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 (ZnQPc 4+ ). Then, ZnQPc 4+ was used as a photosensitizer for a series of POM catalysts, including Dawson type K 6 [α-P 2 W 18 O 62 ]·14H 2 O (P 2 W 18 ) and K 10 [α-P 2 W 17 O 61 ]·20H 2 O (P 2 W 17 ) and Keggine type H 3 PW 12 O 40 · x H 2 O (PW 12 ). The Keggin type PW 12 showed higher efficiency with 18.2 μmol of H 2 evolution (turnover number (TON) = 14,550) for 6 h upon ZnQPc 4+ sensitization in relation to two Dawson P 2 W 17 and P 2 W 18 in a visible light–driven water-soluble system with isopropanol and H 2 PtCl 6 ·6H 2 O. In addition, the complexes of ZnQPc 4+ with a series of POM catalysts (P 2 W 17 , P 2 W 18 , and PW 12 ) were also used as photocatalysts for the degradation of methylene blue (MB) in water, and it was found that the complexes of ZnQPc 4+ with P 2 W 17 and PW 12 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 H 2 evolution and the degradation of MB were attributed to the sensitization of POMs by ZnQPc 4+ , which was enabled by the transfer of photogenerated electrons of ZnQPc 4+ to the lowest unoccupied molecular orbital (LUMO) of POM.