Photocatalytic reduction of Cr(VI) in wastewater using TiO₂ coatings synthesized by plasma electrolytic oxidation (PEO): Influence of duty cycle and EDTA addition

Abstract. The contamination of water bodies with hexavalent chromium (Cr(VI)) poses a serious environmental threat due to its toxicity and persistence. This study investigates the photocatalytic efficiency of TiO₂ coatings synthesized by plasma electrolytic oxidation (PEO) on titanium substrates under varying duty cycles (5 %, 20 %, and 35 %) and evaluated under UVC irradiation (256 nm). The coatings were characterized by XRD, SEM, AFM, and UV-Vis spectroscopy, and SEM images were analyzed using Fourier Transform methods. Results showed that coatings produced at 20 % and 35 % duty cycles exhibited enhanced Cr(VI) reduction to Cr(III), with 20 % offering the best balance between performance and energy consumption. The inclusion of EDTA in the photocatalysis process significantly improved Cr(VI) removal. Structural analysis indicated that higher duty cycles promoted rutile phase formation and a qualitative evolution of surface morphology; porosity was discussed qualitatively based on SEM at the magnification employed. The Fourier Transform analysis of SEM images was used as a complementary qualitative descriptor consistent with the observed performance trends, supporting the development of optimized photocatalytic materials for wastewater treatment applications.