ZIF-L-derived porous C-doped ZnO/CdS graded nanorods with Z-scheme heterojunctions for enhanced photocatalytic hydrogen evolution

This study presents a novel approach for synthesizing C–ZnO/CdS graded nanorods derived from metal–organic frameworks (MOFs) that can be applied as a catalyst for photocatalytic hydrogen evolution from pure water. Porous C-doped ZnO was prepared by a self-template method using imidazole-like metal–organic backbone (ZIF-L) as a precursor through a two-step calcination method. CdS nanoparticles were deposited on ZIF-L surface by chemical deposition. The two-step calcination method introduced elemental C, and the unique architecture of ZIF-L played an essential role in forming the hierarchical structure of the porous ZnO nanorods. Compared with other ZnO/CdS catalysts, the C-doped ZnO/CdS graded nanorods exhibited remarkable photocatalytic activity for hydrogen production. The highest hydrogen production rate of 20.25 mmol g−1 h−1 with an apparent quantum yield (AQY) of 24.7% at 365 nm obtained over C–ZnO/CdS with Pt as co-catalyst, which was 24.4 and 65.3 times higher than that over CdS (0.83 mmol g−1 h−1) and ZnO (0.31 mmol g−1 h−1), respectively. This outcome was attributed to (i) the formation of Z-scheme heterojunction that significantly promoted the separation and migration of photogenerated electron–hole pairs; (ii) C doping that reduced the bandgap of ZnO and broadened its spectral response range; and (iii) the ordered arrangement of porous nanorods that effectively reduced the recombination rate of the electron–hole pairs.