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This paper describes the fabrication and characterization of a hybrid nanostructure comprised of carbon nanotubes (CNTs) grown on graphene layers for supercapacitor applications. The entire nanostructure (CNTs and graphene) was fabricated via atmospheric pressure chemical vapor deposition (APCVD) and designed to minimize self-aggregation of the graphene and CNTs. Growth parameters of the CNTs were optimized by adjusting the gas flow rates of hydrogen and methane to control the simultaneous, competing reactions of carbon formation toward CNT growth and hydrogenation which suppresses CNT growth via hydrogen etching of carbon. Characterization of the supercapacitor performance of the CNT-graphene hybrid nanostructure indicated that the average measured capacitance of a fabricated graphene-CNT structure was 653.7 μF cm(-2) at 10 mV s(-1) with a standard rectangular cyclic voltammetry curve. Rapid charging-discharging characteristics (mV s(-1)) were exhibited with a capacitance of approximately 75% (490.3 μF cm(-2)). These experimental results indicate that this CNT-graphene structure has the potential towards three-dimensional (3D) graphene-CNT multi-stack structures for high-performance supercapacitors.

Zinc oxide films derived from drop-coating solutions of zinc acetate in ethanol followed by chemical bath deposition were examined for their suitability as buffer layers for high temperature vapor phase deposition of large area, aligned, zinc oxide nanorod arrays. An X-ray photoelectron spectroscopy analysis of substrates drop coated with zinc acetate solutions clarifies the chemistry of the deposition mechanism of the initial acetate-derived ZnO seeds. Scanning electron microscopy, atomic force microscopy, and white light profilometry studies show that while zinc acetate-derived buffer layers are suitable for chemical bath deposition of aligned zinc oxide nanorod arrays, during high temperature vapor phase depositions these buffer layers undergo substantial changes leading to a loss of nanorod alignment and poor substrate coverage. We present a method to deposit aligned zinc oxide nanorod arrays uniformly over large area substrates, which combines zinc acetate drop coating, chemical bath deposition of buffer layers, and vapor phase transport deposition of nanorods.

Electrospray ionization (ESI)/quadrupole ion trap mass spectrometry is used to evaluate the heavy metal binding selectivities of five caged crown ethers and two polyether reference compounds in methanol solution. The binding preferences for Hg2+, Pb2+, Cd2+, and Cu2+ were analyzed by comparison of ESI mass spectral intensities with the aim of developing this method for the rapid screening of binding selectivities of new synthetic ligands. The cage compounds preferentially bind Hg2+, except for the cage cryptand derivative, which favors Pb2+. The preference for Hg2+ stems from the favorable positioning of the nitrogen or sulfur atoms for linear coordination of Hg2+, whereas the cryptand derivative favors Pb2+ because of its larger cavity size. The counterions of the metal salts influence the type of complexes observed in the ESI mass spectra because the strengths of the metal-anion bonds affect retention of the anion in the complexes.

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In most envisioned applications, full utilization of a graphene-carbon nanotube (CNT) construct requires maintaining the integrity of the graphene layer during the CNT growth step. In this work, we exhibit an approach towards controlled CNT growth atop graphene substrates where the reaction equilibrium between source hydrocarbon decomposition and carbon saturation into and precipitation from the catalyst nanoparticles shifts towards CNT growth rather than graphene consumption. By utilizing C 2 H 4 feedstock, we demonstrate that the low temperature growth permissible with this gas suppresses undesirable catalytic hydrogenation and dramatically reduces the etching of the graphene layer to exhibit graphene-CNT hybrids with continuous, undamaged structures.Recent efforts in fabricating three dimensional (3D) composite nanostructures consisting of two dimensional (2D) graphene and one dimensional (1D) nanomaterials of carbon 1-3 and conducting polymers 4 are of interest for a number of applications, including next-generation, high capacity, fast-discharge supercapacitors. For these types of energy storage applications, the advantages of graphene, such as large surface area-to-volume ratio and excellent conductivity, may be compromised due to self-aggregation resulting in poor charge transfer between the graphene flakes, the 1D materials, and the current collector. The growth of 1D nanostructures such as carbon nanofibers 5,6 or nanotubes 7,8 directly on graphene to yield hybrid 3D nano-architectures would, by design, circumvent this self-aggregation, while maintaining low contact resistance to enable effective electron transfer. [7][8][9] In our previous work, CNTs were grown by chemical vapor deposition (CVD) directly on graphene using CH 4 gas as a carbon source, and the performance of the resulting 3D nanoarchitecture as an advanced electrical double layer capacitor was characterized. 9 However, during this growth, the graphene layer was often found to be etched away at so-called "etched pits". The formation of these pits proceeded from hydrogenation 10-12 at 800°C in the presence of nickel (Ni) catalyst nanoparticles ((Ni) nanoparticle + C graphene + 2H 2 → Ni + CH 4 ). 13 Elongated etched lines in the graphene are attributed to etching by mobile nanoparticles. Subsequently, the addition of H 2 from the catalytic decomposition of the carbon source during the CNT growth step further contributes to the etching effect and can fully remove the graphene substrate. This etching process of the graphene substrate during CNT growth has thus far not been studied in the literature.Here we show that the high hydrocarbon conversion rate of C 2 H 4 , at lower temperature than CH 4 14 used in our previous study, 9 allows for an approach to CNT growth atop graphene substrates through fine tuning the process parameters including growth temperature and seed density. We confirm that the controlled use of C 2 H 4 is essential for balancing the competing processes of carbon deposition and carbon removal, which ultimately block undesir...

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