Polyoxometalate-Decorated g-C 3 N 4 -Wrapping Snowflake-Like CdS Nanocrystal for Enhanced Photocatalytic Hydrogen Evolution.

Photocatalytic hydrogen evolution technology is recognized as a promising approach to relieving the growing energy crisis. Therefore, the development of a stable high-performance photocatalyst has long been the focus of research. In this work, quaternary composite materials involving a snowflake-like CdS nanocrystal wrapped by different amounts of polyoxometalate-decorated g-C3 N4 and polypyrrole (GPP@CdS) have been synthesized as photocatalysts for hydrogen production under visible-light irradiation. It has been revealed that the best composite (40 % GPP@CdS composite) exhibits hydrogen production activity of 1321 μmol, which exceeds that of CdS by a factor of more than two, and can be used in at least seven cycles with negligible loss of activity. The enhanced photocatalytic performance has been primarily attributed to the efficient synergy of CdS, g-C3 N4 , polypyrrole (PPy), and the polyoxometalate Ni4 (PW9 )2 . It should be noted that the introduction of PPy and g-C3 N4 into the title composite simultaneously promotes electron/hole pair separation and photocatalytic stability, whereas Ni4 (PW9 )2 serves as an efficient electron modulator and extra catalytic active site.