In this research work, we prepared for the first time TiO 2 nanosheets and nanobowls assembled on an arrangement of TiO 2 nanocavities, and studied their morphological, optical, and structural properties. The assembled nanostructures were synthesized by a fast two-step electrochemical anodization using fluorides and ethylene glycol. By Field Emission Scanning Electron Microscopy, we showed that these nanostructures have a morphology well organized and ordered with a homogeneous distribution. Also, other characteristics such as photoluminescence, reflectance spectra, band gap energy, and Raman spectra were studied and compared with the optical and structural properties of TiO 2 nanotubes. We found that the time of anodization is a key parameter to control the final shape of the individual elements in the nanostructure. Our results show that when nanobowls or nanosheets are self-assembled on nanocavities the morphological, optical, and structural properties change significantly in comparison to TiO 2 nanotubes. Furthermore, the emission was improved considerably and the band gap energy was modified to higher energy values. Likewise, the interference fringes are generated in the reflectance spectra by the length of the nanocavities and by the thickness of the nanobowls and the nanosheets. Finally, a reduction on the displaced the E g(1) Raman mode was observed with decreasing of the length of the nanocavities.

In this paper, we report the results of the optical and electrical properties of TiO2 nanotubes with different morphologies for gas sensing applications. Four nanomaterials of TiO2 were prepared by electrochemical anodization using four different electrolyte solutions: 0.255 wt% NH4F with 1 wt%, 3 wt%, 6 wt% and 9 wt% of deionized water in ethylene glycol. Micrographs by scanning electron microscopy (SEM) showed different morphologies caused by the variation in the water content of the solutions. Consequently, as an effect of morphology, the photoluminescence intensity in the visible spectrum was modified. By a change of the crystalline phase of TiO2 nanotubes, the oxygen vacancies increased and affected to the optical and electrical properties of TiO2 films. These films were used for detecting gas at room temperature. Hence, we studied and analyzed the relationship of the morphology, elemental composition, phase composition, band gap energy and defect states as a function of the electrical resistance change of TiO2 nanotubes to understand and improve the sensor response.

In this research work, we present the synthesis and characterization of four different TiO2 structures, such as nanotubes, nanocavities, nanosheets assembled on nanocavities and nanobowls assembled on nanocavities, prepared by electrochemical anodization using organic electrolytes. After synthesis, the structures were thermally annealed to pass from the amorphous phase to the anatase phase, which is one of the most important crystalline structures of TiO2 due to its high photocatalytic activity and stability. The unique morphology and topography were studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The elemental composition was determined by energy-dispersive X-ray spectroscopy (EDS). The anatase phase was verified by Raman microscopy and X-ray diffraction (XRD), the band gap energy was calculated by the Kubelka–Munk function, and the main defect states that generate the emission, as well as their lifetime, were determined by photoluminescence spectroscopy and time response photoluminescence (TRPL), respectively. The TiO2 nanomaterials were tested as catalysts in the photodegradation of a solution of methylene blue using a UV lamp at room temperature. The results showed complex morphologies and different surface roughness areas of these nanomaterials. Furthermore, a relationship between defect states, band gap energy, and photocatalytic activity was established. We found that the catalytic activity was improved as an effect of geometric parameters and oxygen vacancies.

No abstract

No abstract

No abstract

No abstract

No abstract