The same behaviour was also reported in the case of Cr and Ce dopants (concantration ratio Mn+:Ti4+ =5:100), which are photocatalytic inactive to phenol degradation compared with Li dopant [13]. The authors concluded that various dopant types induced different changes on catalyst photoactivity according to ionic radii and redox potential o Mn+/M(n-1)+ couple of dopants. Beside dopant type, its concentration can modify the adsortion property ofcatalyst and consequently the pollutant's dagradation rate.