Silica supported submicron SiO2@Y2SiO5 : Eu3+ and SiO2@Y2SiO5 : Ce3+/Tb3+ spherical particles with a core-shell structure: Sol-gel synthesis and characterization

X-1-y(2)SiO(5):Eu3+ and X-1-Y2SiO5:Ce3+ and/or Tb3+ phosphor layers have been coated on nonaggregated, monodisperse, submicron spherical SiO2 particles by a sol-gel process, followed by surface reaction at high temperature (1000 degrees C), to give core/shell structured SiO2@Y2SiO5:Eu3+ and SiO2@Y2SiO5:Ce3+/Tb3+ particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), TEM, photoluminescence (PL), low voltage cathodoluminescence (CL), and time-resolved PL spectra and lifetimes are used to characterize these materials. The XRD results indicate that X-1-Y2SiO5 layers have been successfully coated on the sur- face Of SiO2 particles, as further verified by the FESEM and TEM images. The PL and CL studies suggest that SiO2@Y2SiO5:Eu3+, SiO2@Y2SiO5:Tb3+ (or Ce3+/Tb3+), and SiO2@Y2SiO5:Ce3+ core/shell particles exhibit red (Eu3+, 613 rim: D-5(0)-F-7(2)), green (Tb3+, 542nm: D-5(4)-F-7(5)), or blue (Ce3+, 450nm: 5d-4f) luminescence, respectively. Pl, excitation, emission, and time-resolved spectra demonstrate that there is an energy transfer from Ce3+ to Tb3+ in the SiO2@Y2SiO5:Ce3+,Tb3+ core/shell particles.

Monodisperse spherical core-shell structured SiO2-CaTiO3 : Pr3+ phosphors for field emission displays

Nanocrystalline CaTiO3:Pr3+ phosphor layers were coated on nonaggregated, monodisperse, and spherical SiO2 particles by the sol-gel method, resulting in the formation of core-shell structured SiO2-CaTiO3:Pr3+ particles. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO2-CaTiO3:Pr3+ phosphor particles. The obtained core-shell structured phosphors consist of well dispersed submicron spherical particles with a narrow size distribution. The thickness of the CaTiO3:Pr3+ shell could be easily controlled by changing the number of deposition cycles (about 70 nm for four deposition cycles). The core-shell SiO2-CaTiO3:Pr3+ particles show a strong red emission corresponding to D-1(2)-H-3(4) (612 nm) of Pr3+ under the excitation of ultraviolet (326 nm) and low voltage electron beams (1-5 kV). These particles may be used in field emission displays.

Luminescence properties of sol-gel derived spherical SiO2@Gd-2(WO4)(3): Eu3+ particles with core-shell structure

Monodisperse, core-shell structured SiO2@Gd-2(WO4)(3):Eu3+ particles were prepared by the sol-gel method. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy, photoluminescence (PL) and low-voltage cathodoluntinescence (CL). PL and CL study revealed that the core-shell structured SiO2@Gd-2(WO4)(3):Eu3+ particles show strong red emission dominated by the D-5(0)-F-7(2) transition of Eu3+ at 615 nm with a lifetime of 0.89 ins. The PL and CL emission intensity can be tuned by the coating number of Gd-2(WO4)(3):Eu3+ phosphor layers on SiO2 particles, the size of the SiO2 core particles, and by accelerating voltage and the filament current, respectively.

Surface Functionalization of Monodisperse Magnetic Nanoparticles

We present a systematic methodology to functionalize magnetic nanoparticles through surface-initiated atom-transfer radical polymerization (ATRP). The magnetite nanoparticles are prepared according to the method proposed by Sun et al. (2004), which leads to a monodisperse population of ~ 6 nm particles stabilized by oleic acid. The functionalization of the nanoparticles has been performed by transforming particles into macro-initiators for the ATRP, and to achieve this two different routes have been explored. The first one is the ligand-exchange method, which consists of replacing some oleic acid molecules adsorbed on the particle surface with molecules that act as an initiator for ATRP. The second method consists in using the addition reaction of bromine to the oleic acid double bond, which turns the oleic acid itself into an initiator for the ATRP. We have then grown polymer brushes of a variety of acrylic polymers on the particles, including polyisopropylacrylamide and polyacrylic acid. The nanoparticles so functionalized are water soluble and show responsive behavior: either temperature responsive behavior when polyisopropylacrylamide is grown from the surface or PH responsive in the case of polyacrylic acid. This methodology has potential applications in the control of clustering of magnetic nanoparticles.

Monodisperse binary nanocomposite in silica with enhanced magnetization for magnetic separation

The majority of research on magnetic nanoparticles has focused on optical, electrical, and magnetic storage areas. Recently, the application of magnetic nanoparticles as magnetically separable nanovehicles for chemical or biological species has become an area of intensive research but with rather different challenging criteria that are yet to be addressed. For example, the enhancement of intrinsically weak magnetic properties, avoidance of magnetic interactions among particles, and improvement of the stability of the nanoparticles remain key issues. Here, it is demonstrated using sequential nanochemistry preparation techniques that exchange-coupled nanomagnets, such as FePt-Fe3Pt or FePt-Fe3O4 with dramatically enhanced magnetization, can be placed inside a silica nanosphere. The advantages of enhanced magnetization and the provision of protective coating and anchored sites on the silica shell surface render these new coated particles suitable for use in magnetic separation.

Designer synthesis of monodisperse heterodimer and ferrite nanoparticles

The work presented in this doctoral thesis is a facile procedure, thermal decomposition, forrnthe synthesis of different types of monodisperse heterodimer M@iron oxide (M= Cu, Co, Nirnand Pt) and single ferrites, MFe2O4 (M= Cu and Co), nanoparticles. In the following chapter,rnwe study the synthesis of these monodiperse nanoparticles with the similar iron precursorrn(iron pentacarbonyl) and different transition metal precursors such as metalrnacetate/acetylacetonate/formate precursors in the presence of various surfactants and solvents.rnAccording to their decomposition temperatures and reducing condition, a specific and suitablernroute was designed for the formation of Metal@Metal oxide or MFe2O4 nanoparticlesrn(Metal/M=transition metal).rnOne of the key purposes in the formation of nanocrystals is the development of syntheticrnpathways for designing and controlling the composition, shape and size of predictedrnnanostructures. The ability to arrange different nanosized domains of metallic and magneticrnmaterials into a single heterodimer nanostructure offers an interesting direction to engineerrnthem with multiple functionalities or enhanced properties of one domain. The presence andrnrole of surfactants and solvents in these reactions result in a variety of nanocrystal shapes. Therncrystalline phase, the growth rate and the orientation of growth parameters along certainrndirections of these structures can be chemically modulated by using suitable surfactants. In allrnnovel reported heterodimer nanostructures in this thesis, initially metals were preformed andrnthen by the injection of iron precursor in appropriate temperature, iron oxide nanoparticlesrnwere started to nucleate on the top or over the surfaces of metal nanoparticles. Ternary phasesrnof spherical CuxFe3-xO4 and CoFe2O4 ferrites nanoparticles were designed to synthesis just byrnlittle difference in diffusion step with the formation of mentioned phase separated heterodimerrnnanoparticles. In order to use these magnetic nanoparticles in biomedical and catalysisrnapplications, they should be transferred into the water phase solution, therefore they werernfunctionalized by a multifunctional polymeric ligand. These functionalized nanoparticles werernstable against aggregation and precipitation in aqueous media for a long time. Magneticrnresonance imaging and catalytic reactivities are two promising applications which have beenrnutilized for these magnetic nanoparticles in this thesis.rnThis synthetic method explained in the following chapters can be extended to the synthesis ofrnother heterostructured nanomaterials such as Ni@MnO or M@M@iron oxide (M=transitionrnmetal) or to use these multidomain particles as building blocks for higher order structures.

Unexpected Polymorphism and Unique Particle Morphologies from Monodisperse Droplet Evaporation

The particle sizes, morphologies, and structures are presented for succinic acid particles formed from the evaporation of uniform droplets created with a vibrating orifice aerosol generator. Particle sizes are monodisperse, and solvent choice is found to be the dominant factor in determining the final morphology and structure. The external particle morphologies range from round to cap shaped, while the surface roughness ranges from fairly smooth to extremely rough and pitted. Internally, the particles have significant void space and noticeable crystals. X-ray diffraction confirms that the particles are crystalline. Thus, the morphologies of the particles take on a crystal filled structure that is unique in comparison to previous particles formed through droplet evaporation. The structure of the particles contains β succinic acid; however, the particles formed from water also contain α succinic acid. α Succinic acid has not previously been able to be formed from solution at near atmospheric conditions. The unique morphologies and ability to identify unexpected polymorphs provide for a potential tool to not only enhance particle engineering but also to identify metastable polymorphs.

Dynamics of settling charged particles in turbulence : theory and experiments

It has been proposed that inertial clustering may lead to an increased collision rate of water droplets in clouds. Atmospheric clouds and electrosprays contain electrically charged particles embedded in turbulent flows, often under the influence of an externally imposed, approximately uniform gravitational or electric force. In this thesis, we present the investigation of charged inertial particles embedded in turbulence. We have developed a theoretical description for the dynamics of such systems of charged, sedimenting particles in turbulence, allowing radial distribution functions to be predicted for both monodisperse and bidisperse particle size distributions. The governing parameters are the particle Stokes number (particle inertial time scale relative to turbulence dissipation time scale), the Coulomb-turbulence parameter (ratio of Coulomb ’terminalar speed to turbulence dissipation velocity scale), and the settling parameter (the ratio of the gravitational terminal speed to turbulence dissipation velocity scale). For the monodispersion particles, The peak in the radial distribution function is well predicted by the balance between the particle terminal velocity under Coulomb repulsion and a time-averaged ’drift’ velocity obtained from the nonuniform sampling of fluid strain and rotation due to finite particle inertia. The theory is compared to measured radial distribution functions for water particles in homogeneous, isotropic air turbulence. The radial distribution functions are obtained from particle positions measured in three dimensions using digital holography. The measurements support the general theoretical expression, consisting of a power law increase in particle clustering due to particle response to dissipative turbulent eddies, modulated by an exponential electrostatic interaction term. Both terms are modified as a result of the gravitational diffusion-like term, and the role of ’gravity’ is explored by imposing a macroscopic uniform electric field to create an enhanced, effective gravity. The relation between the radial distribution functions and inward mean radial relative velocity is established for charged particles.

Elasto-plastic impact of fine particles and fragmentation of small agglomerates

Surface deposition of dense aerosol particles is of major concern in the nuclear industry for safety assessment. This study presents theoretical investigations and computer simulations of single gas-born U3O8 particles impacting with the in-reactor surface and the fragmentation of small agglomerates. A theoretical model for elasto-plastic spheres has been developed and used to analyse the force-displacement and force-time relationships. The impulse equations, based on Newton's second law, are applied to govern the tangential bouncing behaviour. The theoretical model is then incorporated into the Distinct Element Method code TRUBAL in order to perform computer simulated tests of particle collisions. A comparison of simulated results with both theoretical predictions and experimental measurements is provided. For oblique impacts, the results in terms of the force-displacement relationship, coefficients of restitution, trajectory of the impacting particle, and distribution of kinetic energy and work done during the process of impact are presented. The effects of Poisson's ratio, friction, plastic deformation and initial particle rotation on the bouncing behaviour are also discussed. In the presence of adhesion an elasto-plastic collision model, which is an extension to the JKR theory, is developed. Based on an energy balance equation the critical sticking velocity is obtained. For oblique collisions computer simulated results are used to establish a set of criteria determining whether or not the particle bounces off the target plate. For impact velocities above the critical sticking value, computer simulated results for the coefficients of restitution and rebound angles of the particle are presented. Computer simulations of fracture/fragmentation resulting from agglomerate-wall impact have also been performed, where two randomly generated agglomerates (one monodisperse, the other polydisperse), each consisting of 50 primary particles are used. The effects of impact angle, local structural arrangements close to the impact point, and plastic deformation at the contacts on agglomerate damage are examined. The simulated results show a significant difference in agglomerate strength between the two assemblies. The computer data also shows that agglomerate damage resulting from an oblique impact is determined by the normal velocity component rather than the impact speed.

Diesel bus emissions of submicrometer particles measured in a tunnel study

The emission factors of a bus fleet consisting of approximately three hundreds diesel powered buses were measured in a tunnel study under well controlled conditions during a two-day monitoring campaign in Brisbane. The number concentration of particles in the size range 0.017-0.7 m was monitored simultaneously by two Scanning Mobility Particle Sizers located at the tunnel’s entrance and exit. The mean value of the number emission factors was found to be (2.44±1.41)×1014 particles km-1. The results are in good agreement with the emission factors determined from steady-state dynamometer testing of 12 buses from the same Brisbane City bus fleet, thus indicating that when carefully designed, both approaches, the dynamometer and on-road studies, can provide comparable results, applicable for the assessment of the effect of traffic emissions on airborne particle pollution.

Indoor exposure to submicrometer particles and PM2.5 in residential houses in Brisbane, Australia

As part of a large study investigating indoor air in residential houses in Brisbane, Australia, the purpose of this work was to quantify indoor exposure to submicrometer particles and PM2.5 for the inhabitants of 14 houses. Particle concentrations were measured simultaneously for more than 48 hours in the kitchens of all the houses by using a condensation particle counter (CPC) and a photometer (DustTrak). The occupants of the houses were asked to fill in a diary, noting the time and duration of any activity occurring throughout the house during measurement, as well as their presence or absence from home. From the time series concentration data and the information about indoor activities, exposure to the inhabitants of the houses was calculated for the entire time they spent at home as well as during indoor activities resulting in particle generation. The results show that the highest median concentration level occurred during cooking periods for both particle number concentration (47.5´103 particles cm-3) and PM2.5 concentration (13.4 mg m-3). The highest residential exposure period was the sleeping period for both particle number exposure (31%) and PM2.5 exposure (45.6%). The percentage of the average residential particle exposure level in total 24h particle exposure level was approximating 70% for both particle number and PM2.5 exposure.

Relationship between indoor/outdoor concentrations of particles : a critical review

The relationship between indoor and outdoor concentration levels of particles in the absence and in the presence of indoor sources has been attracting an increasing level of attention. Understanding of the relationship and the mechanisms driving it, as well as the ability to quantify it, are of importance for assessment of source contribution, assessment of human exposure and for control and management of particles. It became particularly important to address this topic when evidence came from epidemiological studies on the close association between outdoor concentration levels of particles and health effects, yet with many studies showing that indoor concentrations could be significantly higher than those outdoors. This paper presents a summary of an extensive literature review on this topic conducted with an aim to identify general trends in relation to the I/O relationship emerging from studies conducted worldwide. The review considered separately a larger body of papers published on PM10, PM2.5, as well as the smaller database on particle number and number or volume size distribution. A specific focus of this paper is on naturally ventilated houses. The conclusion from the review is that despite the multiplicity of factors that play role in affecting the relationship, there are clear trends emerging in relation to the I/O relationship for particle mass concentration, enabling more general predictions to be made about the relationship. However, more research is still needed on particle number concentration and size distribution.