Preparation and enhanced properties of Fe3O4 nanoparticles reinforced polyimide nanocomposites

Polyimide (PI) nanocomposite reinforced with Fe3O4 nanoparticles (NPs) at various NPs loadings levels of 5.0, 10.0, 15.0, and 20.0 wt% were prepared. The chemical interactions of the Fe3O4 NPs/PI nanocomposites were characterized using Fourier Transform Infrared (FT-IR) spectroscopy. X-ray Diffraction (XRD) results revealed that the addition of NPs had a significant effect on the crystallization of PI. Scanning electron microscope (SEM) and the atomic force microscope (AFM) were used to characterize the dispersion and surface morphology of the Fe3O4 NPs and the PI nanocomposites. The obtained optical band gap of the nanocomposites characterized using Ultraviolet-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS) was decreased with increasing the Fe3O4 loading. Differential scanning calorimetry (DSC) results showed a continuous increase of Tg with increasing the Fe3O4 NPs loading. Some differences were observed in the onset decomposition temperature between the pure PI and nanocomposites since the NPs and the PI matrix were physically entangled together to form the nanocomposites. The contact angle of pure PI was larger than that of Fe3O4/PI nanocomposites films, and increased with increasing the loading of Fe3O4. The degree of swelling was increased with increasing the Fe3O4 loading and the swelling time. The dielectric properties of the nanocomposite were strongly related to the Fe3O4 loading levels. The Fe3O4/PI magnetic property also had been improved with increasing the loading of the magnetic nanoparticles

Multifunctional Carbon Nanostructures for Advanced Energy Storage Applications

Carbon nanostructures—including graphene, fullerenes, etc.—have found applications in a number of areas synergistically with a number of other materials. These multifunctional carbon nanostructures have recently attracted tremendous interest for energy storage applications due to their large aspect ratios, specific surface areas, and electrical conductivity. This succinct review aims to report on the recent advances in energy storage applications involving these multifunctional carbon nanostructures. The advanced design and testing of multifunctional carbon nanostructures for energy storage applications—specifically, electrochemical capacitors, lithium ion batteries, and fuel cells—are emphasized with comprehensive examples

Hexavalent chromium synthesized polyaniline nanostructures: Magnetoresistance and electrochemical energy storage behaviors

In this work, the oxidant Cr(VI) dose was observed to have influenced the polyaniline (PANI) nanostructures as well as the crystallization structure. The temperature dependent resistivity study revealed a quasi 3-dimensional variable range hopping (VRH) electrical conduction mechanism. The permittivity was found to be affected by the PANI nanostructures. The observed positive MR at room temperature in the synthesized PANI samples was analyzed by the wave-function shrinkage model. The electrochemical energy storage was investigated using the cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. The highest gravimetric capacitance of 298.5 F g-1 was obtained in the prepared PANI sample using 3 mmol K2Cr2O7 derived from the CV at a scan rate of 5 mV s-1 and the maximum value of gravimetric capacitance of 330.2 F g-1 was achieved in the galvanostatic charge-discharge measurements at a current density of 0.5 A g -1. After applying an external magnetic field, the capacitance decreased due to the observed positive magnetoresistance phenomenon. The cyclic stability studies revealed that the synthesized PANI samples exhibited good durability and retained around 80% of the capacitance even after 1000 charge-discharge galvanostatic cycles. © 2013 Elsevier Ltd. All rights reserved

Hexavalent chromium synthesized polyaniline nanostructures: Magnetoresistance and electrochemical energy storage behaviors

In this work, the oxidant Cr(VI) dose was observed to have influenced the polyaniline (PANI) nanostructures as well as the crystallization structure. The temperature dependent resistivity study revealed a quasi 3-dimensional variable range hopping (VRH) electrical conduction mechanism. The permittivity was found to be affected by the PANI nanostructures. The observed positive MR at room temperature in the synthesized PANI samples was analyzed by the wave-function shrinkage model. The electrochemical energy storage was investigated using the cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. The highest gravimetric capacitance of 298.5 F g-1 was obtained in the prepared PANI sample using 3 mmol K2Cr2O7 derived from the CV at a scan rate of 5 mV s-1 and the maximum value of gravimetric capacitance of 330.2 F g-1 was achieved in the galvanostatic charge-discharge measurements at a current density of 0.5 A g -1. After applying an external magnetic field, the capacitance decreased due to the observed positive magnetoresistance phenomenon. The cyclic stability studies revealed that the synthesized PANI samples exhibited good durability and retained around 80% of the capacitance even after 1000 charge-discharge galvanostatic cycles. © 2013 Elsevier Ltd. All rights reserved

Magnetite-polypyrrole metacomposites: Dielectric properties and magnetoresistance behavior

The conductive polypyrrole (PPy) polymer nanocomposites (PNCs) reinforced with different magnetite (Fe3O4) nanoparticle loadings have been successfully synthesized by using a facile surface initiated polymerization (SIP) method. The scanning electron microscope (SEM) is used to characterize the surface morphology of the as-received Fe3O 4 nanoparticles (NPs), pure PPy and Fe3O4/PPy PNCs. The high-resolution transmission electron microscope (HRTEM) is used to observe the nanoparticle dispersion within the polymer matrix. The chemical structure of the PNCs is characterized by Fourier transform infrared (FT-IR) spectroscopy. The thermal stability of the Fe3O4/PPy PNCs is assessed by thermogravimetric analysis (TGA). X-ray diffraction (XRD) results reveal that the addition of NPs has a significant effect on the crystallization of PPy. The switching frequency, at which the permittivity switches from negative to positive, is observed in the synthesized pure PPy and Fe 3O4/PPy PNCs. The optical band gap of Fe3O 4/PPy PNCs is studied by ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). The Fe3O4/PPy PNCs exhibit no hysteresis loop, indicating the superparamagnetic behavior. Temperature- dependent resistivity indicates a quasi-3-dimensional variable range hopping (VRH) electrical conduction mechanism for the synthesized samples. The positive magnetoresistance (MR) is observed in the synthesized pure PPy at room temperature and analyzed by the wave function shrinkage model. Meanwhile, the negative MR is obtained in the synthesized magnetic PNCs at room temperature and analyzed by the orbital magnetoconductivity theory (forward interference model). © 2013 American Chemical Society

Positive and negative magnetoresistance phenomena observed in magnetic electrospun polyacrylonitrile-based carbon nanocomposite fibers

Unique temperature dependent resistance behavior (positive/negative temperature coefficient switching at 240 K), and tunable negative and positive magnetoresistance switching phenomena were observed in the magnetic carbon nanocomposite fibers prepared from heat treatment of the nitrate soaked oxidation stabilized polyacrylonitrile (PAN) nanofibers. The physical mechanisms were revealed by considering the variable range hopping electron transportation model, electron quantum interference and spin-dependent scattering effects. © 2013 The Royal Society of Chemistry

Electropolymerized Polyaniline Stabilized Tungsten Oxide Nanocomposite Films: Electrochromic Behavior and Electrochemical Energy Storage

Polyaniline (PANI)/tungsten oxide (WO₃) nanocomposite films were fabricated by electropolymerization of aniline monomers onto WO₃ coated indium tin oxide (ITO) glass slides, which were prepared by spin coating technique and followed by annealing at 500 °C for 2 h. The morphology and crystalline structure of the composite films were studied using Fourier transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results confirm chemical interactions between the polymer matrix and the WO₃ particles and reveal a well crystallized PANI/WO₃ nanocomposite structure. The optical properties and electrochemical capacitive behaviors of the composite films for electrochromic (EC) and energy storage devices applications were investigated using spectroelectrochemistry (SEC), cyclic voltammetry (CV) and galvanostatic charge–discharge measurements. The composite films show dual electrochromism at both positive and negative potentials arising from PANI and WO₃, respectively. A coloration efficiency of 98.4 cm² C^–1 was obtained for the composite film, which was much higher than that of WO₃ (36.3 cm² C^–1) and PANI (50.0 cm² C^–1) thin film. An areal capacitance of 0.025 F cm^–2 that is comparable to that of pure PANI (0.075 F cm^–2) is derived from CV at a scan rate of 5 mV/s with a broader working potential window of 1.3 V. The cyclic stability studies reveal that the composite films exhibit much more enhanced durability and retain significant charge storage or discharge capacity after 1000 charge–discharge cycles. However, pure PANI loses most of the charge storage or discharge capacity after 350 cycles. The chemical bonding between PANI matrix and WO₃ particles is believed to play an important role in enhancing the stability of the nanocomposite film

Synergistic interactions between activated carbon fabrics and toxic hexavalent chromium

The synergistic interactions between the activated carbon fabrics (ACFs) and the toxicCr(VI) were investigated aiming to functionalize the ACFs and to remove the toxic Cr(VI). The effects of pH, treatment time, initial Cr(VI) concentration and ACFs dose on the Cr(VI) removal were studied. Different pH values had different effects on the Cr(VI) removal by ACFs, pH = 1.0 was found to be the optimum. For the pH = 1.0 solution, the Cr(VI) in the aqueous solution was reduced to Cr(III) and adsorbed onto the ACFs, and the C-O and C=O functional groups were found on the ACFs surface. The redox kinetic in the pH = 1.0 solution could be described by the pseudo-first-order model and the typical value of the pseudo-first-order rate constant was calculated to be 0.0872 min?1. Langmuir, Freundlich, and Temkin adsorption isotherm models were applied to describe isotherm behaviors. The Cr(VI) equilibrium data agreed well with the Langmiur isotherm model with a maximum adsorption capacity of 5.59 mg g?1. The ACFs could be easily regenerated by 1.0 mol L?1 sodium hydroxide and effectively recycled 7 times with the removal percentage decreased by 16.5%, which was caused by the irreversible formation of oxygen functional groups on the surface of ACFs. © 2013 The Electrochemical Society. All rights reserved

Carboxyl Multiwalled Carbon-Nanotube-Stabilized Palladium Nanocatalysts toward Improved Methanol Oxidation Reaction

Carboxyl-functionalized multiwalled carbon nanotubes (MWNT-COOH) decorated with palladium (Pd) nanoparticles (NPs, Pd-MWNT-COOH) are prepared by using a one-pot thermal decomposition method without addition of reductant or surfactant. An increased ratio of the Dband to Gband in Raman spectra and a decreased ratio of oxygen-containing groups measured using X-ray photoelectron spectroscopy suggest the interaction between Pd NPs and carboxyl groups in Pd-MWNT-COOH. TEM studies reveal improved dispersion of Pd NPs after introducing MWNT-COOH or MWNTs; the carboxyl groups act as anchors to perfectly disperse Pd NPs in Pd-MWNT-COOH, which is responsible for the highest peak current of Pd-MWNT-COOH for the methanol oxidation reaction. The best catalytic performance is observed in conditions that afford a balanced adsorption between hydroxide and methanol through varying the concentrations of methanol and KOH. Increasing temperature can also improve the catalyst performance due to enhanced reaction kinetics

Polarization Measurements and Evaluation Based on Multidimensional Polarization Indices Applied in Analyzing Atmospheric Particulates

Online identification and characterization of suspended aerosols can provide a scientific basis for understanding aerosol transformations, quantitatively evaluating the impacts on air quality, public health, and the source apportionment of different atmospheric particulate matters. In this study, we confirm the validity of our developed high-throughput multi-angle polarized scattering vector detection of aerosols and multidimensional polarization scattering index systems. By observation of the mean values, variance, and Wilk’s Lambda of multidimensional polarization indices for different aerosol types, the polarization index shows unique characterization abilities for aerosol properties, and the optimal combination of polarization indices can always be found for a specific aerosol category with a high resolution and discrimination. Clearly, the multidimensional polarization indices of individual aerosols are more suitable for online and real-time aerosol identification and even help to explain the in situ microphysical characteristics of aerosols or evaluate the dynamic evolution of aerosols