Self-assembly of Nafion molecules onto silica nanoparticles formed in situ through sol-gel process

Self-assembly of Nafion onto in situ formed silica nanoparticles in ethylene glycol–water mixture solvent has been investigated in this study. It was found that the formation of silica nanoparticles depends on the concentration of Nafion in dispersions. At relatively low concentration, 0.8% in weight in this case, the existing Nafion is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the concentration of Nafion increased to 2% in weight, self-assembled Nafion layer on the surface stabilizes the initial formed silica nanoparticles and silica particles with average diameters of 4.2±0.5 nm were found to be uniformly distributed in the dispersion. With further increasing the concentration of Nafion, the number of Nafion aggregates increases and silica nanoparticles were mainly formed inside the entangled Nafion chains, resulting in an observation of clusters of silica nanoparticles.     

General one-pot strategy to prepare multifunctional nanocomposites with hydrophilic colloidal nanoparticles core/mesoporous silica shell structure

A general and facile strategy was developed to coat hydrophilic inorganic nanoparticles directly with mesoporous silica nanoparticles (MSNs). The cationic surfactant of cetyltrimethylammonium bromide (CTAB) was adsorbed to various negatively charged CdTe quantum dots, Fe(3)O(4) nanocrystals or Au nanoparticles, introducing the bilayer of CTAB overcoating with positive charge. The subsequent sol-gel reaction of TEOS with the basic catalyst resulted in uniform nanocomposites. The concentration of CTAB and NH(4)OH in the recipe strongly influenced the number of inorganic nanoparticles in the nanocomposites and the homogeneity of MSNs shell. One dimensional Au nanorods and larger size of solid SiO(2) nanoparticles were also able to coat with MSNs using a similar synthetic procedure. The proposed method was greatly simplified without the help of any mediators or silane coupling agents and excellent mesostructural performance was readily achieved. Compared to the methods known from the literatures for the coating of hydrophobic nanoparticles, this efficient way is especially useful for trapping different hydrophilic nanoparticles with arbitrary sizes and shapes into MSNs. These highly versatile multifunctional nanocomposites, together with the pH-responsible drug release behaviors, non-toxicity to normal cells and ease of uptake into cancer cells, are expected to be utilized as drug delivery system for simultaneous imaging and therapeutic applications.     

Facile synthesis of silver core - silica shell composite nanoparticles

Combining metal nanoparticles and dielectrics (e.g. silica) to produce composite materials with high dielectric constant is motivated by application in energy storage. Control over dielectric properties and their uniformity throughout the composite material is best accomplished if the composite is comprised of metal core - dielectric shell structured nanoparticles with tunable dimensions. We have synthesized silver nanoparticles in the range of 40-100nm average size using low concentration of saccharide simultaneously as the reducing agent and electrostatic stabilizer. Coating these silver particles with silica from tetraalkoxysilanes has different outcomes depending on the alcoholic solvent and the silver particle concentration. A common issue in solution-based synthesis of core-shell particles is heterogeneous nucleation whereupon two populations are formed: the desired core-shell particles and undesired coreless particles of the shell material. We report the formation of Ag@SiO(2) core-shell particles without coreless silica particles as the byproduct in 2-propanol. In ethanol, it depends on the silver surface area available whether homogeneous nucleation of silica on silver is achieved. In methanol and 1-butanol, core-shell particles did not form. This demonstrates the significance of controlling the tetraalkoxysilane hydrolysis rate when growing silica shells on silver nanoparticles.     

Fabrication and characterization of mesoporous Co3O4 core/mesoporous silica shell nanocomposites

A mesoporous Co(3)O(4) core/mesoporous silica shell composite with a variable shell thickness of 10-35 nm was fabricated by depositing silica on Co(3)O(4) superlatticed particles. The Brunauer-Emmett-Teller (BET) surface area of the composite with a shell thickness of ca. 2.0 nm was 238.6 m(2)/g, which varied with the shell thickness, and the most frequent pore size of the shell was ca. 2.0 nm. After the shell was eroded with hydrofluoric acid, mesoporous Co(3)O(4) particles with a pore size of ca. 8.7 nm could be obtained, whose BET surface area was 86.4 m(2)/g. It is proposed that in the formation of the composite the electropositive cetyltrimethylammonium bromide (CTAB) micelles were first adsorbed on the electronegative Co(3)O(4) particle surface, which directed the formation of the mesoporous silica on the Co(3)O(4) particle surface. Electrochemical measurements showed that the core/shell composites exhibited a higher discharge capacity compared with that of the bare Co(3)O(4) particles.     

Synthesis of a multinanoparticle-embedded core/mesoporous silica shell structure as a durable heterogeneous catalyst

A multi-nanoparticle-embedded amorphous aluminum/magnesium oxides (AAMO) core/mesoporous silica (mSiO(2)) shell structure has been successfully synthesized by calcining the presynthesized catalyst precursor-containing layered double hydroxide (LDH) core/mesoporous silica shell composite. The well-dispersed catalytic nanoparticles were fixed at the interface between AAMO core and mesoporous SiO(2) shell, i.e., at the inner pore mouths of the mesoporous SiO(2) shell, which could effectively prevent nanoparticles from growth and/or aggregation with each other and in the meantime allow efficient access of reactants to the catalytic NPs. The final core/shell composite was found to be an efficient and highly recyclable heterogeneous catalyst.     

Synthesis of silica glass using solventless sol-gel process

Silica glass was synthesized form TEOS and deionized water using sol-gel process. To introduce the physicochemical effects of ultrasonic waves, an ultrasonic homogenizer was used to mix reactants instead of adding cosolvents. 2-step method was chosen to separate hydrolysis reaction and condensation reaction, and thus to control the microstructure of wet gels. Wet gels were dried in 5–8 hours without cracks using supercritical drying with ethanol at 300°C and 10.34 MPa. Aerogels thus obtained have hydrophobic surfaces due to the reesterification reactions during supercritical drying. Aerogels were sintered in a tube furnace in the changing atmosphere from N₂ through O₂ to He. Sudden volume change was started at 1050°C and sintering was completed at 1100°C as expected. Large pores of aerogels allowed fast sintering in 16 and a half hours. Incomplete extraction in supercritical drying step produced crystals during sintering.     

Fabrication of uniform magnetic nanocomposite spheres with a magnetic core/mesoporous silica shell structure

A novel kind of magnetic core/mesoporous silica shell nanospheres with a uniform particle diameter of ca. 270 nm was synthesized. The inner magnetic core endues the whole nanoparticle with magnetic properties, while the outer mesoporous silica shell shows high enough surface area and pore volume. The synthesized material is expected to be applied to targeted drug delivery and multiphase separation. The storage and release of ibuprofen into and from the pore channels of the mesoporous silica shell, as a typical example, are demonstrated.     

Synthesis of mesoporous silica materials with ascorbic acid as template via sol-gel process

Mesoporous silica materials with pore diameters of 2-5 nm have been prepared using ascorbic acid as a nonsurfactant template or pore-forming agent in HCl-catalyzed sol-gel reactions of tetraethylorthosilicate,followed by removing the ascorbic acid compound by extraction with ethanol.Characterization results from nitrogen sorption isotherm,powder X-ray diffraction and transmission electron microscopy indicate that the materials have large specific surface areas (e.g.1000 m2/g) and pore volumes (e.g.0.8 cm3/g).The rnesoporosity is arisen from interconnecting disordered wormlike channels and pores with relatively broad size distributions.As the ascorbic acid concentration is increased,the pore diameters and pore volumes of the materials increase.     

A non-enzyme hydrogen peroxide sensor based on core/shell silica nanoparticles using synchronous fluorescence spectroscopy

In our previous study, we have prepared aminated fluorescent silica nanoparticles doped with fluorescein isothiocyanate (FITC) (FSNPs) for the sensing of γ-globulin. Compared with conventional organic dyes, FSNPs show superiorities such as excellent photostability, good water solubility, and biocompatibility, which are in favor of improving the stability and sensitivity of sensors. To extend the application of FSNPs, a convenient and effective method for non-enzyme fluorescent sensor of hydrogen peroxide (H₂O₂) is introduced based on the synchronous fluorescence technique. The sensor includes two-step reactions, typical redox reaction between KI and H₂O₂ and iodination reaction between I₂ produced by the first step reaction and FITC doped in the network of silica nanoparticles, which induce the fluorescence quenching of FSNPs. The results show that the fluorescence signal of FSNPs linearly decreases with the trace amounts of hydrogen peroxide added in the range 5–80 μM with a detection limit of 0.8 μM under the optimal experimental conditions. The method is simple and sensitive and can be applied to the determination of trace amounts of H₂O₂. Good recovery data were obtained for the assay of H₂O₂ in river water by standard addition method with high accuracy and reliability.     

Immobilization of superoxide dismutase onto ordered mesoporous silica nanoparticles and improvement of its stability

In recent years, greater attention has been given to the application of mesoporous materials to the immobilization of enzymes. In this study, the immobilization of superoxide dismutase (SOD) onto the amine-functionalized cubic Ia3d mesoporous silica nanoparticles ([n-PrNH₂-KIT-6]) with an average pore diameter of around 6.5?nm was investigated. This organo-functionalized mesoporous silica was prepared using a non-ionic surfactant and was fully characterized by SEM, XRD, nitrogen adsorption?Cdesorption isotherm and FT-IR spectroscopy. UV?Cvisible spectroscopy studies demonstrated that the immobilized SOD was less prone to thermally induced aggregation than the free moiety. Further investigations using far-circular dichroism measurement intensity indicated that the structure of SOD before and after immobilization onto the [n-PrNH₂-KIT-6] nanoparticles was almost identical and the immobilized enzyme was more stable against GdHCl denaturation relative to the free one.     

Preparation of mesoporous submicrometer silica capsules via an interfacial sol-gel process in inverse miniemulsion

Mesoporous silica capsules with submicrometer sizes were successfully prepared via the interfacial hydrolysis and condensation reactions of tetraethoxysilane (TEOS) in inverse miniemulsion by using hydrophilic liquid droplets as template. The inverse miniemulsions containing pH-controlled hydrophilic droplets were first prepared via sonication by using poly(ethylene-co-butylene)-b-poly(ethylene oxide) (P(E/B)-PEO) or SPAN 80 as surfactant. TEOS was directly introduced to the continuous phase of an inverse miniemulsion. The silica shell was formed by the deposition of silica on the surface of droplets. The formation of capsule morphology was confirmed by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The mesoporous structure was verified by nitrogen sorption measurements. The specific surface area could be tuned by the variation of the amount of cetyltrimethylammonium bromide (CTAB) and TEOS, and the pore size by the amount of CTAB. The influences of synthetic parameters on the particle size and morphology were investigated in terms of the amount of CTAB, pH value in the droplets, TEOS amount, surfactant amount, and type of solvent with low polarity. A formation mechanism of silica capsules was proposed.     

A light-responsive reversible molecule-gated system using thymine-modified mesoporous silica nanoparticles

In this paper, a reversible light-responsive molecule-gated system based on mesoporous silica nanoparticles (MSN) functionalized with thymine derivatives is designed and demonstrated. The closing/opening protocol and release of the entrapped guest molecules is related by a photodimerization-cleavage cycle of thymine upon different irradiation. In the system, thymine derivatives with hydrophilicity and biocompatibility were grafted on the pore outlets of MSN. The irradiation with 365 nm wavelength UV light to thymine-functionalized MSN led to the formation of cyclobutane dimer in the pore outlet, subsequently resulting in blockage of pores and strongly inhibiting the diffusion of guest molecules from pores. With 240 nm wavelength UV light irradiation, the photocleavage of cyclobutane dimer opened the pore and allowed the release of the entrapped guest molecules. As a proof-of-the-concept, Ru(bipy)(3)(2+) was selected as the guest molecule. Then the light-responsive loading and release of Ru(bipy)(3)(2+) were investigated. The results indicated that the system had an excellent loading amount (53 μmol g(-1) MSN) and controlled release behavior (82% release after irradiation for 24 h), and the light-responsive loading and release procedure exhibited a good reversibility. Besides, the light-responsive system loaded with Ru(bipy)(3)(2+) molecule could also be used as a light-switchable oxygen sensor.     

Fabrication of bimodal porous silicate with silicalite-1 core/mesoporous shell structures and synthesis of nonspherical carbon and silica nanocases with hollow core/mesoporous shell structures

In this work, an attempt has been made to modify the shape and nanostructure of core-shell materials, which have been usually generated on the basis of amorphous spherical cores. Novel core-shell silicate particles, each of which consists of a silicalite-1 zeolite crystal core and mesoporous shell (ZCMS), were synthesized for the first time. The ZCMS core-shell particles are unique because they are of pseudohexagonal prismatic shape and have hierarchical porosity of both a uniform microporous core and a mesoporous shell coexisting in a particle framework. The nonspherical bimodal porous core-shell particles were then utilized as templates to fabricate a new carbon replica structure. Interestingly, the pore replication process was carried out only through the mesopores in the shell, and not through the micropores due to the narrower micropore size in the core, resulting in nonspherical carbon nanocases with a hollow core and mesoporous shell (HCMS) structure. Nonspherical silica nanocases with HCMS structure were also generated by replication using the carbon nanocases as templates, which are not possible to synthesize through other synthetic methods. Interestingly, the pseudohexagonal prismatic shape of the zeolite crystals was transferred onto the carbon and silica nanocases.     

Biphasic synthesis of colloidal mesoporous silica nanoparticles using primary amine catalysts

Evanescent wave-cavity ring-down spectroscopy (EW-CRDS) is employed to characterize micellization of anionic surfactants and the related capability of removing cationic substance off the silica surface. Crystal violet (CV(+)) cationic dye is used as a molecular probe to effectively determine critical hemimicelle concentration (HMC) of surfactants on the surface. The HMC results are 1×10(-2), 4×10(-3), 8×10(-4), and 2.5×10(-4) mol/L for sodium sulfate salts with a carbon-chain length of C-10, C-12, C-14, and C-16, respectively. A stronger hydrophobic interaction results in a less concentration required to undergo micellization. The HMC values on the surface are about half of those in solution. When NaCl solution is added, the electrolyte helps reduce the electrostatic repulsion between the anionic sulfate heads to facilitate the surfactant aggregation, and thus, the subsequent HMC is reduced. Furthermore, the probable phase change for dye-surfactant interactions on the surface at the concentration below HMC is observed, and the desorption rates of CV(+) are measured as a function of concentration and carbon-chain length of surfactants above HMC. Given each surfactant concentration at its respective HMC, the corresponding desorption rates are along the order of C-12相似文献   

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.     

Controlled synthesis of uniform and monodisperse upconversion core/mesoporous silica shell nanocomposites for bimodal imaging

Here we report the design and controlled synthesis of monodisperse and precisely size-controllable UCNP@mSiO(2) nanocomposites smaller than 50?nm by directly coating a mesoporous silica shell (mSiO(2)) on upconversion nanocrystals NaYF(4):Tm/Yb/Gd (UCNPs), which can be used as near-infrared fluorescence and magnetic resonance imaging (MRI) agents and a platform for drug delivery as well. Some key steps such as transferring hydrophobic UCNPs to the water phase by using cetyltrimethylammonium bromide (CTAB), removal of the excess amount of CTAB, and temperature-controlled ultrasonication treatment should be adopted and carefully monitored to obtain uniform upconversion core/mesoporous silica shell nanocomposites. The excellent performance of the core-shell-structured nanocomposite in near-infrared fluorescence and magnetic resonance imaging was also demonstrated.