One-pot melamine derived nitrogen doped magnetic carbon nanoadsorbents with enhanced chromium removal

Novel nitrogen doped magnetic carbons (NMC), in-situ synthesized through facile pyrolysis-carbonization processes using Fe(NO3)3 and melamine as precursors, were demonstrated as excellent nanoadsorbents to remove Cr(VI) effectively. The achieved removal capacity in both neutral and acidic solution was 29.4 and 2001.4 mg g−1 respectively, much higher than the reported adsorbents so far. The unprecedented high adsorption performance can be attributed to the incorporation of the nitrogen dopant, which increased the negative charge density on the surface of adsorbent and thereby enhanced the interaction between the adsorbents and Cr(VI) ions. The density functional theory (DFT) calculation demonstrated that the nitrogen dopants can decrease the adsorption energy between the Cr(VI) ions and NMC (−3.456 kJ mol−1), lower than the undoped sample (−3.344 kJ mol−1), which boosted the adsorption behavior. Chemical rather than physical adsorption was followed for these magnetic nanoadsorbents as revealed from the pseudo-second-order kinetic study. Furthermore, the NMC showed high stability with recycling tests for the Cr(VI) removal

Surfactant-free synthesized magnetic polypropylene nanocomposites: Rheological, electrical, magnetic, and thermal properties

A facile surfactant-free process is introduced to prepare multifunctional polypropylene (PP) nanocomposites filled with highly dispersed Fe@Fe 2O3 core@shell nanoparticles (NPs). Transmission electron microscopy (TEM) observations confirm the formation of uniform NPs in the PP matrix and the particle size increases with increasing the particle loading. The melt rheology measurements show an obvious change in the frequency dependent storage modulus (G′), loss modulus (G″) and complex viscosity (η*) particularly at low frequencies. These changes are often related to the filler percolation threshold , which has also been verified in the sharp change of electrical resistance and dielectric permittivity of these nanocomposites in higher particle loadings. The continuous decrease in the resistivity with increasing filler loading from 5 wt % to 20 wt % demonstrates the structural transition of the nanocomposites. The monotonic increase in the dielectric permittivity with increasing particle loadings combined with the direct evidence from the TEM observations indicate that the NPs are well separated and uniformly dispersed in the polymer matrix. Thermal gravimetric analysis (TGA) results reveal a surprisingly high enhancement of the thermal stability by ∼120 °C in air due to the oxygen trapping effect of the NPs and the polymer-particle interfacial interaction. The differential scanning calorimetry (DSC) results show that the crystalline temperature (T c) of the nanocomposites is reduced by 16-18 °C as compared to that of PP, while the melting temperature (Tm) almost maintains the same. The nanocomposites is found to be soft ferromagnetic at room temperature. © 2011 American Chemical Society

Magnetic electrospun fluorescent polyvinylpyrrolidone nanocomposite fibers

Magnetic nanoparticles (MNPs) were synthesized from facile thermodecomposition of iron pentacarbonyl and the subsequent silica coating on the MNP surface was achieved via a modified Stöber process to obtain the core-shell composite structured particles (MNPs-SiO2). MNPs-SiO 2 were then incorporated into polyvinylpyrrolidone (PVP) to form nanocomposite fibers via an electrospinning process with optimized operational parameters such as polymer concentration, applied electrical voltage, feed rate and tip-to-collector distance. All these parameters show an unusual effect on the produced fiber diameter. Contrary to the conventional observation, i.e., increasing the applied voltage and feed rate or decreasing the distance could increase the fiber diameter; a reduced average fiber diameter was observed in this study and could be explained from the stretching and contraction force balance within the fiber during electrospinning. The size of the resulting PVP fibers is correlated to the corresponding rheological behaviors of the PVP solutions with different concentrations. The MNPs-SiO2/PVP nanocomposite fibers exhibit a similar thermal decomposition temperature (386.3 °C) as that (387.8 °C) of pure PVP. Meanwhile, unique fluorescent and magnetic properties have been incorporated simultaneously in the nanocomposite fibers with the addition of small amount of MNPs-SiO2 nanoparticles. © 2012 Elsevier Ltd. All rights reserved

Magnetic high density polyethylene nanocomposites reinforced with in-situ synthesized Fe@FeO core-shell nanoparticles

Magnetic high density polyethylene (HDPE) polymer nanocomposites (PNCs) with different loadings of iron@iron oxide core-shell nanoparticles (NPs) were fabricated by in-situ thermal decomposition of organometallic iron precursors in the HDPE-xylene solution. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) measurement indicated that the HDPE chains were physically adsorbed onto the surface of NPs instead of forming chemical bonding during the formation of these PNCs. Transmission electron microscopy (TEM) micrographs revealed that the iron core NPs surrounded with iron oxide shell were formed in the HDPE hosting matrix with good dispersion, an inter-network structure was formed when the particle loading reached 10.0 wt%. Mössbauer spectrum analysis showed that the oxidization content of the iron NPs decreased with increasing the particle loading. The X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC) characterization demonstrated that the crystalline structure of HDPE matrix was not influenced by the incorporation of the NPs; however, fusion heat and crystalline fraction of the HDPE matrix decreased with the introduction of these NPs. The melt rheological behaviors were significantly changed as indicated by different complex viscosities, storage moduli and loss moduli between pristine HDPE and its PNCs. Magnetic property investigation revealed a soft ferromagnetic behavior for these HDPE PNCs at room temperature and the coercivity was decreased with increasing the particle loading. Thermal gravimetric analysis (TGA) demonstrated that the thermal stability of these HDPE PNCs was enhanced in the presence of the NPs. Dielectric properties of the HDPE PNCs were also investigated and discussed in detail. © 2012 Elsevier Ltd. All rights reserved

Manipulating the dimensional assembly pattern and crystalline structures of iron oxide nanostructures with a functional polyolefin

Controlled crystalline structures (α- and γ-phase) and assembly patterns (1-D, 2-D and 3-D) were achieved in the synthesized iron oxide (Fe2O3) nanoparticles (NPs) using polymeric surfactant-polypropylene grafted maleic anhydride (PP-g-MA) with different concentrations. In addition, the change of the crystalline structure from the α- and γ-phase also led to the significantly increased saturation magnetization and coercivity

Microwave assisted formation of magnetic core-shell carbon nanostructure

This letter describes a facile high temperature microwave assisted process to form the magnetic core-shell carbon nanostructure from polyaniline (PANI)-magnetite (Fe3O4) nanocomposites. The amorphous combined with graphitized carbon shell is observed by the transmission electron microscopy (TEM). The crystalline metallic iron, cementite, Fe3O4 and iron oxide (Fe2O3) are observed in the magnetic core in the M̈ossbauer spectrum measurements. The increased magnetic properties are observed in the formed core-shell carbon nanostructure after microwave annealing. The formed solid carbon nanostructure can protect the material from the acid dissolution and magnetic core favors the recycling of material. © 2013 The Electrochemical Society

Magnetic carbon nanostructures: Microwave energy-assisted pyrolysis vs. conventional pyrolysis

Magnetic carbon nanostructures from microwave assisted- and conventional-pyrolysis processes are compared. Unlike graphitized carbon shells from conventional heating, different carbon shell morphologies including nanotubes, nanoflakes and amorphous carbon were observed. Crystalline iron and cementite were observed in the magnetic core, different from a single cementite phase from the conventional process. © 2012 The Royal Society of Chemistry

Electromagnetic field absorbing polypropylene nanocomposites with tuned permittivity and permeability by nanoiron and carbon nanotubes

Highly efficient electromagnetic field absorption at gigahertz (GHz) was reported in the novel magnetic polymer nanocomposites (MPNCs) with in-situ synthesized Fe@Fe2O3 core@shell nanoparticles (NPs) or their decorated multiwall carbon nanotubes (MWNTs) dispersed in the polypropylene (PP) matrix through a one-pot bottom-up method. PP grafted maleic anhydride (PP-g-MA) with different molecular weights served as surfactant to stabilize the in-situ-formed NPs and simultaneously as compatibilizer to enhance the bonding at the PP-filler interfaces. Because of the strong magnetization of the PP MPNCs filled with 20.0 wt % Fe@Fe2O3 NPs stabilized by PP-g-MA (Mn = 800), a minimum reflection loss (RL) of -31.5 dB was observed at 18.0 GHz, and the frequency bandwidth with RL lower than -10.0 dB was 3.1 GHz (from 16.9 to 20.0 GHz) in the MPNC sample with a thickness of 5.5 mm. However, due to the lack of magnetic loss, only a weak RL of 4.3 dB was found at frequency of 16.8 GHz for the PP/PP-g-MA (Mn = 800)/1.0 wt % MWNTs nanocomposites sample with a thickness of 5.5 mm. When the PP MPNCs filled with Fe@Fe2O3 NPs decorated MWNTs (sample thickness of 5.0 mm) in the presence of low molecular weight PP-g-MA (Mn = 800), the RL of -24.5 dB at 20.0 GHz was observed. Through simply changing Mn of PP-g-MA from 800 to 8000, more oxidized iron resulted in a decreased permeability and smaller RL in the high frequency range. The in-situ-formed nanofillers significantly reduced the flammability of PP for potential wide applications