Abstract: Aseries of studies were carried out to investigate the effect of crystal forms of TiO₂ on the activities in the photocatalyzing degradation of aqueous methyl orange. It is shown that the rutile could hardly catalyze the degradation of the methyl orange and anatase is more effective for catalyzing the degradation than rutile. Moreover, the activities of mixed crystalline forms of TiO₂ vary with the change of the values of A/R, the best of which is 9:1. Some characterizations with XRD, XPSand SPSwere performed and explanations to the phenomena that exist in photodegradation are given out.

Key words: TiO₂, Photocatalyzing degradation, Methyl orange