Cascaded electron transition proved by femto-second transient absorption spectroscopy for enhanced photocatalysis hydrogen generation

Abstract

Regulating flow direction of photo-excited electrons from interior to active sites in surface is critical to enhance the photocatalytic performance. Herein, photoinduced chemical reduction process was utilized to pinpoint deposit CdS and NiS nanodots sequentially onto g-C3N4 nanosheets. The resulted hybrid composite NiS/CdS/g-C3N4 was much more active under visible light, and eventually boosted the hydrogen evolution rate of 3015 µmol g−1 h−1, to be 2.4 folds better than that of g-C3N4. Because of the relative low content of CdS (around 3.0 wt%), the enhanced activity is due to the favoring band overlapping and promoting charge separation rather than increasing light absorption. Femto-second time-resolved transient absorption spectroscopy (fs-TAS) clearly reveals that the photo-excited electrons are from g-C3N4, and then migrate unidirectionally to CdS and finally to NiS, which is caused by the precisely regulate the position of CdS and NiS on g-C3N4 surface. This study elucidates the electron transfer kinetics and processes in multi-component system and affords a new avenue to construct stable photocatalysts with high activity.