Preparation of phthalocyanine/TiO2 nanocomposites for photocatalytic removal of toxic Cr(VI) ions

In this study, a group of novel metal free azomethine-bridged phenolic phthalocyanines (H2Pc) was synthesized. These derivatives are completely new and first time reported. Four derivatives at peripheral or non-peripheral substitution on macro cyclic ring were synthesized and characterized employing various spectroscopic methods. H2Pc derivatives (defined as H2Pc-1, H2Pc-2, H2Pc-3, H2Pc-4) were immobilized on TiO2 nanoparticles to obtain photoactive nanocomposites (H2Pc/TiO2, 1% of the mass of TiO2). H2Pc derivatives were used as photosensitizer to improve the near visible-light photocatalytic efficiency of TiO2 catalyst in wastewater treatment. Photocatalytic abilities nanocomposites were tested for photocatalytic reduction of chromium (VI) ions (10 mg/L) and compared with neat TiO2. A near UV light source (365 nm) was used for illumination in a batch reactor and Cr(VI) concentration was monitored during 150 min treatment period. It is clear that H2Pc sensitized photocatalyst is effective for the reduction of chromium ions. Removal percentages were between 83.70 and 99.75% indicating almost total reduction of toxic Cr(VI) ions. Neat TiO2 was able to reduce only 55.43% of initial Cr(VI) ions. All phthalocyanine containing TiO2 composites are significantly more effective and reduce more Cr(VI) ions than TiO2 itself. Photocatalytic action of the catalysts is decreased in the following order H2Pc-4/TiO2 > H2Pc-2/TiO2 > H2Pc-1/TiO2 > H2Pc-3/TiO2.