Photocatalytic removal of Cr(VI) ions from aqueous solution with phytalocyanine immobilized titanium dioxide (Pc/TiO2)

In this study, photocatalytic removal of Cr(VI) ions with aqueous suspension of phtalocyanine immobilized titanium dioxide (Pc/TiO2) was investigated. Azomethine bridged phenolic phtalocyanines (Pc) were first time used for sensitization of TiO2. Pc molecules were specially designed that containing; i) substituents at non-peripheral or peripheral position, ii) ethyl or methyl end grup, iii) metal ions (Co2+, TiO2+, Zn2+, Fe2+, Cu2+ and Ni2+) at the central cavity of Pc molecule. Total 28 derivatives were used for production of Pc/TiO2 nanocomposite catalysts. Catalysts (2 g/L) were tested for removal of 10 mg/L Cr(VI) solution employing a 365 nm light for 150 min. exposure at pH 2. The Cr(VI) concentration was measured employing spectrophotometric method. Removal percentages (%) were calculated after exposure periods and were compared with neat TiO2. Prepared Pc/TiO2 catalysts were highly effective for photocatalytic removal of Cr(VI) ions. Total removal was achieved with Pc/TiO2 catalyst at 10 mg/L initial Cr(VI) concentration and they were still effective for higher concentration (20 mg/L). Peripheral derivatives with etlhyl/methyl groups were more effective than non-peripheral ones and presence of metal ion in the structure increased the catalyst's photocatalytic action. It is clear that sensitization of TiO2 with Pc derivatives eases the electron transfer and provides more electrons at conductive band of TiO2 semiconductor. These electrons are easily transferred to Cr(VI) ions leading to reduction to Cr(III). As a result, produced Pc/TiO2 nanocomposite catalysts can be used for effective removal of Cr(VI) ions from water. Key Words: Photocatalytic, Phtalocyanine/TiO2 nanocomposite, Cr(VI)