Photocatalytic Activity of Degussa P25 TiO₂/Au Obtained Using Argon (Ar) and Nitrogen (N₂) Plasma

Titania Degussa P25 powder was treated with Argon (Ar) and Nitrogen (N₂) gas plasma inside of a closed homemade chamber system at 50 Pa of pressure. The electric discharge was generated applying an AC voltage (0–15,000 V) to a pair of aluminum electrodes. Two sets of samples were analyzed. In the first one, the plasma is applied directly on a layer of titania P25 that is spread out on top of one of the electrodes and, in the second one, a gold foil substrate is positioned between the titania powder and the electrode, named TiO₂/Au. In the last sample, gold coated titania nanoparticles or clusters of gold are formed, changing the optical properties of the material. The evolution of the optical properties of the obtained samples was analized using UV–Vis diffuse reflectance. The spectra show a shift in the band gap and a broad band in P25/Au associated with the gold plasmonic band. Additionally, the photocatalytic activity was evaluated by monitoring the photodegradation of methylene blue solution (0.01 g/L), using UV–Vis absorption analysis in the range 250–850 nm. After the plasma is applied, the gold impregnation over the titania surface increases the photocatalytic activity.