Abstract In this work, the electrochemical anodization process was carried out on titanium grade 2, using an electrolytic solution of 3 M and 0.15 M HCl with voltages of 11 V, 12 V and 15 V, as well as time variations in the experimental process and later an annealing process at 750 °C. According to the results obtained, the TiO2 coatings presented different morphologies on their surface, which consisted of nanopores, nanowires and clusters of oxide grains, as well as a combination of anatase and rutile crystalline phases. Band Gap variations were found to be non-significant despite changes in the morphology of the coatings at different anodization conditions, with an average value of 2.91 eV. It was observed that the anodized samples treated by the annealing process at 750 °C, thickness values up to 16 μm were obtained.

Abstract TiO2 nanotubes were prepared by the anodization process of a set of titanium foils in order to study the influence of time and voltage on the morphology of them under a 1.2 wt % NH4F salt concentration, taking advantage of this percent and remarking the great importance of the oxide growth-dissolution speed with this electrolyte concentration. The anodization process consists of an organic media of ethylene glycol, a voltage from 5 to 30 V for a time period from 1 to 6 hours, a constant potential of 30 V for a time lapse from 10 to 360 minutes and 5 to 480 seconds. All anodized samples are rinsed and annealed to 400 ° C for 3 hours to obtain an anatase crystalline structure. The morphological characterization was carried out by Field Emission Scanning Electron Microscopy (FESEM) to verify the presence of the main nanostructures: nanopores, nanotubes, and nanograss. Raman spectroscopy was used for optical characterization in order to identify the changes in the signal of the E g (v6) vibrational mode. It was observed the Raman E g (v6) vibrational mode suffers a redshift at the initial anodization stage with the contribution of the stress between the substrate-oxide layer and the stoichiometry defects. The diameter and tube length have a strong correlation with the oxide thickness (ascendant slope), moreover, this oxide is compared and related to the Raman intensity of the E g (v6) mode, from this fact, it is easy to define some time periods and a voltage range for each titania nanostructures observed.

Abstract Many studies, focused in TiO2 anodized, uses frequently a NH4F salt concentration from 0.3- 0.5 wt% and the whole information about how voltage, time and even pH affects to nanotubes morphology, are effective just for these concentration range. It is known that increasing salt concentration, the electrolyte increases their conductivity and anodization speed (oxidation-dissolution) suffers also an increment and for a specifically concentration 1.2wt%, there is no data about morphology repercussions. A TiO2 nanotubular matrix is synthesized, in order to identify the range of time where it is possible to obtain with no presence of nanograss. The anodization process consists of an organic electrolyte of ethylene glycol, deionized water and 1.2 wt% NH4F salts, constant potential of 30 V, and a time lapse from 10 to 60 minutes (short time). All anodized samples are rinsed and annealed to 400oC for 4 hours to obtain an anatase crystalline structure; no samples are cleaned in ultrasonic bath to preserve the nanograss structure. Optical characterization was performed by Raman Spectroscopy to identify the increases in signal intensity, associated with thickness. The morphological characterization was carried out by Scanning Electron Microscopy to verify the presence and density of the nanograss and nanotubes.

Abstract: A functionalization process has to occur in order to employ carbon nanotubes, generally by using certain types of acids. Multiwalled carbon nanotubes synthetized from benzene and ferrocene were oxidized at different temperatures between 270-600 °C through thermal treatment at atmospheric conditions. Samples were characterized by SEM, EDS, XRD, FTIR and Raman. The weight loss is shown with fluctuations from 0-78% according to different temperature conditions. FTIR analysis demonstrated presence of carbonyl groups and decrease of CHx.

Abstract: A stainless steel core catalyst with several green precursors, butanol, diethyl ether, ethyl acetate and hexane, were used to obtain multi-walled carbon nanotubes via chemical vapor deposition. Argon was used as carrier gas at 50-90 ml/min rates. Samples were synthetized at 680-850 ºC, according to the precursor used. The characterization techniques were scanning electronic microscopy, X-ray diffraction, energy dispersive, Fourier transformed infrared and Raman spectroscopy. The micrographs showed tangled carbon nanotubes formation with different diameters from 50-300 nm. Elemental analysis indicated carbon atomic percentages ranging from 93-99 %, 1.0-4.5 % iron and less than 1% of manganese, chrome and silicon. X-Ray diffraction demonstrated the characteristic carbon nanotubes peak (002) at 26°. G and D carbon nanotubes distinctive bands were confirmed by Raman spectra for all samples.