可磁分离的镍锌铁氧体-石墨烯复合材料的制备及其光催化性能

以硝酸锌、硝酸镍、硝酸铁为原料,采用微波水热法快速制备了Ni_0.5Zn_0.5Fe₂O₄-graphene纳米复合材料。该复合材料的XRD、Raman、TEM/HRTEM、XPS和VSM结果表明13 nm左右的尖晶石型镍锌铁氧体纳米颗粒分散锚固在石墨烯片上,纳米复合材料的饱和磁化强度为28.2 A·m²·kg^-1,剩磁和矫顽力基本为零表现为超顺磁性。在H₂O₂存在条件下可见光照射90 min,亚甲基蓝(MB)降解率达到97.5%,较好的光催化活性主要归因于石墨烯的存在有利于光生载流子的分离,产生更多活性中间体用于有机染料污染物的降解。考察了磁性光催化剂的重复利用和催化能力的稳定性,能够满足磁性回收和再使用的要求。     

Impact of Gd3+ and Nd3+ ions substitution on structural and magnetic properties of Co0.5Ni0.5Fe2O4 ferrite system

Co_0.5Ni_0.5(Gd/Nd)_xFe_2-xO₄ (x ?= ?0.0 and 0.06) ferrites were prepared by the solid-state reaction method. These materials were characterized by XRD, FT-IR spectroscopy, and VSM techniques. The XRD analysis revealed the phase formation of all samples and their cubic spinel structure with the Fd-3m space group. Lattice constant was found to increase due to Gd and Nd ions substitution. However, the crystallite size was observed to decrease by the substitution effect. The FT-IR spectra showed the two vibrational frequency bands of the tetrahedral and octahedral sites. From the magnetic properties study, it was identified that the pure and Gd substituted Co_0.5Ni_0.5Fe₂O₄ ferrite showed a ferromagnetic behaviour. While the Nd substituted Co_0.5Ni_0.5Fe₂O₄ ferrite delivered a superparamagnetic behaviour. The substitution of Gd and Nd changed the values of the magnetic parameters of Co_0.5Ni_0.5Fe₂O₄ ferrite. An increase in the saturation magnetization (M_s) value was observed due to substitution of Gd and Nd in Co_0.5Ni_0.5Fe₂O₄ ferrite, indicating that Gd and Nd substitution strengthen the supermagnetic interactions in Co_0.5Ni_0.5Fe₂O₄ ferrite. The highest value of M_s was observed in Gd doped sample.     

可磁分离的镍锌铁氧体-石墨烯复合材料的制备及其光催化性能

以硝酸锌、硝酸镍、硝酸铁为原料,采用微波水热法快速制备了Ni_(0.5)Zn_(0.5)Fe_2O_4-graphene纳米复合材料。该复合材料的XRD、Raman、TEM/HRTEM、XPS和VSM结果表明13 nm左右的尖晶石型镍锌铁氧体纳米颗粒分散锚固在石墨烯片上,纳米复合材料的饱和磁化强度为28.2 A·m~2·kg~(-1),剩磁和矫顽力基本为零表现为超顺磁性。在H_2O_2存在条件下可见光照射90 min,亚甲基蓝(MB)降解率达到97.5%,较好的光催化活性主要归因于石墨烯的存在有利于光生载流子的分离,产生更多活性中间体用于有机染料污染物的降解。考察了磁性光催化剂的重复利用和催化能力的稳定性,能够满足磁性回收和再使用的要求。     

镧掺杂对大洋锰结核制备铁氧体磁性的影响

大洋锰结核又称铁锰结核、多金属结核,常见于4 000～6 000 m的海底沉积物表层,在世界各大洋底均有分布,预计总储量超过3×1012 t[1].天然锰结核含有Mn和Fe,以及Cu、Co、Ni、铂族和稀土等60多种金属元素,其中锰占20%～30%,铁约占3～20%[2].从化学成分而言,大洋锰结核与Mn-铁氧体(铁酸锰)十分接近.以锰结核为原料合成Mn-铁氧体可以为这种天然资源的开发利用提供新思路.     

Synthesis of the ZnO-Ni0.5Zn0.5Fe2O4-Fe2O3 magnetic catalyst in pilot-scale by combustion reaction and its application on the biodiesel production process from oil residual

A magnetic catalyst with composition ZnO-Ni_0.5Zn_0.5Fe₂O₄-Fe₂O₃ was synthesized by a combustion reaction on a pilot-scale and applied in the conversion of residual oil into biodiesel by simultaneous transesterification and esterification reactions (TES). For that, statistical analysis of the factors that influence the process (catalyst concentration, alcoholic route, and temperature) was evaluated by 2³ factorial experimental design. The ZnO-Ni_0.5Zn_0.5Fe₂O₄-Fe₂O₃ magnetic catalyst was characterized in terms of the structure, morphology, magnetic, TPD-NH₃ acidity analysis and catalytic properties. The results indicate the formation of a catalyst with a surface area of 52.9 m²g⁻¹, and density of the sample was 4.8 g/cm³ which is consisted of a mixture of the phases containing 55.87% Fe₂O₃, 36.96% Ni_0.5Zn_0.5Fe₂O₄, and 7.16% ZnO. The magnetic characterization indicated that the synthesized catalyst is ferromagnetic with magnetization 6.12 emu/g and coercive field of 5.3 G. In the TES reactions, the residual oil was active showing conversion to 96.16% ethyl esters and with a long useful life maintaining sustained activity after two consecutive reuse cycles with the conversion of 95.27%, 93.07% and 76.93%, respectively. The experimental design was significant and presented a 95% reliability level. The statistical analysis identified (+1) and (−1) as higher and lower level variables, respectively. The amount of catalyst used was equal to 5%, at 200 °C in methyl alcohol (alcoholic route). In summary, a new catalyst composed of a mixture of magnetically active phases was developed and successfully applied in biodiesel’s synthesis from residual oil. Undoubtedly these results have a positive and significant impact on the environment and to society as a whole.     

Synthesis and neel temperature determination of ferrites from the CuO−ZnO−Fe2O3 system

Conditions were established and individual and mixed ferrites with the general formula Cu_xZn_1?xFe₂O₄ (x=0; 0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 1.0) were synthesized from the CuO?ZnO?Fe₂O₃ system. X-ray phase analysis, Mössbauer spectroscopy and microscopic examinations revealed that the obtained ferrites are monophase samples. A magnetic device was attached to the Q-Derivatograph (MOM, Hungary) and successfully used for sample investigation in a magnetic field, and in particular for Curie (Neel) temperature determination. The ferrite composition and the thermal treatment conditions were shown to correlate with the Neel temperature of the synthesized ferrites.     

Catalytic performance of NiFe2O4 and Ni0.3Zn0.7Fe2O4 magnetic nanoparticles during biodiesel production

In this study, catalytic performance of nanoferrites NiFe₂O₄ and Ni_0.3Zn_0.7Fe₂O₄ is reported. Nickel–ferrite and mixed nickel–zinc ferrite were successfully synthesized by combustion reaction using a conical reactor with production of 10 g per batch. Crystallinity and purity or quantitative analysis of the catalyst were checked by using X-ray diffraction and energy dispersive X-ray analysis. Surface chemistry was examined via Fourier transform infrared (FTIR) analysis; N₂ physisorption at 77 K was conducted to obtain textural properties of the catalyst; a thermogravimetric analysis, a scanning electron microscope and a transmission electron microscopy were used to check the thermal stability and morphology of the catalyst, respectively. The catalysts were used to convert soybean oil into biodiesel in a batch mode and the reaction mixture was analyzed using a pre-calibrated gas chromatograph (GC). The presence of a single-phase spinel structure in the synthesized nanoparticles was confirmed by the XRD results. The Ni_0.3Zn_0.7Fe₂O₄ had a lower surface area value of 71.5 m²g⁻¹ and higher saturation magnetization value of 31.50 emu/g than sample NiFe₂O₄ which had 87.6 m²g⁻¹ and 17.85 emu/g, respectively. Biodiesel yield of 94% was obtained with Ni_0.3Zn_0.7Fe₂O₄ and 49% was obtained with NiFe₂O₄. Better performance of Ni_0.3Zn_0.7Fe₂O₄ when compared to that of NiFe₂O₄ could be attributed to higher acidity of the former. Findings from this study suggest that the development of nickel-zinc ferrite nanoparticles as magnetic heterogeneous catalysts could provide an environmentally friendly platform for biodiesel production.     

New Synthesis and Magnetic Properties of NiFe2O4/SiO2 and Co0.5Zn0.5Fe2O4/SiO2 Nanocomposites Using Tetraglycolatosilane as Precursor

In this work the new synthesis and magnetic properties of NiFe₂O₄/SiO₂ and Co_0.5Zn_0.5Fe₂O₄/SiO₂ nanocomposites using a water‐soluble silica precursor, tetraglycolatosilane (THEOS), by the sol‐gel method were reported. Nanocomposite were obtained by the thermal decomposition of the organic part at different annealing temperatures varying from 400 to 900 °C. Studies carried out using XRD, FT‐IR, TEM, STA (TG‐DTG‐DTA) and VSM techniques. XRD patterns show that NiFe₂O₄ and Co_0.5Zn_0.5Fe₂O₄ have been formed in an amorphous silica matrix at annealing temperatures above 600 and 400 °C, respectively. It is found that when the annealing temperature is up to 900 °C NiFe₂O₄/SiO₂ and Co_0.5Zn_0.5Fe₂O₄/SiO₂ samples show almost superparamagnetic behavior with a magnetization 4.66 emu/g and ferromagnetic behavior with a magnetization 10.11 emu/g, respectively. The magnetization and coercivity values of nanocomposites using THEOS were considerably less than previous reports using TEOS. THEOS as a silica matrix network provides an ideal nucleation environment to disperse ferrite nanoparticles and thus to confine them to aggregate and coarsen. By using THEOS over the currently used TEOS and TMOS, organic solvents are not needed due to the entire solubility of THEOS in water. Synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of ferrites even more versatile.     

Thermomagnetometric analysis of lithium ferrites

In this work, the magneto-phase transitions in pure lithium (Li_0.5Fe_2.5O₄), lithium–zinc (Li_0.4Fe_2.4Zn_0.2O₄) and lithium–titanium (Li_0.6Fe_2.2Ti_0.2O₄) ferrites were studied by the thermogravimetric analysis in magnetic field, which is known as the thermomagnetometry method. The ferrites were prepared by the solid-state synthesis from oxides and carbonates. The Curie point of magnetic phase in ferrites and their composite mixtures was determined from the derivative thermogravimetric curve in the region of ferrite mass change associated with the ferrimagnet–paramagnet transition in the magnetic phase. The method based on the analysis of ferrite mass change at Curie temperature was developed to estimate the ferrite phase concentrations in composite magnetic materials.

     

Structural,textural, morphological,magnetic and electromagnetic study of Cu-doped NiZn ferrite synthesized by pilot-scale combustion for RAM application

The synthesis of the Ni_0.5-xZn_0.5-xCu_2xFe₂O₄ (x = 0; 0.10 and 0.15) ferrite with the differential of pilot-scale production by the combustion reaction method was investigated for RAM application purposes. Combustion temperatures ranging from 682 °C to 738 °C were observed. All ferrites were sintered at 1200 °C for 1 h. A comprehensive study of the influence of substitution with Cu²⁺ in a partial and proportional way to the Ni²⁺ and Zn²⁺ ions, doping mode little reported in the literature, and also of the sintering process over the structural, textural, morphological, magnetic and electromagnetic properties of NiZnCu ferrites was performed. The XRD patterns of the ferrites as synthesized revealed the formation of the cubic structure of the inverse spinel as majoritary phase, and traces of hematite and zinc oxide as segregated phases. After sintering, it was proven the single-phase formation of cubic spinel ferrite structure. The introduction of Cu led to a reduction in the lattice parameter, whose values ranged from 8.337 to 8.385 Å. The EDX results confirm the composition of oxides. The textural and morphological analyses confirmed the densest characteristic, with increase of particle size and reducing of surface area and pore volume after Cu-doping. All ferrites showed characteristics of soft ferrimagnetic material, where the increase in Cu content contributed to a slight reduction in saturation magnetization, whose values were of ~22–29 emu/g for the as synthesized ferrites and ~71–85 emu/g for the sintered ones. The best result of electromagnetic absorption in X-band was presented by the sintered ferrite with 0.3 mol of Cu, reaching an attenuation of 99.8% at 11.5 GHz frequency, thus confirming the efficiency of the pilot-scale combustion synthesis in obtaining a ferrite with great potential for RAM application.     

尖晶石结构MFe2O4(M=Ca,Mg,Cu,Zn)纳米晶粉末的制备和磁性能

采用新型氨基凝胶自燃法成功制备出尖晶石结构MFe₂O₄（M=Ca,Mg,Cu,Zn）纳米晶粉末。对合成粉体样品的物相、形貌和磁性能进行了详细的研究。经能量色散X射线谱分析确定了合成MFe₂O₄粉末的高纯度。系统地研究了所合成的MFe₂O₄纳米晶粉末的磁性能。所有样品的磁滞回线均较窄,表明了它们具有软磁的特征。经测试得出4种铁氧体的饱和磁化强度（M_s）分别为2.1,29.3,24.1和4.2 emu·g^-1;剩余磁化强度（M_r）分别为0.2,2.3,11.4和0.2 emu·g^-1。这4种铁氧体样品的M_r/M_s值均小于0.5。对CaFe₂O₄和MgFe₂O₄两种典型铁氧体的零场冷却和场冷磁性能作了详细的研究。其中CaFe₂O₄样品的磁化强度在75 K以下有不一致的变化趋势,这是由于其发生了磁相变。     

Effect of Cadmium Substitution on Structural and Magnetic Properties of Nano Sized Nickel Ferrite

The structure and crystal phase of the nanocrystalline powders of Ni_1-xCd_xFe₂O₄ (0≤x≤0.5) mixed ferrite, synthesized by wet chemical co-precipitation method, were characterized by X-ray diffraction. Results showed that the lattice parameter increased with increasing Cd concentration. Microstructure was studied by scanning electron microscopy. TG/DTA stud-ies were carried out on co-precipitated sulphate complexes. These studies revealed the low ferritization temperature (650 oC) of the ferrite system synthesized by presently adopted route of synthesis and occurrence of simultaneous decomposition and ferritization processes.Further studies by infrared spectroscopy were also conducted. Moreover, magnetic properties of the prepared nanoparticles were studied by magnetization and a.c. susceptibility mea-surements. The response of prepared Ni_1-xCd_xFe₂O₄ mixed ferrites to magnetic field was investigated. Results show that, magnetic susceptibility, Curie temperature, and effective magnetic moment decreased as the Cd content increases.     

Preparation of Monodisperse Ferrite Nanocrystals with Tunable Morphology and Magnetic Properties

The synthesis of monodisperse magnetic ferrite nanomaterials plays an important role in several scientific and technological areas. In this work, dibasic spinel MFe₂O₄ (M=Mg, Ni, Co, Fe, Mn) and polybasic spinel ferrite MCoFeO₄ (M=Mg, Ni, Mn, MgNi) nanocrystals were prepared by the calcination of layered double hydroxide (LDH) precursors at 900 °C, which was confirmed by X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate that the as‐obtained spinel ferrites present a single‐crystalline nature with uniform particle size and good dispersibility. The composition, morphology, and particle size can be effectively tuned by changing the metal ratio, basicity, reaction time, and temperature of the LDH precursors. In addition, these spinel ferrites show high magnetic saturation values in the range 21.7–84.3 emu g^?1, which maintain a higher level than the previously reported magnetic nanoparticles. Therefore, this work provides a facile approach for the design and fabrication of spinel ferrites with controllable nanostructure and improved magnetism, which could potentially be used in magnetic and biological fields, such as recording media, sensors, drug delivery, and intracellular imaging.     

Formation of Nickel-Zinc Ferrite Embedded in a Silica Xerogel Matrix

We report a study using X-ray diffraction, refinement Rietveld, IR absorption spectroscopy and vibrating sample magnetometry of the formation of particles of Ni-Zn ferrites embedded in a xerogel SiO₂ matrix. Initial solutions were prepared mixing TEOS, distilled water, ethanol, and three different nitrates: iron, nickel and zinc. A molar ratio H₂O:TEOS:Et-OH of 11.66:1.0:4.0 was used in all solutions. Formation of Ni_0.5Zn_0.5Fe₂O₄ as well as structural modifications of the SiO₂ matrix induced by these particles are discussed. Ni-Zn crystals having dimensions varying from 4 to 16.5 nm have been synthesized by a suitable heat treatment schedule at temperatures varying from 700 to 1100°C. The coercivity values for different heat-treated samples are found in the range 11–193 Oe, which are significantly larger than those presented by bulk Ni-Zn ferrites.     

Synthesis and neel temperature determination of ferrites from the MO−ZnO−Fe2O3 systems (M=Cu,Co and Ni)

The Curie (Neel) temperature is successfully determined by means of a simple magnetic device attached to the Q Derivatograph (MOM, Hungary), which is widely used in many laboratories. This possibility is demonstrated by a study of ferrite materials with general formula M_xZn_1?xFe₂O₄ (M=Cu, Co and Ni;x=0.0; 0.2; 0.4; 0.5; 0.6; 0.8; 1.0). X-ray phase analysis, Mössbauer spectroscopy and microscopic examinations revealed that the obtained ferrites are monophase samples. The mixed ferrites possess more strongly expressed magnetic properties than those of the individual ferrites; the maximum magnetic interaction in these ferrites is observed at different zinc contents.     

Reactivity of nanoparticles; interaction between zinc and copper oxide nanoparticles and iron ions in an alkaline medium

The reactivity of zinc and copper oxide nanoparticles was investigated upon their interaction with iron oxides. It was ascertained that, depending on the reaction conditions, nanoparticles of zinc and copper ferrites (ZnFe₂O₄ and CuFe₂O₄) or core/shell nanoparticles (Fe₃O₄/ZnO) are produced. Size, composition, and structure of the resulting nanoparticles were determined by transmission electron microscopy and X-ray diffraction analysis. The average size of zinc and copper ferrite nanoparticles was ascertained to be 9–10 and 2–3 nm, respectively. For core/shell Fe₃O₄/ZnO nanoparticles, the average size is 20 nm. It was experimentally proved that the photoluminescence radiative characteristics of ZnO nanoparticles are retained in core/shell Fe₃O₄/ZnO nanoparticles.     

High-Resolution Transmission Electron Microscopy Studies of Sol-Gel-Derived Cobalt-Substituted Barium Ferrite

Nanocrystal specimen of cobalt (II)-doped magnetoplumbite (M-type) BaFe₁₂O₁₉ were synthesized via a sol-gel method using ethylene glycol as precursor. Hexagonal-like platelets and other morphologies of ferrites were obtained at the final stage of annealing process. The specimens were characterized using X-ray diffraction, SQUID magnetometry measurement and high-resolution transmission electron microscopy. The saturation magnetization of the specimen at 300 K was found to be greatly reduced from 48 (3) emu/g in parent ferrite to 28 (3) emu/g in the doped ferrite. A total reduction of 74% in the value of intrinsic coercivity was recorded, 276 (15) G from the doped ferrite compared to 1080 (54) G in the parent ferrite.     

Microstructural Characteristics and Magnetic Properties of Gadolinium-Substituted Cobalt Ferrite Nanocrystals Synthesized by Hydrothermal Processing

Gadolinium substituted cobalt ferrite nanocrystals with composition of CoFe_2?xGd_xO₄ (x = 0–0.04 in a step of 0.01) were prepared by a hydrothermal process and without subsequent annealing. X-ray diffraction, field-emission scanning electron microscopy, and vibrating sample magnetometer were used to investigate the effect of Gd³⁺ cation substitution on structural Characteristics and magnetic properties of cobalt ferrite nanocrystals. The X-ray diffraction analysis demonstrated that single phase spinel ferrites were obtained. The FE-SEM micrographs of the synthesized samples indicated the presence of two distinct groups of grains exhibiting different sizes and, more important, different shapes. The results of magnetic hysteresis at a room temperature showed that with an increase in gadolinium content, the coercive field decreased from 1250 Oe for x = 0 to 450 Oe for x = 0.03. In addition, it was observed that with substitutions of gadolinium cations, the values of saturation magnetization decreased.     

Structural,morphological and magnetic properties of nano-crystalline zinc substituted cobalt ferrite system

Nano-crystalline zinc-substituted cobalt ferrite powders, Co_1−xZn_xFe₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1), have been synthesized by the combustion route. The structural, morphological and magnetic properties of the products were determined and characterized in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and vibrating sample magnetometer (VSM). X-ray analysis showed that the samples were cubic spinel. The increase in zinc concentration resulted in an increase in the lattice constant, unit cell volume, X-ray density, ionic radii, the distance between the magnetic ions and bond lengths on tetrahedral sites and octahedral sites of cubic spinel structure. Opposite behavior was observed for the average crystallite size of the as synthesized solids. The variation of saturation magnetization (M_s) value of the samples was studied. The maximum saturation magnetization value of the Co_o.25Zn_0.75Fe₂O₄ sample reached 76.87 emu/g. The high saturation magnetization of these samples suggests that this method is suitable for preparing high-quality nano-crystalline magnetic ferrites for practical applications.     

Spark plasma sintering synthesis of Ni1−xZnxFe2O4 ferrites: Mössbauer and catalytic study

Nickel-zinc ferrite nanoparticles, Ni_1−xZn_xFe₂O₄ (x = 0, 0.2, 0.5, 0.8, 1.0) were prepared by combination of chemical precipitation and spark plasma sintering (SPS) techniques and conventional thermal treatment of the obtained precursors. The phase composition and structural properties of the obtained materials were investigated by X-ray diffraction and Mössbauer spectroscopy and their catalytic activity in methanol decomposition was tested. A strong effect of reaction medium leading to the transformation of ferrites to a complex mixture of different iron containing phases was detected. A tendency of formation of Fe-carbide was found for the samples synthesized by SPS, while predominantly iron-nickel alloys ware registered in TS obtained samples. The catalytic activity and selectivity in methanol decomposition to CO and methane depended on the current phase composition of the obtained ferrites, which was formed by the influence of the reaction medium.