Template synthesis of monodisperse carbon nanodots

Monodisperse carbon nanodots in pores of mesoporous silica particles are obtained by template synthesis. This method is based on introducing a precursor (organosilane) into pores, its thermal decomposition with formation of carbon nanodots, and the template removal. Structural analysis of the nanomaterial has been performed, which showed that carbon nanodots have an approximately spherical form and a graphite-like structure. According to dynamic light scattering data, the size of carbon nanodots is 3.3 ± 0.9 nm.

     

Synthesis, characterization of ceria-coated silica particles and their chemical mechanical polishing performance on glass substrate

Nano-sized ceria particles were coated on the silica surface by the precipitation method using ammonium cerium nitrate and urea as precipitant with poly(vinylpyrrolidone) (PVP) as assistant. The structures and compositions of ceria-coated silica particles were characterized using X-ray diffraction (XRD), field-emission scanning microscopy (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. The results show that nano-size ceria particles were coated uniformly around the surface of silica particles when PVP was used as assistant during coating process, while without PVP, the ceria particles were grown sparsely on the silica particle surface and many ceria particles grow up through independent nucleation in the solution. Then, the chemical mechanical polishing (CMP) behaviors of the as-prepared ceria-coated silica particles on glass substrate were investigated. The CMP test results suggest that the as-prepared ceria-coated silica particles exhibit higher removal rate than pure silica particles without deteriorating the surface quality. In addition, online coefficient of friction (COF) was conducted during the polishing process. The COF data indicate that the COF values of ceria-coated silica particles are larger than those of pure silica particles due to their surface properties.     

Convective burning of fine ammonium nitrate–aluminum mixtures in a closed volume bomb

It is commonly assumed that the burning of ammonium nitrate–aluminum mixtures is much less prone to undergo a transition to explosion and detonation than similar mixtures based on ammonium perchlorate. However, this conclusion has been made for mixtures based on commercial-grade ammonium nitrate with large particles. In this study, the combustion of fine loose-packed mixtures of ammonium nitrate and aluminum in a closed-volume bomb has been examined. It has been shown that fine mixtures (ammonium nitrate with a particle size of less than 40 µm and an ASD-4 aluminum powder with spherical particles with a size of about 4 µm) undergo high-intensity combustion; in experiments with a stoichiometric mixture, explosions are observed. The explosions occur in the initial phase of convective combustion and lead to abrupt pressure pulsations with an amplitude of a few kilobars and to the destruction of the cup in which the sample is placed. The dynamics of development of the explosion has been analyzed in detail using numerical simulation. According to the results of experiments with varied parameters—the degree of dispersion of the ammonium nitrate powders, the aluminum content in the mixture, the length and diameter of the charge, and the level of pressure generated by the combustion of the igniter,—threshold conditions have been determined to separate the following modes: the absence of ignition, layer-by-layer combustion, or convective combustion with a transition into an explosion in experiments with a stoichiometric mixture.     

Magnetic iron oxide nanoparticle-hollow mesoporous silica Spheres:Fabrication and potential application in drug delivery

A facile method is developed for the fabrication of magnetic iron oxide nanoparticle-hollow mesoporous silica spheres (IONP-HMSs) and explored their potential application in drug delivery. Through the self-assembling process of IONPs and the formation of mesoporous silica shells, the IONP-HMSs with hollow interior cavity were obtained. The cetyltrimethyl ammonium bromide (CTAB) encapsulated IONP-containing spheres served as the template to establish the mesoporous silica shells. Typical anti-cancer drug, doxorubicin hydrochloride (DOX) was applied for drug loading and release process of IONP-HMSs, which demonstrated the IONP-HMSs have a high drug loading efficiency and allow pH-trigged release of DOX in vitro. Moreover, the IONP-HMSs exhibited excellent biocompatibility and enhanced DOX therapeutic efficacy to HeLa cells. Compared with traditional methods, the reported microemulsion-based method for the synthesis of IONP-HMSs enables the formation of hollow-structured nanocomposite without any complex template-removing process, which could pave the way to improving the therapeutic efficacy in drug delivery system.     

Tuning the morphology of mesoporous silica by using various template combinations

By using different dual-template combinations, four types of mesoporous silica materials with different morphologies were successfully synthesized. A solid-sphere mesoporous (SSM) silica was obtained using a combination of tri-block copolymer (F127) and 1,12-diaminododecane (DADD), but when F127 was substituted with poly(vinylpyrrolidone) (PVP), a leaf-shaped mesoporous (LSM) silica was obtained. In addition, a hollow-sphere mesoporous (HSM) silica was obtained by using a combination of PVP and dodecylamine (DDA), but a cotton-like mesoporous (CLM) silica was obtained using F127 instead of PVP. All four types of synthesized materials were characterized by SEM, TEM, XRD, and N₂ adsorption–desorption isotherms, and the results showed that all of them exhibited high surface area, large pore volume, worm-like pore structure, and beautiful shapes. The results of storage experiments revealed that the HSM and CLM showed good adsorption and storage properties. The HSM (the largest pore volume) seemed to have the larger storage capacity when compared to the CLM, albeit CLM had the highest surface area among all.     

Onset and development of convective burning in highly porous charges of ammonium perchlorate and its mixtures with aluminum

The onset and development of convective burning in the charges with a high porosity prepared from the finely dispersed ammonium perchlorate and its mixtures with aluminum ASD-4 is studied. The experiments were carried out in a constant volume bomb with the record of the pressure-time history and in the confinement with a slit, which makes it possible to perform simultaneously the photographic and piezometric recording of the process. Special attention is given to the mixtures with the increased aluminum content. The minimum lengths of samples are determined at which convective burning or explosion occur. The dependence of these lengths on the aluminum concentration in the mixture is determined. The possibility of convective burning and low-velocity detonation in ammonium perchlorate without the combustible additive is shown. It is established that the introduction of aluminum causes the ignition of the dispersed suspension behind the front of convective burning with the formation of the brightly glowing high-pressure zone (the secondary wave), which intensively expands in both sides from the place of origin. When the secondary wave overtakes the front of convective burning, the low-velocity detonation appears. The obtained results are of interest for explosion safety of the mixtures of ammonium perchlorate with aluminum and for designing generators of high-temperature suspensions with aluminum particles.     

Hierarchically Structured Porous Silica Spheres by Microemulsion/Vesicle Templating for Hydrodesulfurization of Fluid Catalytic Cracking Diesel

A series of hierarchically structured porous silica sphere (HSPSS) materials are successfully fabricated by a facile, one‐step microemulsion/vesicle bimodal method in a multicomponent microemulsion system of P123/n‐butanol/1,3,5‐trimethylbenzene/KCl/H₂O (surfactant/cosurfactant/oil/salt/water). The pore structures of the obtained HSPSS products consist of mesocellular foam and mesostructured vesicles. In contrast to the traditional porous silica materials the new structures combine two separate, distinct mesophases with different‐sized mesovoids in a single porous sphere. Moreover, the proportion of every mesophase in obtained HSPSS can be easily adjusted by tuning the initially added amount of n‐butanol or KCl in this multicomponent microemulsion system. When the molar ratio of KCl/tetraethoxysilane is 2.15, the obtained HSPSS material is turned into uniform mesostructured vesicle silica spheres, which consist of many small diameter vesicle particles. The hydrodesulfurization (HDS) activity of fluid catalytic cracking diesel over the HSPSS was tested. HSPSS‐0.75‐1.43 catalyst support with multiple mesoporous structures shows the highest HDS efficiency (98.5%) among all the studied catalysts.     

Effect of drying technique on the physicochemical properties of sodium silicate-based mesoporous precipitated silica

The conventional drying (oven drying) method used for the preparation of precipitated mesoporous silica with low surface area (>300 m²/g) and small pore volume is often associated with a high production cost and a time consuming process. Therefore, the main goal of this study was to develop a cost-effective and fast drying process for the production of precipitated mesoporous silica using inexpensive industrial grade sodium silicate and spray drying of the precipitated wet-gel silica slurry. The precipitated wet-gel silica slurry was prepared from an aqueous sodium silicate solution through the drop-wise addition of sulfuric acid. Mesoporous precipitated silica powder was prepared by drying the wet-gel slurry with different drying techniques. The effects of the oven drying (OD), microwave drying (MD), and spray drying (SD) techniques on the physical (oil, water absorption, and tapping density), and textural properties (specific BET surface area, pore volume, pore size, and % porosity) of the precipitated mesoporous silica powder were studied. The dried precipitated mesoporous silica powders were characterized with field-emission scanning electron microscopy; Brunauer, Emmett and Teller and BJH nitrogen gas adsorption/desorption methods; Fourier-transform infrared spectroscopy; thermogravimetric and differential analysis; N₂ physisorption isotherm; pore size distribution and particle size analysis. There was a significant effect of drying technique on the textural properties, such as specific surface area, pore size distribution and cumulative pore volume of the mesoporous silica powder. Additionally, the effect of the microwave-drying period on the physicochemical properties of the precipitated mesoporous silica powder was investigated and discussed.     

Initial stage of the explosion of ammonium nitrate and its powder mixtures

There is an obvious contradiction between the statistics of the devastating explosions that take place with the participation of ammonium nitrate and explosive properties of this material determined in standard tests. Pure ammonium nitrate does not burn under normal conditions and has a very low sensitivity to conventional mechanical and thermal stimuli. So far, ammonium nitrate has been detonated only by using high explosives. Causes of accidental explosions involving large masses of ammonium nitrate are likely to be found in a nonconventional behavior of ammonium nitrate. These changes may arise due to different chemical or physical factors, such as those associated with the presence of active additives, crushing of particles, etc., and lead to acceleration of the process at the initial stage of explosion. This work is devoted studying the convective burning and the initial stage of deflagration-to-detonation transition in dry and wet mixtures of ammonium nitrate with various, largely combustible additives. Experiments were conducted on loose-packed charges in a constant-volume bomb and by using the method of the critical bed height with recording pressure-time diagrams by a piezoelectric sensor. Ammonium nitrate of two different types was used: granular and powdered. The fuel additives were charcoal and aluminum powder, whereas the additives inhibiting the combustion of ammonium nitrate were water and monosodium salt of phosphoric acid. In addition, finely dispersed mixture of four components (ammonium nitrate, aluminum, powdered sugar, and TNT in a proportion of 76: 8: 12: 4) was used. The experiments in the constant-volume bomb were supplemented by numerical simulations, which made it possible to obtain a better understanding of the convective burning of the test mixtures and to evaluate the possibility of using a constant-volume bomb to collect quantitative information on the intensity of the combustion of the mixture at the initial stage of the explosion.     

Molecular ordering of mixed surfactants in mesoporous silicas: a solid-state NMR study

The use of mixed surfactants in the synthesis of mesoporous silica nanoparticles (MSNs) is of importance in the context of adjusting pore structures, sizes and morphologies. In the present study, the arrangement of molecules in micelles produced from a mixture of two surfactants, cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) was detailed by solid-state NMR spectroscopy. Proximities of methyl protons in the trimethylammonium headgroup of CTAB and protons in the pyridinium headgroup of CPB were observed under fast magic angle spinning (MAS) by (1)H-(1)H double quantum (DQ) MAS NMR and NOESY. This result suggested that CTAB and CPB co-exist in the pores without forming significant monocomponent domain structures. (1)H-(29)Si heteronuclear correlation (HETCOR) NMR showed that protons in the headgroups of CTAB are in closer proximity to the silica surface than those in the CPB headgroups. The structural information obtained in this investigation leads to better understanding of the mechanisms of self-assembly and their role in determining the structure and morphology of mesoporous materials.     

Mixing and segregation of granular materials in chute flows

Mixing of granular solids is invariably accompanied by segregation, however, the fundamentals of the process are not well understood. We analyze density and size segregation in a chute flow of cohesionless spherical particles by means of computations and theory based on the transport equations for a mixture of nearly elastic particles. Computations for elastic particles (Monte Carlo simulations), nearly elastic particles, and inelastic, frictional particles (particle dynamics simulations) are carried out. General expressions for the segregation fluxes due to pressure gradients and temperature gradients are derived. Simplified equations are obtained for the limiting cases of low volume fractions (ideal gas limit) and equal sized particles. Theoretical predictions of equilibrium number density profiles are in good agreement with computations for mixtures of equal sized particles with different density for all solids volume fractions, and for mixtures of different sized particles at low volume fractions (nu<0.2), when the particles are elastic or nearly elastic. In the case of inelastic, frictional particles the theory gives reasonable predictions if an appropriate effective granular temperature is assumed. The relative importance of pressure diffusion and temperature diffusion for the cases considered is discussed. (c) 1999 American Institute of Physics.     

Self‐Assembled Binary Mixtures of Partially Etched Nanowires

Arrays of anisotropic particles are sought after for applications in optics, electronics, and energy. Structures assembled from multiple micro‐ or nanoparticles could incorporate the distinct properties of each component to achieve functions not possible from single‐population assemblies. In mixed‐particle populations, the assembly forces may differ between the particle types, which will in turn influence the final assembled structures. Here, binary particle mixtures are studied and compared to assemblies formed from each of the component particles alone. The particles are partially etched nanowires (PENs, ≈300 nm diameter, and 3–8 μm overall length), which are formed by the silica coating and subsequent etching of striped metal nanowires, such that what remains are silica nanotubes containing segments of metal core (Au, Pt, Rh, or Pt/Au) with controllable location and number, spaced by “empty” regions that fill with water. Binary mixtures of PENs with different core metals and segment patterns are examined here to explore how the different core segment material, length, position, and number affects overall self‐assembly behavior.     

Facile Fabrication of Dendritic Mesoporous SiO2@CdTe@SiO2 Fluorescent Nanoparticles for Bioimaging

A seeded watermelon‐like mesoporous nanostructure (mSiO₂@CdTe@SiO₂, mSQS) composed of a novel dendritic mesoporous silica core, fluorescent CdTe quantum dots (QDs), and a protective solid silica shell is successfully fabricated by loading QDs into dendritic mesoporous silica nanoparticles through electrostatic interaction, and then coating with a solid silica shell by the modified Stöber method. The shell thickness of mSQS can be tuned from 0 to 32 nm as desired by controlling the reaction parameters, including the amount of silica precursor, tetraethyl orthosilicate, that is introduced, the solvent ratio (H₂O:ethanol), and the amount of catalyst (NH₃?H₂O). These fluorescent mSiO₂@QDs@SiO₂ nanoparticles possess excellent stability and thickness‐dependent cytotoxicity, and are successfully applied to bioimaging.     

Structural change of mesoporous silica with sonochemically prepared gold nanoparticles in its pores

Ultrasonic irradiation of mesoporous silica soaked in a mixture of chloroauric acid and isopropanol for 120 min in Ar atmosphere at room temperature yielded Au/SiO₂ mesoporous composite, which was characterized by high resolution transmission electron microscopy and optical absorption measurement. The structure of mesoporous silica after sonochemical preparation of gold (Au) nanoparticles within its pores was studied by nitrogen adsorption technique. It has been shown that the structural parameters, such as specific surface area (SSA), porosity (P), the mean pore diameter (l_p) were increased significantly after ultrasonic irradiation. It is suggested that the collision of Au nanoparticles with pore walls and localized erosion induced by the asymmetric implosive collapse of cavities on the extensive liquid–solid interface that are responsible for the structural change in the mesoporous solid.     

Synthesis and Characterization of Oxazine-doped Silica Nanoparticles for Their Potential Use as Stable Fluorescent Reagents

The synthesis process to obtain silica nanoparticles (NPs) doped with two oxazine dyes, nile blue and cresyl violet, has been investigated using a modification of the reverse micelle microemulsion method and a procedure based on the Stöber method. A micellar medium provided by the non-ionic surfactant Triton X-100 in a hexanol:water mixture and an ethanol:water mixture, have been used to provide the synthesis medium in each case. Tetraethoxysilane has been used as the initiator of the polymerization and condensation reactions after its hydrolysis in basic medium using ammonium hydroxide. Dye-silane precursor NPs have been also synthesized in order to compare their potential advantages against the NPs obtained by the direct encapsulation of the oxazine dyes. Size distribution and fluorescence of the synthesized NPs, which were monitored using Transmision Electron Microscopy (TEM) and a microplate reader, respectively, depend on the molar ratio and total concentration of the reagents involved in the synthesis. NPs obtained using the developed synthesis procedures had sizes below 400 nm in most instances and the best luminescent properties were observed for NPs with sizes ranging from 100 to 300 nm. Lower sizes result in a decrease in the fluorescence intensities of these nanomaterials. Parameters related with the luminescence features of these NPs were calculated in order to compare the feasibility of both synthesis approaches. The repeatability of the reverse-micelle microemulsion procedure performed in different days gave a relative standard deviation of 10% for the fluorescence intensity values.     

The influence of filler modification on its aggregation and dispersion behaviour in silica/PBT composite

In this work, highly dispersed silica is obtained using a precipitation technique from emulsion medium. The selected emulsifier, applied in the process, allows production of silica with almost ideally spherical particles. To examine the tendency to aggregation, the silica powder is treated with commercially available silane coupling agents: 3-mercaptopropyltrimethoxysilane (A-189), N-2-(aminoethyl)-3-aminopropyltrimethoxy silane (A-1120) and 3-methacryloxypropyltrimethoxysilane (A-174). The silica microstructure is characterised by scanning electron microscopy (SEM). Size distribution of primary particles, aggregates and agglomerates structures is determined using dynamic light scattering (DLS) method. Surface treatment of silica generally enhances powder dispersibility. The pristine spherical silica and silica modified with silanes are introduced to poly(butylene terphthalate) (PBT). Dispersion of nanosize precipitated silica particles in PBT matrix is studied by SEM technique. For the visualisation of silica particles covered by polymer layer, the composite fracture surfaces are etched by air-plasma. The agglomerates of untreated silica are not efficiently destroyed during the extrusion process, whereas surface treatment by selected silanes leads to a significant reduction of agglomerate number. However, a large number of small, strongly bonded aggregates still occupied the composite structure.     

Synthesis, characterization and comparison of sediment electro-codeposited nickel-micro and nano SiC composites

Nickel-silicon carbide composites were produced using 1 μm and 50 nm size powders from a conventional Watt's bath using tetra methyl ammonium hydroxide as the surfactant. Sediment codeposition technique with horizontal electrodes was used. The effect of silicon carbide concentration and bath operating parameters on the volume percents and deposition rates of coatings obtained with the two different particles was studied. Substantial improvements in mechanical properties such as hardness, wear resistance, scratch resistance and roughness were obtained with the nanocomposite material, as compared with composites containing microsized particles.     

One-step synthesis of hydrophobic mesoporous silica and its application in nonylphenol adsorption

Highly CH₃-functionalized mesoporous silica with nearly spherical morphology was synthesized under acidic conditions by co-condensation of two different silica precursors polymethylhydrosiloxane (PMHS) and tetraethoxysilane (TEOS) in the presence of triblock copolymer P123 as template. XRD, N₂ adsorption–desorption, HRTEM, SEM and ²⁹Si MAS NMR were used to identify its highly-ordered mesopore array structure, nearly spherical particle morphology and CH₃ functionalization of the as-synthesized material. The resulting hydrophobic mesoporous silica possessed regular mesochannel arrays, indicating that the introduction of PMHS had little impact on the formation of an ordered mesostructure. Also, PMHS played an important role in morphology control and organic functionalization, ensuring nearly spherical particle morphology and high CH₃ functionalization degree of the obtained mesoporous silica material. As compared with pristine mesoporous silica SBA-15, the hydrophobic mesoporous silica showed the higher adsorption performance when they were used as adsorbents to remove organic pollutant nonylphenol at a very low concentration from aqueous solution.     

TiO_2纳米粒子的Ram an光谱表征和紫外可见光吸收特性

用 Sol- Gel方法制备粒径约 1 0 - 50 nm的 Ti O2 微粒。Raman光谱测量显示 ,水解时 p H值不同 ,在同样热处理温度下得到的 Ti O2 微粒的晶体结构不尽相同。在低于 673K热处理温度下得到的 Ti O2 微粒是板钛矿和锐钛矿的混合晶体。用谱峰拟合技术可以将样品 A1的1 57cm-1 Raman谱峰分解成分属于板钛矿和锐钛矿的两个振动峰。 UV- Vis测量表明 ,锐钛矿型 Ti O2 微粒的紫外光吸收性能最好。而粒度约 2 0 μm的市售锐钛矿型 Ti O2 的紫外光吸收性能甚至比板钛矿型和金红石型 Ti O2 纳米粒子的还略低些 ,表明小尺寸效应和表面缺陷对紫外光吸收亦有贡献     

Surface modification on a glass surface with a combination technique of sol-gel and air brushing processes

This study fabricated the large area and optically transparent superhydrophobic silica based films on glass surface with optimized hardness. A silane coupling agent, tetraethoxysilane (TEOS), effectively bonds silica particles onto the glass substrate. Desired surface roughness was obtained by adjusting nano silica particles concentration of the precursors prepared by the sol-gel process. Silica suspension was coated onto the glass substrate by the air brushing methods. This method can deposit a uniform, transparent coating on the glass substrate efficiently. Diluting the precursor by adding ethanol or a mixture of D.I. water and ethanol further improved the transmittance and superhydrophobicity efficiency. The results showed that as the silica particle concentration and the thickness of the coating were increased, the surface roughness was enhanced. Rougher surface displayed a higher superhydrophobicity and lower transmittance. Therefore, the concentration of silica particle, volume of coatings, and the ratio of ethanol and D.I. water are of great importance to deposit a transparent, superhydrophobic coating on glass.