Formation of TiO₂ photocatalyst through cold spraying

TiO₂ photocatalyst in the form of coatings are of many advantages over those in powder form in practical applications. Various processes have been used to form TiO₂ coatings including sputtering, Sol-Gel, vapor deposition, thermal spraying, etc. In all those processes, the coatings are deposited under temperatures from 300 to more than 2000°C. High temperature during those processing may change the microstructure of the as-received TiO₂ to a less effective one for photocataltyic performance. In the present study, TiO₂ coating was deposited through cold spraying process using two types of powders, which were agglomerated with anatase ultra-fine particles in micro-size and nano-size. Microstructures of both powders and deposited coatings were characterized using X-ray diffraction and scanning electron microscopy. The photocatalytic performance was examined through acetaldehyde degradation under ultraviolet illumination. The results showed that the nanostructured TiO₂ coatings were evenly deposited on stainless steel substrate through cold spraying. The thickness of the deposits reached up to 15 μm. The coating presented a rough surface and porous structure. Owing to the low temperature of spray powders, no change occurred to the phase and grain size of TiO ₂ during deposition process. It was also found that the cold sprayed TiO₂ deposits were photocatalytically active for photodegradation of acetaldehyde.