El-Shazly M. Duraia

Modifications of Graphite and Multiwall Carbon Nanotubes in the Presence of Urea

The effect of high-energy ball milling on two carbon allotropes, graphite and multiwall carbon nanotubes (MWCNT) in the presence of urea has been studied. Samples were investigated using Raman spectroscopy, x-ray diffraction, scanning electron microscope (SEM) and x-ray photoelectron spectroscopy (XPS). Nitrogen-doped graphene has been successfully synthesized via a simple scalable mechanochemistry method using urea and graphite powder precursors. XPS results revealed the existence of the different nitrogen atoms configurations including pyridine, pyrrodic and graphitic N. SEM observations showed that the graphene nanosheets morphology become more wrinkles folded and crumbled as the milling time increased. The ID/IG ratio also increased as the milling time rose. The presence of both D′ and Gxa0+xa0D bands at 1621xa0cm−1 and 2940xa0cm−1, respectively, demonstrated the nitrogen incorporation in the graphene lattice Two factors contribute to the used urea: first it helps to exfoliate graphite into graphene, and second it preserves the graphitic structure from damage during the milling process as well as acting as a solid-state nitrogen source. Based on the phase analysis, the d-spacing of MWCNT samples in the presence of urea decreased due to the mechanical force in the milling process as the milling time increased. On the other hand, in the graphite case, due to its open flat surface, the graphite (002) peak shifts toward lower two theta as the milling time increase. Such findings are important and could be used for large-scale production of N-doped graphene, diminishing the use of either dangerous chemicals or sophisticated equipment.

Humic acid-derived graphene–SnO 2 nanocomposites for high capacity lithium-ion battery anodes

Humic acid obtained from wood, soil, and coal provides a naturally occurring highly oxidized carbonaceous two-dimensional material. Humic acid obtained from Leonardite coal and tin(II) chloride were used to synthesize graphene–SnO2 nanocomposites using scalable, thermal treatment processes. The humic acid-derived graphene–SnO2 nanocomposites showed the presence of graphene sheets with a unique crumpled and wrinkled morphology and SnO2 nanoparticles. The graphene–SnO2 nanocomposites were tested as anodes for lithium-ion batteries and showed high reversible specific capacities (641xa0mAhxa0g−1). In addition, the graphene–SnO2 nanocomposites also exhibited high capacity retention upon cycling which is attributed to the interaction of SnO2 nanoparticles with the humic acid-derived graphene nanosheets that allows accommodation of highly reversible volumetric changes upon Li-ion insertion/de-insertion within the structure. In comparison, humic acid treated without the incorporation of SnCl2 during the synthesis process resulted in stacking of the nanosheets leading to low surface areas and low specific capacities. The scalable production of graphene nanocomposites from earth-abundant precursors opens up significant opportunities for low-cost and high performance materials for numerous energy storage and conversion devices.

Study of the structure–property relationships in a high impact and shape memory polyester by the stereoisomer selection of the cyclobutane diol monomer

The diol and dicarboxylic acid in polyester synthesis are significant independent variables that relate directly to the structure–property-dependent variables of polyesters. The choice of the stereoisomers of the diol in the polyester synthesis can significantly alter the mechanical and thermal performance. Terephthalate polyesters prepared from the proper ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) and 1,3-propanediol have superior impact resistance when compared to ballistics grade polycarbonate. In addition these polymers exhibit very strong self-healing behavior that is activated by heat. These copolymers were all produced with a mixture of cis and trans isomers with a ratio of 43/57, respectively. This study reports research conducted to determine the structure–property relationships that can be attributed to the stereoisomers of the CBDO monomer. The polyester prepared with 99xa0% cis (CBDO) monomer has significantly improved mechanical and thermal performance when compared with the polyester prepared with a 43:57 mixture of cis and trans isomers or 100xa0% trans isomer. Thermal gravimetric analysis and differential scanning calorimetry demonstrated that the cis CBDO polymer exhibit a much higher Tg (99xa0°C for cis and 69xa0°C for the trans 84.5xa0°C for the mixed polymer) and better thermal stability than the trans form of the polymer (onset of decomposition of trans at 345 and 360xa0°C for cis). Dynamic mechanical analysis and the Notched Izod demonstrated that the cis form of the polymer was much tougher than the trans form. Wide angle X-ray diffraction showed that the trans form was semicrystalline and the cis form was amorphous. The Notched Izod impact was 1070xa0J/m for the cis CBDO-based copolymer with the trans form having an impact factor of 841xa0J/m with the mixed polymer exhibiting an intermediate value of 944xa0J/M. Molecular modeling supports the experimental evidence that the choice of stereoisomers for the diol significantly influences the molecular architecture of the polyesters. The molecular architecture of polyesters in addition to polar attraction and molecular weight variables provides a dramatic increase in mechanical and thermal performance.

Microwave-Assisted Synthesis of N-Doped Graphene-Wrapped MnO 2 Nanoflowers

Nitrogen-doped graphene wrapped MnO2 nanoflowers (N-G-MnO2) have been successfully synthesized via a simple scalable method. N-graphene nanosheets were prepared first by ball milling graphite and urea followed by mixing of N-graphene and MnO2 nanoflowers that was microwaved for only a few minutes to form N-G-MnO2 nanoflowers. The self-assembled layer of N-G-MnO2 nanoflowers over a silicon wafer was prepared using a reverse meniscus convective self-assembly technique. The as-prepared samples were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD), transmission electron microscope, Raman and Fourier transform infrared spectroscopy. The final product of this process revealed the successful formation of N-G-MnO2 with great uniformity and high purity. SEM investigations reveals good dispersion and uniform distribution of N-G-MnO2 nanoflowers over a wide area. The addition of humic acid was found to be a crucial factor for the formation of the flower morphology. XRD phase studies show the formation of birnessite-MnO2 structure. This cost-effective, eco-friendly, and scalable process could be used for industrial applications such as energy storage materials.