Magnetic properties of RE2MnGe6 (RE = La,Ce) and YMn0.3Ge2 germanides

The magnetic data of RE₂MnGe₆ (RE = La, Ce) and YMn_0.3Ge₂ are reported. La₂MnGe₆ and Ce₂MnGe₆ crystallize in the orthorhombic Ce₂CuGe₆ structure type, space group Amm2 (No. 38). The non-stoichiometric YMn_0.3Ge₂ compound crystallizes with the orthorhombic CeNiSi₂-type structure (space group Cmcm (No. 36)). The studied RE₂MnGe₆ (RE = La, Ce) intermetallics are characterized by ferromagnetic properties with Curie temperatures 177 (La) and 150 K (Ce), respectively. For YMn_0.3Ge₂ the low-field magnetic measurements indicate the antiferromagnetic property below 395 K with the small ferromagnetic component. The values of the magnetic moments in the ordered state indicate the ferromagnetic ordering in La₂MnGe₆ and complex magnetic order with the ferromagnetic component in YMn_0.3Ge₂ and Ce₂MnGe₆. The hysteresis loop and values of the coercivity field indicate that these compounds are soft magnetic materials.     

焙烧温度对Ni0.3Cu0.2Zn0.5Fe2O4纳米纤维的微结构和磁性能的影响

采用溶胶-凝胶法结合静电纺丝技术成功制备了直径在100 nm左右的Ni_0.3Cu_0.2Zn_0.5Fe₂O₄铁氧体纳米纤维. 并使用热重-差热分析(TG-DTA)、X射线衍射(XRD)、傅立叶红外变换光谱(FT-IR)、场发射扫描电镜(FE-SEM)、透射电镜(TEM)和振动样品磁强计(VSM)对电纺的复合纳米纤维及其焙烧产物进行了表征. 实验结果表明, 复合纳米纤维在450 ℃焙烧时, 立方尖晶石结构就已基本形成. 随着焙烧温度的升高, 纳米纤维中Ni_0.3Cu_0.2Zn_0.5Fe₂O₄晶粒的尺寸逐渐增大, 纤维表面也越发粗糙, 其形貌逐渐向项链状结构转变. 与此同时, 目标纳米纤维的比饱和磁化强度(M_s)单调增大, 而矫顽力(H_c)则呈现先增大后减小的趋势, 在650 ℃达到最大值, 这暗示以纳米纤维形式存在的Ni_0.3Cu_0.2Zn_0.5Fe₂O₄的单畴临界尺寸可能在53 nm左右. 此外, 发现在单畴临界尺寸以下, Ni_0.3Cu_0.2Zn_0.5Fe₂O₄纳米纤维的矫顽力与其平均晶粒尺寸(D)的0.71次方成正比, 即H_c∝D^0.71, 较好地符合随机各向异性模型所预测的结果H_c∝D^2/3.     

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.     

Preparation and ferromagnetic properties of Ni0.5Zn0.5Fe2O4/polyaniline core–shell nanocomposites

Magnetic Ni_0.5Zn_0.5Fe₂O₄‐crosslinked polyaniline composites with a core–shell structure were prepared in the presence of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder in a toluene solution containing iron chloride as a surfactant and dopant. Structural characterization by Fourier transform infrared, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy proved that Ni_0.5Zn_0.5Fe₂O₄ in the composites was responsible for the ferromagnetic behavior of the composites. The effects of the polyaniline and temperature on the magnetic properties of the Ni_0.5Zn_0.5Fe₂O₄/polyaniline composites were studied with electron paramagnetic resonance and superconducting quantum interference device techniques. A clear evolution from ferromagnetic resonance to electron paramagnetic resonance was observed as a function of temperature, which was related to the passage through the Curie point (～420 K). The magnetic properties of the resulting composites showed ferromagnetic behavior, such as high‐saturated magnetization (saturation magnetization = 35–39 emu/g), low coercive force (coercivity = 22–28 G), and low blocking temperatures (～23 K). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2657–2664, 2006     

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.     

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.     

Improvement of magnetoelectric coupling effect in Ba0.8Sr0.2TiO3-Co0.5Cu0.5Fe2O4 multiferroic fluids by tuning the composition

Ba_0.8Sr_0.2TiO₃ (BST) and Cu_0.5Co_0.5Fe₂O₄ (CCFO) nanopowders were prepared by hydrothermal method and chemical coprecipitation, respectively. Barium strontium titanate nanopowder–nano mixed oxides containing copper, cobalt, and iron (BST-CCFO) multiferroic fluids with different mass ratios (m_BST/m_CCFO = 1:2, 1:1, and 2:1) were prepared by using dimethyl silicone oil and silane coupling agent. Effect of mass ratio on the magnetoelectric performance was comparatively investigated. X-ray diffraction (XRD) showed that the BST and CCFO powders had no secondary phases, which are tetragonal perovskite structure and cubic spinel structure, respectively. Scanning electron microscopy (SEM) showed that the average grain size of BST and CCFO was 26.34 nm and 26.82 nm, respectively. The agglomeration of BST nanopowder was serious. Under the external magnetic field, the BST-CCFO multiferroic fluid will form a chain structure due to the directional movement of magnetic particles, thus enhancing the dielectric properties and ferroelectric properties of multiferroic fluid. The chain structure under the action of magnetic field will change the motion of ferroelectric particles, so that the magnetoelectric coupling effect of multiferroic fluid is significantly enhanced, which is much higher than that of the same type of magnetoelectric composite ceramics. This study is expected to provide a new way to improve the magnetoelectric coupling effect of multiferroic materials.     

Rare earth-rich compounds RE9TMg4 (RE = Y,Dy-Tm,Lu; T = Ru,Rh, Os,Ir) with an ordered Co2Al5-type structure

The rare earth-rich intermetallic phases RE₉TMg₄ (RE = Y, Dy-Tm, Lu; T = Ru, Rh, Os, Ir) were synthesized by induction melting of the elements using sealed niobium ampoules as crucible material. The melted samples were additionally annealed in muffle furnaces and subsequently characterized by X-ray powder diffraction. The RE₉TMg₄ compounds adopt an ordered Co₂Al₅ type structure, space group P6₃/mmc. Four structures were refined from single-crystal X-ray diffractometer data: a = 953.71(5), c = 968.41(5) pm, wR2 = 0.00273, 603 F² values, 21 parameters for Tm_8.76RuMg_4.24; a = 958.37(5), c = 975.66(5), wR2 = 0.00384, 661 F² values, 20 parameters for Dy₉OsMg₄; a = 943.70(5), c = 967.91(5) pm, wR2 = 0.00430, 592 F² values, 21 parameters for Tm_8.74OsMg_4.26; a = 968.09(5), c = 978.25(5) pm, wR2 = 0.0439, 623 F² values, 21 parameters for Y_9.18IrMg_3.82. The compounds are prone to small homogeneity ranges (RE/Mg mixing). The transition metal atoms have tricapped trigonal prismatic rare earth coordination. These T@RE₉ units (TP) are condensed with empty RE₆ octahedra (O) via common triangular faces forming infinite strands with a sequence –TP–O–O–. These strands show the motif of hexagonal rod packing and they are separated by chains of edge- and corner-sharing tetrahedra. The magnesium substructures in the hexagonal Laves phase YMg₂ and the prototype Y₉CoMg₄ are structurally closely related. Charge transfer trends, electronic band structures and bonding properties were studied within DFT. The resulting picture is that cobalt brings covalent character by reducing the overall charge transfer and modifies the Laves phase YMg₂ by providing larger localization in the density of states. The Y–Co bonding in Y₉CoMg₄ prevails while weakening the Y–Mg bonds. The investigations of the magnetic properties of selected RE₉TMg₄ compounds revealed Pauli paramagnetic behavior for Y₉CoMg₄, Y₉OsMg₄ and Y₉IrMg₄. A ferromagnetic ground state with Curie temperatures of 46.0 and 47.6 K was observed for Dy₉RuMg₄ and Dy₉OsMg₄, respectively. Ho₉RuMg₄, Ho₉OsMg₄ and Tm₉OsMg₄ reveal antiferromagnetic ordering with Neél temperatures below 20 K.     

Crystal Structure and Properties of Some Filled and Unfilled Skutterudites: GdFe4P12, SmFe4P12, NdFe4As12, Eu0.54Co4Sb12, Fe0.5Ni0.5P3, CoP3, and NiP3

The new cubic compound Fe_0.5Ni_0.5P₃ (a = 775.29(5) pm) as well as the known compounds CoP₃ and NiP₃ were synthesized from the elemental components using tin as a flux. Their skutterudite (CoAs₃) type structures were refined from single‐crystal X‐ray data. The new compound GdFe₄P₁₂ was prepared by reaction of an alloy Gd_1/3Fe_2/3 with phosphorus in a tin flux. Its cubic “filled” skutterudite (LaFe₄P₁₂ type) structure was refined from single‐crystal X‐ray data: a = 779.49(4) pm, R = 0.019 for 304 structure factors and 11 variable parameters. SmFe₄P₁₂ shows Van Vleck paramagnetism while GdFe₄P₁₂ is a soft ferromagnet with a Curie temperature of T_C = 22(5) K. Both are metallic conductors. The new isotypic polyarsenide NdFe₄As₁₂ (a = 830.9(1) pm) was obtained by reacting NdAs₂ with iron and arsenic in the presence of a NaCl/KCl flux. The new isotypic polyantimonide Eu_0.54(1)Co₄Sb₁₂ (a = 909.41(8) pm) was prepared by reaction of EuSb₂ with cobalt and antimony. Its structure was refined from single‐crystal X‐ray data to a residual of 0.024 (137 F values, 12 variables). A comparison of the Fe–P and P–P bond lengths in the compounds AFe₄P₁₂, where the A atoms (A = Ce, Eu, Gd, Th) have differing valencies, suggests that the Fermi level cuts through Fe–P bonding and P–P antibonding bands.     

Evaluation of the catalytic effect of ZnO as a secondary phase in the Ni0.5Zn0.5Fe2O4 system and of the stirring mechanism on biodiesel production reaction

In search of efficient ways to produce biodiesel under environmentally friendly conditions, catalytic reactions have been explored with emphasis on replacing homogeneous by heterogeneous catalysis with the use of new catalyst types, such as the spinel ferrites, which are described as a viable option, since they are stable, highly active, inexpensive, reusable, and allow the easy recovery of the reaction medium through the application of magnetic fields. In this context, the present work proposes to contribute to the consolidation of the catalytic viability of the Ni_0.5Zn_0.5Fe₂O₄ system obtained by combustion reaction, because although previous studies indicate the catalytic effectiveness of this system in polyphasic form, the present work seeks as differential to evaluate the influence of the secondary phases and magnetization of the Ni-Zn system in the conversion to biodiesel, and for this purpose, it aims to evaluate the catalytic effect of ZnO formed as secondary phase and obtained concomitantly in the Ni-Zn ferrite synthesis, besides evaluating the effect of the stirring mechanism used in biodiesel production reaction by the ethyl transesterification of soybean oil. The synthesized Ni-Zn ferrites and ZnO sample were characterized by X-ray diffraction (XRD), nitrogen adsorption textural analysis (BET), particle size distribution, and then, tested in two reactor types, one with magnetic stirring, and another of mechanical stirring, to observe the magnetization effect of the material, and the characterization of the obtained biodiesels by gas chromatography (GC) and acidity index. The performed catalytic tests showed that the Ni-Zn ferrites promoted excellent ester conversions with values near and above 94%, thus confirming that although ZnO also promotes good ester conversion (83.9%), the catalytic effectiveness of the Ni-Zn ferrite is evident and independent of secondary phases. Moreover, the catalytic tests performed in the magnetic stirring reactor using the Ni-Zn ferrites as catalysts made it possible to realize that their magnetic properties may be interference in the catalytic effectiveness, being this, a more determining factor than the surface characteristics.     

Raman study of ACu3Fe4O12 (A = Ca,Sr, Y and Eu)

A vibrational study of ACu₃Fe₄O₁₂ (A = Ca, Sr, Y and Eu) compounds was carried out by means of micro-Raman scattering and lattice dynamics calculations. Polarized Raman scattering measurements were performed on rectangular microcrystals, with sizes close to 7 μm, and six Raman active modes were observed among the eight expected. It was then possible to assign the observed modes to the correct symmetry. Moreover, lattice dynamics calculations led to determine the main atomic displacements and a good agreement was found between experimental and theoretical wavenumbers. Furthermore, wavenumbers evolution versus A cation showed two behaviors separating the samples into two groups.     

Polyol-mediated low-temperature synthesis of crystalline tungstate nanoparticles MWO4 (M = Mn,Fe, Co,Ni, Cu,Zn)

A polyol-mediated synthesis is presented as a general access to nanoscaled transition-metal tungstates MWO₄ (M = Mn, Fe, Co, Ni, Cu, Zn). Using simple inorganic salts as starting materials, uniform and readily crystalline nanoparticles are prepared under mild conditions (T < 220 °C). The nanoparticles are of high quality in terms of small diameter (<20 nm), high surface area (up to 200 m² g⁻¹), phase purity and yield (>85%). Size, morphology and composition can be adjusted by precise variation of the reaction parameters, including type of starting material, duration and temperature of reaction. The transition-metal tungstate nanoparticles are fully functional, exhibiting typical properties of this class of materials, for instance, superparamagnetism (CoWO₄), luminescence (ZnWO₄) and photocatalytic activity (CuWO₄).     

Influence of rare earth cation size on the crystal structure in rare earth silicates,Na2RESiO4(OH) (RE = Sc,Yb) and NaRESiO4 (RE = La,Yb)

Crystals of Na₂ScSiO₄(OH) and Na₂YbSiO₄(OH) were synthesized at low temperatures using a sodium hydroxide based hydroflux, while crystals of NaLaSiO₄ and NaYbSiO₄ were grown at high temperatures using a sodium fluoride/sodium chloride eutectic flux. Both structure types were crystallized under reaction conditions that, when used for medium sized rare earths (RE = Pr, Nd, Sm – Tm) yield the Na₅RE₄X[SiO₄]₄ structure type, where X is OH in the hydroflux conditions and F in the eutectic flux conditions. Herein, we report the synthesis, structure, size effect, and magnetic properties of these compositions and introduce the new structure type of Na₂RESiO₄(OH), which crystallizes in the orthorhombic space group Pca2₁, of NaLaSiO₄, which crystallizes in the orthorhombic space group Pna2₁, and of NaYbSiO₄, which crystallizes in the orthorhombic space group Pnma, where both NaRESiO₄ compounds have one silicon structural analog.     

Cesium carbonate supported on hydroxyapatite coated Ni0.5Zn0.5Fe2O4 magnetic nanoparticles as an effi cient and green catalyst for the synthesis of pyrano[2,3-c]pyrazoles

Cesium carbonate supported on hydroxyapatite coated Ni0.5Zn0.5Fe2O4 magnetic nanoparticles (Ni0.5Zn0.5Fe2O4@Hap-Cs2CO3) was found to be magnetically separable, highly efficient, green and recyclable heterogeneous catalyst. The synthesized nanocatalyst has been characterized with several methods (FT-IR, SEM, TEM, XRD and XRF) and these analyzes confirmed which the cesium carbonate is well supported to catalyst surface. After full characterization, its catalytic activity was investigated in the synthesis of pyranopyrazole derivatives and the reactions were carried out at room temperature in 50:50 water/ethanol with excellent yields (88-95%). More importantly, the Ni0.5Zn0.5Fe2O4@Hap-Cs2CO3 was easily separated from the reaction mixture by external magnetic field and efficiently reused at least six runs without any loss of its catalytic activity. Thus, the developed nanomagnetic base catalyst is potentially useful for the green and economic production of organic compounds.     

Vacuum ultraviolet spectroscopic properties of rare earth (RE) (RE = Eu,Tb, Dy,Sm, Tm)-doped K2GdZr(PO4)3 phosphate

The luminescent characteristics of RE (RE³⁺ = Eu, Tb, Dy, Sm and Tm)-doped K₂GdZr(PO₄)₃ have been investigated. The band in the range of 130–157 nm in the VUV excitation spectra of these compounds is attributed to the host lattice or PO₄^3? group absorption and the band from 157 nm to 215 nm with the maximum at 188 nm is due to the O–Zr charge transfer transition. For Eu³⁺-doped sample, the relatively weak band of O^2?–Eu³⁺ charge transfer (CTB) at 222 nm is observed and for Tb³⁺-doped sample, the band at 223 nm is related to the 4f–5d spin-allowed transition of Tb³⁺. For Dy³⁺- and Sm³⁺-doped samples, the O^2?–Dy³⁺ and O^2?–Sm³⁺ CTBs have not been observed, probably due to the 2p electrons of oxygen tightly bound to the zirconium ion in the host lattice. In Tm³⁺-doped sample, the weak O^2?–Tm³⁺ CTB is located at 170 nm. It is observed that there is energy transfer between the host and the luminescent activators (e.g. Eu³⁺, Tb³⁺ and Sm³⁺) except for Tm³⁺.     

Crystal structures and magnetic properties of the honeycomb-lattice antiferromagnet M2(pymca)3(ClO4), (M = Fe,Co, Ni)

We report on the syntheses, crystal structures, and magnetic properties of a series of transition metal coordination polymers M₂(pymca)₃(ClO₄), (pymca = pyrimidine-2-carboxylic acid, M = Fe (1), Co (2), and Ni (3)). These compounds are found to crystallize in a trigonal crystal system, space group P31m, with the lattice constants a = 9.727 Å and c = 5.996 Å for 1, a = 9.608 Å and c = 5.996 Å for 2, and a = 9.477 Å and c = 5.958 Å for 3 at room temperature. In these compounds, each pymca ligand connects to two M²⁺ ions, forming a honeycomb network in the ab plane. The temperature dependences of magnetic susceptibilities in these compounds show broad maxima, indicating antiferromagnetic interactions within two-dimensional honeycomb layers. We also observed an antiferromagnetic phase transition at low temperatures by magnetic susceptibility and heat capacity measurements. From the crystal structures and magnetic properties, we conclude that the compounds 1, 2, and 3 are good realizations of honeycomb-lattice antiferromagnets.     

Studies on magnetocapacitance,dielectric, ferroelectric,and magnetic properties of microwave sintered (1-x) (Ba0.8Sr0.2TiO3) - x (Co0.9Ni0.1Fe2O4) multiferroic composite

Present paper reports the synthesis of multiferroic composite (1-x) [Ba_0.8Sr_0.2Ti)O₃]-x[Co_0.9Ni_0.1Fe₂O₄] were x = 0.1, 0.2, 0.3 and 0.4. Both phases of the composite i.e. ferroelectric (BST) and ferrite (CNFO) are synthesized via hydroxide co-precipitation method followed by microwave sintering technique at 1100 °C. These composites were characterized for their structural, microstructural, dielectric analysis, magnetodielectric (MD) effect and ferroelectric properties. Presence of both the phases ferroelectric (BST) and ferromagnetic (CNFO) are confirmed by the x-ray diffraction and scanning electron microscopic analysis. Maxwell-Wagner type dielectric dispersion is observed in frequency dependent dielectric measurement. Temperature-dependent dielectric properties were measured from 25 °C to 500 °C at various applied frequencies. Ferroelectric behavior in the composites was confirmed by the polarization vs. Electric field analysis. The magnetodielectric effect was studied in the presence of applied magnetic field from 0 to 1 Tesla. Magnetocapacitance (%) increases with increase in the ferrite concentration in the ferroelectric phase. The maximum percentage of magnetocapacitance is observed in 60BST-40CNFO composite which is MC = 30% at the frequency 1 KHz with the applied magnetic field is 1-Tesla. Room temperature magnetic hysteresis loops show an increase in saturation magnetization (Ms) with an increase in ferrite concentration.     

Nanostructured spinel-type M(M = Mg,Co, Zn)Cr2O4 oxides: novel adsorbents for aqueous Congo red removal

Nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides with novel adsorbents for aqueous Congo red removal were synthesized by a polyacrylamide gel method and studied for their phase structure, microstructure, adsorption performance, and multiferroic behavior. The phase structure and purity analysis revealed that the nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides presented a spinel-type cubic structure, and the formation of a secondary phase such as Cr₂O₃, MgO, ZnO, or Co₃O₄ was not observed. The microstructure characterization confirmed that the spinel-type MCr₂O₄ oxides grew from fine spherical particles to large rhomboid particles. Adsorption experiments of spinel-type MCr₂O₄ oxides for adsorption of Congo red dye were fitted well with the pseudo-second-order kinetics. The adsorption capacity of the ZnCr₂O₄ oxide (44.038 mg/g, pH 7, temperature 28 °C, initial dye concentration 30 mg/L) was found to be higher than that of MgCr₂O₄ oxide (43.592 mg/g, pH 7, temperature 28 °C) and CoCr₂O₄ oxide (28.718 mg/g, pH 7, temperature 28 °C). The effects of initial adsorbent concentration, initial dye concentration, pH, and temperature between the ZnCr₂O₄ oxide and Congo red dye at which optimal removal occurs, were performed. The thermodynamic studies confirmed that a high temperature favors the adsorption of Congo red dye onto ZnCr₂O₄ oxide studied. The nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides that exhibited high adsorption performance for adsorption of Congo red dye can be ascribed to the synergistic effect of electrostatic interaction, pore filling, and ion exchange. The present work suggested that the nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides have excellent adsorption performance and multiferroic behavior, which shows potential applications for removal of the Congo red dye from wastewater, magnetic memory recording media, magnetic sensor, energy collection and conversion device, and read/write memory.     

Preparation of core-shell magnetic Fe3O4@SiO2-dithiocarbamate nanoparticle and its application for the Ni2+, Cu2+ removal

A typical superparamagnetic nanoparticles-based dithiocarbamate absorbent (Fe₃O₄@SiO₂-DTC) with core-shell structure was applied for aqueous solution heavy metal ions Ni²⁺, Cu²⁺ removal.