Síntese de Eletrodos Constituídos de Nanotubos de TiO2 Modificados com Titanatos via Deposição Eletroforética Estimulada Mecanicamente

Studies involving modification of TiO2nanotubes (TiO2NT) are particularly performed aiming to increase the surface area and enhancement of electrocatalytic properties. One of the key challenges is the insertion of nanostructures of titanates into the pores of TiO2NT[1]. The studies reported until now have no successfully demonstrated this incorporation. In our work, we have described for the first time the electrophoretic deposition (EPD) of two different titanates -nanosheets (TiNS) and nanotubes (TiNT) -into the pores of TiO2nanotubes. The electrochemical anodization was employed to synthesis of TiO2NT using HF/NaH2PO4as electrolyte applying 20 Vfor 2 hours and Ti foil as working electrode. The TiNT were synthesized via alkaline hydrothermal method (KOH:NaOH 1:25 ;25 g TiO2), refluxed for 2 days at 100 C, washed with HCl diluted and dried at 140 °C [1].To the TiNS via sol-gel synthesis,10 ml of titanium n-butoxide was added to TMAOH and refluxed under argon at 95 °C for 24 h. The EPD of TiNS/TiNT was carried out onto the surface of TiO2NT (2.4 x 2.4 cm2) where was added 1 cm3 of the electrolyte containing 5% (v/v) of the TiNS or TiNT suspension in methanol-water (50:50, vol.). The TiO2NT anode and the stainless steel cathode were kept at distance of 0.5 mm. The anodic potential of 20 V was applied over 20 minutes at 25 °C. The incorporation of titanates without application of potential or use of brush revealed thicker film of nanosheets on the top of TiO2NT.To avoid blocking the surface of TiO2NT with titanates, a modified brush (nylon bristles) was used near the counter electrode, moving it on the surface of the working electrode. The potential applied and the movements of counter electrode were fundamental to incorporation of TiNS/TiNT inside of the nanotubes of TiO2NT. SEM characterization clearly shows that the movements of counter electrode (containing the brush) in the surface of TiO2-NT reduced the thickness of TiNS/TiNT layer distributing them more homogeneously inside the tubes. As a result, there was an enhanced the surface area of the electrode and subsequently increase of the short circuit current, observed in the cyclic voltammetries with methylene blue0.025 mol L-1. Moreover, the electrodes show an increase the hydrophobicity (contact angle measurement) after incorporation which decreases the adsorption of water molecules on the surface. Therefore, our results confirm that titanates can be facilely deposited onto pores of TiO2 nanotube via EPD avoiding formation of compact layer on the top.