Haitao Gao

Phase separated Cu@Fe3O4 heterodimer nanoparticles from organometallic reactants

Cu@Fe3O4 heteroparticles with distinct morphologies were synthesized from organometallic reactants. The shape of the magnetic domains could be controlled by the solvent and reaction conditions. They display magnetic and optical properties that are useful for simultaneous magnetic and optical detection. After functionalization, the Cu@Fe3O4 heterodimers become water soluble. The morphology, structure, magnetic and optical properties of the as-synthesized heterodimer nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), mossbauer spectroscopy, superconducting quantum interference device (SQUID) magnetometry, and dark field imaging. A special advantage of these heterodimers lies in the fact that the nanodomains of different composition can be used e.g. for the formation of nitric oxide (NO) through the Cu domain and heterodimer nanoparticles can be removed from the reaction mixture by means of the magnetic domain (Fe3O4).

Controlling phase formation in solids: rational synthesis of phase separated Co@Fe2O3 heteroparticles and CoFe2O4 nanoparticles

A wet chemical approach from organometallic reactants allowed the targeted synthesis of Co@Fe(2)O(3) heterodimer and CoFe(2)O(4) ferrite nanoparticles. They display magnetic properties that are useful for magnetic MRI detection.

Synthesis, characterization and functionalization of nearly mono-disperse copper ferrite CuxFe3−xO4 nanoparticles

Magnetic nanocrystals are of great interest for a fundamental understanding of nanomagnetism and for their technological applications. CuxFe3−xO4 nanocrystals (x ≈ 0.32) with sizes ranging between 5 and 7 nm were synthesized starting from Cu(HCOO)2 and Fe(CO)5 using oleic acid and oleylamine as surfactants. The nanocrystals were characterized by high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), magnetization studies and Mossbauer spectroscopy. The CuxFe3−xO4 particles are superparamagnetic at room temperature 300 K with a saturation magnetization of 30.5 emu g−1. Below their blocking temperature of 60 K, they become ferrimagnetic, and at 5 K they show a coercive field of 122 Oe and a saturation magnetization of 36.1 emu g−1. The CuxFe3−xO4 nanoparticles were functionalized using a hydrophilic multifunctional polymeric ligand containing PEG(800) groups and a fluorophore. By virtue of their magnetic properties these nanoparticles may serve as contrast enhancing agents for magnetic resonance imaging (MRI).

Self-assembled FeCo/gelatin nanospheres with rapid magnetic response and high biomolecule-loading capacity.

Properly functionalized magnetic nanocrystals (NCs) with small uniform size have attracted much attention for use in binding/immobilizing biomolecules including proteins, enzymes, DNA, and so on due to their huge accessible surface area. However, in many cases, small magnetic NCs only exhibit slow to moderate magnetic response for separation owing to their small sizes. It has been proved successful that, through the interactions of hydrogen bonding, electrostatic forces, and p–p interactions, different types of small primary nanocrystals can assemble into bigger densely assembled ordered nanomaterials. Once small magnetic NCs self-assemble into bigger ones, they demonstrate rapid magnetic response to external magnetic field during separation, albeit the reduced active surface area of the bigger nanomaterials lower the density of anchoring sites for targeted biomolecules, as compared to the small primary NCs. A simple yet effective approach to achieve the balance is to

Substitution Effects in Double Perovskites: How the Crystal Structure Influences the Electronic Properties

We systematically studied substituted Sr2FeReO6 with respect to experimental characterization and theoretical band structure calculations. In the framework of the tight-binding approach, hole- or electron-doping of Sr2MM’O6 were performed at the M or M’ positions either by transition or main group metals. Hole-doping, rather than electron-doping, has a favorable effect to improve the half-metallicity (Curie temperature and saturation magnetization) of the parent compound. When M is substituted by another metal, the original M’ metal will serve as a redox buffer (and vice versa). Substituting M by another metal with a size similar to that of the metal at M’ position causes disorder, which has high impact on the properties of the starting compound. Main group metals block the super-exchange pathways that underlie the half-metallic properties in Sr2FeReO6. Thus a Mott-insulating and spin-frustrated state is produced in an ordered phase due to the geometrical arrangement, e.g. in Sr2InReO6. However, M/M’ disorder is significant in the main group elements containing double perovskites, this triggers electronic conductivity arising from electron hopping from Re to adjacent Re ions as observed in Sr2GaReO6.