Modificação da superfície do titânio através da técnica de PEO (Oxidação Eletrolítica assistida por Plasma), dopagem do óxido e a investigação das propriedades fotocatalíticas

Abstract

This study investigates the development and characterization of titanium dioxide TiO2 semiconductor films synthesized via Plasma Electrolytic Oxidation (PEO) for applications in heterogeneous photocatalysis. The primary objective was to evaluate the impact of incorporating various elements — including transition metals (Nb, Ni, Cu, Mo, W, and Fe) and rare earths (Ce) — combined with systematically controlled pH variations (acidic, neutral, and basic media), on the structural, optical, and morphological properties of the resulting coatings. The results demonstrated that the electrolyte composition plays a major role in oxide growth kinetics and crystallinity. While H3PO4 -based solutions favored the detection of crystalline phases, the basic medium containing NH4OH led to a mostly amorphous structure across most samples. Scanning electron microscopy revealed rough surfaces with pores typical of plasma discharges, with diameters and distribution strongly dictated by the electrolyte. Optically, diffuse reflectance spectroscopy estimated the films' bandgap values, showing subtle shifts in the electronic absorption edge induced by the incorporated elements within the TiO2 matrix. Additionally, current transient curves precisely mapped the dielectric breakdown behavior during the transition to the plasma regime. Regarding the incorporation process, niobium achieved the highest rate in an acidic medium (12.4%), though it did not yield substantial performance gains in photocatalysis. Assays revealed that the top three efficiencies for Rhodamine B degradation under UVA radiation were achieved by molybdenum-modified samples in a basic medium (44.8%), followed closely by molybdenum-iron co-incorporated systems (29.3%) in a basic medium and molybdenum-iron (21.6%) in an acidic medium.