Phthalocyanine-sensitized evolution of hydrogen and degradation of organic pollutants using polyoxometalate photocatalysts

In this study, 2 (3), 9 (10), 16 (17), 23 (24)-tetrakis-(8-quinoline-oxy) phthalocyanine zinc(II) (ZnQPc) was prepared and then quaternized to obtain water soluble zinc phthalocyanine (ZnQPc4+). Then, ZnQPc4+ was used as a photosensitizer for a series of POM catalysts, including Dawson type K6[α-P2W18O62]·14H2O (P2W18) and K10[α-P2W17O61]·20H2O (P2W17) and Keggine type H3PW12O40·xH2O (PW12). The Keggin type PW12 showed higher efficiency with 18.2 μmol of H2 evolution (turnover number (TON) = 14,550) for 6 h upon ZnQPc4+ sensitization in relation to two Dawson P2W17 and P2W18 in a visible light–driven water-soluble system with isopropanol and H2PtCl6·6H2O. In addition, the complexes of ZnQPc4+ with a series of POM catalysts (P2W17, P2W18, and PW12) were also used as photocatalysts for the degradation of methylene blue (MB) in water, and it was found that the complexes of ZnQPc4+ with P2W17 and PW12 showed improved photocatalytic activity, and the degradation rates of MB reached 100% at a small dosage under natural pH and visible light. The high efficacy of POM catalysts for H2 evolution and the degradation of MB were attributed to the sensitization of POMs by ZnQPc4+, which was enabled by the transfer of photogenerated electrons of ZnQPc4+ to the lowest unoccupied molecular orbital (LUMO) of POM.