The effect of layer number and substrate on the stability of graphene under MeV proton beam irradiation

The use of graphene electronics in space will depend on the radiation hardness of graphene. The damage threshold of graphene samples, subjected to 2 MeV proton irradiation, was found to increase with layer number and also when the graphene layer was supported by a substrate. The thermal properties of graphene as a function of the number of layers or as influenced by the substrate argue against a thermal model for the production of damage by the ion beam. We propose a model of intense electronically-stimulated surface desorption of the atoms as the most likely process for this damage mechanism.Comment: 20 pages, 5 figure

Synthesis of titanium decorated graphene for renewable energy applications

Reduced graphene oxide (RGO) was prepared from natural graphite by Hummers method. Few layers graphene was decorated with titanium by an incipient wetness impregnation method. The pristine graphene shows hydrogen storage capacity equal to 1.3 wt % while graphene decorated by titanium (RGO-Ti) enhanced hydrogen storage capacity to 1.4 wt%. We showed that titanium addition improved hydrogen storage capacity by chemical interactions. These interactions can be used for fabrication of different graphene-based materials as potential candidates for developing new absorbents for energy application

Exploring the photothermo-catalytic performance of brookite tio2-ceo2 composites

The thermocatalytic, photocatalytic and photothermo-catalytic oxidation of some volatile organic compounds (VOCs), 2-propanol, ethanol and toluene, was investigated over brookite TiO2-CeO2 composites. The multi-catalytic approach based on the synergistic effect between solar photocatalysis and thermocatalysis led to the considerable decrease in the conversion temperatures of the organic compounds. In particular, in the photothermo-catalytic runs, for the most active samples (TiO2-3 wt% CeO2 and TiO2-5 wt% CeO2). the temperature at which 90% of VOC conversion occurred was about 60◦ C, 40◦ C and 20◦ C lower than in the thermocatalytic tests for 2-propanol, ethanol and toluene, respectively. Furthermore. the addition of cerium oxide to brookite TiO2 favored the total oxidation to CO2 already in the photocatalytic tests at room temperature. The presence of small amounts of cerium oxide allowed to obtain efficient brookite-based composites facilitating the space charge separation and increasing the lifetime of the photogenerated holes and electrons as confirmed by the characterization measurements. The possibility to concurrently utilize the photocatalytic properties of brookite and the redox properties of CeO2, both activated in the photothermal tests, is an attractive approach easily applicable to purify air from VOCs

Glucosyl OPE-modified halloysite nanotubes and their potential as phototherapy agents for bacterial infections

Bacterial infections pose a significant health threat, worsened by the growing issue of antibiotic resistance and biofilm formation. Phototherapies, particularly photodynamic therapy (PDT), offer promising non-invasive alternatives due to their high efficacy and minimal side effects. These therapies utilize photosensitizers (PSs), which, when activated by light, generate reactive oxygen species (ROS) that lead to bacterial cell death. Recent advancements have focused on enhancing PDT by integrating PSs with nanomaterials. Halloysite nanotubes (HNTs), a natural clay mineral, are of particular interest due to their unique properties, including intrinsic antibacterial activity and the ability to integrate into bacterial biofilms. By combining HNTs with photosensitizers, we aimed to improve treatment efficacy. In this study, we synthesized a novel glucosyl OPE derivative and covalently attached it to HNTs, forming the composite HNTs@Glu-OPE. This system was thoroughly characterized, and its ROS generation capabilities were tested under 365 nm light irradiation using uric acid as a probe. Loaded with vancomycin, HNTs@Glu-OPE represents a multifunctional approach to PDT, enhancing both the delivery and effectiveness of therapeutic agents against resistant bacterial strains

Investigation of sp carbon chain interaction with silver nanoparticles by Surface Enhanced Raman Scattering

Surface Enhanced Raman Spectroscopy (SERS) is exploited here to investigate the interaction of isolated sp carbon chains (polyynes) in a methanol solution with silver nanoparticles. Hydrogen-terminated polyynes show a strong interaction with silver colloids used as the SERS active medium revealing a chemical SERS effect. SERS spectra after mixing polyynes with silver colloids show a noticeable time evolution. Experimental results, supported by density functional theory (DFT) calculations of the Raman modes, allow us to investigate the behavior and stability of polyynes of different lengths and the overall sp conversion towards sp2 phase.Comment: 19 pages, 7 figures, 1 table

The circumstellar envelope of the C-rich post-AGB star HD 56126

We present a detailed study of the circumstellar envelope of the post-asymptotic giant branch ``21 micron object'' HD 56126. We build a detailed dust radiative transfer model of the circumstellar envelope in order to derive the dust composition and mass, and the mass-loss history of the star. To model the emission of the dust we use amorphous carbon, hydrogenated amorphous carbon, magnesium sulfide and titanium carbide. We present a detailed parametrisation of the optical properties of hydrogenated amorphous carbon as a function of H/C content. The mid-infrared imaging and spectroscopy is best reproduced by a single dust shell from 1.2 to 2.6 arcsec radius around the central star. This shell originates from a short period during which the mass-loss rate exceeded 10^(-4) M_sun/yr. We find that the strength of the ``21'' micron feature poses a problem for the TiC identification. The low abundance of Ti requires very high absorption cross-sections in the ultraviolet and visible wavelength range to explain the strength of the feature. Other nano-crystalline metal carbides should be considered as well. We find that hydrogenated amorphous carbon in radiative equilibrium with the local radiation field does not reach a high enough temperature to explain the strength of the 3.3-3.4 and 6-9 micron hydrocarbon features relative to the 11-17 micron hydrocarbon features. We propose that the carriers of these hydrocarbon features are not in radiative equilibrium but are transiently heated to high temperature. We find that 2 per cent of the dust mass is required to explain the strength of the ``30'' micron feature, which fits well within the measured atmospheric abundance of Mg and S. This further strengthens the MgS identification of the ``30'' micron feature.Comment: 20 Pages, 10 Figures, accepted for publication in Astronomy and Astrophysic

Oxidative protein labeling in mass-spectrometry-based proteomics

Oxidation of proteins and peptides is a common phenomenon, and can be employed as a labeling technique for mass-spectrometry-based proteomics. Nonspecific oxidative labeling methods can modify almost any amino acid residue in a protein or only surface-exposed regions. Specific agents may label reactive functional groups in amino acids, primarily cysteine, methionine, tyrosine, and tryptophan. Nonspecific radical intermediates (reactive oxygen, nitrogen, or halogen species) can be produced by chemical, photochemical, electrochemical, or enzymatic methods. More targeted oxidation can be achieved by chemical reagents but also by direct electrochemical oxidation, which opens the way to instrumental labeling methods. Oxidative labeling of amino acids in the context of liquid chromatography(LC)–mass spectrometry (MS) based proteomics allows for differential LC separation, improved MS ionization, and label-specific fragmentation and detection. Oxidation of proteins can create new reactive groups which are useful for secondary, more conventional derivatization reactions with, e.g., fluorescent labels. This review summarizes reactions of oxidizing agents with peptides and proteins, the corresponding methodologies and instrumentation, and the major, innovative applications of oxidative protein labeling described in selected literature from the last decade

Nanostructural characterization of amorphous diamondlike carbon films

Nanostructural characterization of amorphous diamondlike carbon (a-C) films grown on silicon using pulsed-laser deposition (PLD) is correlated to both growth energetic and film thickness. Raman spectroscopy and x-ray reflectivity probe both the topological nature of 3- and 4-fold coordinated carbon atom bonding and the topographical clustering of their distributions within a given film. In general, increasing the energetic of PLD growth results in films becoming more ``diamondlike'', i.e. increasing mass density and decreasing optical absorbance. However, these same properties decrease appreciably with thickness. The topology of carbon atom bonding is different for material near the substrate interface compared to material within the bulk portion of an a-C film. A simple model balancing the energy of residual stress and the free energies of resulting carbon topologies is proposed to provide an explanation of the evolution of topographical bonding clusters in a growing a-C film