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 TiO2photocatalysts and dye sensitization has been used frequently to extend the optical response of TiO2into 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 TiO2surface 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–TiO2bonds 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 TiO2were 0.98 [Formula: see text]mol/g TiO2for CoPc and 0.86 [Formula: see text]mol/g TiO2for ZnPc, nearly independent of the amount of TiO2used. 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 TiO2and the difference was attributed to the cooperation of the two elements, namely TiO2and MPc. Experiments show that in two hours nearly complete degradation of POPs were observed.