We present the decoration of N-doped graphene entangled
in mesoporous
carbon by nickel and/or cobalt nanoparticles. The textural properties
of the mesoporous materials were characterized by nitrogen desorption
isotherms. The materials presented metallic nanoparticles of at least
20 nm and diffraction peaks typical of cubic cobalt or nickel. Transmission
microscopy revealed the presence of graphene layers, organized mostly
in an onionlike fashion around the metallic nanoparticles, suggesting
that these might promote the formation of extra graphene sheets from
the surrounding amorphous carbon. The formation of a metallic alloy
when nickel and cobalt were mixed is strongly suggested. Differential
scanning calorimetry of these materials filled with LiBH4 demonstrated that the presence of nanoparticles displaced the typical
transition, melting, and decomposition peaks of this hydride toward
lower temperatures. Volumetric studies revealed that the liberation
of hydrogen started at lower temperatures when nanoparticles were
present, slowing down at higher temperatures. Cobalt-decorated materials
liberated 8 wt % H2 at 325 °C during the first cycle
(with 1 wt % released at 226 °C). After rehydrogenation at 400
°C, the materials decorated with nickel liberated 8 wt % H2, a 2 wt % excess compared to that of the nondecorated materials.
Arsenic (As) contamination of water and foodstuff has
motivated
the development of methods to sense, quantify, and/or remediate As
contamination in such samples. Nanoscale zero-valent iron (nZVI) particles
have recently emerged as a suitable material for adsorbing As. In
order to enhance its performance, these nanoparticles were assembled
into reduced graphene oxide (rGO) sheets via a direct iron reduction
to yield nZVI/rGO materials. Transmission electron microscopy images
showed that nZVI particles of 7 nm mean particle size were well dispersed
over the rGO sheets. Zeta potential was measured in a pH range from
2 to 12 and showed a point of zero charge at pHpzc 6.5. As adsorption
onto nZVI/rGO materials, using 15 ppm As solutions of pH ranging from
3.6 to 7.9, showed that adsorption is better in acidic pH, reaching
approximately 80% of As adsorption in 10 min. Density functional theory
calculations were carried out to evaluate the As adsorption over nZVI/rGO
by using simplified models of magnetite nanoparticles supported on
graphene. As bonds to surface oxygen atoms and adsorption are greatly
favorable near lattice defects, with adsorption energies between −6.61
and −6.44 eV. After adsorption, As transfers electron density
to the surface, resulting in a positive charge of +3.
We investigated by first principle calculations the adsorption of Liq (q = -1, 0 or +1) on a silicene single layer. Pristine and three different defective silicene configurations with and without Li doping were studied: single vacancy (SV), double vacancy (DV) and Stone-Wales (STW). Structural studies and the adsorption energies of various sites were obtained and compared in order to understand the stability of the Li on the surface. Moreover, electronic structure and charge density difference analysis were performed before and after adsorption at the most stables sites, which showed the presence of a magnetic moment in the undoped SV system, the displacement of the Fermi level produced by Li doping and a charge transfer from Li to the surface. Additionally, quantum capacity (QC) and charge density studies were performed on these systems. This analysis showed that the generation of defects and doping improves the QC of silicene in positive bias, because of the existence of 3p orbital in the zone of the defect. Consequently, the innovative calculations performed in this work of charged lithium doping on silicene can be used for future comparison with experimental studies of this Li-ion battery anode material candidate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.