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.