Rationally designed ternary CdSe/WS2/g-C3N4 hybrid photocatalysts with significantly enhanced hydrogen evolution activity and mechanism insight

Excellent light harvest, efficient charge separation and sufficiently exposed surface active sites are crucial for a given photocatalyst to obtain excellent photocatalytic performances. The construction of two-dimensional/two-dimensional (2D/2D) or zero-dimensional/2D (0D/2D) binary heterojunctions is one of the effective ways to address these crucial issues. Herein, a ternary CdSe/WS2/g-C3N4 composite photocatalyst through decorating WS2/g-C3N4 2D/2D nanosheets (NSs) with CdSe quantum dots (QDs) was developed to further increase the light harvest and accelerate the separation and migration of photogenerated electron-hole pairs and thus enhance the solar to hydrogen conversion efficiency. As expected, a remarkably enhanced photocatalytic hydrogen evolution rate of 1.29 mmol g−1 h−1 was obtained for such a specially designed CdSe/WS2/g-C3N4 composite photocatalyst, which was about 3.0, 1.7 and 1.3 times greater than those of the pristine g-C3N4 NSs (0.43 mmol g−1 h−1), WS2/g-C3N4 2D/2D NSs (0.74 mmol g−1 h−1) and CdSe/g-C3N4 0D/2D composites (0.96 mmol g−1 h−1), respectively. The superior photocatalytic performance of the prepared ternary CdSe/WS2/g-C3N4 composite could be mainly attributed to the effective charge separation and migration as well as the suppressed photogenerated charge recombination induced by the constructed type-II/type-II heterojunction at the interfaces between g-C3N4 NSs, CdSe QDs and WS2 NSs. Thus, the developed 0D/2D/2D ternary type-II/type-II heterojunction in this work opens up a new insight in designing novel heterogeneous photocatalysts for highly efficient photocatalytic hydrogen evolution.