Preparation of SiO2/TiO2 Janus particles by electrostatic assembly,hydrolysis and calcination

This paper describes a novel chemical method for preparing SiO₂/TiO₂ Janus particles.First,polystyrene（PSt）/SiO₂ particles with a raspberry-like structure are prepared by electrostatic assembly.The influences of the reaction time of sulfonation and the treatment times of polyelectrolyte solutions（PDADMAC,PSS）on PSt and SiO₂ are investigated with respect to the surface charge density of the particles.SiO₂/TiO₂ Janus particles are then obtained by hydrolysis of butyl titanate on the surface of PSt/SiO₂ particles followed by a calcination process.Particle size analyzer,Zeta potential instrument,FTIR,TEM and SEM are used to characterize the particle size,the amount of charge on the surface of PSt and SiO₂ particles and the compositions and morphologies of PSt/SiO₂,SiO₂/TiO₂ and PSt/SiO₂/TiO₂.The diameters of the PSt,SiO₂,PSt/SiO₂ and SiO₂/TiO₂ particles are 2.0 μm,303 nm,2.7 μm and 330nm,respectively.     

Atmospheric pressure plasma-assisted green synthesis of amphiphilic SiO2 Janus particles

A facile green approach for the synthesis of amphiphilic SiO₂ Janus particles using low temperature atmospheric pressure plasma is reported in this study. Monodispersed SiO₂ particles were masked by embedding half of their surface inside a polystyrene film. The exposed surfaces of the SiO₂ particles were readily modified using He/CF₃CFH₂ low-temperature atmospheric pressure plasma to obtain amphiphilic Janus particles. Their amphiphilic nature was confirmed using fluorescent microscopy by tagging their hydrophilic part with a fluorescent dye. The present method can be used to generate amphiphilic Janus particles with a variety of functionalities, which may find applications as surfactants and surface modifying agents.     

纳米SiO2／CeO2复合磨粒的制备及其抛光特性研究

以尿素[CO(NH2)2]、(NH4)2Ce(NO3)6和SiO2为原料,采用均相沉淀法制备1种新型纳米SiO2/CeO2复合磨粒,通过X射线衍射仪、X射线光电子能谱仪、飞行时间二次离子质谱仪和扫描电子显微镜等分析手段对其结构进行表征,并将SiO2/CeO2复合磨粒配置成抛光液在数字光盘玻璃基片上进行化学机械抛光试验.结果表明:所制备的SiO2/CeO2复合磨粒的平均晶粒度为19.64 nm,粒度分布均匀;经过1 h抛光后,玻璃基片的平均表面粗糙度(Ra)由1.644 nm降至0.971 nm;抛光后玻璃基片表面变得光滑、平坦,表面微观起伏较小.     

In situ synthesis of Ag-SiO2 Janus particles with epoxy functionality for textile applications

A facile method for the synthesis of silver-silica（Ag-SiO₂） Janus particles with functionalities suitable for textile applications is reported.Silica nanoparticles prepared by the Stober method were functionalized with epoxy,amine,and thiol groups,which were confirmed by Fourier transform infrared analysis.The functionalized silica nanoparticles were used to produce Pickering emulsions,and the exposed surface was used for the attachment of silver nanoparticles（AgNPs） via the low-temperature chemical reduction method.The morphology and structure of the Ag-SiO₂ Janus particles were characterized by scanning electron microscopy,scanning transmission electron microscopy,high-resolution transmission electron microscopy,energy-dispersive X-ray analysis,and UV-vis spectroscopy.Because of their specific functionalities,these Ag-SiO₂ Janus particles are proposed for applications on textile substrates,as they can overcome several drawbacks of direct application of AgNPs on textiles,such as leaching,agglomeration,and instability during storage.     

SiO2-coated pure anatase TiO2 catalysts for enhanced photo-oxidation of naphthalene and anthracene

Our current efforts reveal the preparation of SiO₂@TiO₂ nanocomposites having different thicknesses of silica shell and the relationship to photocatalytic activity (PCA) for the photo-oxidation of naphthalene and anthracene. The presence of SiO₂ coating over TiO₂ surface was demonstrated by FT-IR analysis, with peaks corresponding to SiOSi (1081 cm⁻¹) and SiOTi (950 cm⁻¹) bonds observed. High-resolution transmission electron microscopy analysis confirmed the presence of SiO₂ in the as-prepared nanocomposites and the amount of Si, Ti, and O was determined by energy dispersive X-ray spectroscopy analysis. Increasing the SiO₂ shell thickness increases the surface area of the nanocomposites (69–235 m²/g), which enhances naphthalene/anthracene adsorption. However, the observed PCA trend presents an inverse correlation to the adsorption studies, where the as-prepared samples possessing the highest surface areas exhibited the least PCA, while catalysts having lower surface areas (among silica coated samples) displayed the highest PCA in the degradation of naphthalene and anthracene to CO₂. Despite complete degradation of naphthalene and anthracene, incomplete mineralization occurred, ascribed to the formation of various intermediates, identified by GC–MS analysis.     

Multiphysics numerical investigation of photothermal self-driving characteristics of SiO2@Au Janus microparticles for drug delivery

The photothermal self-driving process of Janus microparticles has wide application prospects in the fields of biomedicine. Since silica and gold have good biocompatibility and high photothermal conversion efficiency, the SiO₂@Au Janus microparticles are widely used as drug carriers. Based on the multiphysics coupling method, the photothermal self-driving process of SiO₂@Au Janus microparticles was investigated, wherein the substrate was SiO₂ particles and one side of the particles was coated with gold film. Under a continuous wave laser with irradiation of 20 W/cm², the distance covered by the Janus particles was increased by increasing the thickness of the gold film and reducing the size of the SiO₂ particles; the self-driving characteristics of the Janus particles were controlled substantially by increasing the intensity of the incident laser. Based on the simulation results, the thermophoretic motion and Brownian motion of particles can be measured by comparing the absolute values of the thermophoretic force impulse, Brownian force impulse, and drag force impulse. The Brownian force acting on Janus microparticles under low laser power cannot be ignored. Furthermore, the minimum laser power required for Janus particles to overcome Brownian motion was calculated. The results can effectively guide the design of Janus particles in biomedicine and systematically analyze the mechanism of particle thermophoretic motion during drug delivery.     

In situ synthesis of Ag-SiO_2 Janus particles with epoxy functionality for textile applications

A facile method for the synthesis of silver-silica(Ag-SiO_2) Janus particles with functionalities suitable for textile applications is reported.Silica nanoparticles prepared by the Stober method were functionalized with epoxy,amine,and thiol groups,which were confirmed by Fourier transform infrared analysis.The functionalized silica nanoparticles were used to produce Pickering emulsions,and the exposed surface was used for the attachment of silver nanoparticles(AgNPs) via the low-temperature chemical reduction method.The morphology and structure of the Ag-SiO_2 Janus particles were characterized by scanning electron microscopy,scanning transmission electron microscopy,high-resolution transmission electron microscopy,energy-dispersive X-ray analysis,and UV-vis spectroscopy.Because of their specific functionalities,these Ag-SiO_2 Janus particles are proposed for applications on textile substrates,as they can overcome several drawbacks of direct application of AgNPs on textiles,such as leaching,agglomeration,and instability during storage.     

Preparation and characterization of LiAlxCoyNi1-x-yO2 particles

Lithium-aluminum-cobalt-nickel oxide (LiAlxCoyNi1-x-yO2) particles, generally used as cathode of lithium battery, were prepared by chemical coprecipitation from an aqueous solution of LiOH, AI(NO3)3, Co(NO3)2 and Ni(NO3)2 with NH4OH. XRD, SEM and FTIR were used to examine the effect of nickel content on the product. FHR patterns showed that increase in nickel content decreased the absorption strength of the peak of spinel structure of the product, attributed to the occupation by nickel in the aluminum sites. Particle size and electrical properties of the lithium-aluminum-cobalt-nickel oxide (abbreviated as LACNO) particles were also determined.     

Effect of ion-beam assisted deposition on the film stresses of TiO2 and SiO2 and stress control

Based on Hartmann-Shack sensor technique, an online thin film stress measuring system was introduced to measure the film stresses of TiO₂ and SiO₂, and comparison was made between the film stresses prepared respectively by the conventional process and the ion-beam assisted deposition. The effect of ion-beam assisted deposition on the film stresses of TiO₂ and SiO₂ was investigated in details, and the stress control methodologies using on-line adjustment and film doping were put forward. The results show that the film stress value of TiO₂ prepared by ion-beam assisted deposition is 40 MPa lower than that prepared by conventional process, and the stress of TiO₂ film changes gradually from tensile stress into compressive stress with increasing ion energy; while the film stress of SiO₂ is a tensile stress under ion-beam assisted deposition because of the ion-beam sputtering effect, and the film refractive index decreases with increasing ion energy. A dynamic film stress control can be achieved through in-situ adjustment of the processing parameters based on the online film stress measuring technique, and the intrinsic stress of film can be effectively changed through film doping.     

Synthesis and electrorheological properties of polar molecule-dominated TiO 2 particles with high yield stress

Two types of amorphous TiO₂ particles with different particle sizes were synthesized by a simple sol–gel method and were characterized by X-ray diffraction analysis, field emission scanning electron microscopy, and Fourier transform infrared spectrometry. The electrorheological (ER) results show that the TiO₂/silicone oil suspensions exhibited a remarkable ER effect. The static shear stress can be up to 130 kPa (shear rate 0.2 s^− 1) under the DC electric field of 4 kV/mm at room temperature. The polar molecules present on the particles’ surface play a decisive role for the observed giant ER effect, which arises from the alignment of polar molecules in the gap between neighboring particles.     

Preparation of ultrafine chitosan particles by reverse microemulsion

Ultrafine chitosan particles were prepared by reverse microemulsion consisting of water, Triton X-100, octanol and cyclohexane. Two methods of preparing ultrafine chitosan particles were adopted and compared using TEM and IR, and possible mechanisms for the formation of ultrafine chitosan particles were proposed. Experimental results show that the method which combined ionic gelation and cross-linking gave uniformly sized chitosan nanoparticles with an average diameter of 92 nm, while the cross-linking without ionic gelation produced spindly chitosan particles with an average length of 943 nm and width of 188 nm.     

Synthesis of TiO2 nanoparticles by propane/air turbulent flame CVD process

Synthesis of TiO2 nanoparticles by the oxidation of titanium tetrachloride (TiCl4) in high-strength propane/air turbulent flame is investigated tentatively for mass production ofTiO2 nanoparticles. Effects of reactor heat flux varying from 247 to 627 kJ/m2 s, initial TiO2 number density from 2×1020> to 1 × 1021 m-3, and apparent residence time of TiO2 nanoparticles in reactor from 0.06 to 0.9 s, on particle morphology, phase composition, UV absorption and photoluminescence (PL) spectra are studied. The TiO2 nanoparti-cles synthesized, with mean size of 30-80 nm and rutile mass fraction from 0.155 up to 0.575, exhibited a strong PL signal at the wavelength of 370-450 nm, with a wide peak signal at 400-420 nm, reflecting significant oxygen vacancies on the surface of the TiO2 nanoparticles.     

Visible light photodegradation of methylene blue by AgBr-TiO2/SiO2@Fe3O4 magnetic photocatalysts

Visible photoactive AgBr/TiO2 was immobilized on a SiO2@Fe3O4 magnetic support by solvother- rnal and sol-gel methods to form a AgBr-TiO2/SiO2@Fe3O4 magnetic photocatalyst. Samples were characterized by X-ray diffraction, high-resolution transmission electron microscopy and magne- tometry. Hereto-structured AgBr/TiO2 was well seeded on the shell-core SiO2@Fe3O4 structure. The AgBr-TiO2/SiO2@Fe3O4 magnetic photocatalyst exhibited high photocatalytic activity in the degrada- tion of methylene blue under visible light. The photocatalyst was superparamagnetic, which is beneficial for facile magnetic separation.     

Rheological properties of suspensions of TiO2 particles in polymer solutions. 1. Shear viscosity

This paper presents results on the rheological behaviour of suspensions of two kinds of TiO₂ particles in two different polymer solutions. The particles differ in their hydrophilic or hydrophobic properties. The dispersing media are a solution of high molecular weight polyisobutylene in decalin and a solution of a low molecular weight polybutene in decalin. The concentrations of polymer are adjusted in order to get the same zero shear viscosity. The shear viscosity measurements display an apparent yield stress in some cases. The existence and the values of the yield stress depend on the volume fraction of solid particles and on the type of particles. The evolution of the intrinsic viscosity and of the maximum packing fraction vs the shear rate is interpreted in terms of evolution of the size and of the shape of aggregates of particles under shear. The effect of temperature on the development of the yield stress is also discussed. The results are completed by microscopic observations.     

Multistability of cantilever MEMS/NEMS switches induced by electrostatic and surface forces

MEMS/NEMS switches are used in a variety of portable electronics and RF telecommunications systems. MEMS/NEMS switches are ideally bi-stable, with one ON and one OFF state and a reliable switching between the two induced by electrical actuation. Presented herein is an exploration into non-ideal behavior, i.e. tri-stability, and parametric sensitivity of a generalization of cantilever MEMS/NEMS switches. The representative system model employs multiphysics features based on Euler–Bernoulli beam theory, parallel plate capacitance for electrostatics, and a Lennard-Jones form of surface interaction. The geometry, material properties, and surface features of the device are condensed into just a few dimensionless quantities, creating a parameter space of low enough dimensionality to provide accessible representations of all system equilibria within physically relevant ranges. Analysis of this system model offers insight regarding conditions necessary for bi- and tri-stability in such systems, which are crucial for informing studies on switching dynamics and various device performance metrics.     

氧化硅/氧化铁复合磨粒用于硬盘基片的抛光研究

本文以HNO3、NaOH、Fe(NO3)3和SiO2浆料为原料,采用沉淀法制备了1种SiO2/Fe2O3复合磨粒,通过X射线衍射仪(XRD)、飞行时间二次离子质谱仪(TOF-SIMS)和扫描电子显微镜(SEM)对其结构进行表征,结果表明Fe2O3包覆到SiO2的表面,复合粒子具有很好的分散性.用UNIPOL-1502抛光机研究了所制备复合磨粒在镍磷敷镀的硬盘基片中的抛光性能,抛光后硬盘基片的表面粗糙度Ra由抛光前的8.87nm降至3.73nm;抛光后表面形貌的显微镜观测结果表明新制备的复合磨粒表现出较好的抛光性能.     

Synthesis and characterization of PMMA/Al2O3 composite particles by in situ emulsion polymerization

In order to improve its dispersibility, superfine alumina （A1203） was encapsulated with poly（methyl methacrylate） （PMMA） by in situ emulsion polymerization. It was found that only when the concentration of sodium dodecyl sulfate （SDS） was much higher than its critical micelle concentration, could PMMA/Al2O3 composite particles with high percentage of grafting （PG） be prepared. The same results were obtained between the experimental and stoichiometric amounts of tris（dodecylbenzenesulfonate） isopropoxide （NDZ）, indicating that single-molecule-layer adsorption had taken place between NDZ and Al2O3. Analysis using FTIR, TEM and XPS showed that PMMA/Al2O3 composite particles with core-shell structure had been successfully synthesized by in situ emulsion polymerization. Compared to Al2O3, thermal stability and dispersibility of the composite particles showed marked improvement.     

Synthesis and characterization of PMMA/Al2O3 composite particles by in situ emulsion polymerization

In order to improve its dispersibility, superfine alumina (Al2O3) was encapsulated with poly (methyl methacrylate) (PMMA) by in situ emulsion polymerization. It was found that only when the concentration of sodium dodecyl sulfate (SDS) was much higher than its critical micelle concentration, could PMMA/Al2O3 composite particles with high percentage of grafting (PG) be prepared. The same results were obtained between the experimental and stoichiometric amounts of tris (dodecylbenzenesulfonate) isopropoxide (NDZ), indicating that single-molecule-layer adsorption had taken place between NDZ and Al2O3. Analysis using FTIR. TEM and XPS showed that PMMA/Al2O3 composite particles with core-shell structure had been successfully synthesized by in sire emulsion polymerization. Compared to Al2O3, thermal stability and dispersibility of the composite particles showed marked improvement.     

Bio-oxidation of galena particles by Acidithiobacillus ferrooxidans

This paper deals with the bio-oxidation of galena particles （-80 meshes） using Acidithiobacillus ferrooxidans and compares it with Fe^3＋ oxidation. Experimental results show that, at least, 0.00197 mol galena was leached from lOOmL pulp （density of 3.8%） with 39 days＇ bio-oxidation, as compared to 0.00329 mol galena by Fe^3＋ with 9 days＇ oxidation. Because Fe^3＋ was constantly consumed, leaching by Fe^3＋ almost stopped after 9 days. Large amounts of lead sulfate were detected in both bio-oxidation and Fe^3＋ oxidation of galena. A. ferrooxidans followed a unique growth pattern during the bio-oxidation of galena. In the initial 15 days, the bacteria attached themselves to the galena surface with the formation of erosion pits similar in shape and length to those of the bacteria, and there were hardly any bacteria suspended in the solution. After 15 days, suspended bacteria increased. It is thus suggested that A. ferrooxidans may directly oxidize galena.