Synthesis and characterization of CuOxZrO2(1-x) nanocomposite thin films prepared by spray pyrolysis: Structural, morphological, optical, and photocatalytic degradation properties

In this study, CuO x ZrO 2(1-x) nanocomposite films were successfully synthesized using the spray pyrolysis technique at a substrate temperature of 450°C with various CuO x volume fractions (x = 0, 25, 50, 75, and 100 vol%). The structural, morphological, optical, and electrical properties of the resulting films were investigated. X-ray diffraction confirmed a structural transition from the cubic ZrO 2 phase to the monoclinic CuO phase, with phase coexistence observed at intermediate concentrations. Scanning Electron Microscopy imaging revealed a systematic evolution from dense, relatively smooth ZrO 2 surfaces to uniform distributions of distinct spherical CuO nanoparticles. The optical properties showed a significant bandgap narrowing from 4.20 eV for pure ZrO 2 to 1.41 eV at 75% CuO content, effectively shifting the absorption edge into the visible spectrum. Electrical measurements indicated a transition from the intrinsic insulating nature of pure ZrO 2 to ohmic conduction in CuO–rich films, with the sheet resistance dropping significantly to approx (4.6 × 10 5 Ω) at x = 100%. The photocatalytic activity, evaluated through the degradation of methylene blue (MB) under UV-irradiation, peaked at the 75% CuO/25% ZrO 2 composition, achieving a maximum degradation efficiency of 88% and a rate constant of 0.00851 min −1 . This enhanced performance is attributed to the formation of a type-II heterojunction that facilitates the efficient spatial separation of photogenerated charge carriers.