Search results for "graphe"
showing 10 items of 563 documents
Hybrid magnetic materials based on layered double hydroxides: from the chemistry towards the applications
2014
Layered double hydroxides (LDHs) are the leitmotiv of this dissertation. Contradicting the assertion that “any past was better”, LDHs have been continuously revisited from the middle of the twentieth century, and represent an excellent example of the never-ending beauty of Chemistry. New synthetic perspectives are giving a new impetus to LDH chemistry, which among hybrid materials, are finding their heyday. This is resulting in novel materials and also paving the way for new fundamental and practical insights. This dissertation is focused on magnetic LDHs, and for the sake of clarity it is organized in three main parts: we will move from basic synthetic and physical aspects of LDHs, through…
Few-layer Black Phosphorous Catalyzes Radical Additions to Alkenes Faster than Low-valence Metals
2020
Abstract The substitution of catalytic metals by p‐block main elements has a tremendous impact not only in the fundamentals but also in the economic and ecological fingerprint of organic reactions. Here we show that few‐layer black phosphorous (FL‐BP), a recently discovered and now readily available 2D material, catalyzes different radical additions to alkenes with an initial turnover frequency (TOF0) up to two orders of magnitude higher than representative state‐of‐the‐art metal complex catalysts at room temperature. The corresponding electron‐rich BP intercalation compound (BPIC) KP6 shows a nearly twice TOF0 increase with respect to FL‐BP. This increase in catalytic activity respect to t…
Paysage & [et] infrastructures de transport : modélisation des impacts des infrastructures sur les réseaux écologiques
2013
The development of linear infrastructures leads to the fragmentation and the artificialisation of the landscape across scales. Landscape fragmentation is a spatial process that is accompanied by a progressive decrease of the connectivity between the elements needed to conduct ecological processes. Thus, maintaining a good level of connectivity between natural habitats, compatible with human activities, has become a major issue for the preservation of biodiversity.By mobilizing methods from graph theory and landscape ecology, the thesis seeks to demonstrate the value of landscape graphs to model ecological networks and analyze impacts of transportation infrastructures at regional scale.The m…
Scattering of electromagnetic waves from a graphene-coated thin cylinder of left-handed metamaterial
2017
Abstract In this paper, we explored the scattering behavior of thin cylinders made of a left-handed material (LHM) and coated by a monoatomic graphene layer. A spectral tunability of the resonance peaks is evidenced by altering the chemical potential of the graphene coating, a fact that occurs at any state of polarization of the incident plane wave in opposition to the case of scatterers of dielectric core. On the contrary, no invisibility condition can be satisfied for dielectric environments. A singular performance is also found for cylinders with permittivity and permeability near zero. Practical implementations of our results can be carried out in sensing and wave manipulation driven by…
Opportunities and Challenges of Fluorescent Carbon Dots in Translational Optical Imaging
2015
The fluorescent carbon dot (C-dot) is a new class of carbon nanomaterials. It has a discrete or quasispherical structure, typically measures less than 10 nm and contains sp(2)/sp(3) carbon, oxygen/nitrogen-based groups and surface-modified functional groups. Compared with semiconductor quantum dots (QDs), C-dots offer much lower toxicity and a better biocompatibility profile. Their other favorable features include easy and inexpensive synthesis and surface modification potential. C-dots can be morphologically classified into graphene-based quantum dots (GQDs) and amorphous carbon nanodots (ACNDs). Numerous methods have been developed to synthesize C-dots, and are mainly divided into 'top-do…
Time-Resolved Coherent Anti-Stokes Raman Scattering of Graphene: Dephasing Dynamics of Optical Phonon.
2017
We report dynamics of the G-mode in graphene probed with time-resolved coherent anti-Stokes Raman scattering measurements. By applying BOXCARS excitation geometry with three different excitation wavelengths, various nonlinear processes can be selectively detected due to energy and momentum conservation and temporal sequence of the pulses. The Raman signal due to resonant coherent excitation of the G-mode shows exponential decay with lifetime of ∼325 ± 50 fs. This decay time is shorter than expected based on the line width of the G-mode in the Raman spectrum. We propose that the unexpectedly short dephasing time is a result of dynamic variation of nonadiabatic coupling of the photoexcited el…
PHOTO-OXIDATION OF PA6/GRAPHENE OXIDE FILMS
2014
Graphene oxide (GrO) was synthesized with Marcano’s method [1] and added at 0.5 and 1 wt% loading content to a polyamide 6 (PA6). In particular, three different techniques have been used for the preparation of the nanocomposites: (i) melt blending in a batch mixer, (ii) solvent casting in formic acid, (iii) preparation of a masterbatch by solvent casting and further melt processing. The films (80 m) were photo-oxidized in a QU-V chamber up to about 100 hours. The effect of filler content and preparation technique on the photo-stability of the nanocomposites has been followed by monitoring the change of the mechanical and spectroscopic properties undergone upon artificial exposure to UV-B l…
Letizia Battaglia: Shooting the Mafia
2021
The story of the greatest Italian photographer, her relationship with feminism and the mafia
Facile synthesis of L-cysteine functionalized graphene quantum dots as a bioimaging and photosensitive agent
2021
Nowadays, a larger number of aggressive and corrosive chemical reagents as well as toxic solvents are used to achieve structural modification and cleaning of the final products. These lead to the production of residual, waste chemicals, which are often reactive, cancerogenic, and toxic to the environment. This study shows a new approach to the modification of graphene quantum dots (GQDs) using gamma irradiation where the usage of reagents was avoided. We achieved the incorporation of S and N atoms in the GQD structure by selecting an aqueous solution of L-cysteine as an irradiation medium. GQDs were exposed to gamma-irradiation at doses of 25, 50 and 200 kGy. After irradiation, the optical,…
Gamma irradiation of graphene quantum dots with ethylenediamine: Antioxidant for ion sensing
2020
Due to the low consumption of chemicals, the absence of toxic residual side products, the procedure simplicity and time-saving aspects, gamma irradiation offers advantages over the classical chemical protocols. We successfully employed gamma irradiation in order to introduce N-atoms in Graphene Quantum Dots (GQDs). By irradiating GQDs water dispersions in the presence of isopropyl alcohol and ethylenediamine, at doses of 25, 50 and 200 kGy, we attached amino groups onto GQDs in a single synthetic step. At the same time, a chemical reduction is achieved, too. Selected conditions induced incorporation of N-atoms within GDQs atomic lattice (around 3 at%), at all applied doses. Additionally, th…