Luc Huy Hoang

Crystallization process and magnetic properties of amorphous iron oxide nanoparticles

This paper studied the crystallization process, phase transition and magnetic properties of amorphous iron oxide nanoparticles prepared by the microwave heating technique. Thermal analysis and magnetodynamics studies revealed many interesting aspects of the amorphous iron oxide nanoparticles. The as-prepared sample was amorphous. Crystallization of the maghemite ?-Fe2O3 (with an activation energy of 0.71?eV) and the hematite ?-Fe2O3 (with an activation energy of 0.97?eV) phase occurred at around 300??C and 350??C, respectively. A transition from the maghemite to the hematite occurred at 500??C with an activation energy of 1.32?eV. A study of the temperature dependence of magnetization supported the crystallization and the phase transformation. Raman shift at 660?cm?1 and absorption band in the infrared spectra at 690?cm?1 showed the presence of disorder in the hematite phase on the nanoscale which is supposed to be the origin of the ferromagnetic behaviour of that antiferromagnetic phase.

Arsenic removal from water by magnetic Fe1− x Co x Fe2O4 and Fe1− y Ni y Fe2O4 nanoparticles

This article studies the effects of Co and Ni replacement in Fe1− x Co x Fe2O4 and Fe1− y Ni y Fe2O4 (x, y = 0, 0.05, 0.1, 0.2, 0.5) nanoparticles, pH, weight of nanoparticles/mL of water, and time of stirring on the arsenic removal ability. The results showed that a small amount (0.25 g L−1) of Fe3O4 nanoparticles after stirring time of 3 min can reduce the arsenic concentration from 0.1 to 0.01 mg L−1. The removal was also affected by the pH of the water. Absorption of arsenic by nanoparticles was effective when pH was smaller than seven and reduced with the increase of pH. At pH of 13, there was a strong release of arsenic ions from arsenic-absorbed nanoparticles back to water. The time of stirring was studied from 1 min to 2 h and the optimal time was about few minutes. Co and Nis presence was reported to keep saturation magnetisation stable under working conditions. For Co replacement, absorption does not change significantly when x ≤ 0.1 and slightly reduces when x > 0.1. The presence of Ni improved the absorption in most cases.

Control of crystal phase of BiVO4 nanoparticles synthesized by microwave assisted method

Different crystalline phases BiVO4 nanoparticles (tetragonal-zircon, monoclinic-scheelite, and tetragonal-zircon/monoclinic-scheelite heterophase) have been prepared by fast microwave assisted method and annealing treatment. For the heterophase, the ratio of tetragonal-zircon and monoclinic-scheelite phases can be well controlled by controlling the annealing temperature. Furthermore, a tight interface junction has been formed between tetragonal-zircon BiVO4 and monoclinic-scheelite BiVO4 in a nanosize level. This tight interface junction can modify the electronic structure of BiVO4 nanoparticles, which would be very helpful for achieving high photocatalytic activity.

Preparation of g-C3N4/Ta2O5 Composites with Enhanced Visible-Light Photocatalytic Activity

Abstractg-C3N4/Ta2O5 composites have been synthesized by a facile route in which mixtures of Ta2O5 and urea are heated at various temperatures of 450°C, 500°C, and 550°C. The obtained materials (denoted as CN/TaO-T, where T is the heating temperature) were characterized using x-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, diffuse-reflectance ultraviolet–visible (UV–Vis) spectroscopy, thermogravimetric analysis, and x-ray photoelectron spectroscopy. The results show that the as-prepared composites are in orthorhombic Ta2O5 phase coated by g-C3N4. The photocatalytic activity of the composites was evaluated by photodegradation of methylene blue under visible light. Among the three materials, CN/TaO-500 exhibited the highest photocatalytic activity. The improved photocatalytic activity of the g-C3N4/Ta2O5 composites is attributed to the presence of g-C3N4 in the materials.

Photocatalytic activity enhancement of Bi2WO6 nanoparticles by Gd-doping via microwave assisted method

Gd-doped Bi2WO6 nanoparticles were successfully prepared through microwave assisted synthesis. The incorporation of Gd3+ ions into Bi2WO6 crystallite was analyzed by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The optical properties of the nanoparticles were characterized by UV–Vis absorption and photoluminescence spectroscopy. The photocatalytic activity of the nanoparticleswas investigated by degradation of Rhodamine B under visible-light irradiation. Our results showed that Gd-doping plays an important role for enhancing the visible light photocatalytic activity, and the enhanced photocatalytic activity of Gd-doped Bi2WO6 nanoparticles would be mainly correlated with the effective decrease of recombination rate of photogenerated electron–hole pairs.

Study of photocatalytic activities of Bi2WO6/BiVO4 nanocomposites

The Bi2WO6/BiVO4 nanocomposites were successfully synthesized using fast microwave assisted method. The photocatalytic activities of Bi2WO6/BiVO4 nanocomposites were evaluated by the degradation of Rhodamine B under visible irradiation. The optimal BiVO4 content of 30% was observed for improving the photocatalytic activity of Bi2WO6/BiVO4 nanocomposites, and the mechanism of photocatalytic activity enhancement was investigated. Our results suggest that for the Bi2WO6/BiVO4 nanocomposites, particle surface area plays the most important role for improving photocatalytic activity, and electron–hole recombination rate plays more important role than amount of light absorbed by nanocomposites for improving photocatalytic activity.Graphical abstract

Optical and Magnetic Properties of Grown by Plasma-Assisted Molecular Beam Epitaxy

Zn1-xMnxO films (0 ≤ ×≤ 0.070) were grown by plasma-assisted molecular beam epitaxy on Si substrates with AlN buffer layers. For low Mn concentration samples, x ≤ 0.02, photoluminescence spectra show strong near band edge emission. Strong phonon and exciton coupling-induced resonant Raman scattering was observed. Paramagnetic, antiferromagnetic, and ferromagnetic phases were observed. Room temperature ferromagnetism for all samples was attributed to the bound magnetic polaron effect.

Optical and Magnetic Properties of

Zn1-xMnxO films (0 ≤ ×≤ 0.070) were grown by plasma-assisted molecular beam epitaxy on Si substrates with AlN buffer layers. For low Mn concentration samples, x ≤ 0.02, photoluminescence spectra show strong near band edge emission. Strong phonon and exciton coupling-induced resonant Raman scattering was observed. Paramagnetic, antiferromagnetic, and ferromagnetic phases were observed. Room temperature ferromagnetism for all samples was attributed to the bound magnetic polaron effect.

{\rm Zn}_{1-x}{\rm Mn}_{x}{\rm O}

Zn1-xMnxO films (0 ≤ ×≤ 0.070) were grown by plasma-assisted molecular beam epitaxy on Si substrates with AlN buffer layers. For low Mn concentration samples, x ≤ 0.02, photoluminescence spectra show strong near band edge emission. Strong phonon and exciton coupling-induced resonant Raman scattering was observed. Paramagnetic, antiferromagnetic, and ferromagnetic phases were observed. Room temperature ferromagnetism for all samples was attributed to the bound magnetic polaron effect.

Grown by Plasma-Assisted Molecular Beam Epitaxy

We investigate the crystallization process of NiFe2O4 nanoparticles prepared by microwave heating technique, which were then characterized using X-ray diffraction, high-resolution transmission electron microscopy, the differential scanning calorimetry, Raman scattering, Fourier transformed infrared spectra (FTIR), and magnetic measurements. The results showed that crystallization of the amorphous NiFe2O4 nanoparticles occurred at around 300 °C. The best crystallization quality would be obtained by annealing the sample at 500 °C. After crystallization, the sample shows ferromagnetic behavior with a saturation magnetization of about 30 emu/g. The FTIR and Raman measurements also provided further information about the crystallization process and the phase transformation of the NiFe2O4 nanoparticles.