Effect of pH and inorganic salts on the photocatalytic decolorization of methyl orange in the presence of TiO2 P25 and PC500

The photocatalytic decolorization of aqueous solution of methyl orange has been investigated using TiO2 Degussa P25 and Millennium PC500 in the presence of UV medium pressure mercury lamp (UV-A light at lambda(max)=365nm). The effect of pH, electron acceptor such as H2O2, and inorganic anions (Cl-, [GRAPHICS] , [GRAPHICS] , [GRAPHICS] , and [GRAPHICS] ) in the presence of both catalysts is discussed. The evolution of apparent rate constant k(app) as a function of pH indicates that it plays an important role on the kinetics of degradation of MeO in the presence of different protons sources in the range of the acidic medium. The dye adsorption on both catalysts shows a strong dependence on the pH, and the adsorption plays a role in the photocatalytic reaction in acidic and alkaline medium. The decolorization was strongly enhanced in the presence of hydrogen peroxide (H2O2). Addition of salts such as NaCl, KCl, CaCl2, BaCl2, Na2SO4, Na2HPO4, Na2CO3, and NaHCO3 significantly reduces decolorization efficiencies.