratio.     

Synthesis of porous hollow silica nanostructures using hydroxyapatite nanoparticle templates

Porous hollow spherical and rod-like silica nanoparticles were obtained via a surfactant templating method adopting hydroxyapatite (HAp) nanoparticles as an etchable core material.     

Formation of SnO2 hollow nanospheres inside mesoporous silica nanoreactors

We report an interesting approach for efficient synthesis of SnO(2) hollow spheres inside mesoporous silica "nanoreactors". The as-prepared products are shown to have a uniform size distribution and good structural stability. When evaluated for their lithium storage properties, these SnO(2) hollow spheres manifest improved capacity retention.     

Synthesis of hollow spherical silica with MCM-41 mesoporous structure

Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm^–3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N₂ gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N₂ adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased     

Uniform chitosan hollow microspheres prepared with the sulfonated polystyrene particles templates

Biodegradable chitosan hollow microspheres have been fabricated by employing uniform sulfonated polystyrene (PS) particles as templates. The chitosan was adsorbed onto the surface of the sulfonated polystyrene templates through the electrostatic interaction between the sulfonic acid groups on the templates and the amino groups on the chitosan. Subsequently, the adsorbed chitosan was crosslinked by adding glutaraldehyde. After the removal of the sulfonated polystyrene core, chitosan hollow microspheres were obtained. The longer the sulfonation time used, the smaller the size of the hollow particles and the thicker the chitosan wall obtained. Fourier transform infrared spectrometry was used to characterize the component of the microspheres. The morphologies of the PS templates and the chitosan microspheres were observed by transmission electron microscopy and scanning electron microscopy. The controlled release behavior of the chitosan hollow microspheres was also primarily investigated.     

Synthesis of ordered mesoporous silica membrane on inorganic hollow fiber

This paper reports on a new method for the preparation of mesoporous silica membranes on alumina hollow fibers. A surfactant-silica sol is filled in the lumen of an alpha-alumina hollow fiber. The filtration technique combined with an evaporation-induced self-assembly (EISA) process results in the formation of a continuous ordered mesoporous silica layer on the outer side of alpha-alumina hollow fibers. X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen isothermal adsorption measurements reveal that these membranes possess hexagonal (P6mm) mesostructures with pore diameters of 4.48 nm and BET surfaces of 492.3 m(2) g(-1). Scanning electron microscopy (SEM) studies show that the layers are defect free and energy-dispersive spectroscopy (EDS) mapping images further confirm the formation of continuous mesoporous silica layer on the outer side of alpha-alumina hollow fibers. Nitrogen and hydrogen permeance tests show that the membranes are defect free.     

Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.     

Synthesis and characterization of organic-inorganic hybrid mesoporous silica materials with new templates

1-Hexadecane-3-methylimidazolium bromide and 1-hexadecane-2,3-dimethylimidazolium bromide were used as new templates for the syntheses of periodic mesoporous organosilica (PMO) materials; using these new templates, ethane-bridged PMO materials were successfully synthesized and characterized under basic conditions.     

Transition metal-chelating surfactant micelle templates for facile synthesis of mesoporous silica nanoparticles

Highly ordered mesoporous silica nanoparticles with tunable morphology and pore-size are prepared by the use of a transition metal-chelating surfactant micelle complex using Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions. These metal ions formed a metal-P123 micelle complex in an aqueous solution, while the metal ions are chelated to the hydrophilic domain such as the poly(ethylene oxide) group of a P123 surfactant. The different complexation abilities of the utilized transition metal ions play an important role in determining the formation of nano-sized ordered MSNs due to the different stabilization constant of the metal-P123 complex. Consequently, from a particle length of 1700 nm in the original mesoporous silica materials, the particle length of ordered MSNs through the metal-chelating P123 micelle templates can be reduced to a range of 180–800 nm. Furthermore, the variation of pore size shows a slight change from 8.8 to 6.6 nm. In particular, the Cu²⁺-chelated MSNs show only decreased particle size to 180 nm. The stability constants for the metal-P123 complex are calculated on the basis of molar conductance measurements in order to elucidate the formation mechanism of MSNs by the metal-chelating P123 complex templates. In addition, solid-state ²⁹Si, ¹³C-NMR and ICP-OES measurements are used for quantitative characterization reveal that the utilized metal ions affect only the formation of a metal-P123 complex in a micelle as a template.     

Fabrication of anisotropic silica hollow microspheres using polymeric protrusion particles as templates

Anisotropic polystyrene/poly(styrene-co-divinylbenzene) (PS/P(S-DVB)) protrusion particles with various morphologies such as eyeball-like, snowman-like, and raspberry-like were synthesized using a modified seeded polymerization method by dynamically controlling and stabilizing the phase separation. The effects of swelling agent, crosslinker, and monomer concentrations on the particle morphologies were studied. Using the PS/P(S-DVB) protrusion particles as templates, anisotropic silica (SiO₂) hollow microspheres were fabricated facilely. The obtained anisotropic silica hollow spheres had a potential application in rapid waste removal and detoxification extraction with a very simple procedure.     

A novel method for synthesis of mesoporous ZSM-5 from iron ore tailings

Mesoporous ZSM-5 was prepared from iron ore tailings (IOT) using a two-step process. Mesoporous MCM-41 was first synthesized using cetyltrimethylammonium bromide (CTAB) as mesoporous template and IOT as silica source. The CTAB in the as-synthesized MCM-41 was used as the mesoporogen to produce the mesoporous ZSM-5, by recrystallizing the amorphous walls of MCM-41 with tetrapropylammonium bromide (TPABr) as the structure-directing agent via solid-phase conversion. To evaluate the textural properties of mesoporous ZSM-5, the as-synthesized samples were characterized using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, ²⁹Si, ²⁷Al magic angle spinning nuclear magnetic resonance spectroscopy, and nitrogen adsorption. The results show that phase separation between the surfactant and zeolite crystals was avoided in the solid-phase conversion process, which transforms the as-synthesized MCM-41 to mesoporous zeolite. Therefore, the synthetic route presented herein provides a novel method for the synthesis of mesoporous ZSM-5 from IOT.

     

Sub-micrometer-sized metal tubes from electrospun fiber templates

Metallic tubes have been synthesized by a polymer-based template approach using electroless deposition. Gold, copper, and nickel were deposited as thin films on sub-micrometer polymer fibers which ranged in diameter from approximately 160 to 400 nm. After thermal degradation of the template fibers at 300 and 650 degrees C, tubes between 450 and 730 nm were obtained with wall thicknesses of 50-150 nm. Characterization by scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and powder X-ray diffraction indicate that the tubes have a face-centered cubic structure with [111] preferred orientation for all of the metals investigated and that the tube walls are polycrystalline, composed of nanoparticles, ranging in size from 5.0 to 25.0 nm.