Reverse microemulsion-directed synthesis of hydroxyapatite nanoparticles under hydrothermal conditions

Morphology controllable hydroxyapatite (HA) nanoparticles were synthesized using reverse microemulsion (aqueous solution/TX-100/n-butanol/cyclohexane) systems under hydrothermal conditions. The concentration of cetyltrimethylammonium bromide (CTAB) contained in the aqueous solution and pH value had significant effect on the morphology and crystal phases of the final products. All the as-synthesized HA nanoparticles had a larger a value but smaller c value compared with the standard values of the JCPDs card. The existence of CTAB could be attributed to the growth of HA along an axis, but inhibit the growth along the c-axis to some extent. A proposed model was established to explain the change of the lattice parameters.     

Excess titanium in barium titanate nanoparticles directly synthesized from solution

The formation mechanism of excess titanium in BaTiO₃ nanoparticles is different from that in BaTiO₃ bulk materials. In this study, we analyzed the concentration of excess titanium in BaTiO₃ nanoparticles, which were directly synthesized from solution at 65 °C and it was found that it can reach an abnormal high concentration and keep the normal perovskite structure. The mechanism is discussed from the points of both defect chemistry and surface effect. The dielectric property of the ceramics fabricated from as-prepared nanoparticles with different concentration of excess titanium is also studied.     

Physico-chemical properties and possible photocatalytic applications of titanate nanotubes synthesized via hydrothermal method

Titanate nanotubes (TNTs) were prepared from TiO₂ P25 via hydrothermal method. The reaction temperature was 130 or 140 °C and the reaction time was 24 or 48 h. The samples were characterized by transmission electron microscopy, X-ray diffraction, thermogravimetry and N₂ adsorption as well as Raman, FTIR-DRS and UV-vis/DR spectroscopy. The obtained samples exhibited similar properties, regardless of the preparation temperature and time. The most notable difference between properties of TNTs prepared under different conditions was observed in case of BET surface area, which was increasing from 386 to 478 m²/g along with increasing the reaction time and temperature. Based on TEM, XRD and TG measurements we have suggested that the structure of TNTs was H₂Ti₂O₄(OH)₂. The TEM and Raman spectroscopy measurements showed that the obtained products contained also low amount of anatase phase. The TNTs exhibited no photoactivity towards degradation of model azo dye Acid Red 18. However, TNTs were successfully applied for photocatalytic generation of CH₄ and H₂ in a solution of acetic acid. The amount of methane produced with application of TNTs synthesized at 140 °C was about 2.5 times higher than that generated with use of TiO₂ P25. To the best of our knowledge this is a first report on the photocatalytic generation of hydrocarbons using TNTs in the current state of the art.     

Lanthanide absorption spectral probe in titania nanoparticles synthesized by ultrasonic assistant sol-gel method

Titania nanoparticles were obtained by an ultrasonic assistant sol-gel method. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermal analysis. The optical absorption of the samples has been measured by photoacoustic (PA) spectroscopy, which is powerful for detecting small amount of strongly scattering materials. The structural variations of the sample during the phase transitions were firstly studied using Nd³⁺ as an absorption spectral probe. The PA results show that the TiO₂ gel heated at 50 °C is basically amorphous and still contains abundant trapped water and ethanol, which makes the environment around Nd³⁺ similar with that of its aqueous ion. For the sample calcined at higher temperature, the f-f transitions of Nd³⁺ exhibit a continuous red shift along with the gel-to-anatase transformation, indicating an increase of the “degree of covalency” for Nd³⁺ bonding. For the sample calcined at 1100 °C, however, the f-f transitions of Nd³⁺ show blue shifts and the hypersensitive transition intensities of Nd³⁺ decrease, indicating an increase of ionicity for Nd³⁺ bonding. This can be attributed to the segregation of Nd³⁺ ions to the external surface, forming Nd₄Ti₉O₂₄ during the anatase-to-rutile transition.     

Microwave-assisted synthesis of Fe3O4 nanorods and nanowires in an ionic liquid

Without using inert gas to prevent the oxidation of Fe²⁺, Fe₃O₄ nanorods and nanowires have been successfully synthesized via a microwave-assisted ionic liquid method (MAIL). Compared to the traditional methods, the whole reaction process can be carried out more easily and faster. Our result shows that temperature and time of microwave heat played important roles in the formation of Fe₃O₄ with different morphologies. These products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and FT-IR spectra.     

Low temperature synthesis of ITO nanoparticles using polyol process

A low temperature synthesis technique to prepare indium tin oxide (ITO) nanoparticles by the polyol process is proposed. On examining the phase formation of ITO nanoparticles in polyols and alcohols such as ethylene glycol, trimethylene glycol, and 1-heptanol, it was found that ITO nanoparticles could be synthesized directly without any post--annealing treatments at 175 °C in 1-heptanol. The morphology of the particles is influenced by the type of polyol. The composition of Sn in the ITO system could be easily controlled by simply varying the In/Sn precursor ratio in 1-heptanol. The low temperature synthesis method has enabled the formation of highly crystalline ITO nanoparticles with diameters less than 25 nm even at annealing temperatures as high as 700 °C.     

Structural and optical characterization of CdS nanoparticles prepared by chemical precipitation method

In the present study we have synthesized CdS semiconducting quantum dots by the chemical precipitation method using Thioglycerol as the capping agent. X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) are employed to characterize the size, morphology and crystalline structure of the as-prepared material. The synthesized QPs have a mixture of cubical and hexagonal crystal symmetry with 12 nm average diameter. Ultraviolet-visible (UV-vis) absorption spectroscopy is used to calculate the band gap of the material and blue shift in absorption edge. Confinement of the optical phonon modes in the QPs is studied by Raman spectroscopy, while FTIR for identification of chemical bonds in the nanomaterial. Multiple cadmium and sulphur defects were observed by employing the photoluminescence (PL) method.     

Temperature-dependent magnetic anomalies of CuO nanoparticles

Copper oxide (CuO) nanoparticles with an average size of 25 nm were prepared by a sol-gel method. A detailed study was made of the magnetization of CuO nanoparticles using a maximum field of 60 kOe for temperatures between 8 and 300 K. Antiferromagnetic CuO nanoparticles exhibit anomalous magnetic properties, such as enhanced coercivity and magnetic moments. Significantly, the magnitude of the hysteresis component tends to weaken upon increase in temperature (>8 K). In addition, a hysteresis loop shift and coercivity enhancement are observed at 8 K in the field-cooled (FC, at 50 kOe) case. It is thought that the change in hysteresis behavior is due to the uncompensated surface spins of the CuO nanoparticles. The susceptibility (χ) plot showed that χ varied substantially at temperatures below 12 K, and this transition is due to the exchange interactions between the neighboring atoms at the nanoscale.     

Fabrication of novel Cu microspheres assembled with nanoparticles by a solvothermal reduction route

Copper microspheres assembled with nanoparticles have been synthesized by a simple solvothermal route at 160 °C for 24 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX), transmission electron microscopy (TEM) and electron diffraction (ED) techniques. The results show that the diameters of the microspheres range from 2 to 4 μm. The formation mechanism of the morphology control over the copper microspheres assembled by nanoparticles was investigated; the use of polyvinylpyrrolidone (PVP) as the surfactant and the choice of N,N-dimethylformamide (DMF) as the reducing agent were found to be important for the final generation of copper microspheres.     

Single-crystal ZnO flocky sphere formed by three-dimensional oriented attachment of nanoparticles

The nanostructure of a single-crystal ZnO flocky sphere was synthesized by using a simple chemical route in the Zn²⁺–triethanolamine system. Formation of such quasi-single-crystal nanostructures was achieved through oriented attachment of a large number of ZnO nanoparticles in three dimensions. It is suggested that the adsorption of triethanolamine molecules on the surface of ZnO particles plays an important role in their oriented attachment, leading to the formation of flocky spheres with single-crystal structure.     

Size-controlled hydrothermal synthesis and electrochemical behavior of orthorhombic LiMnO2 nanorods

Large amount of uniform orthorhombic LiMnO₂ (o-LiMnO₂) nanorods was fabricated by a hydrothermal route in 180 °C using γ-MnOOH nanorods as precursors through an isomorphous ion exchange process. The size of as-obtained o-LiMnO₂ nanorods was determined by that of γ-MnOOH precursors, which could be deliberately controlled. The electrochemical performance of o-LiMnO₂ nanorods was characterized via galvanostatic tests, which suggested that the size of as-obtained products played an important role in their electrochemical performances.     

Synthesis and luminescence properties of needle-like SrAl2O4:Eu, Dy phosphor via a hydrothermal co-precipitation method

Needle-like SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors had been prepared by calcining the precursors obtained from hydrothermal process at the temperature of 1100 °C in a weak reductive atmosphere of active carbon. The crystal structure, morphology and optical properties of the composites were characterized. X-ray diffraction (XRD) patterns illustrated that the single-phase SrAl₂O₄ was formed at 1100 °C, which is much lower than that prepared by the traditional method. The transmission electron microscope (TEM) observation revealed the precursors and the resulted SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors had well-dispersed distribution and needle-like morphology with an average diameter about 150 nm at the center and the length up to 1 μm. After irradiation by ultraviolet radiation with 350 nm for 5 min, the phosphors emit green color long-lasting phosphorescence corresponding to the typical emission of Eu²⁺ ion, both the PL spectra and luminance decay revealed that the phosphors had efficient luminescent and long lasting properties.     

Preparation of nitrogen-doped titanium dioxide with visible-light photocatalytic activity using a facile hydrothermal method

Nitrogen-doped TiO₂ (N-TiO₂) nanoparticles have been successfully prepared via a direct and simple hydrothermal reaction of a commercial Degussa P25 with triethanol amine as solvent and nitrogen source. As-prepared N-TiO₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible light (UV-vis) absorption spectra, electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) techniques. The results confirm that hydrothermal reaction is an effective way to incorporate nitrogen into the TiO₂ lattice, especially nitrogen substitute for titanium. The nitrogen concentration in TiO₂ can be as high as 21% (molar ratio), which is described as Ti_1−yO_2−xN_x+y (in this paper, x=0.36, y=0.27, i.e., Ti_0.73O_1.64N_0.63). The chemical statuses of N have been assigned to N-Ti-O and O-N-O in the TiO₂ lattice as identified by XPS. Photocatalytic degradation of methyl orange has been carried out in both UV-vis (simulated solar light) and the visible region (λ>400 nm). N-TiO₂ exhibits higher activity than the Degussa P25 TiO₂ photocatalyst, particularly under visible-light irradiation. This study has developed a promising and practical pathway to new nitrogen-doped photocatalysts.     

Synthesis and magnetic properties of the size-controlled Mn-Zn ferrite nanoparticles by oxidation method

Size-controlled Mn_0.67Zn_0.33Fe₂O₄ nanoparticles in the wide range from 80 to 20 nm have been synthesized, for the first time, using the oxidation method. It has been demonstrated that the particle size can be tailor-made by varying the concentration of the oxidant. The magnetization of the 80 nm particles was 49 A m² kg⁻¹ compared to 34 A m² kg⁻¹ for the 20 nm particles. The Curie temperatures for all the samples are found to be within 630±5 K suggesting that there is no size-dependent cation distribution. The critical particle size for the superparamagnetic limit is found to be about 25 nm. The effective magnetic anisotropy constant is experimentally determined to be 7.78 kJ m⁻³ for the 25 nm particles, which is about an order of magnitude higher than that of the bulk ferrite.     

Synthesis and characterization of MnWO4 nanoparticles encapsulated in mesoporous silica SBA-15 by fast microwave-assisted method

The MnWO₄ nanoparticles encapsulated in mesoporous silica (MnWO₄/SBA-15) was successfully synthesized by a fast microwave-assisted method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen absorption–desorption isotherm, and Fourier transform infrared spectroscopy (FTIR). Our results showed that the MnWO₄/SBA-15 nanocomposites have the ordered hexagonal meso-structure of SBA-15, indicating MnWO₄ nanoparticles were successfully distributed into the channels of SBA-15. The size of MnWO₄ nanoparticles in SBA-15 is significantly smaller than the size of MnWO₄ nanoparticles prepared without SBA-15, indicating that the MnWO₄/SBA15 nanocomposites would be very promising for improving photocatalytic activity of MnWO₄ nanoparticles.     

Synthesis process and the luminescence properties of rare earth doped NaLa(WO4)2 nanoparticles

Rare earth doped NaLa(WO₄)₂ nanoparticles have been prepared by a simply hydrothermal synthesis procedure. The X-ray diffraction (XRD) pattern shows that the Eu³⁺-doped NaLa(WO₄)₂ nanoparticles with an average size of 10-30 nm can be obtained via hydrothermal treatment for different time at 180 °C. The luminescence intensity of Eu³⁺-doped NaLa(WO₄)₂ nanoparticles depended on the size of the nanoparticles. The bright upconversion luminescence of the 2 mol% Er³⁺ and 20 mol% Yb³⁺ codoped NaLa(WO₄)₂ nanoparticles under 980 nm excitation could also be observed. The Yb³⁺-Er³⁺ codoped NaLa(WO₄)₂ nanoparticles prepared by the hydrothermal treatment at 180 °C and then heated at 600 °C shows a 20 times stronger upconversion luminescence than those prepared by hydrothermal treatment at 180 °C or by hydrothermal treatment at 180 °C and then heated at 400 °C.     

Characterization of ZnGa2O4:Mn nanophosphor synthesized by the solvothermal method in 1,4-butanediol-water system

We characterized ZnGa₂O₄:Mn²⁺ (ZnGa₂O₄—zinc gallate) nanophosphor synthesized by the solvothermal method in 1,4-butanediol-containing water to increase the amount of Mn²⁺ ions incorporated in the ZnGa₂O₄ matrix without post-heat treatment. We investigated the influence of water content in the solvent on the photoluminescence (PL) intensity and the Mn amount, the latter being measured by X-ray fluorescence analysis and electron paramagnetic resonance spectroscopy. The PL intensity per Mn amount reached the maximum at the 50 wt% water content. The addition of water promotes repeated dissolution and precipitation, resulting in homogeneous Mn²⁺ distribution in the ZnGa₂O₄ matrix. This suggests that the solvothermal method in the 1,4-butanediol-water system is useful for increasing the amount of Mn²⁺ ions incorporated in the ZnGa₂O₄ matrix without post-heat treatment. At the water content >50 wt%, the decrease in PL intensity is attributed to the optical absorption of the by-product, MnOOH.     

Intrinsic room-temperature ferromagnetism of V-doped TiO2 (B) nanotubes synthesized by the hydrothermal method

Nanotubes of TiO₂(B) phase doped with 5 at.% of vanadium (V) have been synthesized by a hydrothermal method, followed by calcination at 300 °C in air and argon atmosphere, respectively. These nanotubes exhibit ferromagnetic character with clear hysteresis loop at room-temperature. X-ray diffraction and Fourier transform infrared spectroscopy confirm that the ferromagnetic behavior is intrinsic to the material and not due to other phases and/or metallic clusters. The photoluminescence and hysteresis loop characteristics are found to be dependent on calcination conditions, and implicate the role of oxygen vacancies. Existence of higher oxygen vacancies in V-doped TiO₂(B) nanotubes synthesized in argon than the air atmosphere is supported by the room-temperature photoluminescence spectra. The enhanced ferromagnetic behavior observed in V-doped TiO₂(B) nanotubes synthesized in argon than the air atmosphere is explained in terms of bound magnetic polaron (BMP) model.     

Preparation of cerium hydroxycarbonate by a surfactant-assisted route

Cerium hydroxycarbonate (CeOHCO₃) with shuttle-like morphology has been conveniently synthesized at 90 °C from aqueous solution in the presence of polyvinylpyrrolidone (PVP). The products were characterized by X-ray diffraction, transmission electron microscopy and photoluminescent (PL) techniques. The as-prepared CeOHCO₃ was found to have a PL emission at about 347 nm. Experimental conditions as well as the role of PVP played in the reaction were also explored.     

Polyol-assisted synthesis of TiO2 nanoparticles in a semi-aqueous solvent

TiO₂ (anatase and rutile) nanoparticles with an average crystallite size of 20-40 nm have been prepared at room temperature by polyol-mediated synthesis technique in a semi-aqueous solvent medium using titanium iso-propoxide as the titanium source, acetone as the oil phase and ethylene glycol as the stabilizer. Phase and microstructure of the resultant materials have been characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Photocatalytic degradation of acetaldehyde using TiO₂ nanoparticles was investigated by gas-chromatography technique.