1. Introduction 20642. Synthesis of Magnetic Nanoparticles 20662.1. Classical Synthesis by Coprecipitation 20662.2. Reactions in Constrained Environments 20682.3. Hydrothermal and High-TemperatureReactions20692.4. Sol-Gel Reactions 20702.5. Polyol Methods 20712.6. Flow Injection Syntheses 20712.7. Electrochemical Methods 20712.8. Aerosol/Vapor Methods 20712.9. Sonolysis 20723. Stabilization of Magnetic Particles 20723.1. Monomeric Stabilizers 20723.1.1. Carboxylates 20733.1.2. Phosphates 20733.2. Inorganic Materials 20733.2.1. Silica 20733.2.2. Gold 20743.3. Polymer Stabilizers 20743.3.1. Dextran 20743.3.2. Polyethylene Glycol (PEG) 20753.3.3. Polyvinyl Alcohol (PVA) 20753.3.4. Alginate 20753.3.5. Chitosan 20753.3.6. Other Polymers 20753.4. Other Strategies for Stabilization 20764. Methods of Vectorization of the Particles 20765. Structural and Physicochemical Characterization 20785.1. Size, Polydispersity, Shape, and SurfaceCharacterization20795.2. Structure of Ferro- or FerrimagneticNanoparticles20805.2.1. Ferro- and Ferrimagnetic Nanoparticles 20805.3. Use of Nanoparticles as Contrast Agents forMRI20825.3.1. High Anisotropy Model 20845.3.2. Small Crystal and Low Anisotropy EnergyLimit20855.3.3. Practical Interests of Magnetic NuclearRelaxation for the Characterization ofSuperparamagnetic Colloid20855.3.4. Relaxation of Agglomerated Systems 20856. Applications 20866.1. MRI: Cellular Labeling, Molecular Imaging(Inﬂammation, Apoptose, etc.)20866.2.

Magnetic Iron Oxide Nanoparticles: Synthesis, Stabilization, Vectorization, Physicochemical Characterizations, and Biological Applications

Sol-gel chemistry of transition metal oxides

Controlled self-organization of nanoparticles can lead to new materials. The colloidal crystallization of non-spherical nanocrystals is a reaction channel in many crystallization reactions. With additives, self-organization can be stopped at an intermediary step-a mesocrystal-in which the primary units can still be identified. Mesocrystals were observed for various systems as kinetically metastable species or as intermediates in a crystallization reaction leading to single crystals with typical defects and inclusions. The control forces and mechanism of mesocrystal formation are largely unknown, but several mesocrystal properties are known. Mesocrystals are exiting examples of nonclassical crystallization, which does not proceed through ion-by-ion attachment, but by a modular nanobuilding-block route. This path makes crystallization more independent of ion products or molecular solubility, it occurs without pH or osmotic pressure changes, and opens new strategies for crystal morphogenesis.

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Mesocrystals: Inorganic superstructures made by highly parallel crystallization and controlled alignment

Developments in water gas shift (WGS) catalysis, especially during the last decade, are reviewed. Recent developments include the development of 1 chromium‐free catalysts that can operate at lower steam to gas ratios and 2 more active catalysts that can operate at gas hourly space velocities above 40,000 h−1. A current challenge is to develop catalysts for use in fuel cell applications. Precious metal catalysts supported on partially reducible oxide supports (Pt‐ceria, Pt‐titania, Au‐ceria, etc.) are the current front runners. A critical review of the mechanism of the WGS reaction is also presented.

Water Gas Shift Catalysis

A number of unusual electromagnetic scattering effects for magnetic spheres are described. When ∊ = μ, the backscatter gain is zero; the scattered radiation is polarized in the same sense as the incident radiation. In the small-particle (or long-wavelength) limit, conditions are described for zero forward scatter, for complete polarization of scattered radiation in other directions, and for asymmetry of forward scatter to backscatter. The special case in the small-particle limit of m = 1, i.e., μ = 1/∊, provides interesting special instances of complete polarization and forward-scatter-to-backscatter asymmetry.

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Electromagnetic scattering by magnetic spheres

The methods of preparation of ferric hydrous oxide sots consisting of particles, uniform in shape, of narrow size distribution are described in detail. To produce such sots, acidic solutions, containing ferric ions and nitrate, perchlorate, or chloride ions, respectively, were aged at elevated temperatures for times ranging from a few hours to a few weeks. Solids formed from the solutions containing chloride consisted of either β-FeOOH or α-Fe2O3 depending on the concentration of ferric and chloride ions, whereas particles generated in solutions containing nitrate or perchlorate ions consisted of α-Fe2O3. Particle shape varied greatly as the conditions of colloid preparation were altered. It was possible to produce systems consisting of cubic, ellipsoidal, pyramidal, rodlike, and spherical particles. Such dispersions differed greatly in color. Complete domains are given in terms of ferric salt and corresponding acid concentrations which delineate regions of particle formation of given chemical composition and shape. Electrokinetic measurements show relatively small difference in point of zero charge for the various sots studied.

Ferric hydrous oxide sols

A light scattering method is described which permits determination of the absorption index of colloidal particles. This technique requires transmission and scattering measurements but not particle size information provided that the particles are small compared to the wavelength (Rayleigh scatterers). It has been applied to hematite (α - Fe 2 O 3 ) pigment particles over the visible wavelengths. The results were checked by comparing measured values of the Rayleigh ratio for a dispersion of larger particles of known particle size distribution with calculations based upon the newly determined absorption index. The agreement was within the experimental error. When literature values of the absorption index were used in such calculations, there were significant differences from the measured values. Color calculations based upon tristimulus color theory which utilized the new values of the absorption index agreed with qualitative observation of color, both in dilute sols where single scattering predominates and in multiply scattering concentrated sols.

Absorption index and color of colloidal hematite

The small-particle limit for scattering by spheres (Rayleigh scattering) has an upper limit on the refractive index. Also, the limiting expression for perfectly reflecting spheres has a lower limit on the refractive index. These limits are delineated here for both absorbing and nonabsorbing spheres.

Paul Scheiner

Papers

Ferric hydrous oxide sols

Absorption index and color of colloidal hematite

The range of validity of the Rayleigh and Thomson limits for Lorenz-Mie scattering