Photocatalytic degradation of 4-chlorophenol under visible light by using TiO₂ catalysts impregnated with Co(II) and Zn(II) phthalocyanine derivatives

In order to realize the photocatalytic reactions by visible light more efficiently, the photocatalytic activity of polycrystalline TiO₂ samples impregnated with carboxy functionalized Co(II) or Zn(II)-phthalocyanine as heteregoneous photocatalyst has been investigated. For this purpose, metallophthalocyanines(MPc) substituted with mercapto benzoic acid groups on each benzo moiety were incorporated into TiO₂ semiconductors to prepare TiO₂-MPc composites as heterogeneous catalysts. TiO₂ and TiO₂-MPc composites were characterized by making use of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and UV-vis diffuse reflectance spectroscopy. The characterization results show that MPcs are anchored on the surface of TiO₂ through CO-O-TiO₂ bonds. The optimum loading of the dyes on TiO₂ were 0.49 μmol/g TiO₂ for ZnPc and 0.56 μmol/g TiO₂ for CoPc, nearly independent of TiO₂ used. These novel heterogeneous photocatalysts were used for the degradation of 4-chlorophenol (4-CP) in aqueous media in the presence of visible irradiation monitored by GC-MS spectroscopy. The catalysts revealed enhanced activity in visible region for the degradation of 4-CP when compared with that of pure TiO₂, which is attributed to the cooperative function of the two components of the photocatalyst. The amount of remaining 4-chlorophenol residue was determined by using an internal standard (phenol) with gas chromatography-mass spectrometry and during the first 30 minutes 99% degradation of 4-chlorophenol was observed.