Synthesis, characterization and evaluation of Na2Ti2O5.H2O nanotubes as dye adsorber for water remediation.

Resumo

Titanium oxide-derived materials are interesting candidates for application in the catalytic photodegradation of organic pollutants. In particular, the use of one-dimensional nanostructures, derived from titanium oxide materials, exhibits greater directionality in charge conduction and a larger surface area where redox reactions can occur. Furthermore, quantum confinement effects lead to modifications in the bandgap and an increase in the oscillator force constant, resulting in more intense absorption bands compared to bulk materials. Therefore, the electronic and optical properties are strongly dependent on morphology, which allows for their rational design. 
This work presents the structural and morphological characterization (XRD, SAXS, AFM, Raman), as well as the  electrical and electrochemical characterization by IS means and the optical properties are evaluated in terms of diffuse reflectance UV-vis.
This work investigated the structure and morphology of sodium titanate nanotubes (NaNTs), systems widely explored by different groups due to their promising applications in the energy sector. However, significant controversy persists regarding their crystal structure. This work successfully proposed a coherent structural model that explains both the complex X-ray diffraction patterns and the EXAFS absorption spectrum of the system.
Obtaining a reliable structural model is key to predicting and understanding the physical chemical properties of nanotubes. In this study, a dititanate-based structure was presented, composed of layers formed by [TiO₅] units in the form of square-based pyramids joined at their edges. This model is innovative because it deviates from the traditional approach that considers octahedral [TiO₆] blocks as the predominant components in layered titanates. DFT is used for understanding its electronic and optical behavior through DOS and dielectric function analysis, furthermore, the adsorption of methylene blue is studied on a Na₂Ti₂O₅.H₂O surface.       
Finally, the methylene blue adsorption is studied experimentally, as well as de adsorption kinetics. Giving place to a maximum capacity of around 220 mg/g and a pseduo second order reaction kinetics.