Ni_(0.3)Zn_(0.6)Cu_(0.1)Sm_(0.05)Fe_(1.95)O_4纳米纤维的结构及磁性能研究

采用静电纺丝法制备出直径分布均匀、表面相对光滑的Ni_(0.3)Zn_(0.6)Cu_(0.1)Sm_(0.05)Fe_(1.95)O_4纳米纤维前驱丝,并经过500—900℃的不同温度煅烧后得到Ni_(0.3)Zn_(0.6)Cu_(0.1)Sm_(0.05)Fe_(1.95)O_4纳米纤维。并用XRD,SEM,EDS和VSM现代分析手段对Ni_(0.3)Zn_(0.6)Cu_(0.1)Sm_(0.05)Fe_(1.95)O_4纳米纤维的结构、形貌、组成成分及其磁学性能进行测试表征。结果表明:在空气气氛中经500—900℃不同温度煅烧后可得到纯相的、结晶良好的Ni_(0.3)Zn_(0.6)Cu_(0.1)Sm_(0.05)Fe_(1.95)O_4纳米纤维;煅烧温度为500—800℃时,得到的Ni_(0.3)Zn_(0.6)Cu_(0.1)Sm_(0.05)Fe_(1.95)O_4纳米纤维的表面光滑,直径均匀,其直径大约在80—140 nm之间;随着煅烧温度的逐渐升高,Ni_(0.3)Zn_(0.6)Cu_(0.1)Sm_(0.05)Fe_(1.95)O_4纳米纤维的饱和磁化强度逐渐增大,在900℃时饱和磁化强度为53.30 emu/g;矫顽力呈现先增大后减小的趋势,800℃时达到最大值为31.13 Oe。     

钕离子掺杂铁氧体纳米晶的结构和磁性能

采用化学共沉淀法制备了钕离子(Nd3 )掺杂铁氧体纳米晶材料.利用Gouy磁天平、X射线衍射、红外光谱、透射电镜(transmission electron microscope,TEM)和X射线能谱分析等对产物进行了表征,研究了Nd3 掺杂量对Fe3O4纳米晶的结构和磁性的影响.结果表明:在Fe3O4晶格中掺杂适量Nd3 能提高材料的磁性,当摩尔比n(Fe3 ):n(Nd3 )=29∶1时.其磁性最强,此时Nd3 以直接充填的方式占据Fe3O4晶格中的B位.随着Nd3 掺杂量的增加,Nd3 '取代B位的Fe3 的进入晶格,使磁矩降低.TEM分析表明:制得的Nd3 掺杂铁氧体纳米晶颗粒大小较均匀,平均粒径约为8nm.     

锰锌铁氧体空心纤维的制备及其磁性能

以柠檬酸及金属盐为原料,采用有机凝胶-热分解法制备出Mn1-xZnxFe2O4(x=0.2～0.8)铁氧体空心纤维.通过Fourier红外光谱、热重-差示扫描量热仪、X射线衍射和扫描电镜分别对凝胶前驱体的结构、热分解过程及热处理产物的物相和形貌进行了表征,用振动样品磁强计对纤维的磁性能进行了检测.结果表明:所得Mn1-xZnxFe2O4铁氧体空心纤维的晶粒尺寸约为10nm,纤维表面光滑、致密,直径在0.5～5.0 μm之间,且具有较大的长径比.纤维的饱和磁化强度和矫顽力以及平均晶粒尺寸都随焙烧温度的升高和保温时间的延长而增大,400℃热处理制得的Mn-Zn铁氧体纤维由于其晶粒粒径小于临界尺寸而表现出超顺磁特征.随Zn含量的提高,纤维的饱和磁化强度先增加后减小,在x=0.63附近达到最大值,而矫顽力在x=0.43左右达到最小值.具有形状各向异性的Mn-Zn铁氧体空心纤维的矫顽力明显高于经相同工艺制得的同组分粉体的矫顽力.     

静电纺丝制备纳米级纤维的研究

首先介绍了静电纺丝制备纳米纤维的原理及其影响因素,然后归纳、总结了当前国内外静电纺丝制备纳米纤维的研究内容,并对今后的研究提出了建设.     

碳纳米管/NiCuZn铁氧体复合物的制备及磁性能研究

本文采用化学共沉淀法和水热法制备了MWCNT/Ni Cu Zn铁氧体复合物,通过XRD、FT-IR、SEM和TEM对样品的晶型、结构和微观形貌进行了表征,并通过VSM检测复合物的磁性能。FT-IR、XRD表明Ni2+、Cu2+、Zn2+离子已进入铁氧体结构中,即Ni Cu Zn铁氧体被成功地制备。SEM和TEM照片表明Ni Cu Zn铁氧体稳定地与碳纳米管结合在一起。当Cu掺杂量为0.30,Zn掺杂量为0.20时,MWCNT/Ni0.2Cu0.3Zn0.5Fe2O4复合物具有较好的磁性能,矫顽力、磁饱和强度和磁剩余强度数值分别为48.6 Oe、55.1 emu·g-1和5.0 emu·g-1。     

静电纺丝制备纳米级纤维的研究

介绍了静电纺丝制备纳米纤维的原理及其影响因素,归纳、总结了当前国内外静电纺丝制备纳米纤维的研究内容,并对今后的研究提出了建议.     

静电纺丝法制备PVA/Fe_3O_4磁性纳米纤维

将纳米Fe3O4磁性颗粒加入含分散剂的聚乙烯醇水溶液中,选取卵蛋白粉为分散剂,利用静电纺丝制备磁性纳米纤维。通过扫描电镜(SEM)和透射电镜(TEM)表征纤维形貌和分析溶液中粒子分散情况,选用古埃磁天平对纳米纤维毡进行磁性测试。实验结果表明,所制得的复合纳米纤维成纤性良好,粒子分散均匀,且具有一定的磁性。     

静电纺丝制备具有扭曲螺旋结构的微/纳米纤维

天然纤维大多具有一种自扭曲螺旋结构,这种结构使得天然纤维具有较强的柔韧性和很高的孔隙度。主要介绍了两种可以用来制备扭曲螺旋结构微/纳米纤维的静电纺丝装置,并分别阐述了用这两种装置制备具有自扭曲螺旋结构微/纳米纤维的聚合物体系,最后指出了其发展现状和前景。     

CoFe2-xZnxO4纳米管的制备、微观结构及磁性能

通过静电纺丝法制备了一系列CoFe_(2-x)Zn_xO_4(x=0,0.1,0.2,0.3 0.4)纳米管。采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)和振动样品磁力计(VSM)来研究样品的微观形貌、结构、成分及磁性能。SEM和TEM图像显示,样品由连续且随机定向的纳米管组成。XRD结果表明,随着Zn2+含量的增加,晶体尺寸从25.97 nm逐渐减小至14.78nm。铁磁性能研究表明,所有样品在室温下都表现出亚铁磁性。饱和磁化强度和矫顽力随Zn2+浓度的增加而降低。     

静电纺聚乳酸纳米纤维的制备及其孔结构调控

为了调控聚乳酸(PLA)纳米纤维的孔结构,采用静电纺丝技术,以PLA母粒为原料,三氯甲烷(CF)和N,N-二甲基甲酰胺(DMF)按一定比例混合的溶液为溶剂,制备了平均直径在1.37μm的PLA纳米纤维,并对其结构进行表征。结果表明,PLA纳米纤维的平均直径随着纺丝液中CF含量、聚合物浓度、环境湿度的增加而增大;随纺丝电压和灌注速度的增大而呈减小的趋势。同时,环境湿度对纤维表面孔结构有显著影响。随着湿度的增加,纤维表面孔的分布密度增加,且形状由圆形转变为椭圆形。此外,与表面光滑的PLA纳米纤维(2.4 m²/g)相比,所制备的PLA多孔纤维的比表面积提升了10倍(24.0 m²/g)。     

钒掺杂TiO2纳米纤维的制备及其光催化性能

以体积比为1∶2的N,N-二甲基甲酰胺和丙酮为溶剂、钛酸四丁酯[Ti(OiPr)4]和氯化钒[VC13]为前驱体、醋酸纤维素(CA)为模板,采用静电纺丝法制备了V-TiO2/醋酸纤维素纳米纤维.将V-TiO2/醋酸纤维素纳米纤维用0.1 mol/L NaOH/乙醇溶液水解得到V-TiO2/纤维素纳米纤维.在500℃煅烧V-TiO2/纤维素纳米纤维5h,得到直径为(200±53)nm的V-TiO2纳米纤维.利用扫描电子显微镜、X射线粉末衍射仪和紫外-可见漫反射光谱对纤维形貌、物相和结构进行了表征.以染料罗丹明B为目标降解物考察了纤维的光催化活性.结果表明:掺杂少量V后,TiO2对紫外光的最大吸收峰和吸收带边发生了红移,说明V-TiO2对光响应更宽、光利用率更高.TiO2和V-TiO2纳米纤维在20min内对罗丹明B的降解率分别为67％和77％.     

Ni-Ti复合取代锂铁氧体的显微结构及磁性能

采用氧化物法陶瓷工艺制备Li0.5–0.5x＋0.5yNixTiyFe2.5–0.5x–1.5yO4（x=0.2;y=0.05,0.10,0.15,0.20,0.25）锂铁氧体,研究材料的显微结构和磁性能。X射线衍射和扫描电镜测试结果表明：经1050℃烧结得到物相单一、结晶良好锂铁氧体陶瓷;随着Ti离子掺量的增加,材料...     

再生丝素/壳聚糖共混纳米纤维的结构与性能

以98%的甲酸为溶剂,不同质量分数的再生丝素溶液和3.5%的壳聚糖溶液以质量比70∶30共混静电纺丝。测定了壳聚糖的含量对共混膜的结构及力学、溶解等性能的影响。结果表明:随着壳聚糖相对含量的增加,丝素β化程度提高,纤维结晶度增大,丝素与壳聚糖以70∶30共混时的溶失率最小;甲醇处理后,溶失率明显降低;共混纳米纤维的断裂强度随着壳聚糖相对含量的增大而增加,柔软性也逐渐提高;共混纤维膜具有优异的抗菌性。     

Highly‐Aligned Electrospun Luminescent Nanofibers Prepared from Polyfluorene/PMMA Blends: Fabrication,Morphology, Photophysical Properties and Sensory Applications

Highly‐aligned luminescent electrospun nanofibers were successfully prepared from two binary blends of PFO/PMMA and PF⁺/PMMA. The PFO/PMMA aligned electrospun fibers showed a core/shell structure but the PF⁺/PMMA fibers exhibited periodic aggregate domains in the fibers. The aligned fibers had polarized steady‐state luminescence with a polarized ratio as high as 4, much higher than the non‐woven electrospun fibers or spin‐coated film. Besides, the PF⁺/PMMA aligned electrospun fibers showed an enhanced sensitivity to plasmid DNA. Such aligned electrospun fibers could have potential applications in optoelectronic or sensory devices.

     

Dependence of Structural,Morphological and Magnetic Properties of Manganese Ferrite on Ni-Mn Substitution

This paper presents the influence of Mn²⁺ substitution by Ni²⁺ on the structural, morphological and magnetic properties of Mn_1−xNi_xFe₂O₄@SiO₂ (x = 0, 0.25, 0.50, 0.75, 1.00) nanocomposites (NCs) obtained by a modified sol-gel method. The Fourier transform infrared spectra confirm the formation of a SiO₂ matrix and ferrite, while the X-ray diffraction patterns show the presence of poorly crystalline ferrite at low annealing temperatures and highly crystalline mixed cubic spinel ferrite accompanied by secondary phases at high annealing temperatures. The lattice parameters gradually decrease, while the crystallite size, volume, and X-ray density of Mn_1−xNi_xFe₂O₄@SiO₂ NCs increase with increasing Ni content and follow Vegard’s law. The saturation magnetization, remanent magnetization, squareness, magnetic moment per formula unit, and anisotropy constant increase, while the coercivity decreases with increasing Ni content. These parameters are larger for the samples with the same chemical formula, annealed at higher temperatures. The NCs with high Ni content show superparamagnetic-like behavior, while the NCs with high Mn content display paramagnetic behavior.     

Polyvinylpyrrolidone electrospun nanofibers doped with Eu3+: Fabrication,characterization, and application in gas sensors

Polymer nanofibers (NFs)-based optical sensors hold great potential to fabricate low-cost devices capable to monitor different volatile organic compounds (VOCs) related to healthcare and environmental conditions. For instance, ammonia detection is a subject of paramount importance, owing to the serious health problems associated to the exposition to this volatile. In this context, here, we report on the development of optical electrospun NFs composed of polyvinylpyrrolidone (PVP) doped with Europium (Eu³⁺) aiming at the detection of ammonia. The fabricated NFs were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, fluorescence microscopy, photoluminescence, and excited state lifetime spectroscopies. The luminescence properties changes were evaluated by exposing the PVP_Eu³⁺ NFs to ammonia and other distinct interfering VOCs including toluene, tetrahydrofuran, acetone, triethylamine, acetic acid, and chloroform. The sensor exhibited a linear response to ammonia exposition in the concentration range from 0 to 50 ppm, yielding a detection limit of 4.7 ppm. Our results indicate the potential application of PVP_Eu³⁺ electrospun NFs in optical sensors for ammonia detection at room temperature based on luminescence quenching. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47775.     

Tunable Thermo‐Responsive Poly(N‐vinylcaprolactam) Cellulose Nanofibers: Synthesis,Characterization, and Fabrication

Temperature‐responsive PVCL homopolymers and functional PVCL polymers containing carboxylic acids are prepared in organic and aqueous solutions. PVCL bulk polymers are characterized using ¹H NMR, photometry, ATR‐FTIR, and thermal analysis. A finite phase transition at 37–40 °C occurs in aqueous solutions of PVCL and PVCL‐COOH. PVCL and PVCL‐COOH polymers are electrospun into fibers ranging from 100 to 2300 nm in diameter. PVCL/cellulose bi‐component films are obtained by electrospinning of CA and PVCL followed by alkaline hydrolysis. These tunable thermo‐responsive PVCL/cellulose nanofibers have potential applications in developing affinity membranes.

     

Correlation of the crystal features,magnetic parameters,and electronic structure of Bi-substituted BaFe12-xBixO19 hexaferrites: Theoretical background

Herein, using first-principles density functional theory (DFT) calculations, we have investigated the effects of Bi substitution on the structural, electronic, and magnetic properties of barium hexaferrite (BaFe_12-xBi_xO₁₉, x = 0; 0.5; 1.5 and 2). As a result of the calculation, it was determined that the most stable structure exists if the spin of the Fe atom on the 2a, 2b, and 12k positions of the barium hexaferrite compound is taken in the upward direction. The calculated lattice constant $\left(\raisebox{1ex}{$\mathrm{c}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{a}$}\right.=3.9\right)$ and magnetic moment $\left(4.24{\mu }_{\mathrm{B}}\right)$ of iron ions are in reasonable agreement with other experimental works. Moreover, the presence of bismuth reduces the electronic band gap. Energy gain and magnetic anisotropy energy calculations for FIM, FM, and NM states were performed for the most stable states. It has been established that the most stable structural state is characteristic of х = 0.5. It has been calculated that substitution by the large Bi³⁺ ion dramatically changed the electronic structure and sharply reduced the band gap. This paper is the first step towards establishing the nature of the distribution of ions in M-type hexaferrites under conditions of substitution by ions with a large ionic radius.     

Schottky–Richardson,Poole–Frenkel,and Space Charge Limited Current Mechanisms in M‐Type Sr(MnTi)xFe(12‐2x)O19 Ferrite

The Static Current Density–Electric Field characteristics of Sr(MnTi)_xFe_(12‐2x)O₁₉ ferrite compositions (x = 0.5, 1.0, 1.5, and 2.0) have been investigated from 4.15 to 36.30 kV/m at room temperature. Ohmic and nonohmic regions are observed at low and high field regimes. The various models, governing nonlinear conduction, are discussed qualitatively in terms of Space charge limited current (SCLC), Ionic hopping, Poole–Frenkel, Schottky–Richardson, and Fowler–Nordheim mechanisms. The results depict Child‐Langmuir type SCLC in the investigated compositions.