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

ANABELA N. DWOJAK; ESTELA S. PAVÓN; HERNÁN D. TRAID; VERA, MARÍA LAURA; CARLOS E. SCHVEZOV; MARTA I. LITTER

Bueno Aires

Congreso; WCCE11 11th WORLD CONGRESS OF CHEMICAL ENGINEERING; 2023

Asociación Argentina de Ingenieros Químicos

The development of photoreactors for use in heterogeneous photocatalysis with immobilized TiO2 in the treatment ofpolluted water is of great relevance for the transfer of this technology. One of the simplest, most versatile, and cheapesttechniques 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 characterizationof coatings [1]. However, the construction of a concentric annular photoreactor, whose efficiency is higher than thosewith a flat geometry, requires obtaining TiO2 inside substrates with tubular geometry. This change in the geometryimplies 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 crystallinityof 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 anethylene glycol solution, 0.27 M FNH4 and 3.5% v/v water as the electrolyte. Subsequently, thermal treatments of 2 h at450 °C were carried out. The coatings were characterized by scanning electron microscopy, X-ray diffraction, and diffusereflectance 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 (Figure1). The synthesis of oxides with the desired characteristics for photocatalytic applications on tubular substrates, togetherwith the versatility and repeatability of the anodic oxidation technique, are highly promising results for its application inthe construction of photoreactors with immobilized TiO2.