Template-free synthesis of core-shell Fe_(3)O_(4)@MoS_(2)@mesoporous TiO_(2) magnetic photocatalyst for wastewater treatment

TiO_(2)is the dominant and most widely researched photocatalyst for environmental remediation,however,the drawbacks,such as only responding to UV light(<5%of sunlight),low charge separation efficiency,and difficulties in recycling,have severely hindered its practical application.Herein,we synthesized magnetically separable Fe_(3)O_(4)@MoS_(2)@mesoporous TiO_(2)(FMmT)photocatalysts via a simple,green,and template-free solvothermal method combined with ultrasonic hydrolysis.It is found that FMmT possesses a high specific surface area(55.09 m2·g−1),enhanced visible-light responsiveness(~521 nm),and remarkable photogenerated charge separation efficiency.In addition,the photocatalytic degradation efficiencies of FMmT for methylene blue(MB),rhodamine B(RhB),and tetracycline(TC)are 99.4%,98.5%,and 89.3%within 300 min,respectively.The corresponding degradation rates are 4.5,4.3,and 3.1 times higher than those of pure TiO_(2)separately.Owing to the high saturation magnetization(43.1 A·m^(2)·kg^(−1)),FMmT can achieve effective recycling with an applied magnetic field.The improved photocatalytic activity is closely related to the effective transport of photogenerated electrons by the active interlayer MoS_(2) and the electron–hole separation caused by the MoS_(2)@TiO_(2)heterojunction.Meanwhile,the excellent light-harvesting ability and abundant reactive sites of the mesoporous TiO_(2)shell further boost the photocatalytic efficiency of FMmT.This work provides a new approach and some experimental basis for the design and performance improvement of magnetic photocatalysts by innovatively incorporating MoS2 as the active interlayer and integrating it with a mesoporous shell.

Electrostatic switch of magnetic core-shell in 0-3 type LSMO/PZT composite film

By dispersing La1-xSrxMnO3 (LSMO) granule into PbZrxTi1-xO3 (PZT) matrix, the 0-3 type LSMO/PZT composite film is synthesized through chemical solution method. The asymmetry of the top and bottom electrodes introduces novel electrostatic screening on LSMO/PZT interface. As electric polarization is switched between upward and downward orientations, the evolution of exchange bias, diode transport, and magnetoresistance is observed. The result implies the electrostatic switch of magnetic core-shell in the present film. In detail, as the spontaneous polarization is upward or downward in the PZT matrix, the ferromagnetic/antiferromagnetic or ferromagnetic/ferromagnetic core-shell structure is formed in LSMO granule, respectively. This work would develop a novel device for spintronics and metamaterial.

Preparation and Magnetic Properties of Cu-Ni Core-shell Nanowires in Ion-track Templates

Cu-Ni core-shell nanowires, with an inner Cu core diameter of about 60 nm and varying Ni shell thicknesses （10, 30, 50, 60, and 80 nm）, were successfully fabricated in porous polycarbonate （PC） ion- track templates by a two-step etching and electrodeposition method. In our experiment, the thickness of Ni shell can be effectively tuned through the etching time of templates. The core-shell structure was confirmed by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The X-ray diffraction （XRD） pattern elucidates the co-existence of characteristic peaks for both Cu and Ni, indicating no other phases were formed during preparation. Magnetic hysteresis loops measured via vibrating sample magnetometry （VSM） revealed that Cu-Ni core-shell nanowires with thinner Ni shell exhibited obviously diamagnetic character and together with a weak ferromagnetic activity, whereas ferromagnetic behavior was primarily measured for the wires with thicker Ni shell. With increasing Ni shell thickness, the squareness and coercivity value became smaller due to the shape anisotropy and the formation of multi-domain structure.

Fluorescent Superparamagnetic Core-Shell Nanostructures: Facile Synthesis of Fe@C-CN_xParticles for Reusable Photocatalysts

Synthesis and characterization of hybrid fluorescent superparamagnetic core-shell particles of Fe@C-CNx composition are presented for the first time. The prepared Fe@C-CNx hybrid nanoparticles were found to possess multifunctionality by exhibiting strong superparamagnetic properties and bright fluorescence emissions at 500 nm after the excitation with light in the UV-visible range. Fe@C-CNx also exhibits photocatalytic activities for organic dye degradation comparable to pure amorphous CNx with reusability through magnetic separation. The combination of magnetic and fluorescent properties of core-shell Fe@C-CNx nanoparticles opens opportunities for their application as sensors and magnet manipulated reusable photocatalysts. Superparamagnetic Fe@C core-shell nanoparticles were used as the template material in the synthesis, where the carbon shell was functionalized through one-step free-radical addition of alkyl groups terminated with carboxylic acid moieties. The method utilizes the organic acyl peroxide of dicarboxylic acid (succinic acid peroxide) as a non-oxidant functional free radical precursor for functionalization. Further, covalently functionalized succinyl-Fe@C core-shell nanoparticles were coated with the amorphous carbon nitride (CNx) generated by an in-situ solution-based chemical reaction of cyanuric chloride with lithium nitride. A detailed physicochemical characterization of the microstructure, magnetic and fluorescence properties of the synthesized hybrid nanoparticles is provided.

Manufacturing of Surface Nanostructured Fibers Featuring an Antibacterial Effect by Magnetic Field Transportation of Magnetite@Silver Core-Shell Nanoparticles

Magnetic core-shell nanoparticles of type Fe3O4@Ag were synthesized in gram scale following a combined co-precipitation phase-transfer method and afterwards, processed to nanoparticle polymer (polypropylene and polyamide) composites. These composites were used as sheath material for the fabrication of core-sheath fibers. During the melt spinning process, a magnetic field was applied around the roving, whereby the particles move in the still liquid sheath polymer towards the surface. The produced fiber materials were investigated by AFM showing a nanostructuring of the surface, which was indirectly confirmed by determination of a slight surface tension lowering. Nanoparticle movement was shown by cross-section SEM and EDX measurements. The antibacterial activity of the spun fibers was proven by contacting them with Escherichia coli. A long-term stability of this effect was observable by carrying out a standard washability test. In contrast to previous works this new approach uses no deposition technique to introduce surface changes. It rather applies a magnetic force to move appropriately equipped nanoparticles from the inside of the fiber to the surface. This leads in only one step to a strong superficial anchoring of the particles resulting in a unique combination of long-term stable antibacterial and improved anti-soiling effects.

Hierarchical Magnetic Network Constructed by CoFe Nanoparticles Suspended Within “Tubes on Rods” Matrix Toward Enhanced Microwave Absorption

Hierarchical magnetic-dielectric composites are promising functional materials with prospective applications in microwave absorption(MA)field.Herein,a three-dimension hierarchical“nanotubes on microrods,”core–shell magnetic metal–carbon composite is rationally constructed for the first time via a fast metal–organic frameworksbased ligand exchange strategy followed by a carbonization treatment with melamine.Abundant magnetic CoFe nanoparticles are embedded within one-dimensional graphitized carbon/carbon nanotubes supported on micro-scale Mo2N rod(Mo2N@CoFe@C/CNT),constructing a special multi-dimension hierarchical MA material.Ligand exchange reaction is found to determine the formation of hierarchical magnetic-dielectric composite,which is assembled by dielectric Mo2N as core and spatially dispersed CoFe nanoparticles within C/CNTs as shell.Mo2N@CoFe@C/CNT composites exhibit superior MA performance with maximum reflection loss of−53.5 dB at 2 mm thickness and show a broad effective absorption bandwidth of 5.0 GHz.The Mo2N@CoFe@C/CNT composites hold the following advantages:(1)hierarchical core–shell structure offers plentiful of heterojunction interfaces and triggers interfacial polarization,(2)unique electronic migration/hop paths in the graphitized C/CNTs and Mo2N rod facilitate conductive loss,(3)highly dispersed magnetic CoFe nanoparticles within“tubes on rods”matrix build multi-scale magnetic coupling network and reinforce magnetic response capability,confirmed by the off-axis electron holography.

PREPARATION AND CHARACTERIZATION OF PVA COATED MAGNETIC NANOPARTICLES

Polyvinyl alcohol coated magnetic particles (PVA ferrofluids) have been synthesized by chemical co-precipitation of Fe(II)/Fe(III) salts in 1.5 mol/L NH4OH solution at 70 degreesC in the presence of PVA. The resultant colloidal particles have core-shell structures, in which the iron oxide crystallites form the cores and PVA chains form the shells. The hydrodynamic diameter of the colloidal particles is in the range of 108 to 155 nm, which increases with increasing PVA concentration from 5 wt% to 20 wt%, The size of the magnetic cores is ca. 5-10 nm, which is relatively independent of PVA concentration. Under transmission electron microscopic (TEM) examination, the magnetic cores exhibit somewhat irregular shapes varying from spherical, oval, to cubic. Magnetometry measurement revealed that the PVA coated magnetic particles are superparamagnetic. The saturation magnetization of 5 wt% and 20 wt% PVA ferrofluids at 300 K is 54 and 49 emu/g, respectively. All the PVA ferrofluids exhibited excellent colloidal stability in pure water and phosphate buffer saline (PBS, pH = 7.4). The ferrofluids can remain stable in above solutions for more than three months at 4 degreesC.

Preparation and Characterization of Nano-Sized (Mg_(x)Fe_(1–x)O/SiO₂) (x = 0.1) Core-Shell Nanoparticles by Chemical Precipitation Method

Magnetic core-shell nanoparticles have been widely studied because of their excellent and convenient magnetic and electrical properties.In this present work core-shell magneticnanoparticles (MNPs) were synthesized by simple chemical precipitation method. Firstly Mg(x)Fe(1–x)O (magnesiwuestite) nano powder samples were synthesised by low temperature chemical combustion method. Secondly the as synthesised Mg(x)Fe(1–x)O nanoparticles are used to synthesis magnetic core-shell Nano particles byusing 2-propanol, poly ethylene glycol (PEG), ammonia solution 30 wt%, tetraethyl orthosilicate (TEOS). Separation of the core-shell magnetic nanoparticles from the aqueous suspension using a centrifuge. The synthesised MNPs and core shell MNP were characterized by X-ray diffraction (XRD), Thermal gravimetric-differential thermal analyzer (TG-DTA), Transmission electron microscopy (TEM), scanning electron microscopy (SEM), (EDAX) for structural, thermal and morphological respectively. It is observed that the particle size of spherical sampleis 32.5 nm.

Micromagnetic simulations of reversal magnetization in cerium-containing magnets

Single-grain models with different cerium contents or structural parameters have been introduced to investigate the reversal magnetization behaviors in cerium-containing magnets. All the micromagnetic simulations are carried out via the object oriented micromagnetic framework(OOMMF). As for single(Nd,Ce)_2 Fe_(14)B type grain, the coercivity decreases monotonously with the increase of the cerium content. Four types of grain structure have been compared: single(Nd,Ce)_2 Fe_(14)B type, core((Nd,Ce)_2 Fe_(14)B)-shell(Nd_2 Fe_(14)B) type with 2 nm thick shell, core(Ce_2 Fe_(14)B)-shell(Nd_2 Fe_(14)B) type, and core(Nd_2 Fe_(14)B)-shell(Ce_2 Fe_(14)B) type. It is found that core((Nd,Ce)_2 Fe_(14)B)-shell(Nd_2 Fe_(14)B)type grain with 2 nm thick shell always presents the largest coercivity under the same total cerium content. Furthermore,the relationship between the coercivity and the shell thickness t in core((Nd,Ce)_2 Fe_(14)B)-shell(Nd_2 Fe_(14)B) type grain has been studied. When the total cerium content is kept at 20.51 at.%, the analyzed results show that as t varies from 1 nm to 7 nm, the coercivity gradually ascends at the beginning, then quickly descends after reaching the maximum value when t = 5 nm. From the perspective of the positions of nucleation points, the reasons why t affects the coercivity are discussed in detail.

Fenton-like oxidation of azo dye in aqueous solution using magnetic Fe3O4-MnO2 nanocomposites as catalysts

In order to overcome the drawback of the low degree of separation from an aqueous solution of MnO_2, Fe_3 O_4-MnO_2 core-shell nanocomposites were used as heterogeneous Fenton-like catalysts for the removal of acid orange 7. On the basis of the catalyst characterization, the catalytic ability of the as-synthesized nanocomposites was examined. The results showed that Fe304-Mn02 core-shell nanocomposites had greater catalytic ability than Fe_3 O_4 or MnO_2 used alone. Meanwhile, the catalyst dosage, H_2 O_2 dosage, temperature, and initial pH had significant effects on the removal of acid orange 7. A high degree of stability and reusability were exhibited by Fe_3 O_4-MnO_2 core-shell nanocomposites. Both HO· and HO_2· were generated in the reaction and HO· was the main radical for the removal of acid orange 7. A mechanism for H_2 O_2 catalytic decomposition using Fe_3 O_4-MnO_2 core-shell nanocomposites to produce HO·is proposed.

Novel Fe_3O_4@SiO_2@Ag@Ni trepang-like nanocomposites:High-efficiency and magnetic recyclable catalysts for organic dye degradation

A facile step-by-step approach is developed for synthesizing the high-efficiency and magnetic recyclable Fe3O4@SiO2@Ag@Ni trepang-like nanocomposites.This method involves coating Fe2O3 nanorods with a uniform silica layer,reduction in 10%H2/Ar atmosphere to transform the Fe2O3 into magnetic Fe3O4,and finally depositing Ag@Ni core-shell nanoparticles on the L-lysine modified surface of Fe3O4@SiO2 nanorods.The fabricated nanocomposites are further characterized by x-ray diffraction,transmission electron microscopy,scanning electron microscope,Fourier transform infrared spectroscopy,and inductively coupled plasma mass spectroscopy.The Fe3O4@SiO2@Ag@Ni trepang-like nanocomposites exhibit remarkably higher catalytic efficiency than monometallic Fe3O4@SiO2@Ag nanocomposites toward the degradation of Rhodamine B（RhB） at room temperature,and maintain superior catalytic activity even after six cycles.In addition,these samples could be easily separated from the catalytic system by an external magnet and reused,which shows great potential applications in treating waste water.

Memory Effect up to Room-temperature in Ni/Ni_2P Core-shell Structured Nanoparticles

Memory effect has been studied in the system using magnetic nanoparticles with Ni nanocore encapsulated by non-magnetic and oxidation-resistant Ni2P nanoshell acquired through surface-phosphatizing Ni nanoparticles. The self-assembled array with interparticle spacing of about 6 nm shows memory effect up to 200 K below its average blocking temperature of 260 K. And reducing the interparticle spacing of the self-assembled array via annealing can further enlarge the temperature range of memory effect up to room-temperature. The memory effect can be understood based on the thermal relaxation theory of single-domain magnetic nanoparticles. Furthermore, the read-write magnetic coding is realized based on the temperature changes, using the memory effect up to room-temperature, which may be useful for future memory devices.

A Comparative Study on the Selected Area Electron Diffraction Pattern of Fe Oxide/Au Core-shell Structured Nanoparticles

The selected area electron diffraction （SAED） pattern of magnetic iron oxide core/gold shell nanoparticles has been studied. For the composite particles with mean size less than 10 nm, their SAED pattern is found to be different from either the pattern of pure Fe oxide nanoparticles or that of pure Au particles. Based on the fact that the ring diameters of these composite particles fit the characteristic relation for the fcc structure, the Au atoms on surfaces of the concerned particles are supposed to pack in a way more tightly than they usually do in pure Au nanoparticles. The driving force for this is the coherency strain which enables the shell material at the heterostructured interface to adapt the lattice parameters of the core.

Preparation and characterization of TiO_2-SiO_2-Fe_3O_4 core-shell powders in nano scale

TiO2/SiO2/Fe3O4 nanoparticles have bigger specific area which can greatly increase the efficiency of photo-catalysis.The TiO2/SiO2/Fe3O4 particles in nano scale were prepared with reduction method at high temperature in this paper,and their morphology,particle size and magnetic property were characterized by transmission electron microscope(TEM),Xray diffraction(XRD) and magnetometer.The results show that the grain sizes of Fe3O4,SiO2-Fe3O4 and TiO2-SiO2-Fe3O4 particles were 50nm,70nm and 120nm,respectively.With the modification of SiO2,Fe3O4 magnetic cores are protected from oxidation.Moreover,by the addition of TiO2 function layer,TiO2-SiO2-Fe3O4 functional nanoparticles,with the saturation magnetization density of 34.1emu/g,is magnetically recoverable.The processes of this method are so simple that the nanoparticles can be produced in large quantity.

Photodegradation of Binary Azo Dyes Using Core-Shell Fe₃O₄/SiO₂/TiO₂Nanospheres

Photodegradation has emerged as an environmentally friendly method of decomposing harmful dyes in wastewater. In this study, core-shell Fe3O4/SiO2/ TiO2 nanospheres with magnetic cores were obtained from synthesised magnetic Fe3O4 nanoparticles through the precipitation method, the surface of the magnetic Fe3O4 nanoparticles was coated with a silica (SiO2) layer by hydrolysis of tetramethoxysilane (TMOS) as a silica source, and finally, Fe3O4/SiO2 nanospheres were coated with titanium (TiO2) layer using tetrabutyltitanate (TBT) as a precursor through the sol-gel process. The morphology and structure of the prepared materials were characterised by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), X-ray energy dispersive spectrometry (EDAX), Fourier transform infrared spectroscopy (FT-IR), and atomic force microscopy (AFM). The photocatalytic activities of the prepared core-shell nanospheres were studied using binary azo dyes, namely methyl orange (anionic dye, MO) and methylene blue (cationic dye, MB) in aqueous solution under UV light irradiation (365 nm), and UV-Vis spectrophotometer was utilised to monitor the amount of each dye in the mixture. It was found that 90.2% and 100% of binary MO and MB were removed for 5 h, respectively. The results revealed that the efficiency of the photocatalytic degradation of the core-shell nanospheres was not degreased after five runs that can be used as recyclable photocatalysts. The results show that the performance of the prepared core-shell nanospheres was better than that of commercial TiO2 nanoparticles. Moreover, the magnetic separation properties of the core-shell Fe3O4/SiO2/TiO2 nanospheres can enable the prepared materials to have wider application prospects.

Optimization of core-shell structure distribution in sintered Nd-Fe-B magnets by titanium addition

In view of the uneven distribution of the core-shell structure of sintered Nd-Fe-B magnets after grain boundary diffusion,this study proposes to use high-melting-point and reactive element titanium(Ti)as an additive to increase the diffusion channels and to enhance the diffusion of heavy rare earth elements along the grain boundary phase.By adding Ti element,the diffusion depth and hence the intrinsic coercivity of magnets are increased significantly.The addition of Ti increases the coercivity at two stages:initially from 16.07 to 16.29 kOe by addition effect,and then from 16.29 to 25.16 kOe by facilitating the diffusion of Tb element.The formation of TiB_(2) phase improves the periodic arrangement of the crystal structure in the surroundings of the grain boundary phase and enhances its activity.The improved grain boundary diffusion and better core-shell structure distribution provide a theoretical guidance fo r solving the problem of diffusion depth in bulk magnets.

MOFs derived magnetic porous carbon microspheres constructed by core-shell Ni@C with high-performance microwave absorption

Lightweight and high-performance are two determining factors for metal-organic-frameworks(MOFs)derived microwave absorbers.However,most of the reported MOFs derived absorbers usually possess high filler loading.Herein,a series of MOFs derived magnetic porous carbon microspheres with tunable diameter and high specific surface area have been synthesized via a pyrolysis process.The synthesized magnetic porous carbon microspheres,constructed by uniformly distributed core-shell Ni@C,exhibit high-performance microwave absorption with a low filler loading of 10 wt%.Considering the mciro-mesoporous structures,matched impedance,strong conductive loss,enhanced dipolar/interfacial polarization as well as strong magnetic coupling network,a minimum reflection loss of-60 dB and an absorption bandwidth of 7.0 GHz can be achieved at 2.6 mm.Moreover,the bandwidth reaches as wide as 10.2 GHz when the thickness is 4 mm.In addition,compared with other MOFs derived absorbers,this work provides us a simple strategy for the synthesis of porous carbon microspheres with lightweight and high-performance microwave absorption for practical applications.

Purification of starch and phosphorus wastewater using core-shell magnetic seeds prepared by sulfated roasting

Core-shell magnetic seeds with certain adsorption capacity that were prepared by sulfated roasting, served as the core of a magnetic separation technology for purification of starch wastewater. XRD and SEM results indicate that magnetite's surface transformed to be porous α-Fe_2O_3 structure. Compared with magnetite particles, the specific surface area was significantly improved to be 8.361 from 2.591 m^2/g, with little decrease in specific susceptibility. Zeta potential, FT-IR and XPS experiments indicate that both phosphate and starch adsorbed on the surface of the core-shell magnetic seeds by chemical adsorption, which fits well with the Langmuir adsorption model. The porous surface structure of magnetic seeds significantly contributes to the adsorption of phosphate and starch species, which can be efficiently removed to be 1.51 mg/L(phosphate) and 9.51 mg/L(starch) using magnetic separation.

Synthesis of magnetic core-shell iron nanochains for potential applications in Cr(Ⅵ)ion pollution treatment

Fe nanochains with diameters of 50-150 nm and average length of about 1μm were synthesized by titrating NaBH_(4)solution into FeCl_(2) aqueous solution(i.e.,reduction of Fe(II)ions).The microstructures and magnetic properties were studied by X-ray diffraction(XRD),transmission electron microscope(TEM),and vibrating sample magnetometer(VSM).The results reveal that the nanochains have a core-shell structure with a-Fe as the core and amorphous iron oxide as the shell.The Fe coreshell nanochains show the characteristic of soft magnetic materials,achieving the highest magnetization of200.74 mA-m^(2)·g^(-1).The influences of the titrating rate of NaBH_(4)aqueous solution on the morphology of the Fe nanochains were also studied.It reveals that low titrating rate is beneficial for synthesizing Fe nanochains with uniform morphology.The reduction experiments indicate that these Fe nanochains are of high reducibility.About 90%Cr(VI)ions are successfully removed after 10 min reaction of 100 mg Fe nanochains in the 100 ml K_(2)Cr_(2)O_(7) solution(100 mg·L^(-1))and more than 99%after 30 min.

Preparation of core-shell magnetic Fe_3O_4@SiO_2-dithiocarbamate nanoparticle and its application for the Ni^(2+), Cu^(2+) removal

A novel magnetic nanoparticles-based dithiocarbamate absorbent（Fe3O4@SiO2-DTC） with core-shell structure was synthesized under mild conditions and used in aqueous solution Ni2＋ and Cu2＋ ions treatment. The structure, morphology and magnetic properties of the adsorbent were characterized by Xray diffraction（XRD）, fourier transformed infrared spectroscopy（FTIR）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, and vibrating sample magnetometer（VSM）.Fe3O4@SiO2-DTC exhibited a typical superparamagnetic with a saturation magnetization value of52.7 emu/g, which could be rapidly separated from aqueous solution under external magnetic field. We investigated the effects of solution p H, adsorption time, and the initial concentration of heavy metal ions on the adsorption of Ni2＋ and Cu2＋. The adsorption equilibrium times of Ni2＋and Cu2＋ on Fe3 O4@SiO2-DTC were reached at 15 min and 90 min, respectively. The adsorption kinetic data were fitted to the pseudosecond-order model, and the adsorption data were consistent with the Frenudlich isotherm model. When the initial concentration of heavy metal ions was 250 mg/L, the maximum adsorption capacity of Ni2＋ and Cu2＋ at room temperature was 235.23 mg/g and 230.49 mg/g, respectively. In addition, we discussed the plausible adsorption mechanism. The results indicated that the adsorption was mainly dominated by chelation.