Photoinduced oxidation of carbon nanotubes (original) (raw)
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UV-light enhanced oxidation of carbon nanotubes
Applied Surface Science, 2003
Ab initio density functional theory (DFT) calculations of the interactions between selected semiconducting and metallic single-walled carbon nanotubes (SWCNTs) (as well between single and double graphene sheets) and single oxygen molecules are carried out in order to provide a rationale for the recent experimental observations of UV-light accelerated oxidation of carbon nanotubes and the accompanying changes in the thermoelectric power. The computational results obtained show that these experimental findings can be related to UV-light excitation of oxygen molecules from their ground spin-triplet state into a higher-energy spin-singlet state. Such excitation lowers the activation energy for molecular-oxygen chemisorption to a nanotube, increases the adsorption energy and promotes charge transfer from the nanotube to the oxygen molecule. Lattice defects such as 7-5-5-7 and Stone-Wales defects are found to play a critical role in enhancing oxygen molecule/nanotube bonding and in affecting the extent of charge transfer. Contrary to this, the effects of nanotube diameter and chirality and the number of walls appear to be less significant. #
Photodesorption of oxygen from carbon nanotubes
Physical Review B, 2004
We propose to use photodesorption as a noninvasive tool to clean carbon nanotubes from oxygen, offering a clear advantage over thermal and chemical treatments. The detachment of chemisorbed oxygen from atomic vacancies is triggered by a resonant Auger process, initiated by an O 1s → O 2p transition, which leaves two holes in the O 2s level. In the electronically excited state, oxygen desorbs spontaneously, with no damage to the carbon network or the cylindrical nanotube shape. Subsequent reaction of oxygen atoms with H 2 molecules is shown to prevent reoxidation of the nanotube.
Atomic Oxygen Chemisorption on Carbon Nanotubes Revisited with Theory and Experiment
The Journal of Physical Chemistry C, 2013
Density-functional-theory based calculations of two single-walled carbon nanotubes of different chirality settle open issues on the sidewall chemisorption of atomic oxygen at low concentrations. Ether groups are the thermodynamically favored configurations. If kinetically trapped in epoxide groups, oxygen introduces characteristic new levels in the gap of the nanotube that are detected with scanning tunneling spectroscopy experiments. Discrepancies with previous predictions are shown to originate from the inadequacy of previous models to describe low-concentration oxygen adsorbated on nanotubes.
We have used high-resolution photoemission spectroscopy to study the interaction of single wall nanotubes with gas phase molecules as O 2 and NO 2 . The first aim of our investigation was to state the purity of commercial nanotubes, in the form of a bucky paper, and to follow the removal of the contaminants (Na, S, Si, Ni) present in the sample by annealing at increasing temperatures. Rapid annealing treatments of a few minutes up to 1800 K determined Ni evaporation and elimination of Na only from the near surface layer, whereas an Na-free clean sample could be obtained only after a prolonged annealing of a couple of hours at 1250 K. We have compared the interaction between the single wall nanotubes and O 2 for the Na-contaminated and clean bucky paper. In the first case the adsorption was strongly altered by the Na traces, which simulated an intense sample oxidation leading to a modification of the electronic properties of the nanotubes. On the contrary, for clean single wall nanotubes, the lack of oxygen detection and the inertness of the C1s core level to large O 2 doses demonstrated the absence of any chemical interaction between nanotubes and O 2 , up to pressures of the order of 10 -6 mbar and temperatures between 150 and 300 K. Instead, a significant charge transfer was observed for NO 2 adsorption. In this case the hole doping induced in the tubes by the adsorbed molecules led to a dramatic change in the C1s line shape and energy position, which corresponds macroscopically to a decrease of the resistance of the bucky paper sample.
Surface oxidation study of single wall carbon nanotubes
Nanotechnology, 2011
Functionalization of single wall carbon nanotubes (SWCNTs) is desirable to enhance their ability to be incorporated into polymers and enhance their bonding with the matrix. One approach to carbon nanotube functionalization is by oxidation via a strong oxidizing agent or refluxing in strong acids. However, this approach can damage the nanotubes, leading to the introduction of defects and/or shorter nanotubes. Such damage can adversely affect the mechanical, thermal, and electrical properties. A more benign approach to nanotube functionalization has been developed involving photo-oxidation. Chemical analysis by XPS revealed that the oxygen content of the photo-oxidized SWCNTs was 11.3 at.% compared to 6.7 at.% for SWCNTs oxidized by acid treatment. The photo-oxidized SWCNTs produced by this method can be used directly in various polymer matrices or can be further modified by additional chemical reactions.
Oxidation of Single-Walled Carbon Nanotubes under Controlled Chemical Conditions
Journal of the Brazilian Chemical Society, 2018
Single-walled carbon nanotubes are oxidized in the presence of H 2 SO 4 /HNO 3 mixtures containing distinct concentrations of the nitronium ion, [NO 2 + ]. The spectroscopic analyses of the final samples suggest a higher structural disorder in the oxidized systems with increasing [NO 2 + ]. This is due to a considerable oxygen amount on the tube surface, reaching up to 30%, depending on the reaction time and [NO 2 + ]. Interestingly, if long reaction time is considered, the oxygen amount on the tube surface is maximum for low [NO 2 + ] and reduces slightly for larger [NO 2 + ]. On the other hand, the oxidation process occurs gradually at 4 h, allowing a fine control of the oxidation process. Therefore, if fine tuning of the oxidation degree is desirable, the reaction must be conducted during short time (4 h) using increasing [NO 2 + ] as those obtained from 2:1, 2.5:1 and 3:1 H 2 SO 4 /HNO 3 acid mixtures to produce increasing content of functionalization.
Environmental Science & Technology, 2010
Very limited information exists on transformation processes of carbon nanotubes in the natural aquatic environment. Because the conjugated π-bond structure of these materials is efficient in absorbing sunlight, photochemical transformations are a potential fate process with reactivity predicted to vary with their diameter, chirality, number and type of defects, functionalization, residual metal catalyst and amorphous carbon content, and with the composition of the water, including the type and composition of materials that act to disperse them into the aqueous environment. In this study, the photochemical reactions involving colloidal dispersions of carboxylated single-walled carbon nanotubes (SWNT-COOH) in sunlight were examined. Production of reactive oxygen species (ROS) during irradiation occurs and is evidence for potential further phototransformation and may be significant in assessing their overall environmental impacts. In aerated samples exposed to sunlight or to lamps that emit light only within the solar spectrum, the probe compounds, furfuryl alcohol (FFA), tetrazolium salts (NBT 2+ and XTT), and p-chlorobenzoic acid (pCBA), were used to indicate production of 1 O 2 , O 2 · -, and · OH, respectively. All three ROS were produced in the presence of SWNT-COOH and molecular oxygen ( 3 O 2 ). 1 O 2 production was confirmed by observing enhanced FFA decay in deuterium oxide, attenuated decay of FFA in the presence of azide ion, and the lack of decay of FFA in deoxygenated solutions. Photogeneration of O 2 ·and · OH was confirmed by applying superoxide dismutase (SOD) and tert-butanol assays, respectively. In air-equilibrated suspensions, the loss of 0.2 mM FFA in 10 mg/L SWNT-COOH was ∼85% after 74 h. Production of 1 O 2 was not dependent on pH from 7 to 11; however photoinduced aggregation was observed at pH 3.
A Comparison of Defects Produced on Oxidation of Carbon Nanotubes by Acid and UV Ozone Treatment
2009
Oxidation using ozone in the presence of ultraviolet light was used to reduce the number of defects on carbon nanotubes. Fourier transform infra red spectra showed that the treatment promotes milder oxidation in introducing carboxylic functional group than conventional acid treatment. Transmission electron microscope images suggest that ozone treated carbon nanotubes suffered reduced attrition of broken tips, bent tips and bent walls in comparison to that of acid treated carbon nanotubes. Raman spectra indicate that the acid treated carbon nanotubes exhibited a lower I G :I D ratio than these ozone treated carbon nanotubes, confirming that the former samples contain a higher number of defects. While the dispersion stability of the ozone treated carbon nanotubes was found at a level similar to that of acid treated carbon nanotubes, the former showed a slightly larger amount of organic functional groups than the latter as suggested from the thermal gravimetric analysis.