137 research outputs found
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 60â—¦ C, 40â—¦ C and 20â—¦ 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
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
Polymer-stable magnesium nanocomposites prepared by laser ablation for efficient hydrogen storage
Hydrogen is a promising alternative energy carrier that can potentially
facilitate the transition from fossil fuels to sources of clean energy because
of its prominent advantages such as high energy density (142 MJ per kg), great
variety of potential sources (for example water, biomass, organic matter), and
low environmental impact (water is the sole combustion product). However, due
to its light weight, the efficient storage of hydrogen is still an issue
investigated intensely. Various solid media have been considered in that
respect among which magnesium hydride stands out as a candidate offering
distinct advantages. Recent theoretical work indicates that MgH2 becomes less
thermodynamically stable as particle diameter decreases below 2 nm. Our DFT
(density functional theory) modeling studies have shown that the smallest
enthalpy change, corresponding to 2 unit-cell thickness (1.6 {\AA} Mg/3.0{\AA}
MgH2) of the film, is 57.7 kJ/molMg. This enthalpy change is over 10 kJ per
molMg smaller than that of the bulk. It is important to note that the range of
enthalpy change for systems that are suitable for mobile storage applications
is 15 to 24 kJ permolH at 298 K. The important key for the development of
air/stable Mg/nanocrystals is the use of PMMA (polymethylmethacrylate) as an
encapsulation agent. In our work we use laser ablation, a non-electrochemical
method, for producing well dispersed nanoparticles without the presence of any
long range aggregation. The observed improved hydrogenation characteristics of
the polymer/stable Mg-nanoparticles are associated to the preparation procedure
and in any case the polymer laser ablation is a new approach for the production
of air/protected and inexpensive Mg/nanoparticles.Comment: Hydrogen Storage, Mg - Nanoparticles, Polymer Matrix Composites,
Laser Ablation, to appear in International Journal of Hydrogen Energy, 201
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
- …