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possible arrangement for  the  capture  of  H2,  and  electric  field  was  applied  over  the  system, longitudinally to the carbon nanotube length, promoting the rise of an evanescent field, able  to  trap  H2,  which  orbited  the  carbon  nanotube.  Simulations  for  electric  fields intensities in a range of 10-8 au up to 10-6 au were performed, and mean orbit radius are estimated, as well as, some physical quantities of the system. The quantities calculated were:  kinetic  energy,  potential  energy,  total  energy  and  temperature  in  situ,  among molar entropy variation. Our results indicates that a combination of electric field and van  der  Walls  interactions  derivatives  of  carbon  nanotube  is  enough  to  create  an evanescent field with attractive potential, showing it system as a good H2 sensor.

been shown to be superior and a green methodology. Photosensitization of TiO2 with high specific surface areas would allow taking advantage of the high catalytic activity of the TiO2 and harvest sun light with production of hydrogen and simultaneous degradation of pollutants.

Photocatalytic performance of three types of TiO2 photocatalysts will be presented according to the preparation method: i) MWAC (nanotubes, NTs); ii) anodization (NTs) and iii) electrospinning (nanofibers, NFs). TiO2 nanostructures were photosensitized by impregnation with Ag nanoparticles (NPs) prepared by MWAC or Pt/Au NPs by DC-magnetron sputtering deposition method. Prototype dyes were used to test the photodegradation activity of the prepared photocatalysts. Hydrogen generation was measured by gas chromatography. The prepared TiO2 photocatalysts were characterized by TEM, SEM (EDX), XRD, XPS, BET and UV-diffuse.

TiO2 NTs (i) with lengths between 50-500 nm, internal diameters of about 3.7 nm and wall thickness of 2.1-5.5 nm were impregnated with Ag NPs of sizes of 1.8 nm by simple immersion process. TiO2 NTs (ii) (1.5 mm length, 60 nm diameter and ~20 nm wall thickness) were impregnated with ultrasmall Pt [1] or Au NPs [2]. TiO2 NFs (iii) of 250-1000 nm in diameter were prepared using electrospinning by dispersions of TiO2 NPs (AEROXIDE®TiO2-P25) on a synthetic biodegradable aliphatic-aromatic copolyesterpoly(butylenesadipate-co-terephthalate) (PBAT) polymer. After thermal treatment the TiO2 NFs dispersion was maintained.

The obtained results are summarized according to the preparation method:

i) Under UV-vis irradiation the TiO2 NTs/Ag NPs photocatalyst degraded the Methyl Orange dye to complete decolouration of the solution in 3 h. Additionally, irradiation of this system with λ ≥ 400 nm shows an efficient photodegradation process without direct photochemical activation of TiO2.

ii) Highly toxic and mutagenic formaldehyde water solutions were degraded on supported TiO2 NTs loaded with noble NPs. Photocatalysis of formaldehyde solutions led to mineralization of the pollutant with simultaneous production of hydrogen. A high selectivity in hydrogen photocatalytic evolution with respect to CO2 and CO was obtained by choosing the right amount of Pt NPs loaded.  In addition, hydrogen was also produced using only visible light irradiation (λ ≥ 400 or 450 nm) when Au NPs were loaded on the TiO2 NTs [2].

iii) Preliminary results using TiO2 NFs showed promising hydrogen generation rates. These experiments are under way. Impregnation of TiO2 NFs with Ag NPs prepared by MWAC will be a next step.

The prepared photocatalysts have the potential to be used for efficient treatment of effluents using UV or solar light. Depending on the NPs used, Au or Ag, solar light harvesting is possible.

entropy. Also, we estimated, for a large temperature range, the important parameter specific heat ratio of each natural gas, which allowed us to compare the results with those of empirical functions of these parameters, showing a great agreement between them. In addition, relevant information on the mechanical resistance of natural gases was also investigated. Moreover, standards thermodynamics properties for combustion of natural gas are presented. Thus, we show that density functional theory can be used for thermodynamic characterization of natural gas in equilibrium.