有机蒙脱土/聚(丙烯酸-丙烯酰胺)高吸水性纳米复合材料的制备、性能及表征

首先通过阳离子交换反应,用烷基季铵盐十六烷基三甲基溴化铵(CTAB)对钠基蒙脱土进行插层改性,使其成为有机蒙脱土(OMMT);然后通过反相悬浮聚合法使之与丙烯酸(AA)、丙烯酰胺(AM)共聚,利用单体溶液插层原位聚合的方式制备了高吸水性树脂P(AA-AM/OMMT)的纳米复合材料。通过傅立叶红外光谱(IR)、X射线衍射实验(XRD)等手段对其结构进行表征。研究了有机蒙脱土的加入量对材料吸液率影响。结果表明:季铵盐成功插层进入蒙脱土片层,并且AA、AM可顺利进入蒙脱土片层中发生插层聚合,使蒙脱土片层剥离,达到纳米级分散。所制备树脂的吸水速率明显提高,吸液率也有所提高,最大吸水吸盐率分别达到890mL/g和72.5mL/g。     

Lattice structure analysis and optimised microwave dielectric properties of LiAl1-x(Zn0.5Si0.5)xO2 solid solutions

Low-permittivity LiAl_1-x(Zn_0.5Si_0.5)_xO₂ microwave dielectric ceramics were prepared by the solid-state reaction method. Single-phase LiAlO₂ solid solutions with a tetragonal structure were achieved at x ≤ 0.12. Partial substitution of [Zn_0.5Si_0.5]³⁺ for Al³⁺ could improve the microstructure and prevent from absorbing moisture of pure LiAlO₂ ceramics, which slightly increases their relative permittivity (ε_r). The quality factor (Q × f) and temperature coefficient of resonant frequency (τ_f) were closely related to the crystallinity and cation disorder of the B-site characterized by the full width at half-maximum of B₁⁽¹⁾ –mode assigned to Li–O–Al stretching. The optimum microwave dielectric properties (ε_r = 6.12, Q × f = 56986 GHz and τ_f = -122 ppm/°C) were obtained in the sample with x = 0.02 sintered at 1300 °C.     

Synthesis and characterization of ZnS/hyperbranched polyester nanocomposite and its optical properties

The ZnS/hyperbranched polyester nanocomposite with higher refractive index was prepared by incorporating the acrylated 2-(2-mercapto-acetoxy)-ethyl ester-capped ZnS nanoparticles into the acrylated Boltorn™ H20 (H20). The acrylated 2-(2-mercapto-acetoxy)-ethyl ester-capped colloidal ZnS nanoparticles were synthesized by the reaction of zinc acetate with thioacetamide in N,N-dimethylformamide. The acrylated hyperbranched polyester was obtained by reacting acryloyl chloride with hydroxyl group of H20. The acrylated H20 plays an important role in stabilizing and dispersing ZnS nanoparticles with a diameter of 1-4 nm. The refractive indices of ZnS/hyperbranched polyester nanocomposites, depending on ZnS content, were determined to be in the ranges of 1.48-1.65.     

Role of exchange coupling between the hard and soft magnetic phases on the absorption of microwaves by SrFe10Al2O19/Co0.6Zn0.4Fe2O4 nanocomposite

(1-x)SrFe₁₀Al₂O₁₉/(x)Co_0.6Zn_0.4Fe₂O₄-(SFAO/CZFO) hard/soft nanocomposite ferrite materials were synthesized by ‘one-pot’ self-propagating combustion route. The co-existence of the two magnetic phases were confirmed by XRD, FESEM, EDS and VSM. The prepared nanocomposite samples were also characterized by TGA/DSC, Raman spectroscopy and VNA. Exchange coupling between the hard and the soft magnetic grains was observed by determining the switching field distribution (SFD) curve. As a result of the competing effects of exchange interaction and dipolar interaction, magnetic parameters were observed to be sensitive to the incorporation of soft magnetic phase into the nanocomposite. Results showed that with the inclusion of soft magnetic phase, exchange coupling behaviour between the hard and the soft ferrite phases had significant influence on the microwave absorption capacity of the samples. Related electromagnetic parameters and impedance matching ratio of the nanocomposite system were discussed. A minimum reflection loss of ?42.9 dB with an absorber thickness of 2.5 mm was attained by the nanocomposite (90 wt%)SrFe₁₀Al₂O₁₉/(10 wt %)Co_0.6Zn_0.4Fe₂O₄ at a matching frequency of 11.45 GHz. This assured the candidacy of SrFe₁₀Al₂O₁₉/Co_0.6Zn_0.4Fe₂O₄ nanocomposite as a promising microwave absorption material in the X-band (8–12 GHz).     

BaFe9(Ti0.5Mn0.5)3O19铁氧体粉末的合成及磁性能研究

采用溶胶-凝胶自蔓延法合成了BaFe9(Ti0.5Mn0.5)3O19铁氧体粉末,利用XRD、TEM和VSM对样品进行表征及磁性能研究。结果表明,合成样品为均匀单一的纳米级铁氧体粉末,平均粒径80nm,焙烧温度对磁能影响显著,焙烧温度过高不利于提高样品磁性能。     

(BaTiO3)1-x + (Co0.5Ni0.5Nb0.06Fe1.94O4)x nanocomposites: Structure,morphology, magnetic and dielectric properties

Two phase-based nanocomposites consisting of dielectric barium titanate (BaTiO₃ or BTO) and magnetic spinel ferrite Co_0.5Ni_0.5Nb_0.06Fe_1.94O₄ (CNNFO) have been synthesized through solid state route. Series of (BaTiO₃)_1-x + (Co_0.5Ni_0.5Nb_0.06Fe_1.94O₄)_x nanocomposites with x content of 0.00, 0.25, 0.50, 0.75, and 1.00 were considered. The structure has been examined via X-rays diffraction (XRD) and indicated the occurrence of both perovskite BTO and spinel CNNFO phases in various nanocomposites. A phase transition from tetragonal BTO structure to cubic structure occurs with inclusion of CNNFO phase. The average crystallites size of BTO phase decreases, whereas that for the CNNFO phase increases with increasing x in various nanocomposites. The morphological observations revealed that the porosity is highly reduced, and the connectivity between grains is enhanced with increasing x content. The optical properties have been investigated by UV−vis diffuse reflectance spectroscopy. The deduced band gap energy (E_g) value is found to reduce with increasing the content of spinel ferrite phase. The magnetic as well as the dielectric properties were also investigated. The analysis showed that CNNFO ferrite phase greatly affects the magnetic properties and dielectric response of BTO material. The obtained findings can be useful to enhance the performances of magneto-dielectric composite-based systems.     

Preparation,characterization and anticorrosive properties of a novel polyaniline/clinoptilolite nanocomposite

Nanocomposite of polyaniline (PANI) with natural clinoptilolite (Clino) was prepared. Formation of nanocomposite and incorporation of polyaniline in the clinoptilolite channels was confirmed and characterized using FTIR spectroscopy studies, X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM) and cyclic voltammetry techniques. The anticorrosive properties of a 20 μm thickness coating of PANI/Clino nanocomposite with various weight ratios (1, 3 and 5%, w/w) of clinoptilolite content on iron coupons was evaluated and compared with pure polyaniline coating. According to the results in acidic environments PANI/Clino nanocomposite has enhanced corrosion protection effect in comparison to pure polyaniline coating. Comparative experiments revealed that PANI/Clino nanocomposite with 3% (w/w) clinoptilolite content has the best protective properties. Further experiments showed that the PANI/Clino nanocomposite has considerably different corrosion protection efficiencies in various corrosive environments.     

Degree of inversion of A/B lattice sites and microwave/millimeter wave/terahertz dielectric properties of MgAl2-x(Zn0.5Mn0.5)xO4 ceramics

In this work, spinel-structured MgAl_2-x(Zn_0.5Mn_0.5)_xO₄ (0 ≤ x ≤ 0.08) single-phase ceramics were prepared through a solid-state reaction route. The substitution of (Zn_0.5Mn_0.5)³⁺ for Al³⁺ at the octahedral site affected the degree of inversion of A/B lattice sites, bond length/strength/valence, and covalency of metal-oxygen bond in the tetrahedron and hence microwave dielectric properties of MgAl₂O₄. The variation in ε_r and tanδ of ceramics is investigated in the millimeter wave-terahertz frequency band by combining infrared reflection spectrum and terahertz time-domain spectroscopy. A high Q×f value of 111,010 GHz @ 12.01 GHz, low ε_r = 8.3, and slightly lower τ_f = −60 ppm/°C is obtained for MgAl_1.98Zn_0.01Mn_0.01O₄ ceramics, which is tuned by adding a small amount of SrTiO₃. The composite ceramics exhibited a near-zero τ_f (2.8 ppm/°C), high Q×f (55,400 GHz @ 11.15 GHz), and low ε_r (= 8.5), showing a great potential application prospect for 5G/6G wireless communication.     

Structural,electromagnetic properties and broad microwave absorption bandwidth of SrFe12-2xCoxRuxO19

SrFe_12-2xCo_xRu_xO₁₉ become magnetically soft with Co and Ru doping. The magnetization is high, but the anistropic field becomes low. The FT-IR spectra suggest that Co and Ru substitute for Fe at the 4f1 site. At this site, the substitution of Co and Ru with low magnetic moments weakens the anisotropy. The sharp magnetic resonances observed in x = 0.3, 0.5 and 0.7 are due to the domain wall movement. The natural magnetic resonance frequency falls in the frequency of 2–18 GHz. The Co and Ru doping increases both the magnetic loss tangent and the dielectric loss tangent. The high magnetic and dielectric loss tangents are in favor of high attenuation factors. With good impedance matching and high attenuation factor, the microwave absorption properties are excellent in x ≥ 0.3. In x = 0.5, the bandwidth is 11.8 GHz centered at 10.5 GHz. In each x > 0.5 sample, the optimum bandwidth is broader than 9 GHz. In x = 1.1, at 1.9 mm, the absorption bandwidth is broader than 9 GHz from 9 GHz to higher than 18 GHz centered at 11.6 GHz. Compared with the advanced materials published in recent decades, the bandwidth of the present work are very competitive.     

Effects of Sr doping on the structure,magnetic properties and microwave absorption properties of LaFeO3 nanoparticles

Lightweight, broadband microwave absorbing materials, with strong absorption capacities, are an urgent demand for practical applications. The microstructural and microwave absorption properties of LaFeO₃ samples prepared by a sol-gel method using different amounts of Sr are investigated systematically. X-ray diffraction and Rietveld refinement studies showed that Sr²⁺ doping can distort the crystal structure of LaFeO₃, leading to lattice expansion and spin tilt of the Fe-O-Fe bond angle. The improvement of magnetic properties mainly originates from the synergistic effect of the bond angle spin tilt and crystal structure defects. Oxygen vacancies will be generated due to the fluctuations in the valence state of Fe³⁺ resulting from the substitution of La³⁺ by Sr²⁺ as deduced from the X-ray photoelectron spectroscopy analysis. The generation of oxygen vacancies, electronic hopping and polarization loss may be one of the main reasons for changes in the electromagnetic parameters. The minimum reflection loss (RL) of La_1–xSr_xFeO₃ nanoparticles with the Sr doping of 0.2 can reach approximately -39.3 dB at 10 GHz for the thickness of 2.2 mm, and the effective absorption bandwidth (RL ≤ -10 dB) can reach approximately 2.56 GHz. In addition, the La_1–xSr_xFeO₃ nanoparticles also can obtain better microwave absorbing performance in the C-band (4–8 GHz) with the minimum RL of -36.8 dB for the matching thickness of 3.0 mm and Sr content of 0.3. Consequently, La_1–xSr_xFeO₃ nanoparticles are promising materials for use in a high-performance and adjustable electromagnetic wave absorber, particularly in C-band and X-band.     

Preparation and characterization of a composite ceramic coating containing absorber LaFe12O19 by plasma spraying

A ceramic coating with both heat-resistant and electromagnetic (EM) wave absorption performances is prepared by the atmospheric plasma spraying (APS) method. The spraying powder is a composite material mainly containing LaFeO₃ and La(Mg/Fe)Al₁₁O₁₉ without EM absorption ability. During APS procedure, a new phase of LaFe₁₂O₁₉ is fabricated by the chemical reaction between Fe₂O₃ and LaFeO₃ at extremely high temperatures. The ceramic coating exhibits larger saturation magnetization (M_s) and higher EM absorption performance than that of the unsprayed sample. The coating Ms is 31 emu/g, and the optimal reflection loss is −39.30 dB at 3.5–5.2 GHz with 4.5 mm thickness. The ceramic coating with both heat-resistant and EM absorption properties is a potential application prospect material in the military industry.     

Novel conductive magnetic nanocomposite based on poly (indole-co-thiophene) as a hemoglobin diagnostic biosensor: Synthesis,characterization and physical properties

The novel conductive nanocomposite has been successfully prepared by emulsion polymerization. First, magnetite nanoparticles were synthesized via coprecipitation reaction. Then, poly (indole-co-thiophene)@Fe₃O₄ nanocomposite was prepared via emulsion copolymerization of indole and thiophene monomers using sodium dodecyl sulfate as an emulsifier and ammonium persulfate as an oxidant in the presence of Fe₃O₄ nanoparticles. Characterization of the synthesized copolymer, Poly (In-co-T), and its magnetic nanocomposite were studied by Fourier transform infrared spectra, X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, differential scanning calorimetric, UV-vis spectrophotometer, and vibrating sample magnetometer. Also, the electrical conductivity of copolymer and nanocomposite were determined by four-probe instrument. Results showed a synergic effect in thermal stability by good interaction between polymer chain and magnetic nanoparticles. The conductivity of the nanocomposite was higher than bare copolymer, and increase of nanoparticles content caused an increment in the conductivity of the nanocomposites. The applicable properties of proposed conductive nanocomposite as a base at electrochemical biosensing have been investigated.     

Structural, morphological, magnetic and optical properties of chromium substituted strontium ferrites, SrCrxFe12 − xO19 (x = 0.5, 1.0, 1.5, 2.0 and 2.5) annealed with potassium halides

Chromium substituted strontium ferrites SrCr_xFe_12 − xO₁₉ (x = 0.5, 1.0, 1.5, 2.0 and 2.5) have been synthesized via sol gel method and the dry gels obtained have been annealed with various inorganic template agents (KCl, KBr and KI). The powder X ray diffraction studies reveal a crystallite size of ~ 40-45 nm. The use of KCl as inorganic template agent leads to an increase in the crystallite size. This may be attributed to the fact that the coordination ability of Cl⁻ is maximum due to its larger charge to size ratio, which promotes crystal growth in one dimension leading to needle-like morphology. On the other hand, KI undergoes sublimation to form I₂ which gets entrapped in the strontium ferrite crystal leading to a bubble-like morphology. A systematic change in the lattice constants, a and c, is not observed because the radius of Cr³⁺ ion (0.63 Å) is similar to that of Fe³⁺ ion (0.64 Å). The saturation magnetization decreases with increase in the chromium concentration from 43.03 emu/g to 17.40 emu/g due to the substitution of Fe³⁺ ions by less magnetic Cr³⁺ ions in 2a and 12k sites of the lattice. The coercivity decreases with increase in the chromium concentration due to decrease in magnetocrystalline anisotropy. In the presence of KCl and KBr, both saturation magnetization and coercivity increase and the saturation magnetization has the maximum value in case of samples annealed with KBr. However, with KI, the values of both saturation magnetization and coercivity decrease sharply which may be due to lower crystallinity due to bubble-like morphology because of the decomposition of KI to I₂. The energy band gap for all the ferrite compositions is found to be ~ 2.2 eV and its value increases in the samples annealed with KI.     

Formation of Sn filled CNTs nanocomposite: Study of their magnetic,dielectric properties and enhanced microwave absorption performance at gigahertz frequencies

The Simplistic formation, advantageous configuration, non-colossal magnetoresistance and broadband absorption are important parameters for microwave absorbent materials. In this study, a core-shell nanocomposite comprising of Sn-filled carbon nanotubes (Sn/CNTs) was prepared by arc discharge method. The microstructure, morphology and surface composition of Sn/CNTs-based core-shell nanocomposites were characterized in detail. Sn/CNTs nanocomposite showed a magnetic signal due to the broken bonds and defects at interfaces in Sn/CNTs. The weak ferromagnetism was found to be helpful in improving magnetic permeability in the Sn/CNTs which confirms its role as a magnetic loss material under incident electromagnetic wave. Sn-filled CNTs revealed an appropriate value of dielectric constant, which plays an important role in impedance matching upon incident electromagnetic wave. The composite of Sn-CNTs and paraffin with a 50 wt % loading showed the lowest reflection loss (RL) of ?43.87 dB at 10 GHz, with a wide effective absorption band (RL ≤ ?10 dB) of 3 GHz in thickness of 2.3 mm. This enhanced performance is attributed to the combined effect of the conduction loss in one-dimensional core-shell architecture, the interfacial loss Sn-CNT interface, the magnetic loss due to defects-induced ferromagnetism in Sn shell, and in the carbon-containing atomic layers of CNTs.     

Tailoring La0.8Sr0.2MnO3/La/Sr nanocomposite using a novel complementary method as well as dissecting its microwave,shielding, optical,and magnetic characteristics

In this work, a novel approach was introduced to reduce the oxide nanoparticles and extract the pure metal from them. Accordingly, La_0.8Sr_0.2MnO₃ nanoparticles were prepared through the conventional citrate gel method, and then they were reduced using a solvothermal method by ethylene glycol as a reductive agent. Chemical species, magnetic parameters, crystal structures, and morphological properties of the fabricated structures were deeply studied by Fourier transform infrared (FT-IR), vibrating sample magnetometer (VSM), X-ray powder diffraction (XRD), and field emission scanning electron microscopy (FE-SEM) analyses, respectively. Noticeably, the curves of the diffuse reflection spectroscopy (DRS) suggested a lower energy gap for the La_0.8Sr_0.2MnO₃/La/Sr nanocomposite. Finally, the microwave absorbing characteristics of the specimens were scrupulously investigated using the polystyrene (PS) and polyvinylidene fluoride (PVDF) media. It was found that La_0.8Sr_0.2MnO₃/La/Sr blended in PVDF gained a remarkable reflection loss of 94.68 dB at 15.31 GHz with an only thickness of 1.75 mm, meanwhile displaying an efficient bandwidth as wide as 6.74 GHz (reflection loss (RL) > 10 dB). Noteworthy, La_0.8Sr_0.2MnO₃/PS illustrated a considerable efficient bandwidth of 2.36 GHz (RL > 20 dB). Moreover, La_0.8Sr_0.2MnO₃ composites demonstrated more than 88% electromagnetic interference shielding efficiency (SE) along the X and Ku-band frequency.     

A novel magnetic photocatalyst Bi3O4Cl/SrFe12O19: Fabrication,characterization and its photocatalytic activity

A novel Bi₃O₄Cl/SrFe₁₂O₁₉ magnetic photocatalyst has been fabricated by a hydrothermal-roasting method. Its structure and performance were studied through XRD, XPS, SEM, UV–vis DRS, PL, EIS and VSM, and the photocatalytic property was tested by photodegradation of RhB irradiation with solar-simulated light. The optimum sample of Bi₃O₄Cl/SrFe₁₂O₁₉(20%) displayed the excellent photocatalytic activity, and the degradation rate was more than 99.7% in 80 min. In addition, the Bi₃O₄Cl/SrFe₁₂O₁₉(20%) showed the quite high magnetic performance, of which the saturation magnetization was 7.65 emu·g⁻¹ and the recovery percent was 92.4%. Meantime, the product revealed the great photocatalytic stability, with the photodegradation leave reaching 84.1% after five cycles. The trapping experiments demonstrated that the hydroxyl radicals, photoproduction holes and superoxide radicals played a critical part in photodegrading of RhB. This research provided a new method to synthesize composite magnetic photocatalyst and studied the possible photodegradation mechanism.     

A comparative study on the magnetic properties of MFe12O19 and MAlFe11O19 (M = Sr, Ba and Pb) hexaferrites with different morphologies

M-type nano hexaferrites MFe₁₂O₁₉ and MAlFe₁₁O₁₉ (M = Sr, Ba and Pb) have been prepared by the sol-gel method to investigate the shielding effect of inorganic ions KCl, KBr and KI on the phase growth of ferrites. FTIR frequency bands in the range 560-580 cm⁻¹ and 430-470 cm⁻¹corresponds to the formation of tetrahedral and octahedral clusters of metal oxides in ferrites, respectively. X-ray powder diffractographs do not show any peaks for the as obtained samples showing the amorphous nature of the samples, however regular peaks for M-type structure have been obtained for all the annealed samples. There is negligible small change in the lattice parameters ‘a’ and ‘c’ with substitution of the hexagonal ferrites with aluminium. Magnetic measurements showed that the coercivity (Hc) values of all the samples with KCl and KBr enhance due to KCl and KBr to act as deactivators. However, the coercivity value decreases with KI as it oxidise to I₂ during annealing. The saturation magnetization of the hexaferrites decreases with Al³⁺ ion substitution for Fe³⁺ ion due to preferential occupancy of aluminium in octahedral sites.     

A new conducting polymer bearing 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) subunit: Synthesis and characterization

A new monomer system based on thiophene, pyrrole and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene dye (SNS-BODIPY) was synthesized and its corresponding polymer (PSNS-BODIPY) was obtained via repetitive cycling or constant potential electrolysis in 0.1 M tetrabutylammonium hexafluorophosphate dissolved in dichloromethane. The PSNS-BODIPY film has very stable and well-defined reversible redox couples during p-doping process. Multi-electrochromic polymer film has a band gap of 2.9 eV with two absorption bands in its neutral state at 351 and 525 nm, attributed to the polymer backbone and BODIPY subunits, respectively. The percentage transmittance changes between both states (neutral and oxidized) were found as 12.1% for 351 nm and 17.7% for 525 nm in the visible region as well as 46.2% for 1050 nm in the near-infrared region. Beyond the robustness, the PSNS-BODIPY film has high redox stability (retaining 53.3% of its electroactivity at 351 nm after 2000 switching) with a low response time of 1.0 s.