Nanoparticles-decorated coal tar pitch-based carbon foam with enhanced electromagnetic radiation absorption capability

In the present study, to replace existing high-density radar-absorbing materials (RAM) for civil and military aerospace applications, lightweight coal tar pitch-based carbon foam (CFoam) was developed by a sacrificial template technique. The CFoam was decorated with Fe3O4 and ZnO nanoparticles to improve electromagnetic (EM) radiation absorption to make it useful as RAM. To ascertain the effect of the decorated nanoparticles on the CFoam, it was characterized by scanning electron microscopy, X-ray diffraction, a vector network analyzer and a vibration sample magnetometer. It was observed that Fe3O4 and Fe3O4-ZnO nanoparticles have a positive effect on the overall properties of CFoam. The compressive strength of CFoam increases by 22% and its thermal stability increases by 100 degrees C, whereas its electrical conductivity decreases by almost 25%. The total shielding effectiveness (SE) of CFoam increases from -25 dB to -54 and -56 dB, respectively, for Fe3O4- and Fe3O4-ZnO nanoparticles-decorated CFoam. The enhancement in total SE for Fe3O4- and Fe3O4-ZnO-coated CFoam is basically due to the contribution of absorption losses by -42 and -45 dB. The Fe3O4 and Fe3O4-ZnO coatings increase surface resistance and magnetic properties because the ferromagnetic nanoparticles act as tiny dipoles, which become polarized in the presence of an EM field and result in the better absorption of EM radiation. This clearly demonstrates that decorated nanoparticles on conducting lightweight CFoam are useful as RAM for different applications to attenuate EM radiation

Development of structurally stable electrospun carbon nanofibers from polyvinyl alcohol

Continuous carbon nanofibers are of great interest in research nowadays due to their outstanding properties. But synthesis of cost effective, stable and straight carbon nanofibers from low cost polymeric precursor is still a challenge. In this direction, in the present study efforts are made to prepare stable and straight carbon nanofibers from low cost polyvinyl alcohol (PVA). The PVA nanofibers are drawn by electrospinning technique from the solution of PVA and stabilization of nanofibers was carried out in the presence of iodine vapors for different time interval with applying the load. The stabilized nanofibers were carbonized at 1000 degrees C and semi-graphitized at 2200 degrees C. The resultant nanofibers were characterized by analytical and spectroscopic techniques. The microscopic study reveals that there is not much difference in stabilized, carbonized and semi graphitized nanofiber diameter, derived from PVA nanofiber stabilized with the application of load. The XRD and TEM study reveals the presence of amorphous as well as crystalline phases in semi graphitized nanofibers with different interlayer spacing. The higher value of electrical conductivity obtained as a consequence of alignment of carbon layer in the case of nanofiber stabilized with applying load and further increases in conductivity due to crystallinity and decreases in sp(3) content

Electrospun chitosan-polyvinyl alcohol composite nanofibers loaded with cerium for efficient removal of arsenic from contaminated water

Contamination of water due to arsenic has been extensively reported all over the world. It has led to massive epidemics of arsenic poisoning. An urgent need is being felt to develop efficient techniques for the removal of arsenic from contaminated water. In this context, cerium (Ce) loaded chitosan (CHT)-polyvinyl alcohol (PVA) composite (Ce-CHT/PVA) nanofibers were developed by electrospinning technique and have been employed for removing As(III). The Ce-CHT/PVA composite nanofibers efficiently adsorb As(III) and purify water below the prescribed limit of WHO/EPA. As(III) adsorption over the surface of Ce-CHT/PVA has been confirmed by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDAX), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The quantitative estimation of As(111) has been carried out by flameless atomic adsorption spectrophotometer-hydride generator (AAS-HG) system. The As(m) adsorption efficiency of Ce-CHT/PVA composite nanofibers has been established as a function of pH, time, temperature and adsorbent dose. The adsorption data were best fitted to Langmuir isotherm, and the maximum adsorption capacity (gm) was found to be 18.0 mg g(-1). The interference studies of several ionic species individually as well multi-element for As removal have also reported. The measurement of the uncertainty of As(m) determination was calculated after determining the contributing factors. The data are reported with a confidence level of 95% (K = 2). The Ce-CHT/PVA composite nanofibers are non toxic and can be directly used for water purification or after being embedded in the form of membrane or candles

High rate capability and cyclic stability of hierarchically porous Tin oxide (IV)-carbon nanofibers as anode in lithium ion batteries

Tin oxide-carbon composite porous nanofibres exhibiting superior electrochemical performance as lithium ion battery (LIB) anode have been prepared using electrospinning technique. Surface morphology and structural characterizations of the composite material is carried out by techniques such as XRD, FESEM, HR-TEM, XPS, TGA and Raman spectroscopy. FESEM and TEM studies reveal that nanofibers have a uniform diameter of 150-180 nm and contain highly porous outer wall. The carbon content is limited to similar to 10% in the nanofibers as shown by the TGA and EDAX which does not fade the high capacity of SnO2. These nanofibers delivered a higher discharge capacity of 722 mAh/g even after 100 cycles at high rate of 1C. The excellent electrochemical performance can be ascribed to the synergy effect of small amount of carbon in the composite and the hierarchically porous structure which accommodate large volume changes associated with Li-ion insertion-desertion. The porous nano- architecture would also provide a short diffusion path for Li ? ions in addition to facilitating high flux of electrolyte percolation through micropores. The electrochemical performance of composite material has also been tested at 60 degrees C at a higher rate of 2C and 5C. Post cycling FESEM analysis shows no volumetric and morphology changes in porous nanofibers after completing rate capability at high rate of 10C

A facile fabrication of poly(methyl methacrylate)/α-NaYF4:Eu3+ tunable electrospun photoluminescent nanofibers

The photoluminescent nanofibers (PLNs) were successfully produced by incorporating α-NaYF4:Eu3+ nanophosphor into the polymethylmethacrylate (PMMA) matrix using electrospinning technique. The morphology of PLNs was investigated by scanning electron microscope (SEM) with the diameter in the range of 165–450 nm. The nanofibers revealed hypersensitivity in emission regime from orange to red (589–707 nm) with 5% concentration of nanophosphor at the excitation wavelength of 239 nm. X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy confirm the uniform co-ordination (dispersion) of nanophosphor with the carbonyl group of PMMA molecular chain. The PMMA/ α-NaYF4:Eu3+ composite nanofibers have the potential application in colored light-emitting diode (LED)

Effect of graphitization temperature on structure and electrical conductivity of poly-acrylonitrile based carbon fibers

Carbon fibers (CF) with perfect graphitic crystallographic ordering is highly desirable for numerous applications such as carbon interconnects, as electrode material for lithium ion battery, in composites and as hydrogen storage material. In the present manuscript, we report about the effect of graphitization temperature on the crystallinity and electrical conductivity of Poly-acrylonitrile based CF. The change in the crystallinity of graphitized fibers has been explored by using High resolution transmission electron microscopy, X-ray diffractometry, Raman spectroscopy and X-ray photoelectron spectroscopy. Upon graphitization at 1800 degrees C and 2200 degrees C both the in-plane crystallinity (L-a) and out of plane crystallinity (L-c) are found to monotonically increase. The observed spectral features in the Raman spectra have been correlated with graphitic order achieved. The electrical conductivity monotonically increases from 5.32 S/cm to 51.01 S/cm and 75.91 S/cm for PAN fibers graphitized at 1000 degrees C, 1800 degrees C and 2200 degrees C respectively making it one of the promising material for electrical applications

Growth of single and bilayer graphene by filtered cathodic vacuum arc technique

The authors present a viable process to grow the high quality graphene films with control over number of layers by the filtered cathodic vacuum arc (FCVA) technique. In the FCVA process, the different carbon concentrations can be controlled by precisely tuning the arc time (1-4 s). The arc generated carbon was deposited on the nickel catalyst at 800 degrees C, annealed for 10 min, and cooled down to room temperature in the presence of hydrogen gas, resulting in the graphene films with control over number of layers. Prior to arcing, hydrogen etching of nickel was carried out to clean the surface of the substrate. A growth model to prepare the high quality graphene has also been proposed. The as-grown graphene films were transferred to different substrates and are characterized by Raman spectroscopy, optical microscopy, high resolution transmission electron microscopy, and atomic force microscopy to determine the number of layers present in these films. Raman spectra of the prepared graphene films exhibit change in the G peak position from 1582.4 to 1578.1 cm(-1), two-dimensional (2D) peak shifts from 2688.5 to 2703.8 cm(-1), the value of I-2D/I-G increased from 0.38 to 3.82, and the full width at half maxima of 2D peak changed from 41 to 70 cm(-1), for different layers of graphene films. The high resolution transmission electron microscopy image revealed that the graphene films prepared for 1 and 2 s arc times have single and bi-or trilayered structures, respectively