Self-organized TiO₂ nanotubes arrays, formed by electrochemical anodization of Ti, have attracted tremendous scientific and technological attention, due to their remarkable properties such as the tunability of dimensions, their directionality, high surface area, low density, and ability to absorb significant amount of incident light [1,2].

The most widely used electrolyte for the synthesis of TiO₂ nanotube layers is based on ethylene glycol containing small amounts of water and fluoride ions. However, nanotubes prepared in these electrolytes present a double-walled structure, with the outer wall consisting of almost pure TiO₂ and the inner wall consisting of TiO₂ contaminated with carbon and fluoride species [3,4]. In the recent years, the selective etching of the inner nanotube wall on Ti layer enabled synthesis of single-wall nanotubes that showed a superior photo-electrochemical performance compared to their double-walled counterparts [5]. An extensive etching enabled also the synthesis of single tube powders, which could be effectively decorated with Fe₃O₄ nanoparticles to act as magnetically guidable photocatalyst [6,7].

The presentation will focus on the influence of all these nanotube morphologies on the photocatalytic degradation in the liquid phase. In particular, we will discuss, how the annealing temperature of single nanotubes influences their photocatalytic performance [7] and how the wall thickness of the single wall nanotubes can be optimized for the best performance [8]. Experimental details and photocatalytic results will be presented and discussed.

References:

[1] J. M. Macak et al., Curr. Opin. Solid State Mater. Sci., 2007, 1-2, 3.

[2] K. Lee et al., Chem. Rev., 2014, 114, 9385.

[3] S.P Albu et al., Adv. Mater. 2008, 20, 4135.

[4] A. Dronov et al., Appl. Surf. Sci., 2018, 434, 148.

[5] M. Motola et al., Electrochem. Commun., 2018, 97, 1.

[6] D. Beketova et al., ACS Appl. Nano Mater., 2020, 3, 155.

[7] M. Sepuvelda et al., Ms in preparation.

[8] M. Motola et al., Appl. Surf. Sci., 2021, 549, 149306.