Zheng-Guang Yan

Large-Scale Synthesis of Single-Crystalline Iron Oxide Magnetic Nanorings

We present an innovative approach to the production of single-crystal iron oxide nanorings employing a solution-based route. Single-crystal hematite (alpha-Fe2O3) nanorings were synthesized using a double anion-assisted hydrothermal method (involving phosphate and sulfate ions), which can be divided into two stages: (1) formation of capsule-shaped alpha-Fe2O3 nanoparticles and (2) preferential dissolution along the long dimension of the elongated nanoparticles (the c axis of alpha-Fe2O3) to form nanorings. The shape of the nanorings is mainly regulated by the adsorption of phosphate ions on faces parallel to c axis of alpha-Fe2O3 during the nanocrystal growth, and the hollow structure is given by the preferential dissolution of the alpha-Fe2O3 along the c axis due to the strong coordination of the sulfate ions. By varying the ratios of phosphate and sulfate ions to ferric ions, we were able to control the size, morphology, and surface architecture to produce a variety of three-dimensional hollow nanostructures. These can then be converted to magnetite (Fe3O4) and maghemite (gamma-Fe2O3) by a reduction or reduction-oxidation process while preserving the same morphology. The structures and magnetic properties of these single-crystal alpha-Fe2O3, Fe3O4, and gamma-Fe2O3 nanorings were characterized by various analytical techniques. Employing off-axis electron holography, we observed the classical single-vortex magnetic state in the thin magnetite nanorings, while the thicker rings displayed an intriguing three-dimensional magnetic configuration. This work provides an easily scaled-up method for preparing tailor-made iron oxide nanorings that could meet the demands of a variety of applications ranging from medicine to magnetoelectronics.

Controlled synthesis of rare earth nanostructures

Rare earth compounds form a large family of functional materials with diverse applications in electric, magnetic, optical, and catalytic fields, originating from their unique 4f electrons. Rare earth nanocrystals stir significant interest with their special properties, such as reliable optical applications and enhanced catalytic performances, allowing them to serve as building blocks to construct functional assemblies. In this feature article, we highlight recent works on controlled synthesis of rare earth nanostructures through solution-based routes such as hydrothermal/solvothermal methods and precipitation in high-boiling solvents. Various rare earth nanostructures are obtained both by rationally utilizing intrinsic crystal structures and by fine tuning of experimental conditions, such as temperature, acidity, and capping agents. The controlled phase, crystal growth process, and post-treatment are briefly discussed with typical examples. Rare earth nanocrystals exhibit a variety of shapes and thus are of great benefit for the construction of nanocrystal superlattices. Through the simulation of coarse-grained molecular dynamics, the nanocrystals superstructures are also modelled.

Highly luminescent self-organized sub-2-nm EuOF nanowires.

Monodisperse sub-2-nm EuOF nanowires were obtained by manipulating the fluorophilicity between crystalline seeds and capping surfactant molecules during the thermolysis of Eu(CF(3)COO)(3) in oleic acid (OA) and oleylamine (OM). The uniform EuOF nanowires can self-organize on substrates to form parallel aligned superstructures and display strong Eu(3+)red emissions with high quantum yields of 65% under the UV light excitations due to the presence of dense surface Eu(3+) sites in the ultrathin nanowires as well as the passivation of the surface defects by the capping ligands.

Magnetic and magnetotransport properties of Fe2P nanocrystallites via a solvothermal route

Hexagonal nanocrystalline Fe2P has been synthesized via a solvothermal route at a relatively low temperature of 180 °C. X-Ray diffraction (XRD), X-ray photoelectron spectra (XPS) and transmission electron microscopy (TEM) were used to investigate the phase, composition, and morphology of the final crystallized product. The particles with a uniform hexagonal structure are stable in air and their size is in the range of 100–120 nm. A magnetoresistance effect is observed at comparatively low temperatures, which originates from the spin polarized tunneling effect. The super-paramagnetic state transformation can be found at the blocking temperature in Fe2P nanoparticles, further confirmed by electron spin resonance (ESR) experiments. Metamagnetic behavior is also observed in nanocrystalline Fe2P with variation of field because of the coexistence of ferromagnetic and super-paramagnetic states.

(ZrO2)0.85(REO1.5)0.15 (RE=Sc, Y) solid solutions prepared via three Pechini-type gel routes: 1—gel formation and calcination behaviors

Abstract (ZrO 2 ) 0.85 ( RE O 1.5 ) 0.15 ( RE =Sc, Y) nanoparticles with pure cubic fluorite structure have been synthesized by three Pechini-type gel routes, viz . poly(vinyl alcohol) containing-process (route I), poly(ethylene glycol) and formic acid-containing process (route II), and in situ polymerizable complex method (route III). The coordination modes between metal ions and polymers in the gels are shown to be highly correlative with the synthesis route used. The gels prepared by route III have the strongest coordination throughout their network and therefore the best chemical homogeneity. The altered variety of polymer and cross-linking within the gels adopted by these three routes has made the as-synthesized samples show appreciable differences in thermal behavior, powder reactivity and nanoparticle properties.

Luminescence Resonance Energy Transfer Sensors Based on the Assemblies of Oppositely Charged Lanthanide/Gold Nanoparticles in Aqueous Solution

This work demonstrates luminescence resonance energy transfer (LRET) sensors based on lanthanide-doped nanoparticles as donors (D) and gold nanoparticles as acceptors (A), combined through electrostatic interactions between the oppositely charged nanoparticles. Negatively charged lanthanide-doped nanoparticles, YVO(4):Eu and LaPO(4):Ce,Tb, with high luminescence quantum yield and good water-solubility, are synthesized through a polymer-assisted hydrothermal method. Positively charged polyhedral and spherical gold nanoparticles exhibit surface plasmon resonance (SPR) bands centered at 623 and 535 nm, respectively. These bands overlap well with the emission of the Eu(3+) and Tb(3+) ions within the lanthanide nanoparticles. Herein, the gold nanoparticles are synthesized through a seed-mediated cetyltrimethylammonium bromide (CTAB)-assisted method. The assemblies of the oppositely charged donors and acceptors are developed into LRET-based sensors exhibiting a donor quenching efficiency close to 100 %.

Chapter 251 – Controlled Synthesis and Properties of Rare Earth Nanomaterials

Rare earth nanomaterials with nanometer to submicronmeter crystalline sizes are an important class of materials displaying interesting physical and chemical properties especially in luminescence and catalysis fields. In the last decade, the synthetic chemistry and exploring of novel properties on rare earth nanomaterials have been developed rapidly. This review on the topic of controlled synthesis and properties of rare earth nanomaterials should be useful with these literatures mostly up to 2009. The discussion focuses on the controlled synthesis of nanomaterials of inorganic rare earth compounds such as rare earth oxides, oxysalts, halogenides, chalcogenides, and therefore organized according to the different compounds discussed here. The successfully developed solution-based chemical methods, such as traditional sol—Cgel methods, combustion/flaming/pyrolysis methods hydrothermal/solvothermal methods, and those with modifications assisted with microwave radiation and sonochemical methods, the high boiling solvents-based heat treatment methods, and much more have been applied to the controlled synthesis of rare earth compound nanomaterials. Based on the well-developed controlling of pure phase, uniform size and shape, desired doping and composite structure, the rare earth nanocrystals show much more properties and promising application, such as in the medical fields, the energy conversion, pollution controlling, and various displays, which are also mentioned. With the newly developed techniques in top-down and bottom-up strategies for nanomaterials, it is reasonable to anticipate more rational and sophisticated rare earth nanostructures as well as their advanced applications in the future.

(ZrO2)0.85(REO1.5)0.15 (RE=Sc, Y) solid solutions prepared via three Pechini-type gel routes: 2—sintering and electrical properties

Dense (ZrO 2 ) 0.85 (REO 1.5 ) 0.15 (RE = Sc, Y) specimens have been obtained from the nanoparticulate powders prepared by three Pechini-type gel routes, viz. poly(vinyl alcohol) (PVA) containing-process (route I), poly(ethylene glycol) and formic acid-containing process (route II), and in situ polymerizable complex method (route III). During sintering over 1000-1400°C, (ZrO 2 ) 0.85 (ScO 1.5 ) 0.15 samples prepared by routes II and III, and (ZrO 2 ) 0.85 (YO 1.5 ) 0.15 samples prepared by the three routes retain pure cubic fluorite structure, however, a monoclinic phase segregation takes place for the Sc-doped zirconia prepared by route I. Various gel routes are shown to display significant impact on sinterability of the green body, crystallinity and particle size uniformity of the sintered body, and the ionic conductivity of the dense specimens. The specimens prepared from route III exhibit superior sinterability and ionic conductance to those prepared from routes I and II.