Poly (3,4‐ethylenedioxythiophene) γ‐Fe2O3 polymer composite–super paramagnetic behavior and variable range hopping 1D conduction mechanism–synthesis and characterization

The present paper reports the preparation of poly (3,4‐ethylenedioxythiophene) (PEDOT) ferrimagnetic conducting polymer composite by incorporation of ferrite particles in the polymer matrix by emulsion polymerization. Synthesis of PEDOT–γ‐Fe₂O₃ composite was carried out by chemical oxidative polymerization of EDOT with ferrite particles in the presence of dodecylbenzenesulfonic acid (DBSA) that works as dopant as well as surfactant in aqueous medium. The resulting conducting composite possesses saturation magnetization (Ms) value of 20.56 emu/g with a conductivity of 0.4 Scm^?1, which was determined by VSM and four probe technique, respectively. B‐H curve reveals that ferrimagnetic particles of γ‐Fe₂O₃ show super‐paramagnetic behavior at room temperature which was also observed in PEDOT–γ‐Fe₂O₃ composite. The resulting conducting ferrimagnetic composite shows microwave absorption loss of 18.7–22.8 dB in the frequency range of 12.4–18 GHz. Thermogravimetric analysis of the composite revealed that the composite is thermally stable up to 230°C. The characterization of the PEDOT–γ‐Fe₂O₃ composite was carried out using XRD and FTIR spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.     

Electromagnetic properties of Fe3O4‐functionalized graphene and its composites with a conducting polymer

Hybrid materials of Fe₃O₄‐decorated reduced graphene oxide (Fe₃O₄‐RGO) and poly(3,4‐ethylenedioxythiophene) (PEDOT) were prepared by poly(ionic liquid)‐mediated hybridization. In this hybrid material, poly(ionic liquid) was found to perform multiple roles for: (1) stabilizing Fe₃O₄‐RGO against aggregation in the reaction medium, (2) transferring Fe₃O₄‐RGO nanomaterials from aqueous into organic phase, and (3) associating Fe₃O₄‐RGO nanomaterials with PEDOT. The hybrid materials of Fe₃O₄‐RGO with PEDOT showed the lowest surface resistivity of 80 Ω sq^?1 at an RGO‐Fe₃O₄ loading of 1 wt %, and exhibited superparamagnetic behavior with an electromagnetic interference shielding effectiveness of 22 dB. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Facile synthesis of Fe3O4/reduced graphene oxide/polyvinyl pyrrolidone ternary composites and their enhanced microwave absorbing properties

In this paper, ternary nanocomposites of Fe₃O₄/reduced graphene oxide/polyvinyl pyrrolidone (Fe₃O₄/rGO/PVP) as a novel type of electromagnetic microwave absorbing materials were synthesized by a three-step chemical approach. First, Fe₃O₄ nanospheres were made by solvent thermal method. Successively, the Fe₃O₄ particles were assembled with rGO after having activated by para-aminobenzoic acid. PVP grafting and reduction of GO happened simultaneously in the third step. It is found that the electromagnetic absorption (EA) performance of synthesized ternary composites with suitable PVP amount had been significantly enhanced comparing to Fe₃O₄ and Fe₃O₄/rGO. Merely 15?wt% low loading in paraffin and thin as 2.8?mm can reach effective EA bandwidth (below ?10 Db) of 11.2?GHz, and the highest reflection loss reached ?67?dB at 10.7?GHz. It was demonstrated that these composites show an effective route to novel microwave absorbing material design.     

Achieving full effective microwave absorption in X band by double-layered design of glass fiber epoxy composites containing MWCNTs and Fe3O4 NPs

The glass fiber epoxy composites containing MWCNTs and Fe₃O₄ NPs were manufactured by composites liquid molding process. The microwave absorbing properties of single-layered and double-layered glass fiber/MWCNTs/epoxy and glass fiber/Fe₃O₄ NPs/epoxy composites were evaluated. The reflection loss(RL) were calculated by the measured complex permittivity and permeability using waveguide method by vector network analyzer. Based on the mechanism analysis and deficiency of single-layer absorber, the double-layered composites were fabricated by using matching layer and absorbing layer to enhance the microwave absorption performance, which can be modulated by tailoring the electromagnetic parameters and thicknesses of each layer. The optimized microwave absorbing properties of double-layered composites with minimum RL of −45.7 dB and full X-band effective absorption can be achieved when the total thickness of the matching layer and absorbing layer is 1.8 mm, which can be attributed to synergistic effect of improved impedance matching characteristic and superior microwave attenuation characteristic of the absorbing layer. The combined utilization of dielectric loss and magnetic loss absorbent and their double-layered structure design shows great design flexibility and diversity and can be a promising candidate for designing high performance microwave absorbing materials.     

基于Li_(0.35)Zn_(0.3)Fe_(2.35)O_4和碳纳米纤维双层吸波体的结构设计与吸收性能研究

通过静电纺丝技术和热处理制备了Li0.35Zn0.3Fe2.35O4纳米纤维和碳纳米纤维,并将它们各自均匀分散在硅橡胶基质中,测量了相应复合体在2~18 GHz频率范围内的相对复介电常数和复磁导率,并根据传输线理论评估了由它们所构成的单层和双层结构吸波体的微波吸收特性。结果显示由于Li0.35Zn0.3Fe2.35O4纳米纤维与碳纳米纤维的电磁特性的有机结合,双层吸波体的微波吸收性能明显优于同厚度的单层吸波体。当以厚为1.8 mm的Li0.35Zn0.3Fe2.35O4纳米纤维/硅橡胶复合体为吸收层和厚为0.2mm的碳纳米纤维/硅橡胶复合体为匹配层时,双层吸波体的反射率在13.9 GHz达到一个最小值-47.8 dB,反射率低于-10 dB的吸收带宽为8.8 GHz,频率范围为9.2~18 GHz,反射率小于-20 dB的频率范围为11.5~18 GHz,带宽为6.5 GHz,覆盖整个Ku波段。优化设计的双层吸波体有望作为一种轻质高效的Ku波段微波吸收材料。     

基于Li0.35Zn0.3Fe2.35O4和碳纳米纤维双层吸波体的结构设计与吸收性能研究

通过静电纺丝技术和热处理制备了Li_0.35Zn_0.3Fe_2.35O₄纳米纤维和碳纳米纤维,并将它们各自均匀分散在硅橡胶基质中,测量了相应复合体在2~18GHz频率范围内的相对复介电常数和复磁导率,并根据传输线理论评估了由它们所构成的单层和双层结构吸波体的微波吸收特性。结果显示由于Li_0.35Zn_0.3Fe_2.35O₄纳米纤维与碳纳米纤维的电磁特性的有机结合,双层吸波体的微波吸收性能明显优于同厚度的单层吸波体。当以厚为1.8mm的Li_0.35Zn_0.3Fe_2.35O₄纳米纤维/硅橡胶复合体为吸收层和厚为0.2mm的碳纳米纤维/硅橡胶复合体为匹配层时,双层吸波体的反射率在13.9GHz达到一个最小值-47.8dB,反射率低于-10dB的吸收带宽为8.8GHz,频率范围为9.2~18GHz,反射率小于-20dB的频率范围为11.5~18GHz,带宽为6.5GHz,覆盖整个Ku波段。优化设计的双层吸波体有望作为一种轻质高效的Ku波段微波吸收材料。     

Amorphizing of Ag Nanoparticles under Bioinspired One‐step Assembly of Fe3O4‐Ag/rGO Hybrids via Self‐redox Process with Enhanced Activity

Efficient and reusable nanocatalysts fabricated via a facile assembly are highly desirable for the cost‐effective hydrogenation reduction. Inspired by a fishing process with a fishnet, multifunctional nanostructured catalysts are rationally designed to combine interesting features via the self‐redox assembly of Fe₃O₄‐Ag composites on reduced graphene oxide (rGO) (Fe₃O₄‐Ag/rGO). In detail, Fe₃O₄ nanoparticles (NPs) endow the ternary hybrids with superparamagnetism (21.42 emu g^?1), facilitating catalysts to be separated from the reaction system. rGO could provide electron transfer pathways, enhancing catalytic activity. More interestingly, GO and Ag⁺ could behave as oxidants to oxidize Fe²⁺ for the in situ assembly of Fe₃O₄‐Ag/rGO without any addition of reductant/oxidant or organic solvents, and AgNPs endow the ternary hybrids with excellent catalytic behaviour. Meaningfully, the bioinspired process enables the ternary hybrids to possess more abundant micro?/nanopores, larger surface area, and more amorphization. They exhibit exceptional catalytic performance, and could be recycled with excellent activity by means of convenient magnetic separation (at least 7 times). Moreover, the ternary hybrids could degrade methylene blue under UV light due to different valence states of Fe in Fe₃O₄. Therefore, the proposed bioinspired assembly and structure design for hierarchical catalysts would pave a promising way to assemble other catalysts.     

溶剂热法制备四氧化三铁/聚乙烯亚胺修饰的多壁碳纳米管复合粒子及其吸波性能

采用溶剂热法将磁性Fe_3O_4粒子附着在聚乙烯亚胺(PEI)修饰的多壁碳纳米管(MWNTs)表面,制备了兼具介电损耗和磁损耗的复合吸波微粒Fe_3O_4/MWNTs。利用X射线衍射仪(XRD)、傅里叶红外光谱仪(FTIR)、热重分析仪(TGA)、透射电子显微镜(TEM)及矢量网络分析仪等分析了Fe_3O_4/MWNTs复合粒子的结构、形貌和吸波性能。TEM结果表明,由于PEI的修饰作用,Fe_3O_4/MWNTs复合粒子具有良好的分散性。XRD结果显示,附着的Fe_3O_4粒子具有完整的晶型结构。吸波性能结果表明,PEI修饰的Fe_3O_4/MWNTs复合微粒拥有非常优异的吸波性能,随着厚度的增加,复合微粒的吸收峰向低频处移动。在厚度为3.2 mm,频率为6.16 GHz时,出现了最大反射损耗-42.9 d B,反射损耗大于-10 d B的频段为1.42 GHz(5.40~6.82 GHz)。     

Hierarchical Fe3O4@TiO2 Yolk–Shell Microspheres with Enhanced Microwave‐Absorption Properties

A facile and efficient strategy for the synthesis of hierarchical yolk–shell microspheres with magnetic Fe₃O₄ cores and dielectric TiO₂ shells has been developed. Various Fe₃O₄@TiO₂ yolk–shell microspheres with different core sizes, interstitial void volumes, and shell thicknesses have been successfully synthesized by controlling the synthetic parameters. Moreover, the microwave absorption properties of these yolk–shell microspheres, such as the complex permittivity and permeability, were investigated. The electromagnetic data demonstrate that the as‐synthesized Fe₃O₄@TiO₂ yolk–shell microspheres exhibit significantly enhanced microwave absorption properties compared with pure Fe₃O₄ and our previously reported Fe₃O₄@TiO₂ core–shell microspheres, which may result from the unique yolk–shell structure with a large surface area and high porosity, as well as synergistic effects between the functional Fe₃O₄ cores and TiO₂ shells.     

One‐step in situ growth of magnesium ferrite nanorods on graphene and their microwave‐absorbing properties

The magnesium ferrite nanorods/graphene (MgFe₂O₄ NR/G) composites were prepared by a facile one‐step surfactant‐assisted solvothermal method. The structure and morphology of as‐prepared composite materials were characterized by electron microscopy, energy dispersive spectrometry, Raman spectrometry, X‐ray diffraction, FT‐IR and X‐ray photoelectron spectroscopy. The homogeneous MgFe₂O₄ nanorods with a typical diameter of about 100 nm were well distributed on graphene. The electromagnetic parameters were measured using a vector network analyzer. A minimum reflection loss (RL) of ?40.3 dB was observed at 14.9 GHz with a thickness of 3 mm, and the effective absorption frequency (RL  <   ? 10 dB) ranged from 12.0 to 18.0 GHz, indicating the remarkable microwave absorption performance of the MgFe₂O₄ NR/G composites. The absorbing property of as‐obtained composites was better than that of the pure MgFe₂O₄ nanorods. The synergistic effect of MgFe₂O₄ and graphene was responsible for the enhanced absorbing performance.     

Fabrication,characterization and X-band microwave absorption properties of PAni/Fe3O4/PVA nanofiber composites materials

This work presents a study of microwave absorption properties of PAni/Fe₃O₄/PVA nanofiber composites with different ratio of Fe₃O₄ nanoparticles. The morphology of the composites nanofibers study by Field Emission Scanning Electron Microscopes (FESEM) and Transmission Electron Microscope (TEM) showed that the low content of Fe₃O₄ nanoparticles presence in the composites nanofibers indicates very much uniform surface, in the composites nanofiber without many bends, but some bends develop at higher content of Fe₃O₄ nanoparticles as indicated in the TEM image. Image-J software was used to further investigate the diameter of the composites nanofiber and found to be in the range of 152 to 195 nm. The nanofiber composites show excellent electric and magnetic properties and therefore vary with the addition of Fe₃O₄ nanoparticles in the composites nanofiber. In addition the PAni/Fe₃O₄/PVA composites nanofibers were further characterized by X-ray diffraction spectra (XRD) and Four Transformation infrared spectra (FTIR). The XRD pattern shows the presence of PAni nanotubes containing Fe₃O₄ nanoparticles by indicating peaks at 23.4⁰ and 35.43⁰ which was further supported by FTIR analysis. Microwave vector network analyzers (MVNA) were used to estimate the microwave absorption properties of the composites nanofibers. The absorption parameters was found to be −6.4 dB at 12.9 GHz within the range of X-band microwave absorption frequency, this reflection loss is attributed to the multiple absorption mechanisms as a result of the improved of impedance matching between dielectric and magnetic loss of the absorbent materials demonstrating that these materials can be used as protective material for electromagnetic radiation.     

One‐pot multicomponent synthesis of novel 2‐(piperazin‐1‐yl) quinoxaline and benzimidazole derivatives,using a novel sulfamic acid functionalized Fe3O4 MNPs as highly effective nanocatalyst

The immobilization of sulfonic acid on the surface of Fe₃O₄ magnetic nanoparticles (MNPs) as a novel acid nanocatalyst has been successfully reported. The morphological features, thermal stability, magnetic properties, and other physicochemical properties of the prepared superparamagnetic core–shell (Fe₃O₄@PFBA–Metformin@SO₃H) were thoroughly characterized using Fourier transform infrared (FTIR), X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy (EDS), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetric analysis–differential thermal analysis (TGA‐DTA), atomic force microscopy (AFM), dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET), and vibrating sample magnetometer (VSM) techniques. It was applied as an efficient and reusable catalyst for the synthesis of 2‐(piperazin‐1‐yl) quinoxaline and benzimidazole derivatives via a one‐pot multiple‐component cascade reaction under green conditions. The results displayed the excellent catalytic activity of Fe₃O₄@PFBA–metformin@SO₃H as an organic–inorganic hybrid nanocatalyst in condensation and multicomponent Mannich‐type reactions. The easy separation, simple workup, excellent stability, and reusability of the nanocatalyst and quantitative yields of products and short reaction time are some outstanding advantages of this protocol.     

Effect of Manganese Dioxide Dispersion on the Absorbing Properties of Manganese Dioxide (MnO2)‐Epoxy Composites

Manganese dioxide (MnO₂) particle was synthesized and introduced into epoxy resin to be microwave absorber. The spectroscopic characterization of the formation processes of MnO₂ was studied by using X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Microwave absorbing properties with different volume fractions of MnO₂ were investigated by measuring complex permittivity, complex permeability and reflection loss in the 2–18 and 18–40 GHz microwave frequency range using the free space method. The absorbing performance of MnO₂‐epoxy composites at same sample thickness and at various sample thickness were also studied. It was found that the best absorbing property and an absorption frequency range shifting could be obtained at the frequency range of 2–18 and 18–40 GHz.     

Facile Hydrogen‐Bond‐Assisted Polymerization and Immobilization Method to Synthesize Hierarchical Fe3O4@Poly(4‐vinylpyridine‐co‐divinylbenzene)@Au Nanostructures and Their Catalytic Applications

Hierarchical Fe₃O₄@poly(4‐vinylpyridine‐co‐divinylbenzene)@Au (Fe₃O₄@P(4‐VP–DVB)@Au) nanostructures were fabricated successfully by means of a facile two‐step synthesis process. In this study, well‐defined core–shell Fe₃O₄@P(4‐VP–DVB) microspheres were first prepared with a simple polymerization method, in which 4‐VP was easily polymerized on the surface of Fe₃O₄ nanoparticles by means of strong hydrogen‐bond interactions between ? COOH groups on poly(acrylic acid)‐modified Fe₃O₄ nanoparticles and a 4‐VP monomer. HAuCl₄ was adsorbed on the chains of a P(4‐VP) shell and then reduced to Au nanoparticles by NaBH₄, which were embedded into the P(4‐VP) shell of the composite microspheres to finally form the Fe₃O₄@P(4‐VP–DVB)@Au nanostructures. The obtained Fe₃O₄@P(4‐VP–DVB)@Au catalysts with different Au loadings were applied in the reduction of 4‐nitrophenol (4‐NP) and exhibited excellent catalytic activity (up to 3025 h^?1 of turnover frequency), facile magnetic separation (up to 31.9 emu g^?1 of specific saturation magnetization), and good durability (over 98 % of conversion of 4‐NP after ten runs of recyclable catalysis and almost negligible leaching of Au).     

Ultrafast Preparation of Monodisperse Fe3O4 Nanoparticles by Microwave‐Assisted Thermal Decomposition

Thermal decomposition, as the main synthetic procedure for the synthesis of magnetic nanoparticles (NPs), is facing several problems, such as high reaction temperatures and time consumption. An improved a microwave‐assisted thermal decomposition procedure has been developed by which monodisperse Fe₃O₄ NPs could be rapidly produced at a low aging temperature with high yield (90.1 %). The as‐synthesized NPs show excellent inductive heating and MRI properties in vitro. In contrast, Fe₃O₄ NPs synthesized by classical thermal decomposition were obtained in very low yield (20.3 %) with an overall poor quality. It was found for the first time that, besides precursors and solvents, magnetic NPs themselves could be heated by microwave irradiation during the synthetic process. These findings were demonstrated by a series of microwave‐heating experiments, Raman spectroscopy and vector‐network analysis, indicating that the initially formed magnetic Fe₃O₄ particles were able to transform microwave energy into heat directly and, thus, contribute to the nanoparticle growth.     

Synthesis,characterization and microwave absorption properties of polyaniline/Sm-doped strontium ferrite nanocomposite

Sm-doped strontium ferrite nanopowders (SrSm_0.3Fe_11.7O₁₉) and their composites of polyaniline (PANI)/SrSm_0.3Fe_11.7O₁₉ with 10 wt% and 20 wt% ferrite were prepared by a sol–gel method and an in-situ polymerization process, respectively. The structure, magnetic properties and microwave absorption properties of the samples were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and vector network analyzer, respectively. The particle size of SrSm_0.3Fe_11.7O₁₉ was about 35 nm by using XRD. The ferrite successfully packed by PANI. PANI/SrSm_0.3Fe_11.7O₁₉ possessed the best absorption property with the optimum matching thickness of 3 mm in the frequency of 2–18 GHz. The value of the maximum reflection loss (RL) were −26.0 dB at 14.2 GHz with the 6.5 GHz bandwidth and −24.0 dB at 13.8 GHz with the 7.9 GHz bandwidth for the samples with 10 wt% and 20 wt% ferrite, respectively.     

NZFO-PZT磁电复合纳米纤维的制备及其吸波性能

采用静电纺丝法制备(1-x)Ni_0.5Zn_0.5Fe₂O₄-(x)Pb(Zr_0.52Ti_0.48)O₃(简称为(1-x)NZFO-(x)PZT, x=0.1、0.2、0.3、0.4、0.5)磁电复合纳米纤维, 研究了PZT含量对复合纳米纤维结构、电磁特性及微波吸收性能的影响。所有样品均由尖晶石结构NZFO和钙钛矿结构PZT两相所组成。由于NZFO磁损耗与PZT介电损耗的协同效应及界面效应的加强, 适量PZT相的引入可改善复合纳米纤维吸波涂层的电磁阻抗匹配和衰减特性, 提高微波吸收性能。x=0.3和0.4的复合纳米纤维分别在低频和高频范围表现出最强的微波吸收能力。当涂层厚度为2.5~5.0 mm时, x=0.3样品的最小反射损耗在6.1 GHz处达-77.2 dB, 反射损耗小于-10 dB的有效吸收带宽为11.2 GHz(2.8~12.9和16.9~18 GHz);x=0.4样品的最小反射损耗位于18 GHz处为-37.6 dB, 有效吸收带宽达到12.5 GHz(3.3~12.5和14.7~18 GHz)。     

NZFO-PZT磁电复合纳米纤维的制备及其吸波性能

采用静电纺丝法制备(1-x)Ni_0.5Zn_0.5Fe₂O₄-(x)Pb(Zr_0.52Ti_0.48)O₃(简称为(1-x)NZFO-(x)PZT, x=0.1、0.2、0.3、0.4、0.5)磁电复合纳米纤维, 研究了PZT含量对复合纳米纤维结构、电磁特性及微波吸收性能的影响。所有样品均由尖晶石结构NZFO和钙钛矿结构PZT两相所组成。由于NZFO磁损耗与PZT介电损耗的协同效应及界面效应的加强, 适量PZT相的引入可改善复合纳米纤维吸波涂层的电磁阻抗匹配和衰减特性, 提高微波吸收性能。x=0.3和0.4的复合纳米纤维分别在低频和高频范围表现出最强的微波吸收能力。当涂层厚度为2.5~5.0 mm时, x=0.3样品的最小反射损耗在6.1 GHz处达-77.2 dB, 反射损耗小于-10 dB的有效吸收带宽为11.2 GHz(2.8~12.9和16.9~18 GHz);x=0.4样品的最小反射损耗位于18 GHz处为-37.6 dB, 有效吸收带宽达到12.5 GHz(3.3~12.5和14.7~18 GHz)。     

6‐TIPS‐β‐Cyclodextrin‐Modified Fe3O4 for Facile Enantioseparation of 1‐(1‐Naphthyl)ethylamine

A new type of chiral magnetic nanoparticle was prepared from covalently linked magnetic nanoparticles (Fe₃O₄) and heptakis‐(6‐O‐triisopropylsilyl)‐β‐cyclodextrin (6‐TIPS‐β‐CD). The resulting selectors (TIPS‐β‐CD‐MNPs) combined the good magnetic properties Fe₃O₄ and efficient chiral recognition ability of 6‐TIPS‐β‐CD. The enantioselectivity of TIPS‐β‐CD‐MNPs towards 1‐(1‐naphthyl)ethylamine was six times higher than that of the parent β‐CD modified Fe₃O₄ particles.     

NiFe2O4/T-ZnOw复合材料的制备及电磁波吸收性能

采用铁氧体化学镀在四角氧化锌晶须(T-ZnOw)表面包覆NiFe2O4镀层,制备了NiFe2O4/T-ZnOw复合材料。利用X射线衍射仪、扫描电镜、能谱分析仪对镀覆前后T-ZnOw的结构、形貌等进行了表征。利用矢量网络分析仪研究了NiFe2O4/T-ZnOw复合材料的电磁波吸收性能。结果表明,化学镀覆后,在T-ZnOw表面包覆了尖晶石型NiFe2O4镀层,生成了NiFe2O4/T-ZnOw复合材料,该材料为磁损耗型材料。化学镀覆过程中T-ZnOw的装载量会影响复合材料的介电常数和磁导率,当T-ZnOw装载量为0.2g时,所制备的复合材料具有最大的介电常数、磁导率、介电损耗和磁损耗,当吸收层厚度达到3 mm时,反射率在14 GHz处达到-11 dB。