Photocatalytic degradation of persistent organic pollutants under visible irradiation by TiO₂catalysts sensitized with Zn(II) and Co(II) tetracarboxy-phthalocyanines

Abstract

Photo-excitation under visible light has been an important step to acquire solar-driven TiO 2 photocatalysts and dye sensitization has been used frequently to extend the optical response of TiO 2 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 TiO 2 surface and their photocatalytic activities were investigated. Due to covalent bonding of carboxy-terminated molecules onto TiO[Formula: see text]semiconductors, we synthesized symmetric 4-hydroxybenzoic acid-bearing metallophthalocyanines as dye sensitizer molecules. Heterogeneous composites having titanium dioxide and metallophthalocyanines anchored via CO–O–TiO 2 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 TiO 2 were 0.98 [Formula: see text]mol/g TiO 2 for CoPc and 0.86 [Formula: see text]mol/g TiO 2 for ZnPc, nearly independent of the amount of TiO 2 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 TiO 2 and the difference was attributed to the cooperation of the two elements, namely TiO 2 and MPc. Experiments show that in two hours nearly complete degradation of POPs were observed.