Outer Particles Research Articles

Ti containing mesoporous silica submicrometer-sphere, with tunable particle size for styrene oxidation

Ti-containing mesoporous silica materials with size-tunable mesopores and isolated tetrahedrally coordinated Ti species have widely applications in bulk molecular catalysis. Herein, mesoporous titanium silica submicrometer-spheres (Ti-MSSs) with tunable outer particle diameter were synthesized based on developed Stober method using nonionic surfactant P123 as particle dispersing agent at room temperature. P123 molecular assembled structures will interact with silica species through interface hydrogen bond leading to the formation of tunable sized particles. The particle size was controlled ranging from 400 to 80nm by adjusting the P123 concentration. The influence of Ti-MSSs particle size on the oxidation of styrene with aqueous H2O2 as oxidant was investigated in detail. Ti-MSSs showed better catalytical performance compared to mesoporous titanium silica large particles. Moreover, the catalyst activity increased with decrease in particle size of Ti-MSSs. Nano-sized Ti-MSSs of about 80nm demonstrated the optimized performance for styrene oxidation with styrene conversion 44.7%, benzaldehyde selectivity 82.2% and styrene oxide 17.7% while the reaction time was 6h.

Particle Swarm Optimization-Proximal Point Algorithm for Nonlinear Complementarity Problems

A new algorithm is presented for solving the nonlinear complementarity problem by combining the particle swarm and proximal point algorithm, which is called the particle swarm optimization-proximal point algorithm. The algorithm mainly transforms nonlinear complementarity problems into unconstrained optimization problems of smooth functions using the maximum entropy function and then optimizes the problem using the proximal point algorithm as the outer algorithm and particle swarm algorithm as the inner algorithm. The numerical results show that the algorithm has a fast convergence speed and good numerical stability, so it is an effective algorithm for solving nonlinear complementarity problems.

Impact of the virus purification protocol on aggregation and electrokinetics of MS2 phages and corresponding virus-like particles

Previous experimental and theoretical studies have established that electrokinetic and aggregation properties of soft MS2 phages are not only governed by the physico-chemical features of their proteinaceous outer surface but are also significantly impacted by those of their inner RNA component (Dika et al. Appl. Environ. Microbiol., 2011, 14, 4939-4948). These conclusions contradict the recent findings of Nguyen et al. (Soft Matter, 2011, 7, 10449-10456) who reported identical electrokinetic and aggregation characteristics for MS2 and corresponding virus like particles (VLPs) that lack the internal RNA component. We demonstrate here that this contradiction originates from the different purification methods adopted prior to measurements. More generally, we show that stability and electrohydrodynamics of viruses differ according to purification by (i) dialysis, (ii) isopycnic centrifugation in the cesium chloride gradient, and (iii) precipitation using polyethylene glycol (PEG). Methods (i) and (iii) lead to aggregation of MS2 phages at pH ≤ 4 and pH ≤ 6 in 1-100 mM NaNO3 solutions, respectively, while under such conditions aggregation is not observed for MS2 and VLP suspensions prepared according to (ii). In addition, VLPs prepared following methods (i) and (iii) aggregate only at the isoelectric point (pH ~ 3-4) in 1 mM NaNO3 solution. Electrophoretic mobility data of stable MS2 and VLP particles were further examined using a recent formalism for electrokinetics of soft multilayered colloids. The analysis qualitatively shows how the purification protocol may affect either the outer particle surface properties and/or the inner particle content. Finally, the non-DLVO aggregation behavior of MS2 and VLPs purified via the above protocols is discussed in terms of the possible change in corresponding interparticular interactions.

Research on the Coarse Particles Velocity Characteristic in Fluidized Bed

In order to understand the particle velocity distribution characteristics of the 2D bubbling fluidized bed. The paper study that several mainly factors (static bed height, particle size and gas speed) influence on velocity distribution of the outer particles by experiment. The results for particles around bubble show that: ①Under the condition of the same static bed height and particle size, the particle velocity increases with the gas speed; the particle velocity increase at the axial direction and has no rule at radial direction. ②On the basis of the same wind speed and particle size, the particle velocity reduce with the static bed height; the particle velocity decreases at the axial direction and has no regular at radial direction. ③At the same wind speed and static bed height, the particle velocity is gradual reducing with the particle size; the particle velocity also reduce at the axial direction and has no rule at radial direction.

Influence of dissolved oxygen concentration on the oxide film formed on Alloy 690 in high temperature water

Characteristics of the oxide films formed on Alloy 690 under different dissolved oxygen (DO) concentrations in 290°C water were examined. Under 3ppm DO, the oxide film mainly consisted of outer spinel particles and porous NiO base layer. A thin Cr-rich film gradually develops with decreasing DO. Fe and Ni levels in the film decrease while Cr level increases concomitantly. The film preformed under high DO changes slightly when further immersed under low DO. The film preformed under low DO becomes much thicker when immersed under high DO, with gradual development of spinel particles and NiO base layer.

Variations in diesel soot reactivity along the exhaust after-treatment system, based on the morphology and nanostructure of primary soot particles

The reactivity of soot at different sites of the exhaust after-treatment system of a diesel engine (upstream and downstream of the diesel oxidation catalyst (DOC), downstream of the diesel particulate filter (DPF), as well as inside the DPF) was investigated on the basis of morphology and structure of primary soot particles by high resolution transmission electron microscopy (HRTEM). The results indicate that combustion-formed soot particles are susceptible to further transformations of their morphology within the exhaust system. The same primary soot particles can possess both oxidation-promoting and oxidation-inhibiting morphological features, the particle cores being highly reactive. Most reactivity-promoting features are encountered in pre-DOC and post-DOC primary particles, suggesting that soot can be more easily oxidised before it enters the DPF. The residence time of soot in the DPF contributes to modification of its reactivity by affecting size distribution and nanostructure of primary particles. Partial NO2 oxidation and high temperatures during active regeneration modify the morphology of outer particle shells, thus rendering post-DOC and post-DPF primary soot particles less reactive in this respect. Primary soot particles that pass through the DPF and reach the atmosphere are characterised by the highest graphitisation degree and sizes larger than those entering the DPF. Complementary Near-Edge X-ray Absorption Fine Structure (NEXAFS) analyses proved not as relevant regarding soot reactivity but indicate higher chemical inhomogeneity of pre-DOC than of post-DOC and post-DPF soot and high contents of carboxyl carbon in post-DPF particles.

Temperature response of luminescent tris(bipyridine)ruthenium(II)-doped silica nanoparticles

Nanoparticle-based temperature imaging is an emerging field of advanced applications. Herein, the sensitivity of the phosphorescence of tris(bipyridine)ruthenium(II)-doped silica nanoparticles towards temperature is studied. 130nm size particles were prepared by a modification of Stöber’s method, that allows the incorporation of Ru[(bpy)3]2+ into the outer particle shell. The entrapped Ru[(bpy)3]2+ retains its photophysical properties, yet the emission of the particles is not affected by the presence of O2, neither by anionic quenchers; quenching by MV2+, on the other hand, is strongly dependent on pH. Between 20 and 60°C, the steady-state emission of the particles decreases linearly with increasing temperature. The slope of the straight line diminishes slightly on thermal cycling, but soon stabilizes. Fluorescence measurements by scanning confocal microscopy indicate that the silica nanoparticles doped with Ru[(bpy)3]2+ can indeed be employed to probe thermal processes in micro-environments.

Bed Agglomeration Characteristics in Fluidized-Bed Combustion of Biomass Fuels Using Olivine as Bed Material

The bed agglomeration characteristics during combustion of typical biomass fuels were determined in a bench-scale bubbling fluidized-bed reactor (5 kW) using olivine and quartz sand as bed material. The fuels studied include willow, logging residues, wheat straw, and wheat distiller’s dried grain with solubles (wheat DDGS). Bed material samples and agglomerates were analyzed by means of scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), for morphology and elemental composition. Furthermore, bed ash particles were separated by sieving from the bed material samples and analyzed for elemental composition by SEM–EDS and for determination of crystalline phases by powder X-ray diffraction (XRD). Chemical equilibrium calculations were performed to interpret the experimental findings of layer formation and reaction tendencies in both bed materials. Significant difference in the agglomeration tendency between olivine and quartz was found during combustion of willow and logging residues. These fuels resulted in inner layers that were more dependent on the bed material composition, and outer layers that have a composition similar to the fuel ash characteristics. The elemental composition of the inner layer formed on the quartz bed particles was dominated by Si, K, and Ca. In the olivine bed, the inner layer consisted mainly of Mg, Si, and Ca. Chemical equilibrium calculations made for both bed materials showed a low chemical driving force for K to react and be retained by the olivine bed particles, which is in accordance to the experimental findings. For the quartz case, the inner layer was found responsible for the initiation of the agglomeration process. The composition of the fewer and more porous agglomerates found after the experiments in the olivine bed showed neck composition and characteristics similar to the individual bed ash particles found in the bed or outer bed particle coating composition. For DDGS (rich in S, P, K, and Mg) and wheat straw (rich in Si and K), no significant differences in the bed agglomeration tendency between olivine and quartz bed materials were found. The results show that the bed particle layer formation and bed agglomeration process were associated to direct adhesion of bed particles by partly molten fuel ash derived K–Mg phosphates for DDGS and K-silicates for wheat straw.

High Yield Production Process for Shigella Outer Membrane Particles

Gram-negative bacteria naturally shed particles that consist of outer membrane lipids, outer membrane proteins, and soluble periplasmic components. These particles have been proposed for use as vaccines but the yield has been problematic. We developed a high yielding production process of genetically derived outer membrane particles from the human pathogen Shigella sonnei. Yields of approximately 100 milligrams of membrane-associated proteins per liter of fermentation were obtained from cultures of S. sonnei ΔtolR ΔgalU at optical densities of 30–45 in a 5 L fermenter. Proteomic analysis of the purified particles showed the preparation to primarily contain predicted outer membrane and periplasmic proteins. These were highly immunogenic in mice. The production of these outer membrane particles from high density cultivation of bacteria supports the feasibility of scaling up this approach as an affordable manufacturing process. Furthermore, we demonstrate the feasibility of using this process with other genetic manipulations e.g. abolition of O antigen synthesis and modification of the lipopolysaccharide structure in order to modify the immunogenicity or reactogenicity of the particles. This work provides the basis for a large scale manufacturing process of Generalized Modules of Membrane Antigens (GMMA) for production of vaccines from Gram-negative bacteria.

Enhanced fluctuations of interacting particles confined in a box

We study the position fluctuations of interacting particles aligned in a finite cell that avoid any crossing in equilibrium with a thermal bath. The focus is put on the influence of the confining force directed along the cell length. We show that the system may be modeled as a 1D chain of particles with identical masses, linked with linear springs of varying spring constants. The confining force may be accounted for by linear springs linked to the walls. When the confining force range is increased toward the inside of the chain, a paradoxical behavior is exhibited. The outermost particles fluctuations are enhanced, whereas those of the inner particles are reduced. A minimum of fluctuations is observed at a distance of the cell extremities that scales linearly with the confining force range. Those features are in very good agreement with the model. Moreover, the simulations exhibit an asymmetry in their fluctuations which is an anharmonic effect. It is characterized by the measurement of the skewness, which is found to be strictly positive for the outer particles when the confining force is short ranged.

Electrochemical properties of polyaniline composite electrodes prepared by in-situ polymerization in titanium dioxide dispersed aqueous solution

Polyaniline (PANI)/titanium dioxide (TiO2) composites were prepared by a chemical oxidation polymerization. The composites were prepared with various amount of TiO2 to find a relation between electrochemical properties of composites and compositions of TiO2 and PANI in the composites. PANI/TiO2 composites which had PANI as a shell and TiO2 as a core part of the composites were successfully synthesized. Fiber-like PANI was also observed within the composites. The synthesis was explained as two stages of polymerization. First stage is a polymerization reaction occurred by a strong oxidative potential of TiO2. Second stage is started by adding ammonium peroxydisulfate in reaction solution. Diameters of aggregations of the composites increased with the added amounts of TiO2. The composite prepared with 10wt.% of TiO2 per aniline monomer weight showed the highest capacitance of 784Fg−1 among the prepared composites. But the composites prepared with excess amounts of TiO2 showed lower capacitance than the highest one. The lower capacitances of the composites prepared with excess amounts of TiO2 was considered as related with the diameters of the aggregations. The composites prepared with excess amounts of TiO2 had large diameters for the aggregations. The TiO2 particles in the core of composites that had large diameter are hard to participate in electrochemical reaction due to a long pathway from electrolyte to TiO2 core and a blocking effect by outer TiO2 particles.

A detailed view of microparticle formation by in-process monitoring of the glass transition temperature

Biodegradable poly(d,l-lactide-co-glycolide) microspheres were prepared by a well-controlled emulsion solvent extraction/evaporation process. The objective of this study was to investigate how drug release can be modified by changing the morphology of the polymer matrix. The matrix structure was controlled by the preparation temperature which was varied between 10 and 35°C, thus changing the 4weeks release pattern from almost linear kinetics to a sigmoidal profile with a distinct lag phase and furthermore decreasing the encapsulation efficiency. By monitoring the glass transition temperature during the extraction process, it was shown that the preparation temperature determines the particle morphology by influencing the time span in which the polymer chains were mobile and flexible during the extraction process.Further factors determining drug release were found to be the molecular weight of the polymer and the rate of solvent removal. The latter, however, has also influence on the encapsulation efficiency with slow removal causing a higher drug loss. A secondary modification of the outer particle structure could be achieved by ethanolic post-treatment of the particles, which caused an extension of the lag phase and subsequently an accelerated drug release.

Growth Behavior of Surface Oxide Layer on SUS316L Stainless Steel at the Early Stage of Exposure to 288°C Water

Surface oxide layer on SUS316L stainless steels exposed to 288°C pure water with 2 ppm dissolved oxygen (DO) for 1–100 h were analyzed using Focused Ion Beam (FIB) and Scanning Transmission Electron Microscope (STEM) technique to understand the early stage of surface oxide layer formation. In order to analyze the multi layered surface oxide, the interfaces between the outer and the inner oxide layers and that between the inner oxide layer and SUS316L substrate were determined from Energy Dispersive X-ray Spectroscopy (EDX) line profiles. At 1 h exposure, double oxide layer which is composed of compact inner oxide layer and outer oxide layer with Fe-rich and Ni-rich oxide particles was formed. At the outermost region of the SUS316L substrate, Ni and Cr were enriched. At 100 h exposure, growth of the inner oxide layer was suppressed and the Ni and Cr enriched region at the alloy substrate was preserved underneath the Ni-rich outer oxide particles. At 1 h exposure, most of the outer oxide particles were composed of Fe-rich ones, at 10 h exposure, another Ni-rich outer oxide particles were nucleated and grew faster than Fe-rich ones. Consequently, a part of pre-formed Fe-rich outer oxide particles were covered with Ni-rich ones.

Spatial distributions of ions and electrons from the plasma sheet to the inner magnetosphere: Comparisons between THEMIS-Geotail statistical results and the Rice convection model

[1] To understand the processes responsible for the formation and structure of plasma sheet and ring current particles, we have used THEMIS and Geotail data to investigate statistically the distributions of ions and electrons from the midtail to the inner magnetosphere and compared them with results from the Rice convection model (RCM). The observed distributions show clear magnetic local time (MLT) asymmetries in the thermal energy and energy fluxes of plasma sheet particles but many more MLT symmetric ring current particles. Our RCM runs include both self-consistent electric and magnetic fields and realistic MLT-dependent outer particle sources. Starting with no initial particles, particles released from the RCM outer sources move along electric and magnetic drift paths and change energy adiabatically. Comparison of the observation with the simulation indicates that the particles along the open drift paths can account for the observed plasma sheet populations and that the observed significant MLT variations are a combined result of species- and energy-dependent drift and location-dependent source strength. The simulated energy and spatial distributions of the particles within closed drift paths are found to be consistent with the observed ring current particles. These ring current particles are originally plasma sheet particles which became trapped along closed paths due to temporal variations of drift paths. The good agreement in key features of the spatial distributions of thermal energy and energy fluxes between the RCM and observations clearly indicates that electric and magnetic drift transport and the associated energization play dominant roles in plasma sheet and ring current dynamics.

An innovative nanoprobe for magnetic immunoassay: Individual γ-Fe2O3 nanoparticles; towards high sensitive and multiparametric detection

A new type of nanolabels for magnetic immunoassays was designed using individual superparamagnetic γ-Fe 2O 3 nanoparticles. This innovative candidate is confronted here with commonly used micrometric beads. The innovative MIAplex ® technology allows to characterize and to quantify both types of labels with a competitive limit of detection. In this paper, we demonstrate the feasibility of multiparametric immunotests with the MIAplex ® technology. The carboxylic functions at the outer particle surface act as a precursor group for the covalent coupling of biological recognition molecules, such as antibodies, nucleic acids.

Multifunctional Mesoporous Silica Nanoparticles for Combined Therapeutic, Diagnostic and Targeted Action in Cancer Treatment

The main objective in the development of nanomedicine is to obtain delivery platforms for targeted delivery of drugs or imaging agents for improved therapeutic efficacy, reduced side effects and increased diagnostic sensitivity. A (nano)material class that has been recognized for its controllable properties on many levels is ordered mesoporous inorganic materials, typically in the form of amorphous silica (SiO2). Characteristics for this class of materials include mesoscopic order, tunable pore dimensions in the (macro)molecular size range, a high pore volume and surface area, the possibility for selective surface functionality as well as morphology control. The robust but biodegradable ceramic matrix moreover provides shelter for incorporated agents (drugs, proteins, imaging agents, photosensitizers) leaving the outer particle surface free for further modification. The unique features make these materials particularly amenable to modular design, whereby functional moieties and features may be interchanged or combined to produce multifunctional nanodelivery systems combining targeting, diagnostic, and therapeutic actions. This review covers the latest developments related to the use of mesoporous silica nanoparticles (MSNs) as nanocarriers in biomedical applications, with special focus on cancer therapy and diagnostics.

Modelling of the sulfuric acid leaching of mechanically activated titanite

A titanite CaTiSiO 5 concentrate was mechanically activated in a laboratory centrifugal-planetary mill for up to 10 min at dry and wet conditions. XRD analysis showed the weakening and broadening of diffraction peaks are mainly due to dry mechanical activation (MA) than due to wet MA. Leaching experiments were carried out using 30% H 2SO 4 at 20, 40, and 60 °C. Preliminary MA of titanite concentrate lead to significant increase in the leaching rate. Dry MA of titanite for 10 min resulted in ~ 90% Ti dissolved at 60 °C for 2.5 h. Leaching efficiency of unactivated titanite at similar conditions was about 1% Ti dissolved. Wet MA was found to be less effective than dry MA, despite the former attaining significantly larger surface area. This is due to greater degree of amorphization induced by dry MA in comparison to wet MA. In the suggested kinetic model an attempt was made to take into consideration the influence of BET surface area, amorphization of mineral and decrease in average energy stored by mineral due to MA in the course of leaching on the rate of dissolution. Small size crystallites and regions with large lattice strain which are typical of outer particle layers dissolve at a higher reaction rate. As the leaching time increases, the average degree of structure imperfections of the remaining powder decreases. Consequently, the average energy stored by mineral due to MA decreases and activation energy increases leading to decreasing the dissolution rate. The activation energy derived from the model indicates that the reaction of titanite with sulfuric acid is chemically controlled.

Numerical wave flume with improved smoothed particle hydrodynamics

This article presents an improved Nearest Neighboring Particle Searching (NNPS) technique for numerical modeling of water waves with the Smoothed Particle Hydrodynamics (SPH) method. The proposed technique differs from others by introducing the concept of Inner and Outer Particle Searching (IOPS) and shifting most of advanced CPU operations into simple addition operations. The IOPS method is shown to significantly improve the computational efficiency and reduce the CPU time especially for large number of particles, based on comparisons with other two NNPS methods. This method is implemented in a 2DV numerical wave flume conducted by the SPH method. Three test cases are examined, including generations and propagations of dam-breaking induced waves, solitary wave and irregular wave. Calculated results are in good agreements with experimental data and theoretical solutions with fairly satisfactory CPU time-consuming. The wave motions observed in physical facilities are successfully reproduced by the SPH numerical wave flume, revealing its robust capability of modeling realistic wave propagation and substantial potential for a wide variety of hydrodynamic problems.

Sintering and Formation of a Nonporous Carbonate Shell at the Surface of CaO-Based Sorbent Particles during CO2-Capture Cycles

The existence and formation of a carbonate shell at the surface of the particles of CaO-based sorbents is investigated in this paper. Two sorbents were tested: natural Kelly Rock (KR) limestone and synthetic pellets (KR-CA-14) prepared from the same limestone and calcium aluminate cement (CA-14). Various different series of calcination/carbonation cycles were carried out in a thermogravimetric analyzer (TGA) apparatus, and the sorbent samples produced after those cycles were analyzed with a scanning electron microscope (SEM). It is shown that sintering during cycles is more pronounced at the surface of sorbent particles, which results in the formation of nonporous areas or even a totally nonporous shell that surrounds a partially reacted CaO core. However, the dependency of shell formation upon cycle number is difficult to elucidate by SEM because increasing cycle numbers achieve lower conversion levels, which reduce the chance of shell formation. Prolonged carbonation after a series of cycles showed that there is a limit in maximum conversion levels, which cannot be solely explained by product layer formation at the interior sorbent surface area. The SEM images of samples after prolonged carbonation periods clearly show the presence of more sintered areas at the outer particle surface and/or carbonate shell/partially reacted particle pattern. This is explained by the phenomenon of more pronounced sintering at the sorbent particle surface than seen in the particle interior because of surface tension and more pronounced loss of pore volume near the exterior of the particle. The formation of a carbonate shell at the particle surface is a different phenomenon from that of the formation of a product layer at the pore surface area and also limits diffusion during carbonation.

Effects on the dynamic utilization of the adsorptive capacity of chromatographic columns induced by non‐uniform ligand density distributions

The dynamic behavior of the breakthrough curves of a single adsorbate obtained from columns employing adsorbent media which differ from one another only on the spatial distribution of the immobilized ligands in the porous particles is examined. The spatial distributions of the immobilized ligands considered in this study are uniform and non-uniform, but the total number of immobilized ligands in the particles has the same value whether the spatial distribution is uniform or non-uniform. The results clearly show that the columns employing adsorbent particles in which the spatial distribution of the immobilized ligands is non-uniform and such that the concentration of the immobilized ligands increases monotonically from the center of the particle to the outer particle surface, exhibit (i) larger breakthrough times, (ii) steeper breakthrough curves, and (iii) higher dynamic utilization of the adsorptive capacity of the column as the superficial velocity of the flowing fluid stream in the column increases (throughput increase) than the columns using adsorbent particles in which the spatial distribution of the immobilized ligands is uniform. The importance of employing in the columns adsorbent media whose spatial ligand density distributions satisfy the mathematical property of monotonically increasing ligand concentration with increasing from the particle center radial position, will be significantly enhanced when (i) the size of the particle radius is increased, and (ii) continuous counter-current and periodic counter-current (simulated moving beds) operations are employed.