Influence Of The Formation Of Vacancies Of O₂ On The Photocatalytic Activity Of TiO₂ And Of TiO₂ Mixed With Two Different Tungsten Precursors Fibers

Luana Góes Soares*, Annelise Kopp Alves

Federal University of Rio Grande do Sul, Ceramic Materials Laboratory, Av. Osvaldo Aranha 99,
sala 709, Zip Code 90035-190, Porto Alegre-RS, (BRAZIL)

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ABSTRACT – DOI: https://dx.doi.org/10.47204/EMSR.4.1.2022.008-017

The use of TiO₂, as the semiconductor most commonly used in heterogeneous photocatalysis, becomes relevant due to its efficiency in the decomposition of pollutants in water, air, bacteria, cancer cells and in the degradation of toxic organic compounds. However, the fact that only 3% of the visible spectrum can activate its photocatalytic capabilities, due to its wide band gap (3.2 eV), reduces its use in the visible region. Aiming to expand the applicability of TiO₂ as a photocatalyst in the visible range, this work proposes to synthesize TiO₂ and TiO₂ fibers mixed with two tungsten precursors (H₂WO₄ and Na₂WO₄.2H₂O), through the influence of O₂ vacancy formation in semiconductors (fibers) and its photocatalytic activity in the degradation of 125 mL of a 20 ppm solution of methyl orange dye. WO₃ and tungstates (Na₂WO₄) were chosen to increase the photocatalytic activity of TiO₂, as they are compounds with proven efficiency in the degradation of organic compounds, in addition to being distinguished by their luminescent and catalytic properties, which come from their electronic configurations. These compounds have technological applications in the development of devices that produce artificial light, in quantum electronics, in high-efficiency phosphors, among others. The presence of intrinsic and/or extrinsic defects adjusts the stoichiometric behavior of WO₃ and other compounds. The concentration of O₂ vacancies, which can be native (intrinsic conductors) or inserted by partial substitutions (extrinsic conductors), determine the positions of the atomic lattice. In this work, we synthesized by electrospinning fibers containing titanium and tungsten oxides. After the synthesis, these samples were characterized by: X-ray diffraction (XRD) to identify the phases present, scanning electron microscopy (SEM) for microstructural analysis, diffuse reflectance spectroscopy (DRS) to determine the band gap energy and evaluation of photocatalytic activity through photodegradation tests of 125 mL of a 20 ppm solution of methyl orange dye. The results show the TiO₂/Na₂WO₄.2H₂O fibers treated at 700 °C, 750 °C and 800 °C as the most photoactive in dye degradation, mineralizing 100% of the dye. Consequence of the formation of a large amount of O₂ vacancies, responsible for the increase in the optical absorption capacity, due to the narrowing of the gap, and the electrical conductivity.