4 research outputs found

    Multiple Hydrogen Bond Interactions in the Processing of Functionalized Multi-Walled Carbon Nanotubes

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    In a set of unprecedented experiments combining ā€œbottom-upā€ and ā€œtop-downā€ approaches, we report the engineering of patterned surfaces in which functionalized MWCNTs have been selectively adsorbed on polymeric matrices as obtained by microlithographic photo-cross-linking of polystyrene polymers bearing 2,6-di(acetylamino)-4-pyridyl moieties (<b>PS1</b>) deposited on glass or Si. All patterned surfaces have been characterized by optical, fluorescence, and SEM imaging techniques, showing the local confinement of the CNTs materials on the polymeric microgrids. These results open new possibilities toward the controlled manipulation of CNTs on surfaces, using H-bonding self-assembly as the main driving force

    Nitrogen-Doped Silver-Nanoparticle-Decorated Transition-Metal Dichalcogenides as Surface-Enhanced Raman Scattering Substrates for Sensing Polycyclic Aromatic Hydrocarbons

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    The modification of transition-metal dichalcogenides (TMDs), incorporating nitrogen (N) doping and silver nanoparticles (Ag<sub>NPs</sub>) decoration on the skeleton of exfoliated MoS<sub>2</sub> and WS<sub>2</sub>, was accomplished. The preparation of N-doped and Ag<sub>NPs</sub>-decorated TMDs involved a one-pot treatment procedure in a vacuum-sputtering chamber under N plasma conditions and in the presence of a silver (Ag) cathode as the source. Two different deposition times, 5 and 10 s, respectively, were applied to obtain N-doped with Ag<sub>NPs</sub>-decorated MoS<sub>2</sub> and WS<sub>2</sub> hybrids, abbreviated as N5-MoS<sub>2</sub>/Ag<sub>NPs</sub>, N10-MoS<sub>2</sub>/Ag<sub>NPs</sub>, N5-WS<sub>2</sub>/Ag<sub>NPs</sub>, and N10-WS<sub>2</sub>/Ag<sub>NPs</sub>, respectively, for each functionalization time. The successful incorporation of N as the dopant within the lattice of exfoliated MoS<sub>2</sub> and WS<sub>2</sub> as well as the deposition of Ag<sub>NPs</sub> on their surface, yielding N-MoS<sub>2</sub>/Ag<sub>NPs</sub> and N-WS<sub>2</sub>/Ag<sub>NPs</sub>, was manifested through extensive X-ray photoelectron spectroscopy measurements. The observation of peaks at āˆ¼398 eV derived from covalently bonded N and the evolution of a doublet of peaks at āˆ¼370 eV guaranteed the presence of Ag<sub>NPs</sub> in the modified TMDs. Also, the morphologies of N-MoS<sub>2</sub>/Ag<sub>NPs</sub> and N-WS<sub>2</sub>/Ag<sub>NPs</sub> were examined by transmission electron microscopy, which proved that Ag deposition resulted in nanoparticle growth rather than the creation of a continuous metal film on the TMD sheets. Next, the newly developed hybrid materials were proven to be efficient surface-enhanced Raman scattering (SERS) platforms by achieving the detection of Rhodamine B (RhB). Markedly, N10-MoS<sub>2</sub>/Ag<sub>NPs</sub> showed the highest sensitivity for detecting RhB at concentrations as low as 10<sup>ā€“9</sup> M. Charge-transfer interactions between RhB and the modified TMDs, together with the polarized character of the system causing dipoleā€“dipole coupling interactions, were determined as the main mechanisms to induce the Raman scattering enhancement. Finally, polycyclic aromatic hydrocarbons such as pyrene, anthracene, and 2,3-dihydroxynaphthalene, coordinated via Ļ€ā€“S interactions with N-MoS<sub>2</sub>/Ag<sub>NPs</sub>, were screened with high sensitivity and reproducibility. These findings highlight the excellent functionality of the newly developed N-MoS<sub>2</sub>/Ag<sub>NPs</sub> and N-WS<sub>2</sub>/Ag<sub>NPs</sub> hybrid materials as SERS substrates for sensing widespread organic and environmental pollutants as well as carcinogen and mutagen species

    A Simple Road for the Transformation of Few-Layer Graphene into MWNTs

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    We report the direct formation of multiwalled carbon nanotubes (MWNT) by ultrasonication of graphite in dimethylformamide (DMF) upon addition of ferrocene aldehyde (Fc-CHO). The tubular structures appear exclusively at the edges of graphene layers and contain Fe clusters. Fc in conjunction with benzyl aldehyde, or other Fc derivatives, does not induce formation of NT. Higher amounts of Fc-CHO added to the dispersion do not increase significantly MWNT formation. Increasing the temperature reduces the amount of formation of MWNTs and shows the key role of ultrasound-induced cavitation energy. It is concluded that Fc-CHO first reduces the concentration of radical reactive species that slice graphene into small moieties, localizes itself at the edges of graphene, templates the rolling up of a sheet to form a nanoscroll, where it remains trapped, and finally accepts and donates unpaired electron to the graphene edges and converts the less stable scroll into a MWNT. This new methodology matches the long held notion that CNTs are rolled up graphene layers. The proposed mechanism is general and will lead to control the production of carbon nanostructures by simple ultrasonication treatments

    Knitting the Catalytic Pattern of Artificial Photosynthesis to a Hybrid Graphene Nanotexture

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    The artificial leaf project calls for new materials enabling multielectron catalysis with minimal overpotential, high turnover frequency, and long-term stability. Is graphene a better material than carbon nanotubes to enhance water oxidation catalysis for energy applications? Here we show that functionalized graphene with a tailored distribution of polycationic, quaternized, ammonium pendants provides an sp<sup>2</sup> carbon nanoplatform to anchor a totally inorganic tetraruthenate catalyst, mimicking the oxygen evolving center of natural PSII. The resulting hybrid material displays oxygen evolution at overpotential as low as 300 mV at neutral pH with negligible loss of performance after 4 h testing. This multilayer electroactive asset enhances the turnover frequency by 1 order of magnitude with respect to the isolated catalyst, and provides a definite up-grade of the carbon nanotube material, with a similar surface functionalization. Our innovation is based on a noninvasive, synthetic protocol for graphene functionalization that goes beyond the ill-defined oxidationā€“reduction methods, allowing a definite control of the surface properties
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