Fabrication and Properties of Nanosized Material Made by Using Colloidal Assemblies as Templates

Crystallization in Confinement

Many crystallization processes of great importance, including frost heave, biomineralization, the synthesis of nanomaterials, and scale formation, occur in small volumes rather than bulk solution. Here, the influence of confinement on crystallization processes is described, drawing together information from fields as diverse as bioinspired mineralization, templating, pharmaceuticals, colloidal crystallization, and geochemistry. Experiments are principally conducted within confining systems that offer well-defined environments, varying from droplets in microfluidic devices, to cylindrical pores in filtration membranes, to nanoporous glasses and carbon nanotubes. Dramatic effects are observed, including a stabilization of metastable polymorphs, a depression of freezing points, and the formation of crystals with preferred orientations, modified morphologies, and even structures not seen in bulk. Confinement is also shown to influence crystallization processes over length scales ranging from the atomic to hundreds of micrometers, and to originate from a wide range of mechanisms. The development of an enhanced understanding of the influence of confinement on crystal nucleation and growth will not only provide superior insight into crystallization processes in many real-world environments, but will also enable this phenomenon to be used to control crystallization in applications including nanomaterial synthesis, heavy metal remediation, and the prevention of weathering.

Microemulsion based synthesis of Ni/MgO catalyst for dry reforming of methane

The dry reforming of methane has been investigated with two sets of catalysts (pure Ni and Ni/MgO) prepared by microemulsion system.

Unravelling the chemical design of spin-crossover nanoparticles based on iron(ii)-triazole coordination polymers: towards a control of the spin transition

A systematic study of the key synthetic parameters that control the growth of spin-crossover (SCO) nanoparticles (NPs) using the reverse micelle technique has been undertaken in the system [Fe(Htrz)2(trz)](BF4)·H2O, (Htrz = 1,2,4-triazole). This has permitted us to modulate the physical properties of the NPs in a controlled and reproducible manner. In particular, a control over the size of the NPs (in the range 4 to 16 nm) has been achieved by varying the water to surfactant molar ratio. The consequences of this size variation on the cooperativity of the spin transition are discussed. Finally, this approach has been extended to the chemical alloy [Fe(Htrz)2.95(NH2trz)0.05](ClO4)2 in order to prepare NPs exhibiting a cooperative and hysteretic spin transition centred closer to room temperature.

Trends in the synthesis of metal oxide nanoparticles through reverse microemulsions in hydrocarbon media

In recent years, more and more attention is given to production and use of nanoparticles dispersed in hydrocarbon medium and synthesized in reverse microemulsions. In this article the data and research results on synthesis of inorganic nanoparticles in reverse microemulsions are summarized. The major attention is paid to thermochemical approach for nanoparticle synthesis in reverse microemulsions with precursors of Мо, Al, Ni, Co and Fe oxides being active components of the catalysts for petroleum chemistry and refinery. A high efficiency of native crude oil surfactants for the production of catalyst nanoparticles in reverse microemulsions has been found.

Microemulsion-based synthesis of nanoscaled silver hollow spheres and direct comparison with massive particles of similar size

Nanoscale silver hollow spheres are first prepared via a microemulsion approach with 15-20 nm as the outer diameter, 3-5 nm as the wall thickness, and 10-15 nm as the diameter of the inner cavity. The presence of hollow spheres is confirmed by electron microscopy (SEM, BF-/HAADF-STEM, HRTEM) as well as by X-ray diffraction with a line-shape analysis to characterize the microcrystalline properties. In addition to the hollow spheres, massive silver nanoparticles of similar size (outer diameter of 15-20 nm) are gained via microemulsions. Based on the similarity of experimental conditions and the resulting particle size, as-prepared silver hollow spheres and massive nanoparticles are used to compare their optical properties and surface-plasmon resonance. In contrast to reducing the diameter of massive particles, "hollowing" of silver nanoparticles leads to a red-shift of the plasmon resonance. With a red shift of about 33 nm in the case of the hollow spheres, a quantum-size effect is indeed observed and in accordance with the thin sphere wall.

Recent advances in nanoparticle synthesis with reversed micelles

Synthesis of nanoparticles in microemulsions is an area of considerable current interest. This subject can be broadly divided into two sections defined by the nature of the host microemulsion reaction medium. Water-in-oil microemulsions have been used to prepare nanoparticles for more than two decades, and a wide variety of materials has been synthesised by these methods. Control parameters have been elucidated for influencing both nanoparticle concentration and morphology, allowing for tailored syntheses with various applications. More recently, the ability to synthesise nanoparticles in water/supercritical fluid microemulsions was realised. This method promises to be a highly useful route for controlled nanoparticle synthesis due to the added control variables afforded by tuneability of the solvent quality (density) through pressure and temperature. This review presents the current state-of-the-art in both fields.

Lipophilic porphyrin microparticles induced by AOT reverse micelles: a fluorescence lifetime imaging study

Fluorescence Lifetime Imaging Microscopy (FLIM) technique was applied to investigate the fluorescence dynamics and structural features of large colloidal aggregates of meso-tetra(N-dodecyl-4-amino sulfonyl-phenyl)porphyrin (PC12) induced by Sodium 1,4-bis(2-ethyl hexyl)sulfosuccinate (AOT) reverse micelles. The aggregate's particle sizes (down to 1 microm) obtained from the confocal fluorescence images matched with the particle sizes measured in the images obtained from Scanning Electron Microscopy (SEM). The fluorescence decays for those aggregates in the micro spatial domain show triexponential fluorescence lifetimes (tau1 approximately 12 ns, tau2 approximately 3 ns and tau3 approximately 1 ns) which are independent of the aggregate's size.

Existence and stability of new nanoreactors: highly swollen hexagonal liquid crystals

We report the preparation of direct hexagonal liquid crystals, constituted of oil-swollen cylinders arranged on a triangular lattice in water. The volume ratio of oil over water, rho can be as large as 3.8. From the lattice parameter measured by small-angle X-ray scattering, we show that all the oil is indeed incorporated into the cylinders, thus allowing the diameter of the cylinders to be controlled over one decade range, provided that the ionic strength of the aqueous medium and rho are varied concomitantly. These hexagonal swollen liquid crystals (SLCs) have been first reported with sodium dodecyl sulfate as anionic surfactant, cyclohexane as solvent, 1-pentanol as co-surfactant, and sodium chloride as salt (Ramos, L.; Fabre, P. Langmuir 1997, 13, 13). The stability of these liquid crystals is investigated when the pH of the aqueous medium or the chemical nature of the components (salt and surfactant) is changed. We demonstrate that the range of stability is quite extended, rendering swollen hexagonal phases potentially useful for the fabrication of nanomaterials. As illustrations, we finally show that gelation of inorganic particles in the continuous aqueous medium of a SLC and polymerization within the oil-swollen cylinders of a SLC can be conducted without disrupting the hexagonal order of the system.

Structure and catalytic properties of nanosized alumina supported platinum and palladium particles synthesized by reaction in microemulsion

Mixtures of nanosized platinum and palladium particles have been prepared by reduction of salt-containing microemulsion droplets using hydrazine as the reducing agent. To avoid possible negative effects of the presence of sulfur compounds during the preparation the microemulsion was made using the sulfur-free nonionic polyoxyethylene 4 lauryl ether surfactant. Transmission electron microscopy showed that the as-prepared mixtures contained crystalline platinum particles of fairly homogeneous size (20 to 40 nm) with adsorbed amorphous palladium particles 2 to 5 nm in size. Catalyst samples were prepared by depositing the nanoparticles on a gamma-Al(2)O(3) support followed by heating in air at 600 degrees C. Alloyed particles of platinum and palladium with sizes ranging from 5 to 80 nm were obtained during the heating. The majority of the particles had the fcc structure and their compositional range was dependent upon the Pt:Pd molar ratio of the microemulsion. A catalyst prepared from a microemulsion with a 20:80 Pt:Pd molar ratio showed the highest catalytic activity for CO oxidation, while pure platinum and palladium catalysts showed higher sulfur resistance. These results differ from the performance of conventional wet-impregnated catalysts, where a 50:50 Pt:Pd molar ratio resulted in the highest catalytic activity as well as the highest sulfur resistance.

Hot-fluid annealing for crystalline titanium dioxide nanoparticles in stable suspension

Titanium dioxide (TiO(2)) nanoparticles were synthesized by controlled hydrolysis of titanium alkoxide in reverse micelles in a hydrocarbon solvent. Upon annealing in situ in the presence of the micelles at temperatures considerably lower than those required for the traditional calcination treatment in the solid state, the TiO(2) nanoparticles became highly crystalline but still maintained the same physical parameters and remained in a stable suspension. Thus, the method has allowed the preparation of crystalline TiO(2) nanoparticles that are monodispersed in the same way as they are initially produced in the microemulsion. Effects of the fluid properties on the crystallization of nanoparticles are discussed.

Interaction of kappa-carrageenan with nickel, cobalt, and iron hydroxides

In a previous paper, it was shown that the functional polysaccharide kappa-carrageenan acts as an efficient stabilizer to prevent the precipitation of iron oxides and hydroxides up to very high pH values (Jones, et al. Colloid Polym. Sci. 2000, 278, 491-501). Here, this process was investigated for its application to synthesize stable cobalt and nickel oxide particles. Nickel hydroxide nanoparticles were well stabilized for long periods, while the hydroxide of cobalt(II), although initially stable at pH 13, progressively showed some complex structure rearrangement, invoked by alkaline oxidation of the primary particles. The final product of this oxidation/self-assembly process are spherical, fluffy superstructures of cobalt(III) oxide platelets with an overall diameter of 12 microns, in coexistence with 65-75% of free kappa-carrageenan.