We found that very high concentrations (up to 20% vol) of nitrogen in the ethanol/hydrogen gas mixture do not prejudice the diamond quality as determined by Raman spectroscopy. Nitrogen addition also increases the diamond growth rate, as was previously reported at low nitrogen concentrations. We observed that after a second heating cycle in air at temperatures between 300 and 673 K the electrical resistance versus temperature curves of the as-grown films presented a bulk semiconductor behavior. This stabilization was due to the oxidation of the as-grown hydrogenated surface. The electrical ionization energy Ed was found to be in the range of 1.62–1.90 eV corresponding to films produced with 0 to 20% vol nitrogen in the feed. The room temperature photoluminescence spectra of films produced at low nitrogen concentration suggest that Ed results from pure electronic transitions in the nitrogen-vacancy neutral defects; for samples produced with nitrogen concentrations in the range 15–20% vol the Ed values may be due to, among others, GR1 “vibronic” transitions and charged nitrogen-vacancy defects.
Our data demonstrate that multi-walled carbon nanotubes (MWCNTs) are internalized by macrophages, subsequently activating them to produce interleukin (IL)-12 (IL-12). This cytokine induced the proliferative response of T lymphocytes to a nonspecific mitogen and to ovalbumin (OVA). This increase in the proliferative response was accompanied by an increase in the expression of pro-inflammatory cytokines, such as interferon-gamma (IFNγ), tumor necrosis factor-alpha (TNFα) and IL-6, in mice inoculated with MWCNTs, whether or not they had been immunized with OVA. A decrease in the expression of transforming growth factor-beta (TGFβ) was observed in the mice treated with MWCNTs, whereas the suppression of the expression of both TGFβ and IL-10 was observed in mice that had been both treated and immunized. The activation of the T lymphocyte response by the pro-inflammatory cytokines leads to an increase in antibody production to OVA, suggesting the important immunostimulatory effect of carbon nanotubes.
The field emission properties of “porous diamond-like” carbon structures have been characterized. A hot filament chemical vapor deposition system fed with ethyl alcohol vapor diluted in helium was used to deposit the samples. Morphological analysis by field emission scanning electron microscopy revealed that they had a highly porous structure, which was attributed to the modification of the kinetics of the carbon deposition process due to the presence of helium as a buffer gas. Micro-Raman spectroscopy showed two peaks in the graphene and microcrystalline graphite frequencies and a new peak at 1620 cm−1. Low threshold fields (Et) and hysteresis in the current versus voltage characteristic have been observed, and a model to explain the hysteresis is proposed.
Blocking polycrystalline platinum ͑Pt͒ and boron-doped diamond ͑BDD͒ electrodes by 20 phenolic compounds was studied by means of chronoamperometric and theoretical methods ͓i.e., quantitative structure-property relationships ͑QSPRs͔͒ and chemometric methods. The difference between the current densities after 15 and 90 s of oxidation time was proposed for the first time as a quantitative measurement of passivation on the electrodes. Structures of phenolic molecules and their hydrogen-bonding complexes with fluoride ion were modeled and geometry optimized with the B3LYP method and the 6-31G** basis set. Several molecular descriptors were calculated and correlated with the passivation measurements using the partial least-squares ͑PLS͒ regression method. A PLS model with one latent variable from five descriptors was built with high-level predictivity for phenolic passivation on the Pt electrode, and then was externally validated with four phenolics. The Pt model statistical parameters obtained were: Q 2 = 0.786, R 2 = 0.851, and standard error of validation ͑SEV͒ = 0.097. A BDD model with one latent variable and four descriptors was built and validated in the same way; however, the statistical parameters ͑Q 2 = 0.333, R 2 = 0.586, and SEV = 0.159͒ were of inferior quality with respect to the model for the Pt electrode. Both models were applied for prediction of 10 phenolic compounds. The Pt model showed to be suitable for predictive purposes. It was observed that passivation was much weaker on the BDD electrode than on the Pt electrode. Different interactions and reactions involving phenolics at the electrodes are the main reasons for such large differences between the models. Exploratory analyses were also performed and interpreted in terms of chemical concepts, such as phenolic reactivity, size/shape, hydrogen bonding, and electronic features. These findings can be useful to explore the possibility to predict phenolic passivation and to design electrochemical experiments involving different phenolic compounds. Furthermore, these PLS models aid in understanding electrode inactivation by phenolic compounds.
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