Fabrication of lotus-leaf-like nanoporous silica flakes with controlled thickness

Lotus-leaf-like silica flakes with a three-dimensionally (3D) connected nanoporous structure and controllable thickness have been facilely synthesized; the flakes produced exhibited superior performance in adsorbing enzymes to their microspheric analogues.     

Ultrahigh surface area nanoporous silica particles via an aero-sol-gel process

We describe a new salt-assisted aero-sol-gel approach to produce spherical nanosized mesoporous silica particles. As an alternative to expensive templating mediums in prior works, salt (NaCl) was employed as a templating medium because it is thermally stable, recyclable, and easily leached. Furthermore, we demonstrate the ability to carry out traditional sol-gel chemistry within an aerosol droplet. The role of salt in sol-gel chemistry and aerosol processing was investigated as a function of hydrolysis time. It was verified that salt accelerates the kinetics of silica gelation, and simultaneously becomes an excellent templating medium to support nano-sized pores inside silica structures in the aerosol processing route. The presence of salt results in a roughly ten-fold increasing in the pore specific surface area and pore volume, subsequent to leaching of the salt matrix. The surface area and pore volume of the as-produced nanoporous silica particles was found to increase with increasing sol-gel hydrolysis time.     

Novel nanoporous hybrid organic-inorganic silica containing iminodiethanol chelating groups inside the channel pores

Novel nanoporous hybrid organic-inorganic silica with covalently bound iminodiethanol chelating groups inside the channel pores has been synthesized by template-directed co-condensation of tetraethoxysilane (TEOS) and organo-trimethoxysilane (CH3O)3SiR [IDES, R = (HOCH2CH2)2NCH2CH(OH)CH2O(CH2)3], and is shown to be very efficient in recovery of germanium and antimony oxides from water.     

Multifunctional particles: Magnetic nanocrystals and gold nanorods coated with fluorescent dye-doped silica shells

Multifunctional colloidal core-shell nanoparticles of magnetic nanocrystals (of iron oxide or FePt) or gold nanorods encapsulated in silica shells doped with the fluorescent dye, Tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy) were synthesized. The as-prepared magnetic nanocrystals are initially hydrophobic and were coated with silica using a microemulsion approach, while the as-prepared gold nanorods are hydrophilic and were coated with silica using a Stöber type of process. Each approach yielded monodisperse nanoparticles with uniform fluorescent dye-doped silica shells. These colloidal heterostructures have the potential to be used as dual-purpose tags—exhibiting a fluorescent signal that could be combined with either dark-field optical contrast (in the case of the gold nanorods), or enhanced contrast in magnetic resonance images (in the case of magnetic nanocrystal cores). The optical and magnetic properties of the fluorescent silica-coated gold nanorods and magnetic nanocrystals are reported.     

Dual latex/surfactant templating of hollow spherical silica particles with ordered mesoporous shells

Hollow spherical silica particles with hexagonally ordered mesoporous shells are synthesized with the dual use of cetyltrimethylammonium bromide (CTAB) and unmodified polystyrene latex microspheres as templates in concentrated aqueous ammonia. In most of the hollow mesoporous particles, cylindrical pores run parallel to the hollow core due to interactions of CTAB/silica aggregates with the latices. Effects on the product structure of the CTAB:latex ratio, the amount of aqueous ammonia, and the latex size are studied. Hollow particles with hexagonally patterned mesoporous shells are obtained at moderate CTAB:latex ratios. Too little CTAB causes silica shell growth without surfactant templating, and too much induces nucleation of new mesoporous silica particles without latex cores. The concentration of ammonia must be large to induce co-assembly of CTAB, silica, and latex into dispersed particles. The results are consistent with the formation of particles by addition of CTAB/silica aggregates to the surface of latex microspheres. When the size and number density of the latex microspheres are changed, the size of the hollow core and the shell thickness can be controlled. However, if the microspheres are too small (50 nm in this case), agglomerated particles with many hollow voids are obtained, most likely due to colloidal instability.     

荧光二氧化硅纳米胶囊的制备及性能研究

开发出一种简单、重复性好的合成路线得到了中空的荧光二氧化硅纳米胶囊(SiO_2(NCs)),制备的荧光SiO_2(NCs)分散性好,尺寸均匀.此外,探讨了球形荧光SiO_2(NCs)对抗癌药物的负载能力.     

Preparation of hexagonal platy particles of nanoporous silica using hydrotalcite as morphology template

Hexagonal platy composite particles with a hydrotalcite core and a nanoporous silica shell with a thickness of ca. 100 nm were synthesized by the reaction of a Mg-Al hydrotalcite with a homogeneous aqueous solution containing tetraethoxysilane, hexadecyltrimethylammonium chloride, ammonia and methanol at 3 degrees C. The calcination of the products at 500 degrees C in air led to the composite particle with a Mg/Al mixed oxide core and a nanoporous silica shell. Hexagonal platy particles of nanoporous silica with a pore diameter of 2.3 nm and BET surface area of 700 m(2) (g of silica)(-1) were obtained by removing the Mg/Al mixed oxide core.     

Fabrication of an open Au/nanoporous film by water-in-oil emulsion-induced block copolymer micelles

Water-in-oil (W/O) emulsion-induced micelles with narrow size distributions of approximately 140 nm were prepared by sonicating the polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer in the toluene/water (50:1 vol %). The ordered nanoporous block copolymer films with the hydrophilic P2VP interior and the PS matrix were distinctly fabricated by casting the resultant solution on substrates, followed by evaporating the organic solvent and water. The porous diameter was estimated to be about 70 nm. Here, we successfully prepared the open nanoporous nanocomposites, the P2VP domain decorated by Au (5+/-0.4 nm) nanoparticles based on the methodology mentioned. We anticipate that this novelty enhances the specific function of nanoporous films.     

Interaction of alkanethiols with nanoporous cluster-assembled Au films

This article presents a study of the interaction of octadecanethiol molecules (C(18)) with nanoporous cluster-assembled gold films under a liquid environment based on a combined spectroscopic ellipsometry and X-ray photoelectron spectroscopy investigation. By comparing the optical response, following the deposition of C(18), of cluster-assembled films with varying degrees of porosity with that of flat surfaces and by resolving the corresponding features of the molecule-Au bond, we have been able to define the conditions that either favor molecular in-depth diffusion into the pores or promote the formation of a molecular self-assembled monolayer (SAM) restricted to the film surface. In the presence of abundant open pores, C(18) molecules strongly diffuse within the film interior and bind to the pore walls, whereas in the presence of porous films with less abundant open pores we have observed that the molecules tend to remain confined to the surface region, adopting a SAM-like configuration.     

Fabrication of nanowires with polymer shells using treated carbon nanotube bundles as macro-initiators

Nanowires with polymer shells were produced via radical grafting polymerization of methyl methacrylate using treated carbon nanotube bundles as macro-initiators, thereby providing an efficient way to produce high grafting ratio nanocomposites.     

Synthesis,crystal structures and magnetic properties of Co particles encapsulated in carbon nanocapsules

Carbon-coated cobalt particles were produced by arc-evaporation of a Co-packed graphite rod in a modified fullerene generator. Cobalt particles grown were in an fcc phase, with a trace amount of hcp-Co. The particles were nominally spherical in shape, and typically 10–100 nm in diameter. Thickness and structure of outer carbon layers could be controlled by varying the relative area of a Co-packed hole drilled in the graphite rod. Saturation magnetization (M _s) and the coercive force (H _c) was measured between room temperature and 800°C for powder samples: Temperature dependence of the measured M _s was consistent with that for fcc-Co. The highest value of M _s of 160 emu/g at room temperature, nearly the same value for bulk fcc-Co, was obtained for Co particles covered with thin carbon layers. H _c varied from 600 Oe to 300 Oe, depending on the size of Co particles.     

Additive route to lithographically defined nanoporous silica, polymer, and carbon films

A facile method was investigated for patterning microporous and mesoporous silica, polymer, and carbon films using a combination of lithography and solid-state chemistry. This process exploits the difference in chemical reactivity between the lithographically exposed and unexposed regions to control the reaction of a target precursor from the vapor phase. A block copolymer film loaded with a photoacid generator is utilized as a preformed template, and tetraethylorthosilicate (TEOS) and furfuryl alcohol (FA) are the silica and carbon precursors, respectively. Following UV exposure and reaction with vaporized precursors, thermal decomposition of the polymeric template yields a mesoporous film in the exposed regions. Dense line-space patterns down to 1.5 microm features were resolved with I-line lithography. Sharper features were formed using FA; this behavior is attributed to the requirement for water in the system during TEOS condensation. Moisture in the system appears to lead to enhanced diffusion of the photoacid and a small decrease in the feature resolution. This methodology provides a simple etch-free route to patterning mesoporous films using commercially available materials.     

Novel drug delivery system of hollow mesoporous silica nanocapsules with thin shells: preparation and fluorescein isothiocyanate (FITC) release kinetics

Core-shell nanoparticles of Au@silica with a diameter of approximate 45–60 nm and wall thickness in range of 3–10 nm were synthesized by using 40 and 50 nm gold nanoparticles as the templates. The mesoporous particles are regulated by 3-aminopropyltrimethoxysilane addition. Hollow mesoporous silica nanocapsules (HMSNs) were prepared by using sodium cyanide to dissolve the gold cores. The characterization of Au@silica and HMSNs by transmission electronic microscope indicated that the silica shells were uniform and smooth, and also the porosity was proved by fluorescein isothiocyanate (FITC) release experiments. The ratio of hollow core to HMSNs is more than 70%. HMSNs were subsequently used as drug carrier to investigate FITC (as a model drug) release behaviors in vitro. Fluorescent spectrometry was performed to determine the release kinetics from the HMSNs. The release profiles are significantly different as compared with the control (free FITC), which show that HMSNs are good drug carriers to control drug release, and have high potential in therapeutic drugs delivery in future applications.     

Fabrication of silica nanotubes using silica coated multi-walled carbon nanotubes as the template

Silica nanotubes were synthesized using the multi-walled carbon nanotubes (MWCNTs) as the template material. First, we prepared silica coated MWCNT composites by surface oxidation of MWCNTs using KMnO(4) in the presence of a phase transfer catalyst and followed by grafting of 2-aminoethyl 3-aminopropyl trimethoxy silane, AEAPS. The amine groups in grafted AEAPS on MWCNTs could activate the silica shell formation by acid-base interaction. The synthesized silica was formed a uniform layer on MWCNTs with a controllable thickness and possessed sturdy 3-dimensional stability. After calcinations at 800 degrees C, the inner MWCNTs of the composite were completely decomposed and the outer silica shell layer maintained without distortion of its original shape. Finally, we could obtain the silica nanotubes having 13.0 nm of average layer thickness.     

Unique adsorption behavior of H2 and CO over group 8-10 metals encapsulated inside silica nanotubes and nanocapsules

Various silica nanotubes and nanocapsules have been prepared successfully, possessing unique silica walls of selective H2 permeation and encapsulate group 8-10 metal particles inside and exhibit a marked stabilization effect of H2 and CO over the metals in the network of silica wall and inside nanoscale cavities.     

Synthesis and characterization of nanocapsules with shells made up of Al13 tridecamers

The synthesis of samples by the sol-gel method with aluminum tri-sec-butoxide as cation precursor, 2-propanol as solvent, and sulfuric acid as hydrolysis catalyst gave rise to nanocapsules with an average diameter of 20 nm and a shell thickness of 3.5 nm. The analysis of the X-ray diffraction patterns and the 27Al MAS NMR spectra showed that the shell of the nanocapsules was made up of Al13 tridecamers ordered in a noncrystalline symmetry. The interaction between the capsule's shells opened the capsule structure, producing curved fibers, but maintaining the atomic local order. This opening of the capsules favored the reordering of the atomic local order of Al13 tridecamers into the one of crystalline boehmite, when the sample was aged at room temperature for several days; it also increased the pore volume and the specific surface area of the sample. The crystallization transformed the curved fibers into rods made of small crystalline boehmite bars. The capsule morphology was preserved after calcining the nonaged sample at 700 degrees C, indicating that the transformation of the phase made up of ordered Al13 tridecamers into a noncrystalline alumina was pseudomorphic. We describe and partially explain one of the possible atomic ordering evolutions from the one of an isolated Al13 tridecamer, to the phase forming the nanocapsules shell, until eventually coming to the ordering corresponding to boehmite crystalline rods.     

Dissolution of iron oxide nanoparticles inside polymer nanocapsules

The structure of poly(organosiloxane) nanocapsules partially filled with iron oxide cores of different sizes was revealed by small angle X-ray scattering and X-ray diffraction. The nanocapsules are synthesized by the formation of a poly(organosiloxane) shell around iron oxide nanoparticles and the simultaneous partial dissolution of these cores. Due to the high scattering contrast of the iron oxide cores compared to the polymer shell, the particle size distribution of the cores inside the capsules can be measured by small angle X-ray scattering. Additional information can be revealed by X-ray diffraction, which gives insights into the formation of the polymer network and the structure of the iron oxide cores. The study shows how the crystallinity and size of the nanoparticles as well as the shape and width of the size distribution can be altered by the synthesis parameters.     

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.     

Plugged hexagonal templated silica: a unique micro- and mesoporous composite material with internal silica nanocapsules

We describe in this paper the development of plugged hexagonal templated silicas (PHTS) which are hexagonally ordered materials, with internal microporous silica nanocapsules; they have a combined micro- and mesoporosity and a tuneable amount of both open and encapsulated mesopores and are much more stable than other tested micellar templated structures.