Enhanced photocatalytic activity of amorphous MoO₃ thin films deposited by rf reactive magnetron sputtering

The photocatalytic activity of molybdenum trioxide (MoO₃) thin films was studied. The MoO₃ thin films were deposited on Corning glass substrates by radio frequency reactive magnetron sputtering using a metallic Mo target. The dependence of the physical properties of the metal oxides on the sputtering power and working pressure was investigated. X-ray diffraction patterns of the films revealed the formation of amorphous structures. From optical absorption spectra, the band-gap energy was obtained in the range 2.8–3.0 eV for most compounds, while this parameter decreased down to 1.64 eV for samples deposited at 4.5 mTorr and 80 W. X-ray photoelectron spectra disclosed signals associated with the Mo⁶⁺, Mo⁵⁺, and Mo⁴⁺ oxidation states, which correspond to MoO₃ and other substoichiometric molybdenum oxides. The photodegradation of a methylene blue (MB) aqueous solution was chosen to evaluate the photocatalytic performance of the thin films. There was found a dependence of the photocatalytic activity on the working pressure, with the samples deposited at 8.0 mTorr and 40 W displaying the highest MB removal.