Synthesis and characterization of core-shell structure silica-coated Fe29.5Ni70.5 nanoparticles

In view of potential applications of magnetic particles in biomedicine and electromagnetic devices, we made use of the classical Stober method base-catalysed hydrolysis and condensation of tetraethoxysilane (TEOS) to encapsulate FeNi nanoparticles within a silica shell. An original stirring system under high power ultrasounds made possible to disperse the otherwise agglomerated particles. Sonication guaranteed particles to remain dispersed during the Stober synthesis and also improved the efficiency of the method. The coated particles are characterized by electron microscopy (TEM) and spectroscopy (EDX) showing a core-shell structure with a uniform layer of silica. Silica-coating does not affect the core magnetic properties. Indeed, all samples are ferromagnetic at 77 K and room temperature and the Curie point remains unchanged. Only the coercive force shows an unexpected non-monotonous dependence on silica layer thickness.Comment: Regular paper submited to international peer-reveiwed journa

Remote control of diffusion from magnetic hollow silica microspheres

Composite hollow core silica/iron oxide microparticles with the ability to store an encapsulated payload and release a defined quantity “on demand” by the application of a radiofrequency magnetic field were prepared. The microparticles possessed a mesoporous silica shell with iron oxide nanoparticles bound to the external silica surface by electrostatic interaction. The size, morphology and stability of the composite particles were systematically investigated and the effect of iron oxide:silica ratio on their heating rate and the release kinetics of a model compound (vitamin B12) was determined. The composite particles were stable in time and had a high heating ability in the radiofrequency magnetic field, achieving a temperature rise of several 10’s °C per minute. Thanks to the high heating rate, external radiofrequency field was shown to be an effective trigger mechanism for externally controlled diffusion of encapsulated material from within the hollow core at an arbitrary on-off sequence

Coating of upconversion nanoparticles with silica nanoshells of 5–250 nm thickness

A concept for the growth of silica shells with a thickness of 5–250 nm onto oleate-coated NaYF4:Yb3+/Er3+ upconversion nanoparticles (UCNP) is presented. The concept enables the precise adjustment of shell thicknesses for the preparation of thick-shelled nanoparticles for applications in plasmonics and sensing. First, an initial 5–11 nm thick shell is grown onto the UCNPs in a reverse microemulsion. This is followed by a stepwise growth of these particles without a purification step, where in each step equal volumes of tetraethyl orthosilicate and ammonia water are added, while the volumes of cyclohexane and the surfactant Igepal® CO-520 are increased so that the ammonia water and surfactant concentrations remain constant. Hence, the number of micelles stays constant, and their size is increased to accommodate the growing core–shell particles. Consequently, the formation of core-free silica particles is suppressed. When the negative zeta potential of the particles, which continuously decreased during the stepwise growth, falls below −40 mV, the particles can be dispersed in an ammoniacal ethanol solution and grown further by the continuous addition of tetraethyl orthosilicate to a diameter larger than 500 nm. Due to the high colloidal stability, a coalescence of the particles can be suppressed, and single-core particles are obtained. This strategy can be easily transferred to other nanomaterials for the design of plasmonic nanoconstructs and sensor systems

Colloidal Synthesis of Gold Semishells

This work describes a novel and scalable colloid chemistry strategy to fabricate gold semishells based on the selective growth of gold on Janus silica particles (500 nm in diameter) partly functionalized with amino groups. The modulation of the geometry of the Janus silica particles allows us to tune the final morphology of the gold semishells. This method also provides a route to fabricating hollow gold semishells through etching of the silica cores with hydrofluoric acid. The optical properties were characterized by visible near-infrared (vis-NIR) spectroscopy and compared with simulations performed using the boundary element method (BEM). These revealed that the main optical features are located beyond the NIR region because of the large core size

Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex

A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)3Si(OCH3)3]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)3] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 (+/-3 nm) or on mesoporous silica particles. The covalent bonding of Eu(TTA-Si)3 inside the core of uniform silica nanoparticles (40 (+/- 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen

Precious metal core-shell spindles

A simplified method to produce spindle-shaped particles with a hematite core and a silica shell is described. The silica shell can, in turn, serve as the substrate for an outer coating of Ag or Au nanoparticles. The resulting multilayer core-shell particles display a flexible optical extinction spectrum, due primarily to the sensitivity of their plasmon resonance to the morphology of the precious metal outer coating. © 2007 American Chemical Society

Synthesis and Characterization of Superparamagnetic Silica--Homopolypeptide Composite Particles

Hierarchical construction and characterization of core-shell composite particles of interest are presented. The research described shows interest in new types of polymers that provide chirality and responsiveness which have been ignored for so long. The general synthetic design described in this document can be readily used as a model for other systems. Core-shell composite systems of interest consist of silica or silica-coated cobalt cores grafted with a homopolypeptide shell, mostly poly(epsilon-carbobenzyloxy-L-lysine) or poly(gamma-benzyl-L-glutamate). Core particles were decorated with amino groups through a silylation reaction. The amino groups initiated the polymerization (with attachment) of N-carboxyanhydride (NCA) monomers, resulting in a homopolypeptide shell. Homopolypeptide-grafted particles were considered as hierarchical systems due to the two levels of responsiveness. The first level of responsiveness is due to the superparamagnetic nature of the core and the second level of responsiveness is through the thermally responsive polypeptide shell. Both levels of response were confirmed with several characterization methods. Characterization by electron microscopy and dynamic light scattering (DLS) confirmed the uniformity of the particles. Magnetic properties of the silica-coated cobalt core and polypeptide-grafted particles were investigated with a superconducting quantum interference device (SQUID). DLS and digital polarimeter demonstrated helix-coil transitions of the particles through continuous heating and cooling cycles in m-creso

Synthesis of Thermoresponsive Poly(N-isopropyl acrylamide) Based Core-Shell and Hollow Shell Nanogel with Tunable Core and Shell Thickness

Nanogels have emerged as a notably safer and more effective means for drug delivery, primarily due to their adjustable drug-loading capabilities. Hollow-core nanoparticles offer some unique properties that are desirable for drug delivery applications. Initially, silica core nanoparticles were synthesized using the Stöber process at different temperatures where Tetraethoxysilane (TEOS) undergoes hydrolysis in the presence of ethanol and then a condensation reaction to form silica nanoparticles. Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) analysis revealed that the size of silica core particles varied with the synthesis temperature (300 nm at 30°C to 150 at 60°C). The core silica particles were first coated with 3-(Trimethoxysilyl)propyl methacrylate (MPS) layers and used as seeds to grow ultra-low-cross linked thermoresponsive poly(N-isopropyl acrylamide) (NIPAm) shells using surfactant-free emulsion polymerization reaction. SEM and OM (differential contrast Interference Contrast) confirmed the addition of the NIPAm shell. The core was dissolved to get hollow shell nanogels. These hollow shell nanogels are very good candidates for drug delivery applications due to the presence of a hollow compartment in their structures

Synthesis, Characterization, and Applications of Responsive Polymer Brush-Grafted Particles

In this dissertation, I present the synthesis, characterization, and applications of responsive polymer brush-grafted silica/crosslinked polymeric particles. The polymer brush-grafted particles were synthesized by surface-initiated living /controlled radical polymerizations from initiator-functionalized particles in the presence of free initiators. Two types of core particles were used in my research. One was silica particles, which were synthesized by Stöber method. The other one was crosslinked PtBA particles, which were prepared by seeded emulsion polymerization. The responsive properties of the grafted polymer brushes were characterized with 1H NMR and Dynamic Light Scattering

Synthesis and application of silica particles for the removal of heavy metals and pesticide residues from aqueous solutions

In this study, the adsorption behavior of silica adsorbents with different morphology and porosity has been examined in order to evaluate their use for the purification of wastewaters containing toxic environmental chemicals such as heavy metals and pesticide residues. Three different types of silica particles were investigated: (i) microporous silica core particles prepared by the hydrolysis and condensation of tetraethylorthosilicate (TEOS), (ii) mesoporous silica particles generated by the neutralization of highly basic sodium silicate solution and (iii) silica core-shell particles composed of mesoporous silica layers around dense cores. Monodispersed spherical silica particles produced from TEOS have a microporous structure but the lowest adsorption efficiency and adsorption capacity of both heavy metals and pesticides. Polydispersed silica particles of irregular shape prepared from highly basic sodium silicate solution exhibit a mesoporous structure and high efficiency for the removal of heavy metals and pesticides from aqueous solutions. Monodispersed core-shell particles composed of a microporous core and a mesoporous shell also have high adsorption efficiencies in both combinations. Moreover, silica particles can be easily functionalized with ferrite nanoparticles, which allow the magnetic separation of silica adsorbents from aqueous solutions