The present invention provides a process for photocatalytically treating stains of chilly and turmeric caused on kitchen tiles and platforms by coating a thin film of photocatalyst made of a semiconductor such as titanium dioxide uniformly dispersed in dilute silica sol thereon and using a light source such as a fluorescent lamp to irradiate and photoexcite the photo catalytic thin film by the small amount of UV radiation included in the fluorescent light, resulting in photo decomposition and auto-cleaning of the stains.