Photocatalytic degradation of persistent organic pollutants under visible irradiation by TiO2 catalysts sensitized with Zn(II) and Co(II) tetracarboxy-phthalocyanines

Photo-excitation under visible light has been an important step to acquire solar-driven TiO2 photocatalysts and dye sensitization has been used frequently to extend the optical response of TiO2 into the visible region. In the present work, new heterogeneous photocatalysts were prepared by anchoring carboxylic acid substituted Zn(II) and Co(II) phthalocyanines onto polycrystalline TiO2 surface and their photocatalytic activities were investigated. Due to covalent bonding of carboxy-terminated molecules onto TiO2 semiconductors, we synthesized symmetric 4-hydroxybenzoic acidbearing metallophthalocyanines as dye sensitizer molecules. Heterogeneous composites having titanium dioxide and metallophthalocyanines anchored via CO-O-TiO2 bonds were characterized by using X-ray diffraction (XRD), Fourier-transform infrared spectrometry (FT-IR), and ultraviolet-visible diffuse reflectance spectroscopy. The optimum loading value of the dyes on TiO2 were 0.98 mmol/g TiO2 for CoPc and 0.86 mu mol/g TiO2 for ZnPc, nearly independent of the amount of TiO2 used. These newly obtained heterogeneous photocatalysts were employed in the photocatalytic degradation of 4-chlorophenol-(4-CP), chlorobenzene(CB) and 1,2,4-trichlorobenzen(TCB) in aqueous media under visible irradiation. Gas chromatography-mass spectrometry (GC-MS) was used for quantitation. The new photocatalysts showed excellent activities with visible-region irradiation in the photocatalytic degradation of persistent organic pollutants (POPs) as compared to the control experiments used with untreated TiO2 and the difference was attributed to the cooperation of the two elements, namely TiO2 and MPc. Experiments show that in two hours nearly complete degradation of POPs were observed.