Photosensitization of zinc phthalocyanine bearing 15-crown-5 ether moieties on carbon nitride for H2 production: Effect of co-existing alkali metal ions

A zinc phthalocyanine derivative (ZnPc) with one carboxyl group and three 15-crown-5 ether moieties has been synthesized and used as photosensitizer of Pt-loaded graphitic carbon nitride (Pt/g-C3N4) for visible-light-driven H-2 production. By adding alkali metal ions (Li+, Na+, or K+) in the ZnPc solution before the dye-sensitization process, the photosensitization for H-2 production on Pt/g-C3N4 can be improved with an increasing sequence of Li+ < Na+ < K+. Especially, the co-existing K+ ions cause the H-2 production activity enhancing from 163 to 476 mu mol h(-1) with a turnover number (TON) from 3105 to 9067 h(-1). Besides, the coexisting Li+, Na+ and K+ ions exhibiting an impressive apparent quantum yield (AQY) of 2.06%, 2.41% and 2.74% at 700 nm, respectively. All those AQY values are higher than that (1.88%) of the ZnPc-Pt/g-C3N4 without addition of alkali metal ion. The further investigation results indicate that the combination of ZnPc's 15-crown-5 ethers with ions are able to enhance the electron transfer ability and then the photoactivity for H-2 production. Our finding may open a way to highly efficient dye-sensitized semiconductor-based photocatalysis for solar energy conversion by using ZnPc derivative bearing purposeful substituents which can be interacted with proper ions.