Photocatalytic properties of BiFeO3 nanoparticles with different sizes

BiFeO₃ nanoparticles with different average grain sizes have been prepared through a polyacrylamide gel route. In the present synthesis route, the grain size is tailored by varying the ratio of bis-acrylamide to acrylamide. The photocatalytic activity of the as-prepared BiFeO₃ nanoparticles has been investigated by the degradation of methyl orange (MO), a typical azo dye. It is revealed that the products exhibit a pronounced photocatalytic activity under ultraviolet as well as visible-light irradiation. With decrease in particle size, the photocatalytic activity exhibits a rising trend. The influences of catalyst dosage and initial dye concentration on the photocatalytic efficiency have been also investigated. In the present experiments, the optimum loading of BiFeO₃ nanoparticles and initial concentration of MO are obtained to be ~ 2.5 g L⁻¹ and ~ 10 mg L⁻¹, respectively.     

Synthesis and spectroscopic investigations of Mn3O4 nanoparticles

Trimanganese tetraoxide (Mn₃O₄) nanoparticles have been synthesized via hydrothermal process. Nevertheless, homogeneous nanoparticles of Mn₃O₄ with platelet lozange shape were obtained. The crystallite size ranged from 40 to 70 nm. The Mn₃O₄ product was investigated by X-ray diffraction, transmission electron microscopy (MET), and impedance spectroscopy. Electrical conductivity measurements showed that the as-synthesized Mn₃O₄ nanomaterial has a conductivity value which goes from 1.8 10⁻⁷ Ω⁻¹ cm⁻¹ at 298 K, to 23 10⁻⁵ Ω⁻¹ cm⁻¹ at 493 K. The temperature dependence of the conductivity between 298 and 493 K obeys to Arrhenius law with an activation energy of 0.48 eV.     

Facile synthesis and electrochemical properties of Mn3O4 nanoparticles with a large surface area

Mn₃O₄ nanoparticles were prepared by a novel oxidation-precipitation method at a low temperature. The crystal phase, microstructure, surface area and electrochemical properties of the products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N₂ adsorption-desorption isotherms and cyclic voltammetry (CV). The results indicate that the addition of citric acid and tartaric acid remarkably reduced the particle size and increased the specific surface area of Mn₃O₄ nanoparticles. The samples prepared by the addition of citric acid and tartaric acid have a narrow particle size distribution of 5-10 nm, a surface area of 119 and 122 m²/g, and a capacitance of 171 and 172 F g⁻¹, respectively.     

Room temperature ferromagnetism in Ni doped In2O3 nanoparticles

In the present work, Ni doped In₂O₃ nanoparticles were prepared using simple co-precipitation method. From the x-ray diffraction analysis it is observed that all samples exhibit single phase polycrystalline nature. All the diffraction lines correspond to the bixbyite type cubic structure. A UV visible analysis reveals that optical band gap decreases from 4.63 to 3.84 eV with Ni doping. DC magnetization measurements reveal that Ni doped In₂O₃ nanoparticles exhibit room temperature ferromagnetism.     

A novel method to prepare Cr2O3 nanoparticles

By the reaction system of CrO₃ and HCHO in aqueous solution, Cr₂O₃ nanoparticles were first prepared via hydrothermal synthesis. The process can be easily scaled up. The reaction time was only 1 h and the reaction temperature was 170 °C. The products were loosely agglomerated Cr₂O₃ particles of 50-70 nm in average particle size calculated from the Scherrer's formula, whose microstructure and that of the precursor were investigated by SEM. And IR, TG and BET were other characterization methods to study the process. The findings showed that the higher calcination temperature and the higher total concentration were factors to result in the larger average particle size.     

Electron energy-loss spectroscopy investigation of dopant homogeneity in Tb-doped Y2O3 nanoparticles prepared by solution combustion synthesis

The emergence of nanotechnology imposes a new level of control in the synthesis of materials, one in which the structure and chemistry have to be controlled and characterized at the nanoscale. The solution combustion synthesis method has been used to synthesize many different oxides, including luminescent ones. However, a systematic investigation of the dopant homogeneity at the nanoscale in materials produced by this method is lacking. This is of particular relevance in nanophosphors due to the possibility of concentration quenching. In this work, 5 at.% Tb-doped Y₂O₃ was prepared by the solution combustion synthesis method and investigated on its structure and chemical composition homogeneity at the nanoscale by means of electron energy-loss spectroscopy (EELS) scanning transmission electron microscopy (STEM), high resolution TEM, X-ray diffraction and photoluminescence measurements. The results show that it is possible to prepare luminescent materials by the solution combustion synthesis method where the dopant is homogeneously distributed within each nanoparticle.     

Fabrication of nanostructure Al2O3/ZrO2 (Y2O3) eutectic by combustion synthesis melt-casting under ultra-high gravity

A novel method for preparing Al₂O₃/ZrO₂ (Y₂O₃) eutectic was developed by combining combustion synthesis with melt-casting under ultra-high gravity (CSMC-UHG). The application of UHG = 800 g resulted in a high relative density of 99.8%, and an orientation-growth along the UHG direction. The microstructure was composed of aligned growth regimes containing a triangular dispersion of orderly ZrO₂ rods in Al₂O₃ matrix with a spacing of 300 nm. The eutectic had a high fracture toughness up to 17.9 MPa·m^1/2, which was mainly attributed to the nanostructure and the elastic bridge effects of the aligned ZrO₂ rods.     

A novel synthesis of spherical LiFePO4 nanoparticles

An effective, simple and green synthesis method based on hydrothermal stripping technique, in which ferrous ion was stripped and precipitated directly from iron (II)-loaded organic phase, has been successfully developed. X-ray diffraction (XRD) and Transmission Electron Microscope (TEM) showed that the samples synthesized at 140-250 °C with raw materials LiOH, H₃PO₄ and FeSO₄·7H₂O are well-defined spherical LiFePO₄ nanoparticles, and the particle size can be easily controlled by changing the temperature and time. Electrochemical tests showed that the sample has a higher cell performance as a cathode material. Our results suggest that hydrothermal stripping synthesis is a promising method for obtaining spherical LiFePO₄ nanoparticles without agglomeration.     

Size-dependent piezoelectric coefficient d33 of PbTiO3 nanoparticles

Size-dependent piezoelectric coefficient d₃₃(D) (D shows particle diameter) for small ferroelectrics is modeled in this paper. It is found that taking account of size effect is essential in understanding piezoelectric characteristics of nanoferroelectrics. The model prediction is in good agreement with the experimental results for PbTiO₃ nanoparticles, where d₃₃(D) increases correspondingly as D decreases. In addition, the size effect of the dielectric susceptibility coefficient η₃₃(D) is also predicted since η₃₃(D) ∝ d₃₃(D) is considered. Our model estimations for η₃₃(D) function are consistent with other theoretical evidences.     

Hydrothermal synthesis and characterization of LiNbO3 crystal

Lithium niobate crystal was successfully synthesized via hydrothermal synthesis method using LiOH·H₂O or LiNO₃ and Nb₂O₅ as starting materials in water or ammonia solution. X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectra and Scanning electron microscopy (SEM) were used to characterize the as-prepared samples. The synthesis conditions such as crystallization temperature and time as well as ammonia concentration (when using LiNO₃ as Li source) were investigated. The results demonstrate that the crystallization and purity of the as-prepared samples were increased with the increase of time when temperature was at 260 °C. When using LiNO₃ as Li source a basic solution was necessary to synthesize LiNbO₃. In the present work ammonia solution was used instead of water to obtain alkalescence solvent. XRD results revealed that the as-prepared samples had a hexagonal structure. FT-IR results displayed that the LiNbO₃ phase could be completely formed and no secondary phase was found under proper conditions. SEM picture showed that the morphology of the sample was more perfect and bigger with increasing reaction time.     

燃烧合成Ti掺杂LaNiO3及其可见光光催化性能

采用溶液燃烧法制备了一系列不同Ti掺杂量的LaNiO₃光催化剂, 研究了Ti掺杂量对其相结构、 形貌和光催化性能的影响。采用XRD、 SEM、 EDS及光致发光光谱(PL)等对其进行了表征和分析。结果表明: 采用溶液燃烧法可获得单一钙钛矿相的LaNiO₃, 随着Ti掺杂量的增加, 晶面间距逐渐增大; Ti掺杂量对颗粒的形貌大小影响较小, 颗粒近似球形, 粒径分布均匀, 约为80 nm。可见光催化实验结果表明, 当Ti掺杂量为3.0%(质量分数)时, 所得催化剂的催化效果最好, 适量的Ti掺杂可显著降低光生载流子的复合几率。      

Salt-assisted Low Temperature Solid State Synthesis of High Surface Area CoFe2O4 Nanoparticles

A novel salt-assisted low temperature solid state method using CoCl₂?6H₂O, FeCl₃?6H₂O and NaOH as pre- cursor and using NaCl as a dispersant to synthesize high surface area CoFe₂O₄ nanoparticles, has been investigated. The effects of the molar ratio of added salt and calcination temperature on the characteristics of the products were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and Brunauer, Emmett and Teller (BET) surface area analysis. Results showed that the introduction of leachable inert inorganic salt as a hard agglomeration inhibitor in the mixture precursor led to the formation of high dispersive CoFe₂O₄ nanoparticles; and the increase in specific surface area from 28.28 to 73.97 m²/g, and the saturation magnetization is 84.6 emu/g.     

Elastic modulus and hardness of CaTiO3, CaCu3Ti4O12 and CaTiO3/CaCu3Ti4O12 mixture

Three ceramic systems, CaTiO₃ (CTO), CaCu₃Ti₄O₁₂ (CCTO) and intermediate nonstoichiometric CaTiO₃/CaCu₃Ti₄O₁₂ mixtures (CTO.CCTO), were investigated and characterized. The ceramics were sintered at 1100 °C for 180 min. The surface morphology and structures were investigated by XRD and SEM. Elastic modulus and hardness of the surfaces were studied by instrumented indentation. It was observed that CCTO presented the higher mechanical properties (E = 256 GPa, hardness = 10.6 GPa), while CTO/CCTO mixture showed intermediate properties between CTO and CCTO.     

Distribution of pyrochlore phase in Pb(Mg1/3Nb2/3)O3-PbTiO3 films and suppression with a Pb(Zr0.52Ti0.48)O3 interfacial layer

Thin films of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) on Pt/Ti/SiO₂/Si (Pt/Si) substrates both with and without a Pb(Zr_0.52Ti_0.48)O₃ (PZT) interfacial layer were investigated. Perovskite and pyrochlore coexistence was observed for PMN-PT thin films without a PZT interfacial layer. Interestingly, most of the pyrochlore phase was observed in single-coated films and in the first layer of multi-coated films. The pyrochlore phase exhibited grains with an average size of about 25 nm, which is smaller than those of the perovskite phase (about 90 nm). In contrast, for PMN-PT thin films grown on a PZT interfacial layer, the formation of a pyrochlore phase at the interface between PMN-PT layers and the substrate is completely suppressed. Moreover, small grains are not observed in the films with a PZT interfacial layer. The measured polarization-electric field (P-E) hysteresis loops of PMN-PT films with and without PZT layers indicate that enhanced electrical properties can be obtained when a PZT interfacial layer is used. These enhanced properties include an increase in the value of remanent polarization P_r from 2.7 to 5.8 μC/cm² and a decrease in the coercive field E_c from 60.5 to 28.0 kV/cm.     

Variations of microstructures and electrical properties of Bi4Ti3O12/SrTiO3/(La0.5, Sr0.5)CoO3/MgO epitaxial thin films by annealing

Epitaxial thin films of a heterostructure with Bi₄Ti₃O₁₂(BIT)/SrTiO₃(ST) were successfully grown with a bottom electrode consisting of La_0.5Sr_0.5CoO₃(LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT <110>//ST <010>. In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20-40 min induced the BIT (001) plane to contract horizontally with its c-axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm² and 14 kV/cm to 1.7 μC/cm² and 69 kV/cm, respectively.     

Microwave absorption properties of multiferroic BiFeO3 nanoparticles

Multiferroic BiFeO₃ (BFO) nanoparticles ranging from 60 nm to 120 nm were synthesized successfully by a sol-gel method, and the microwave absorption properties of BFO nanoparticles were investigated in the range of 12.4 GHz to 18 GHz. The reflection loss of BFO nanoparticles is more than 10 dB (or more than 90%) in the 13.1 GHz-18 GHz range and reaches to 26 dB at 16.3 GHz, which indicated that the BFO is a good candidate for microwave absorption application. The excellent microwave absorption properties of BFO nanoparticles could be attributed to the good electromagnetic match as a consequence of the coexistence of ferroelectric and weak ferromagnetic order in BFO nanoparticles, which has been confirmed by electric and magnetic measurement. Moreover, the nanosize-confinement effect may also have contribution to the high reflection loss of BFO nanoparticles.     

Salt-assistant combustion synthesis of nanocrystalline Nd2(Zr1 − xSnx)2O7 (0 ≤ x ≤ 1) solid solutions

Nanocrystalline Nd₂(Zr_{1 − x}Sn_x)₂O₇ series solid solutions were prepared by a convenient salt-assisted combustion process using glycine as fuel. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The results showed the Zr ion can be partially replaced by Sn ion. The partial substituted products were still single-phase solid solutions and the crystal form remained unchanged. TEM images reveal that the products are composed of well-dispersed square-shaped nanocrystals. The method provides a convenient and low-cost route for the synthesis of nanostructures of oxide materials.     

Hydrothermal synthesis of Fe3O4 nanoparticles and its application in lithium ion battery

Well dispersed Fe₃O₄ nanoparticles with a mean diameter of about 160 nm were synthesized by a simple hydrothermal method in the presence of sodium sulfate. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectrum, and Fourier transform infrared spectra (FTIR). Electrochemical properties of the nanostructured Fe₃O₄ as cathode electrodes of lithium ion battery were studied by conventional charge/discharge tests, showing a high initial discharge capacity of 1267 mA h g^− 1 at a current density of 0.1 mA cm^− 2.     

Preparation and characterization of new visible-light-driven BaCo0.5Nb0.5O3 photocatalyst

A new type of visible-light-driven photocatalyst BaCo_0.5Nb_0.5O₃ was successfully synthesized via a sol-gel process in this study. After heating the precursors at 1000 °C, a pure perovskite phase was obtained. The particle size and crystallinity of BaCo_0.5Nb_0.5O₃ powders markedly increased with a rise in the calcination temperature. The band gap of BaCo_0.5Nb_0.5O₃ calculated from the UV-visible spectra was found to be less than that of titania. BaCo_0.5Nb_0.5O₃ was demonstrated to have photocatalytic activity under visible light irradiation and this activity significantly depended on the synthesis temperature. The sol-gel derived powders were found to have better photocatalytic activity than the solid-state derived powders because of the reduced particle size and increased surface area.     

Synthesis of Co3O4 nanoparticles via the CTAB-assisted method

Cobalt oxide (Co₃O₄) nanoparticles were successfully synthesized by the cetyltrimethylammonium bromide (CTAB)-assisted method at normal pressure for the first time. The structure and morphology of the as-prepared Co₃O₄ nanoparticles were characterized by powder X-ray diffracton (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N₂-sorption analysis. XRD studies indicated that the as-prepared product was well-crystallized cubic phase of Co₃O₄ with a cell constant of α = 8.0722 Å. The EM images showed that the obtained Co₃O₄ sample consisted of dispersive quasi-spherical particles with the size ranged from 15 to 25 nm.