Immobilized photocatalysts: influence of the substrate geometry on the formation of TiO2 nanotubular coatings by anodic oxidation

A.N. DWOJAK; E.S. PAVÓN; H.D. TRAID; M.L. VERA; C.E. SCHVEZOV; M.I. LITTER

Congreso; WCCE11- 11th world Congress of Chemical Engineering; 2023

The development of photoreactors for use in heterogeneous photocatalysis with immobilized TiO2 in the treatment of polluted water is of great relevance for the transfer of this technology. One of the simplest, most versatile, and cheapest techniques for the synthesis of TiO2 coatings is the anodic oxidation of titanium, which allows obtaining oxides in nanotubular morphologies with a high surface area. In general, flat plates are used for the synthesis and characterization of coatings [1]. However, the construction of a concentric annular photoreactor, whose efficiency is higher than those with a flat geometry, requires obtaining TiO2 inside substrates with tubular geometry. This change in the geometry implies modifications in the synthesis of the coatings that can affect their properties.The objective of this work is to evaluate the influence of the geometry of the substrate on the morphology and crystallinity of the coatings. Commercial pure Ti was used as the substrate in two geometries: plates (3 × 2 cm2 and 2 mm thick) and tubes (3.2 cm external diameter, 2 cm high and 0.89 mm thick). For the surface preparation of the substrates, chemical pickling with HF:HNO3:H2O 1:4:5 was used. The anodic synthesis was carried out at 40 V for 2 h, using an ethylene glycol solution, 0.27 M FNH4 and 3.5% v/v water as the electrolyte. Subsequently, thermal treatments of 2 h at 450 °C were carried out. The coatings were characterized by scanning electron microscopy, X-ray diffraction, and diffuse reflectance spectroscopy. In both substrate geometries, nanotubular coatings were obtained, with external diameters of ~90 nm, wall thicknesses of 5 nm, 5 μm in length, crystalline in anatase phase, and with a bandgap of 3.2 eV (Figure 1). The synthesis of oxides with the desired characteristics for photocatalytic applications on tubular substrates, together with the versatility and repeatability of the anodic oxidation technique, are highly promising results for its application in the construction of photoreactors with immobilized TiO2.