Synthesis and properties of ultra-small BiFeO3 nanoparticles doped with cobalt

Bismuth ferrite (BiFeO₃, BFO) is the most promising material in the field of multiferroics. Additionally, it has excellent potential in photocatalysis applications due to its relatively small bandgap, stable structure, and low cost. Doping this material and enhancing its particle size showed promising results in many applications, especially photocatalysis, but the effect of both parameters has never been combined and studied before.In the present work, we report on the effect of cobalt doping of bismuth ferrite Bi Fe_1-xCo_xO₃ x (with x = 0, 0.02, 0.04, 0.06 and 0.08) synthesized by hydrothermal route. The crystalline phase was obtained at a temperature as low as 200 °C. Rietveld's refinement of X-ray diffraction (XRD) confirmed the rhombohedral structure of the crystalline powders. Transmission Electron Microscopy (TEM) alongside High-Resolution Transmission Electron Microscopy (HRTEM) was conducted to probe microstructural features and showed a remarkable decrease in particle size from 12.5 nm to only 4.5 nm, when increasing the cobalt concentration to 8%. The material's optical properties were also studied and showed an increase in band gap values from 2.12 to 2.33eV.The application of the samples to the photodecomposition of methylene blue (MB) under direct sunlight irradiation was reported and have shown unusual results that were explained by the unique sizes of the samples and the phenomena that can occur at that order of magnitude.     

Synthesis,structural and morphological characteristics,magnetic and optical properties of Co doped ZnO nanoparticles

Zn_1−xCo_xO (x==0.05, 0.10, 0.15) nanoparticles have been synthesized by an alternative wet-chemical synthesis route using the SimAdd technique. The as-obtained powders were investigated by FT-IR spectroscopy, X-ray diffraction and thermal analysis correlated with evolved gas analysis (TG–DTA–FT-IR) in order to determine their chemical nature, crystalline structure and to establish the decomposition sequences. The precipitates are generally amorphous, but low-intensity reflection peaks assigned both to the zinc oxalate dihydrate, and zinc hydroxide can be observed in the recorded patterns, indicating that hydroxy-oxalate precipitates were obtained. The structure, morphology and magnetic properties of the thermally treated samples have been investigated by X-ray diffraction, FT-IR, HRTEM, SAED, UV–vis and EPR. XRD studies reveal a hexagonal wurtzite-type structure for all Zn_1−xCo_xO samples. TEM investigations show particle size between 28 and 37 nm, with spherical and polyhedral shapes and with tendency to form aggregates. The presence of a Co₃O₄ secondary phase was evidenced by XRD, UV–vis and EPR for the Zn_0.85Co_0.15O sample. The ferromagnetic behavior of the samples was revealed. The paper highlights that by varying the cobalt concentration it is possible to modulate the structural, morphological, optical and magnetic properties.     

Thermoluminescence properties of Al doped ZnO nanoparticles

ZnO nanoparticles doped with aluminum (AZO nanoparticles) were investigated using low temperature thermoluminescence (TL) and structural characterization experiments. TL experiments were performed on AZO nanoparticles in the temperature range of 10–300?K. TL curve presented one intensive peak around 123?K and two overlapped peaks to intensive peak around 85 and 150?K for heating rate of 0.1?K/s. Curve fitting and initial rise methods were used to find the activation energies of associated trapping centers. Analyses resulted in the presence of three centers at 0.05, 0.08 and 0.17?eV with peak maximum temperatures (T_m) of 86.2, 121.5 and 147.1?K, respectively. TL experiments were expanded using different heating rates between 0.1?K/s and 0.5?K/s. Behavior of revealed traps was investigated using an experimental technique called as T_m??T_stop method. It was seen that traps are quasi-continuously distributed within the band gap. Structural properties were studied using x-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy experiments.     

Structural,magnetic, thermal and optical properties of Sn2+ cation doped magnetite nanoparticles

Tin doped nanomagnetites, Sn_xFe_3-xO₄, were synthesized with various concentrations of Sn²⁺ ion (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) by co-precipitation method. XRD, VSM, TG-DTA, SEM-EDX and UV–Vis were used to characterize and study the structural, magnetic, thermal, and optical properties of Sn_xFe_3-xO₄ nanoparticles. XRD confirmed the presence of cubic structure and spinel phase of tin doped magnetites. The d-spacing, lattice parameter, density, crystallite size and cation distribution were derived from the XRD analysis. The M − H curves exhibited changes in saturation magnetization (M_s), coercive field (H_c), remanent magnetization (M_r) and susceptibility (χ), with increasing concentration of non-magnetic Sn²⁺ ions. Differential thermal analysis was used to study the thermal stability of Sn_xFe_3-xO₄ nanoparticles. The SEM images revealed the surface morphology of the nanoparticles and the EDX spectra showed an increase in the Sn content and a corresponding decrease in the Fe content for the tin doped samples. The optical bandgap was found to be centered at 3.9 eV for the synthesized materials. This systematic study may be the first comprehensive report on synthesis and characterization of tin doped magnetites.     

Photocatalytic,magnetic, and electrochemical properties of La doped BiFeO3 nanoparticles

We successfully prepared La_1?xBi_xFeO₃ (L_xB_1?xFO, x?=?0.01–0.1) nanoparticles using a sol-gel technique, and studied their photocatalytic, magnetic, and electrochemical properties. Structural refinement studies of the prepared nanoparticles revealed a gradual structural transition from rhombohedral to orthorhombic. The average grain size was observed to decrease with increasing the concentration of La. The photocatalytic degradation of Rhodamine B (RhB) in the presence of the prepared nanoparticles was studied under visible light irradiation. The L_0.06B_0.94FO nanoparticles showed higher degradation efficiency compared to pure BiFeO₃ (BFO) nanoparticles. Magnetic studies showed that La doping improved the magnetization of BFO due to the reduction in grain size and destruction of cycloid coupling of spins. Higher specific capacitance values were obtained for La doped BFO (LBFO) nanoparticles compared to BFO nanoparticles. A maximum specific capacitance of 219?F?g^?1 was obtained at a current density of 1?A?g^?1 for LBFO nanoparticles.     

Polystyrene nanoparticles with tunable interfaces and softness

Polystyrene nanoparticles, cross-linked with divinylbenzene (PS-(DVB)_x) and having radii, R_p ≤ 10 nm, have been synthesized using batch and semi-batch radical microemulsion polymerizations. The nanoparticles were characterized thoroughly using ¹H NMR, size exclusion chromatography, differential scanning calorimetry, and various small-angle scattering techniques (light, X-rays, and neutrons). Control over network and interface morphologies of the PS-(DVB)_x nanoparticles is readily achieved by varying the concentration of divinylbenzene and the polymerization technique (batch vs. semi-batch). Small-angle neutron scattering (SANS) allowed us to identify three distinct nanoparticle morphologies: (i) fuzzy soft gels with flexible chain-segments tethered/looped at the interface of a homogeneous core, (ii) smooth soft gels without a fuzzy interfacial layer, and (iii) dendritic glassy gels exhibiting an inhomogeneous core with an ill-defined interface. Atomic force microscopy imaging supports the morphologies and the softness of the nanoparticles as indicated by SANS.     

Preparation and photochemical properties of nanoparticles of ceria doped with zinc oxide

Abstract

Nanoparticles of CeO₂ doped with ZnO were syn thesised via soft solution chemical processes at 40°C and a final pH of 6. The particle size of CeO ₂decreased markedly after doping with ZnO. The solubility limit of ZnO in Ce_1-xZn_xO_2-x was determined to be x = 0·561. The oxidation catalytic activity of CeO₂ was effectively decreased by doping with ZnO. For the oxidation of phenol, the photocatalytic activity of ZnO doped CeO₂ was much lower than that of fine titania particles. ZnO doped CeO₂ showed excellent UV absorption and transparency in the visible region, in a similar manner to undoped CeO₂.     

纳米粒子掺杂太阳盐复合材料热物性研究

在聚光式太阳能系统中,熔盐被视为良好的储热材料,具有成本低、使用安全、低饱和蒸汽压等特点。合理改善其热物性可实现太阳能高效利用,掺杂纳米颗粒可提高熔盐的储热及传热性能。在之前工作中,采用高温静态熔融法将纳米氧化铝（Nano alumina,NA2）掺杂于太阳盐（SS,质量分数为60%的硝酸钠与质量分数为40%的硝酸钾的混合物）中,获得了具有较高比热容的纳米流体（NA2-SS,N2S）。在此基础上,采用相同方法将纳米石墨粉（GP）和NA2同时掺杂于SS中（NA2-GP-SS,N2GS）,利用差式扫描量热法和瞬态平面热源法对体系比热和导热进行测试。结果表明,优化样品为N2GS-4,比热容与原样SS相比提升21.79%,导热提升20.69%,在高温状态下具有较好的热稳定性。N2GS-4作为一种硝酸盐基纳米复合蓄热材料在热能存储系统中具有广阔的应用前景。     

Synthesis and magnetic properties of Zr doped ZnO Nanoparticles

Zr doped ZnO nanoparticles are prepared by the sol-gel method with post-annealing. X-ray diffraction results show that all samples are the typical hexagonal wurtzite structure without any other new phase, as well as the Zr atoms have successfully entered into the ZnO lattices instead of forming other lattices. Magnetic measurements indicate that all the doping samples show room temperature ferromagnetism and the pure ZnO is paramagneism. The results of Raman and X-ray photoelectron spectroscopy indicate that there are a lot of oxygen vacancies in the samples by doping element of Zr. It is considered that the observed ferromagnetism is related to the doping induced oxygen vacancies.     

Structural,magnetic and electric properties of ZrO2 tapes decorated with magnetic nanoparticles

We produced ZrO₂ ceramic tape decorated with magnetic nanoparticles through tape casting technique. The green and sintered magnetic tapes were characterized by XRD, SEM, EDS, magnetic measurements, and I–V curves. We investigated the changes in the structural, magnetic and electrical properties, after the sintering process, and discussed the connections between them. The magnetic properties, performed in a wide range of external magnetic field and temperature, show magnetite phase for the magnetic nanoparticles governing the magnetic and electric properties of the green tape. On the other hand, for the sintered tape, the increase in the hematite phase led to remarkable changes in the magnetic and electrical properties. The electrical characterization reflects the observed changes in the structural properties after the sintering process. Additionally, the main advantages of the ceramic tapes decorated with magnetic nanoparticles reside in the possibility of producing functional thin ceramic materials that are easily moldable for electronic devices applications.     

Electrical and magnetic properties of magnesium-substituted lithium ferrite

Magnesium-substituted lithium ferrite of different composition (Li_0.5Fe_2.5−xMg_xO_4−δ) were prepared for x = 0.0–1.0 by conventional ceramic technique. The crystal structure characterization and morphology were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM). Initial permeability and quality factor were measured in the frequency range of 1 kHz to 100 MHz. The permeability decreased gradually from μ (f = 10 MHz) = 34.0 for Li_0.5Fe_2.5O₄ to μ (f = 10 MHz) = 11.5 for Li_0.5Fe_1.5Mg_1.0O₄. Electrical conductivity measurements were carried in the range of 250–700 °C in air. The maximum electrical conductivity, σ_700 °C = 0.1274 S/cm has been found to be for Li_0.5Fe_2.5O₄ specimen. With increasing Mg-substituted content, the decreased in the electrical conductivity.     

表面荷正电聚苯乙烯胶体颗粒界面电性质的研究

以偶氮二异丁脒盐酸盐V50(AIBA)为引发剂[1],水为分散介质,采用无皂乳液聚合法制备聚苯乙烯颗粒,制备出颗粒粒径为500 nm左右单分散性的聚苯乙烯颗粒。研究结果表明:在一定条件下用该方法制备的胶体颗粒zeta电位曲线均出现在平台pH2.0~6.0,说明在一定条件下聚苯乙烯胶体颗粒具有良好的稳定性。     

Structural and magnetic characterization of norbornene-deuterated norbornene dicarboxylic acid diblock copolymers doped with iron oxide nanoparticles

A series of iron oxide doped norbornene (NOR)/deuterated norbornene dicarboxylic acid (NORCOOH) diblock copolymers were synthesized and characterized by X-ray photoelectron spectroscopy (XPS), small angle neutron scattering (SANS) and superconducting quantum interference device (SQUID) experiments. γ-Fe₂O₃ nanoparticles were synthesized within the microdomains of diblock copolymers with volume fractions of NOR/NORCOOH 0.64/0.36, 0.50/0.50 and 0.40/0.60. A spherical nanoparticle morphology was displayed in the polymer with 0.64/0.36 volume fraction. Polymers with 0.50/0.50 and 0.40/0.60 volume fractions exhibited interconnected metal oxide nanostructures. The observed changes in the shape and peak positions of the small-angle neutron scattering profiles of polymers after metal doping were related to the scattering from the metal oxide particles and to the possible deformed morphologies due to the strong interparticle interactions between metal particles, which may influence the polymer microphase separation. The combined scattering from both polymer domains and magnetic particles was depicted in SANS profiles of metal oxide doped polymers. γ-Fe₂O₃ containing block copolymers were superparamagnetic at room temperature. An increase in the blocking temperature (T_b) of interconnected nanoparticles was observed and was related to the interparticle interactions, which depends on the average distance (d) between particles and individual particle diameter (2R). The sample with volume fraction of 0.4/0.6 have the lowest d/(2R) ratio and exhibit the highest T_b at 115 K.     

核壳结构磁性纳米复合物的合成及载药性能

利用化学交联法合成了壳聚糖改性的四氧化三铁磁性纳米复合物。通过透射电子显微镜（TEM）、傅里叶转换红外光谱（FTIR）、粒度分析仪（Nano-ZS）和振动样品磁强计（VSM）对该复合物的形貌、粒径、物相组成及磁性能进行了表征分析。表明该磁性纳米复合物具有核壳结构。再用超声法合成了阿霉素-壳聚糖修饰的磁性纳米包合物,用紫外-可见（UV-Vis）分光光度计检测了该复合物的包封率,平均值达到46.13%。通过四唑盐（MTT）比色法证明了包合物对K150细胞的生物抑制作用。以上结果表明,该磁性纳米复合物具有良好的生物相容性和载药活性。     

Electrical and magnetic properties of conjugated schiff base polymers

Two new conjugated poly-Schiff bases (PPpP and PPmP) were synthesized by polycon-densation of p-phenylene diamine or m-phenylene diamine with 2,6-pyridine dicarboxal-dehyde. PPpP and PPmP can from charge transfer complexes with iodine. Maximum conductivity of PPpP-iodine complex at room temperature is 10⁻⁶ S/cm, which is 2 orders of magnitude higher than that of PPmP-iodine complex. Electronic spin resonance measurements discovered that there are stable radicals in both charge transfer complexes; and g value, line width, and spin concentration depend on doping degree. Magnetic susceptibility of charge transfer complexes of PPmP–iodine is composed of Curie magnetic susceptibility (χ_c) and Pauli magnetic susceptibility (χ_p). Its Curie constant (C), Curie spin concentration (N_c), and density of state at the Fermi level also depend on doping degree. © 1996 John Wiley & Sons, Inc.     

Structural,magnetic and electrical properties along with antifungal activity & adsorption ability of cobalt doped manganese ferrite nanoparticles synthesized using combustion route

Ultrafine powders of Cobalt doped manganese ferrite with elemental composition Mn_1-xCo_xFe₂O₄ (x = 0.2, 0.4, 0.6, 0.8) were synthesized using combustion method. The formation of the pure cubic spinel phase of ferrite structure was confirmed using X-ray diffraction and Fourier transform infrared spectroscopy. Structural parameters such as lattice constant, X-ray density, mass density, porosity, and cell volume were seen to be greatly influenced by cobalt doping. The surface morphology of the nanocrystalline samples was studied using a scanning electron microscope. The particle size distribution was determined using a Transmission electron microscope and nanograins of the samples were found to have dimensions in the range 15 nm–30 nm. It also showed its dependence on the extent of cobalt inclusion. Variation of magnetization and magnetic moment as a function of magnetic field and temperature was investigated using a vibrating sample magnetometer (VSM). The parameters such as saturation magnetization ‘M_S’ and inversion temperature T_I were seen to depend upon Co⁺² concentration. The variation dielectric constant ‘Ԑ’ as a function of frequency was studied. Antifungal activity of these ferrite nanoparticles against Rhizopus fungi was also investigated at room temperature. The antifungal activity was seen to increase with increasing Co⁺² content in the manganese ferrite structure and hence cobalt doped manganese ferrites are proposed as a candidate material for industries manufacturing antifungal products. The adsorption studies were also investigated using Methylene dye as the adsorbate.     

Enhanced magnetic and dielectric properties of Y doped bismuth ferrite nanofiber

Yttrium doped Bismuth ferrite (BFO) nanofiber was fabricated via a sol-gel-based electrospinning process with the fiber diameter in the range of 60–220 nm. The crystal structure, magnetic and dielectric properties were investigated at room temperature. The Rietveld refinement results indicate the phase transition from space group R3c to Pbnm by the Y doping. Dramatic increase of magnetization has been achieved in Y doped BFO nanofiber. Compared with BFO nanoparticle, the Bi_0.95Y_0.05FeO₃ nanofiber exhibits nearly eighteen-fold improved magnetization, which is the strongest in the reported Y doped BFO at the same doping level. The largely improved magnetization mainly originates from the serious suppression of spiral spin structure by the small crystal size of nanofiber structure. Moreover, the Bi_0.95Y_0.05FeO₃ nanofiber holds the lower dielectric loss and obvious dependence of the capacitance on bias voltage, indicating the improved ferroelectricity due to the decreased leakage current. The simultaneous enhancement of ferroelectricity and magnetization in Y doped BFO nanofiber suggests that nanofiber structure plays an important role in improving multiferroic performance.     

Electrical properties and stability of praseodymium oxide-based ZnO varistor ceramics doped with Er2O3

The electrical properties and its stability against DC accelerated aging stress of Pr₆O₁₁-based ZnO varistor ceramics were investigated with Er₂O₃ content and sintering time. The nonlinear exponent of varistors with increasing Er₂O₃ content varied with V-shape, reaching minimum at 1.0 mol% Er₂O₃. As sintering time is increased, the nonlinear exponent was decreased, whereas its stability for DC stress was improved. The varistor with 0.5 mol% Er₂O₃ sintered at 1340 °C for 2 h exhibited the best performance for the nonlinearity and stability. This varistor exhibited not only high nonlinearity, with the nonlinear exponent of 43.4 and the leakage current of 1.2 μA, but also high stability, with the variation rates of varistor voltage and nonlinear exponent is −1.5 and −2.5%, respectively, under DC stress, such as (0.80V_{1 mA}/90 °C/12 h)+(0.85V_{1 mA}/115 °C/ 12 h)+(0.90V_{1 mA}/120 °C/12 h)+(0.95 V_{1 mA} /125 °C/12 h) +(0.95V_{1 mA}/150 °C/12 h).     

Manganese ferrite-polyaniline hybrid materials: Electrical and magnetic properties

Magnetic MnFe₂O₄ nanopowders were synthesized by an original solvothermal method in the absence and in the presence of tetra-n-butylammonium bromide (TBAB) and Tween 80 (TW) as surfactants. Manganese ferrite/polyaniline (PANI) hybrid materials were synthesized by in situ polymerization of aniline on the surface of MnFe₂O₄ using ammonium persulfate as oxidant. The purpose of the study was to investigate the influence of the two surfactants on the properties of the MnFe₂O₄ powders and of their composites with PANI. The specific surface area, the cumulative surface area of pores and the cumulative volume of pores are influenced by the nature of surfactant in case of MnFe₂O₄ powders and are higher by comparison to those of the MnFe₂O₄/PANI hybrid materials. The values of saturation magnetization in case of MnFe₂O₄ powders are higher than those of the hybrid materials and are not influenced by the surfactant nature. These features revealed that MnFe₂O₄ powders can be efficiently used as adsorbents for the purification of wastewaters. The values of the electrical conductivity of the composites exhibit a significant increase in comparison to the MnFe₂O₄ powders and depend on the surfactant nature. The highest value of electrical conductivity was achieved by the composite obtained using Tween 80 as surfactant (σ_DC = 54.5·10^?5S?m^?1) which was close to that of PANI (σ_DC = 61.2·10^?5 S?m^?1). The fact that the magnetic and electric properties of the synthesized MnFe₂O₄/PANI composites can be changed by design, demonstrate the high potential of these materials to be used in magneto-electric applications.     

Electrical conductive and magnetic properties of conjugated tetrathiolate nickel polymers

Summary Three tetrathiolate (tetrathiafulvalenetetrathiolate, ethylenetetrathiolate, and butadienetetrathiolate) nickel polymers are prepared. The polymers contain mixed valence Ni ions and are ESR active based on low-spin d⁸ Ni (III) species. Magnetic susceptibility measurement in the range of 30–60 K suggests and antiferromagnetic interaction between the Ni ions in the polymers. Below 30K a weak ferromagnetic interaction is observed. Chemically oxidized polymers are ESR inactive, while electrical conductivity is greatly enhanced.