Photocatalytic decomposition of benzene with plasma sprayed TiO2-based coatings on foamed aluminum

Plasma spraying technique was used to deposit thin TiO₂-based photocatalytic coatings on foamed aluminum. Before plasma spraying, the composites of nano-TiO₂ powder (P25) and nano-ZnO/CeO₂/SnO₂ powders were agglomerated into microsized powders by spray-drying process. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photocatalytic activity evaluation by the decomposition of gas-phase benzene (C₆H₆) were applied to characterize the starting powders and the coatings, respectively. The results showed that all the three plasma sprayed TiO₂-based coatings were the mixture phases of anatase and rutile. On the splats’ surfaces of the as-sprayed coatings, fine nano-crystalline particles were observed. However, grain growth occurred on the surface of plasma sprayed 90%TiO₂–10%ZnO coating. The XPS spectra revealed that the Ti, Zn, Ce and Sn elements existed on the surfaces of plasma sprayed TiO₂-based coatings as the chemical states of Ti⁴⁺, Zn²⁺, Ce⁴⁺ and Sn⁴⁺, respectively, whilst, the oxygen element was composed of three kinds of chemical states, i.e. crystal lattice oxygen, hydroxyl oxygen and physical-adsorbed oxygen. It was found that plasma sprayed 90%TiO₂–10%CeO₂ coating and 90%TiO₂–10%SnO₂ coating exhibited similar photocatalytic activity, which was higher than that of plasma sprayed 90%TiO₂–10%ZnO coating. The photocatalytic activity is not only dependent on the anatase content but also on the surface morphology and the hydroxyl content formed on the surface of plasma sprayed TiO₂-based coatings as well as the additive character.