A method of forming TiO2—ZnO nanoparticles coated by a copper (II) complex includes forming a mononuclear copper complex by treating a ligand with Cu2+ ions; and immobilizing the mononuclear copper complex on TiO2—ZnO nanoparticles to obtain the TiO2—ZnO nanoparticle coated by the copper (II) complex. The TiO2—ZnO nanoparticles coated by a copper (II) complex thus produced have improved catalytic effectiveness and increased efficiency by reducing catalytic reaction time and temperature, particularly in methods of catalyzing oxidation of an alcohol or of catalyzing decarboxylative bromination of an acid.