Van Hong Le

Facile and solvent-free routes for the synthesis of size-controllable Fe 3 O 4 nanoparticles

Magnetite nanoparticles are one of the most important materials that are widely used in both medically diagnostic and therapeutic research. In this paper, we present some facile and non-toxic synthetic approaches for size-controllable preparations of magnetite nanoparticles, which are appropriate for biomedical applications, namely (i) co-precipitation; (ii) reduction‐precipitation and (iii) oxidation‐precipitation. Magnetic characterizations of the obtained nanoparticles have been studied and discussed. The oxidation precipitation route was chosen for investigation of the dependence of kinetic driven activation energy and that of coercive force on particle size (and temperature) during the course of the reaction. The structural‐magnetic behavior was also correlated. Being solvent and surfactant-free, these methods are advantageous for synthesis and further functionalization towards biomedical applications.

Biomedical and environmental applications of magnetic nanoparticles

This paper presents an overview of syntheses and applications of magnetic nanoparticles (MNPs) at the Institute of Materials Science, Vietnam Academy of Science and Technology. Three families of oxide MNPs, magnetite, manganite and spinel ferrite materials, were prepared in various ways: coprecipitation, sol?gel and high energy mechanical milling. Basic properties of MNPs were characterized by Vibrating Sample Magnetometer (VSM) and Physical Properties Measurement Systems (PPMS). As for biomedical application, the aim was to design a novel multifunctional, nanosized magnetofluorescent water-dispersible Fe3O4-curcumin conjugate, and its ability to label, target and treat tumor cells was described. The conjugate possesses a magnetic nano Fe3O4 core, chitosan (CS) or Oleic acid (OL) as an outer shell and entrapped curcumin (Cur), serving the dual function of naturally autofluorescent dye as well as antitumor model drug. Fe3O4-Cur conjugate exhibited a high loading cellular uptake with the help of a macrophage, which was clearly visualized dually by Fluorescence Microscope and Laser Scanning Confocal Microscope (LSCM), as well as by magnetization measurement (PPMS). A preliminary magnetic resonance imaging (MRI) study also showed a clear contrast enhancement by using the conjugate. As for the environmental aspect, the use of magnetite MNPs for the removal of heavy toxic metals, such as Arsenic (As) and Lead (Pb), from contaminated water was studied.

The effect of artificial boundary grain on the magneto- and electro-transport properties of (1 − x)La0.7Ca0.3MnO3+xA (A=Al2O3 and Ag) nanocomposite

The magneto- and electro-transport properties of two series of nanocrystalline (1−x)La0.7Ca0.3MnO3+xA (A: Al2O3 and Ag) composites have been systematically and thoroughly studied. The observed electronic transport behavior over the whole temperature range (5–300 K), especially the change in metal–insulator transition temperature with increasing Al2O3 and Ag content while the ferromagnetic–paramagnetic transition remained unaffected, was explained by applying a two-component phenomenological model. We have attributed the unusual low-temperature resistivity upturn of composites to a change in charging energy. Most interestingly, magneto-transport measurements showed that the low-field magnetoresistance (LFMR), as well as the high-field magnetoresistance (HFMR), displayed a Curie–Weiss-like law behavior. Basing on the spin-polarized transport of conduction electrons at the grain boundaries, we have analyzed our experimental data and found that the temperature dependence of low- and high-field magnetoresistance is controlled predominantly by the nature of the temperature response of surface magnetization of particles. The competition between grain-boundary pinning strength (k), magnetic field and thermal energy (kBT) created the temperature sensitive behavior of magnetoresistance as well as that of surface spin susceptibility (χ b).

Magnetic heating characteristics of La0.7SrxCa0.3-xMnO3 nanoparticles fabricated by a high energy mechanical milling method

Magnetic inductive heating (MIH) of nanoparticles (NPs) attracts considerable research attention, first because of its application to hyperthermia in biological tissues. Most reports so far have dealt with magnetite NPs with a Curie temperature, TC, of as high as above 500 °C. In this paper, we present results of a MIH study in an ac field of frequency 219 and 236 kHz and strength of 40–100 Oe for several samples of La0.7SrxCa0.3−x MnO3 NPs of TC in the region of hyperthermia, that is some tens of degrees above human body temperature. The particle materials were fabricated by a high energy mechanical milling method combined with calcining at various temperatures in the range of 600–900 °C. The heating temperatures of the samples were observed to saturate at a field irradiating time of less than 10 min and at temperatures ranging from 40 to 75 °C depending on the strontium content, the NP concentration, c, and the field parameters. A sudden change in heating rate was clearly revealed in several heating curves for the case of low applied field and low c, which was considered to be related to the onset of a strong decrease in zero-field cooling (ZFC) magnetization of NPs. The initial temperature increase slope, dT/dt, and the saturation temperature, Ts will be analyzed as dependent on the NP concentration. Field dependences of the specific loss power will be analyzed and discussed for various concentrations, c. Evidence of fluid viscosity influence will also be noted.

The structure and magnetic properties of molecule-based magnet nanoparticles KxVy[Cr(CN)6]z.nH2O

We have synthesized KxVy[Cr(CN)6]z. nH2O molecule-based magnet nanoparticles belonging to the Prussian blue (PB) family of compounds. The synthesized samples were characterized by infrared spectroscopy (IR), Raman spectroscopy, UV–Vis spectroscopy, differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The crystal structure was refined from the x-ray powder diffraction profile by the Rietveld method. The samples are cubic, Fm3m space group with lattice parameter a=1.045 nm. The magnetic properties are determined from thermal variation of the magnetization and hysteresis loop. The most interesting result is the successful preparation of KxVy[Cr(CN)6]z. nH2O crystal Prussian blue nanomaterial which had Curie temperature (Tc) approaching room temperature.

Hydrogen generation by photoelectrochemical effect of the Cu-doped TiO2 photoanode

TiO2 film photoanodes with a size of 1???1 cm2 were fabricated by a spin coating method. Cu-doped TiO2 powder with various Cu concentrations (0.2, 0.4, 0.6 and 0.8 at%) and surfactant were used as starting materials in coating Cu-doped TiO2 thin films onto FTO/glass substrate. Crystalline structure of TiO2 material, microstructure of the photoanode films and their thickness were identified by x-ray diffraction and Raman scattering. Hydrogen generation from water by photoelectrochemical effect in the visible light was observed by recording I/V characteristics of the photoanode in dark and light regimes. The obtained results have shown that the hydrogen generation efficiency of photoanode nonlinearly depends on Cu concentration. The nonlinear dependence of the hydrogen generation efficiency may be due to a change of resistivity of the film photoanode that is related with the random distribution of the hetero-junction between interfaces of TiO2 and CuO nanoparticles.

Temperature dependent Raman spectroscopic study of SrTi 0.9 M 0.1 O 3 (M=Fe, Co, Ni) nanoparticles

Strontium titanate (SrTiO3) is useful in many technological applications and its properties are strongly dependent on the doping of its A or B site. We have performed temperature dependent Raman studies of SrTi0.9M0.1O3 (M = transition metal) nanoparticles. Our results indicate that the mode energies and symmetry of the SrTiO3 structure have been changed as doped with various transition metals, such as Fe, Co or Ni. However, these changes depend on the type of the doping element and the doping content.