Enhanced ultraviolet light driven photocatalytic activity of ZnO particles incorporated by plasma electrolytic oxidation into Al2O3 coatings co-doped with Ce3+

This paper presents a new method for improvement of ultraviolet light driven photocatalytic activity of ZnO by immobilizing ZnO particles into Al2O3:Ce3+ coatings which emit intense radiation in the near ultraviolet region when excited by middle ultraviolet radiation. When Al2O3:Ce3+/ZnO coatings are illuminated by ultraviolet light in photocatalytic reactor, emitted ultraviolet radiation originating from Ce3+ ions synergistically participates in photocatalytic reactions on ZnO. Al2O3:Ce3+/ZnO coatings were formed by plasma electrolytic oxidation of aluminum in electrolyte containing 2 g/L of ZnO particles and up to 8 g/L of CeO2 particles. Structural, optical, photoluminescent, and photocatalytic properties of formed surface coatings were examined. All formed coatings feature virtually the same thickness, morphology, phase composition, and absorption properties. Concentration of incorporated Ce3+ ions into Al2O3 host and concentration of immobilized ZnO particles are the only parameters by which the coatings differ from each other resulting in difference in photocatalytic activity. Al2O3:Ce3+/ZnO coatings show better photodegradation of methyl orange with respect to Al2O3/ZnO coatings. The best photocatalytic activity is observed for the coating formed in electrolyte containing 4 g/L of CeO2 particles.