Surface Evolution and Visible-Light Photocatalytic Activity of Sol-Gel Derived Co₃O₄ Thin Films as a Function of...

Thin-film cobalt oxides have attracted increasing attention due to their visible-light activity and potential environmental applications. In this work, Co₃O₄ coatings were prepared on glass substrates through a sol-gel dip-coating process followed by thermal treatment at 450, 500, and 550 °C. Structural characterization was carried out using X-ray diffraction (XRD) and Raman spectroscopy. Diffraction patterns, together with the Raman spectra, indicate the formation of the cubic spinel phase of Co₃O₄, while sharper diffraction peaks appeared at higher annealing temperatures, indicating improved crystallinity of the films. Surface morphology was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM observations revealed continuous polycrystalline coatings, whereas AFM measurements showed clear variations in surface topography and roughness produced by thermal treatment. Wettability measurements obtained from contact angle (CA) analysis indicate modifications in the surface properties of the films as the annealing temperature changes. Optical characterization performed by ultraviolet-visible spectroscopy (UV-Vis) showed strong absorption in the visible region with an indirect band gap close to 1.58 eV. Photocatalytic activity was evaluated through the degradation of methylene blue under visible-light irradiation. Degradation efficiencies of approximately 93.9%, 97.4% and 98.7% were obtained after 5 h for films annealed at 450, 500, and 550 °C, respectively.