Heterogeneous photocatalysis is an attractive approach for the removal of organic pollutants in air and water. However, after nearly 40 years of extensive work on photocatalysis using different chalcogenides (oxides and sulfides) and mainly TiO2, we are not able to explain the differences in activity between the different polymorphs of titania, anatase, rutile and brookite and why TiO2 is the most efficient. These points constitute an important technological lock for improving its efficiency. Our researches were focus on the elaboration of very well defined morphology of anatase, rutile and brookite, their physicochemical and optical caracterisation (RX, surface area, electronic microscopy, ….) but also their electronic properties using Time Resolved Microwave (TRMC) and finally their photocatalytic properties using two model pollutant.