Fabrication of PLA/MWCNT/Fe3O4 composite nanofibers for leukemia cancer cells

The efficient delivery of daunorubicin loaded poly (lactic acid) (PLA)/multiwalled carbon nanotubes (MWCNT)/Fe₃O₄ composite nanofibers was investigated. The synthesized nanofibers were characterized using SEM, TEM, and XRD analysis. The proliferation inhibition effect of PLA/MWCNT/Fe₃O₄ nanofibrous scaffolds on leukemia K562 cell lines was investigated. The effect of nanofiber concentration on the daunorubicin delivery in the absence and presence of external magnetic field was also evaluated. The results indicated that the incorporation of daunorubicin into the prepared nanofibrous scaffold under applied magnetic field could have synergistic cytotoxic effect on leukemia cancer cells. The drug release mechanism followed the non-Fickian transport.     

Structure and electrical conductivity of nitrogen-doped carbon nanofibers

The effect of nitrogen concentration in carbon nanofibers (CNFs) on the structural and electrical properties of the carbon material was studied. CNFs with nitrogen concentration varied from 0 to 8.2 wt.% (N-CNFs) with “herringbone” structure were prepared by decomposition of ethylene and ethylene mixture with ammonia over 65Ni-25Cu-10Al₂O₃ (wt.%) catalyst at 823 K. Detailed investigation of the CNFs and N-CNFs by XPS, FTIR and Raman spectroscopy showed that the nitrogen introduction in carbon material distorts the graphite-like lattice and increases the structure defectiveness. Both effects become more significant as the nitrogen concentration in N-CNFs grows.The electrical conductivity of N-CNFs with different nitrogen concentrations is caused by the competition of the nanofiber graphite-like structure disordering after introduction of nitrogen atoms and doping of an additional electron into the delocalized π-system of the graphite-like material. As a result, the maximum electrical conductivity among the samples studied was observed at nitrogen concentration in N-CNFs equal to 3.1 wt.%.     

Influence of carbon nanotubes on thermal and electrical conductivity of zirconia-based composite

Carbon nanotubes (CNTs) are widely used in ceramic-matrix composites (CMC) as a filler. An individual carbon nanotube exhibits extremely high thermal conductivity, however, the influence of CNTs on the thermal conductivity of CMCs is moderate. In contrast, even a small quantity of CNTs significantly increases the electrical conductivity of CMCs. The present paper studies this contradictory influence for ZrO₂-CNTs composites with 3, 5, 10 and 20 vol% multi-wall carbon nanotubes (MWCNTs). Their thermal and electrical conductivity was studied by the laser flash method and electrochemical impedance spectroscopy. The analysis reveals that the moderate influence of MWCNTs on the thermal conductivity of composites originates from the similar thermal conductivity of MWCNTs in a bundle and zirconia. On the other hand, the substantial difference in the electrical conductivity of MWCNTs and zirconia leads to an exponential increase in the electrical conductivity of the ZrO₂-CNTs composite even with small additions of nanotubes.     

Superparamagnetic polyvinylpyrrolidone/chitosan/Fe3O4 electrospun nanofibers as effective U(VI) adsorbents

Magnetoactive electrospun fibrous membranes consisting of polyvinylpyrrolidone (PVP), chitosan (CS) and pre-fabricated, double-layer oleic acid-coated magnetite nanoparticles (OA.OA.Fe₃O₄) were fabricated and evaluated as new adsorbent materials for the removal and recovery of uranium (U(VI)) from aqueous solutions. The adsorption has been investigated by batch-type experiments and the solid material has been characterized by X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy/energy dispersive X-ray analysis (TEM/EDX) and vibration sample magnetometry (VSM) measurements prior and after uranium adsorption. The experimental adsorption data were found to be well fitted with the Langmuir isotherm and the pseudo-second order kinetic model. The results indicate that PVP/CS/OA.OA.Fe₃O₄ fibrous adsorbents exhibit good adsorption properties towards U(VI) in aqueous solutions, achieving a q_max value of 0.77 mol kg⁻¹ (183.3 mg g⁻¹) at pH 6.0. The experiments regarding the regeneration and reuse of the magnetoactive adsorbents were carried out using Na₂CO₃, at pH ~11. After four cycles, the percentage relative adsorption remained stable (~100%) whereas the desorption percentage decreased from 31.9% to 21.0%. Generally, the presented results demonstrate that the incorporation of the Fe₃O₄ NPs has a positive effect on the adsorption efficiency of U(VI) from aquatic environments.     

Preparation and properties of electrospun PAN/Fe3O4 magnetic nanofibers

Polyacrylonitrile (PAN)/Fe₃O₄ composite nanofibers were prepared via the electrospinning of the PAN spinning solutions with magnetite Fe₃O₄ nanoparticles. The experimental results showed that the morphology and diameter of the nanofibers strongly depended upon concentrations of PAN and salt additives in the spinning solutions. A suitable PAN concentration and LiCl additives could effectively prevent the occurrence of beads in the electrospinning process and affected the diameters of the electrospun nanofibers. The breaking strength and breaking strain decreased when the magnetite Fe₃O₄ nanoparticles were incorporated. The prepared PAN/Fe₃O₄ nanofibers were superparamagnetic at room temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of Al2O3 on the electrical conductivity and structure of calcium-silicate-based melts

Electrical conductivity and structure of the CaO-SiO₂-based mold flux melts with various Al₂O₃ contents were investigated. The results show that the electrical conductivity increases with the addition of Al₂O₃ from 2 wt% to 4 wt%, but decreases with the further increase of Al₂O₃ from 4 wt% to 8 wt%. Correspondingly, the apparent activation energy reduces firstly from 55.12 ± 1.20 kJ mol to 41.09± 0.38 kJ mol, and then increases from 41.09 ± 0.38 kJ mol to 98.99 ± 1.42 kJ mol. The structure analyses suggest that complex structural units, such as Si-O-Al, Al-O⁰, Si-O-Si and Q³(Si), reduce first, but increase with the further addition of Al₂O₃. Conversely, these simple structural units, such as Al-O^-, Q⁰(Si), Q¹(Si) and Q²(Si) vary in the opposite way with the change of Al₂O₃ content. From the variations of electrical conductivity, activation energy and structural units, it can be found that when Al₂O₃ works as network breaker to simplify the melt structure, the energy barrier for transportation of conducting ions/ionic reduce, which results in the increase of electrical conductivity; while when Al₂O₃ becomes into network former, the conductivity increases, correspondingly.     

Effects of transition metal additives on redox stability and high-temperature electrical conductivity of (Fe,Mg)3O4 spinels

Magnetite-based spinels are considered as promising oxide materials to meet the requirements for ceramic consumable anodes in molten oxide pyroelectrolysis process, a breakthrough low-CO₂ steel technology aimed to overcome the environmental impact of classical extractive metallurgy. The present work focuses on the assessment of phase relationships, redox stability and electrical conductivity of Fe_2.6Me_0.2Mg_0.2O₄ (M = Ni, Cr, Al, Mn, Ti) spinel-type materials at 300–1773 K and p(O₂) from 10⁻⁵ to 0.21 atm. The oxidation state of substituting transition metal cation, affecting the fraction of Fe²⁺ in spinel lattice, was found to be a key factor, which determines the electronic transport and tolerance against oxidative decomposition, while the impact of preferred coordination of additives on these properties was less pronounced. At T > 650 K thermal expansion of Fe_2.6Me_0.2Mg_0.2O₄ ceramics exhibited complex behaviour, and, in highly oxidizing conditions, resulted in significant volume changes, unfavourable for high-temperature electrochemical applications.     

Effect of Fe3O4 concentration on 3D gel-printed Fe3O4/CaSiO3 composite scaffolds for bone engineering

In this study, porous calcium silicate (CaSiO₃) scaffolds were prepared by 3D gel-printing (3DGP) method and Fe₃O₄ water-based magnetic fluids (WMFs) were prepared by phacoemulsification compound chemical coprecipitation method. Fe₃O₄ WMFs were coated on CaSiO₃ scaffolds surface to prepare Fe₃O₄/CaSiO₃ composite scaffolds. The effect of WMFs with different Fe₃O₄ concentrations on porous CaSiO₃ scaffolds was studied. The composition and morphological characteristics of porous scaffolds were analyzed by using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis. The magnetic properties were tested by vibrating sample magnetometer (VSM). The stability of Fe₃O₄ WMFs coatings and the degradability of composite scaffolds were tested by immersing them in simulated body fluid (SBF). The results show that when Fe₃O₄ concentration was 5.4% (w/v), the composite scaffolds had the highest saturation magnetization of 69.6 emu/g and the best stability in dynamic SBF. It is obviously that Fe₃O₄ WMFs coatings can be used for bone tissue engineering scaffolds repairing.     

Preparation,morphology and conductivity of polyacrylonitrile/multi-wall carbon nanotubes composite nanofibers

Composite nanofibers of polyacrylonitrile/multi-wall carbon nanotubes (PAN/MWCNTs) were prepared via electrospinning. Samples contained 0, 0.5, 1, 2, 3, and 3.5 wt% of MWCNTs. The viscosity and electrical conductivity of electrospinning solutions were measured. Results revealed that, with the addition of multi-wall carbon nanotubes, viscosity was increased and electrical conductivity was improved. Rheological behavior was studied using two different viscometers. Moreover, morphology and diameters of the composite nanofibers were studied by scanning electron microscopy (SEM) and nanofiber diameter distributions were presented. SEM micrographs showed that by adding MWCNTs, the average diameter of nanofibers was increased. Furthermore, the effect of MWCNTs on glass transition temperature, T _g, was investigated using differential scanning calorimetry (DSC) technique. The results showed that T _g was increased with the addition of MWCNTs. In addition, Fourier transform infrared spectroscopy (FTIR) results showed that MWCNTs can affect the orientation ability of polymer chains. The effects of adding salt, increasing voltage and changing the tip-to-collector distance on the morphology and diameters of composite nanofibers were examined. The electrical conductivity results of electrospun mats were measured by a two-probe method. Electrical conductivity was increased by addition of MWCNTs and its behavior followed the percolation theory. Finally, it was observed that mats with smaller diameters have higher electrical conductivity.     

Fabrication of magnetic polybenzoxazine-based carbon nanofibers with Fe3O4 inclusions with a hierarchical porous structure for water treatment

Hierarchical porous, magnetic Fe₃O₄@carbon nanofibers (Fe₃O₄@CNFs) based on polybenzoxazine precursors have been synthesized by a combination of electrospinning and in situ polymerization. The benzoxazine monomers could easily form thermosetting nanofibers by in situ ring-opening polymerization and subsequently be converted into CNFs by carbonization. The resultant fibers with an average diameter of 130 nm are comprised of carbon fibers with embedded Fe₃O₄ nanocrystals, and could have a high surface area of 1885 m² g^?1 and a porosity of 2.3 cm³ g^?1. Quantitative pore size distribution and fractal analysis were used to investigate the hierarchical porous structure using N₂ adsorption and synchrotron radiation small-angle X-ray scattering measurements. The role of precursor composition and activation process for the effects of the porous structure is discussed, and a plausible correlation between surface fractal dimension and porous parameter is proposed. The Fe₃O₄@CNFs exhibit efficient adsorption for organic dyes in water and excellent magnetic separation performance, suggesting their use as a promising adsorbent for water treatment, and also provided new insight into the design and development of a carbon nanomaterial based on a polybenzoxazine precursor.     

Structure and conductivity of multi-walled carbon nanotube/poly(3-hexylthiophene) composite films

This work reports a structure-property investigation of a conjugated polymer nanocomposite with enhanced conductivity. Regioregular poly(3-hexylthiophene) (rrP3HT) was used to prepare composites with thin, short, multi-walled carbon nanotube (MWNT) addition over a wide range of concentrations. Scanning and transmission electron microscopies demonstrated an excellent dispersion and good wetting properties within the carbon nanotube composites. Coated MWNTs showed superstructures of P3HT self-organized on nanotube surfaces. Changes in the long range order and on the self-ordered mesophase of the bulk material were investigated by infrared and Raman spectroscopies, differential scanning calorimetry and X-ray diffraction. Interplay between charge transport through the semiconducting polymer and carbon nanotube network increased the composite's conductivity after percolation to values close to 10⁻² S cm⁻¹.     

Influence of Fe3O4 nanoparticles decoration on dye adsorption and magnetic separation properties of Fe3O4/rGO nanocomposites

Magnetite (Fe₃O₄) nanoparticles were prepared by solvothermal method and its composites with reduced graphene oxide namely FG1, FG2, and FG3 (changing magnetite precursor loading 0.1, 0.5, and 1 respectively) were used as adsorbents for the removal of methyl violet (MV) dye. The structural and morphological results confirm that rGO sheets were decorated with Fe₃O₄ and it ensures the variation of active sites toward dye removal property. The maximum adsorption capacity obtained for FG2 was 196 mg/g. The adsorption isotherms and kinetics better fit Langmuir and pseudo-second-order kinetic model for FG1 and FG2. Increasing of Fe₃O₄ loading on rGO reduces the dye adsorption sites and too low Fe₃O₄ loading affects the magnetic separation. The optimal loading of Fe₃O₄ on rGO is important parameter for the adsorption process and fast separation of adsorbent.     

Study on orientation in EVA/Fe3O4 composite hot-melt adhesives

EVA hot melt adhesives have tackiness to both external anticorrosion coating made by cross-linked polyethylene and iron-base petroleum pipeline. But, traditional EVA hot melt adhesives cannot meet the requirement of external anticorrosion coating for weaker tackiness. Two types of Fe₃O₄ particles with different particle sizes and magnetic strengths were added in adhesives. One is of 3.665 μm^{Laser particle size analyzer (LPSA)} and 8.403×10¹ emu/g^{vibrating sample magnetometer (VSM)} and the other one is of 0.426 μm^LPSA and 3.997×10¹ emu/g^VSM. The result of peel test indicated that peel strength of composite adhesives increased as Fe₃O₄ content increased when particles size was 3.665 μm^LPSA but the tackiness of composite adhesive decreased as Fe₃O₄ content increased when particles size was 0.426 μm^LPSA. Also, microphotos of SEM revealed that the composite adhesive with 3.665 μm^LPSA Fe₃O₄ was more likely to distribute in a region near the tackiness surface between the adhesive and iron layers, but the one with 0.426 μm^LPSA Fe₃O₄ was more likely to aggregate in the middle region of adhesive. The movement of 3.665 μm^LPSA Fe₃O₄ particles could induce EVA molar chain orientation and this orientation was confirmed by infrared dichroism and XRD. Results of infrared dichroism and XRD showed that the orientation degree of EVA increased as 3.665 μm^LPSA Fe₃O₄ content increased. Furthermore, crystallinity tests by XRD and DSC indicated that crystallinity of PE segment of EVA also increased as 3.665 μm^LPSA Fe₃O₄ content increased, which could support increase of orientation tested by infrared dichroism and XRD.     

Crystallinity,conductivity, and magnetic properties of PVDF‐Fe3O4 composite films

The formation of Fe₃O₄ nanoparticles by hydrothermal process has been studied. X‐ray Diffraction measurements were carried out to distinguish between the phases formed during the synthesis. Using the synthesized Fe₃O₄ nanoparticles, poly(vinyledene fluoride)‐Fe₃O₄ composite films were prepared by spin coating method. Scanning electron microscopy of the composite films showed the presence of Fe₃O₄ nanoparticles in the form of aggregates on the surface and inside of the porous polymer matrix. Differential Scanning calorimetry revealed that the crystallinity of PVDF decreased with the addition of Fe₃O₄. The conductitivity of the composite films was strongly influenced by the Fe₃O₄ content; conductivity increased with increase in Fe₃O₄ content. Vibration sample magnetometry results revealed the ferromagnetic behavior of the synthesized iron oxide nanoparticles with a Ms value of 74.50 emu/g. Also the presence of Fe₃O₄ nanoparticles rendered the composite films magnetic. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of MnO2 and Co3O4 dopants on dielectric properties of Pb(Fe2/3W1/3)O3 ceramics

Dielectric properties of Pb(Fe_2/3W_1/3)O₃ ceramic doped with 0.05–1 mol% of MnO₂ or Co₃O₄ were investigated in a wide temperature range from −160 to 450 °C at frequencies 10 Hz–1 MHz. Besides the maxima corresponding to the ferroelectric–paraelectric transition, at higher temperatures other peaks in temperature dependencies of relative electrical permittivity and dissipation factor were observed, attributed to dielectric relaxation. The location and height of these peaks are strongly related to frequency and the dopant level. Both MnO₂ and Co₃O₄ addition caused a significant increase in the resistivity of PFW ceramic—from 10⁶ Ω cm for undoped samples to 10¹¹ Ω cm for those with 1 mol% of a dopant. The activation energies of relaxation calculated on the basis of dielectric measurements are very close to the conduction activation energies determined in similar temperature range.     

Melt viscosity and electrical conductivity of carbon black-PVC composite

The effect of the structure of carbon black aggregates on the melt behavior and electrical conductivity of carbon black-vinylchloride-vinylacetate copolymer systems was analyzed. As the amorphous carbon aggregates are roll-milled, they become cylindrical, then, as the milling time is prolonged, spherical. During milling, polymer adsorption and dispersivity increases in the same manner, causing the viscosity of the composite to decrease. It was established that during a certain milling time, conductivity rises to a peak, after which it falls. We attribute this phenomenon to there being an optimum aspect ratio and degree of dispersion of the cylindrical carbon aggregates. A model explaining the relationship between milling time and change in conductivity is proposed. When oxidized carbon black was dispersed into the copolymer, it was found that it disperses better than unoxidized carbon black, although the conductivity of the resulting composite is lower.     

聚苯胺/Fe3O4复合吸波材料的制备及表征

用原位聚合法合成了聚苯胺／Fe3O4（PANI/Fe3O4）复合材料,合成产物为以Fe3O4为核,聚苯胺为壳的球状微粒。采用FT-IR、XRD、XPS、TEM等方法对PANI/ Fe3O4进行了结构表征。以矩形波导法测定了PANI/Fe3O4在9．3GHz微波环境中的性能。结果表明,改变Fe3O4含量可以调节复合材料的电磁参数。当Fe3O4质量分数为10％时,复合材料介电损耗tgδε=1．87、磁损耗tgδμ=0．035,达到最大微波损耗7．641（-dB）,具有良好的吸波性能。     

Controlled preparation of Fe3O4/P (St-MA) magnetic composite microspheres by DPE method

In this work, controlled radical polymerization based on 1, 1-diphenylethylene (DPE method) was used to prepare magnetic composite microspheres. By this method, Fe₃O₄/P (St-MA) magnetic composite microspheres were prepared via copolymerization of styrene (St) and maleic anhydride (MA) using DPE as radical control agent in the presence of Fe₃O₄ nanoparticles. The structure and properties of the magnetic composite microspheres obtained were characterized by IR, ¹H-NMR, SEC-MALLS, TEM, TGA, VSM, DLS and other instruments. It was found that the DPE method allows the controlled preparation of magnetic composite microspheres, and Fe₃O₄/ P(St-MA) microspheres possess perfect sphere-shaped morphology, homogeneous particle size, carboxylic surface, superparamagnetism with a saturation magnetization of 14.704 emu/g, and magnetic content with a value of 25%.