Constructing direct Z-scheme heterojunction of NiCo-LDH coated with g-C3N4 for boosting photocatalytic H2 evolution

•NiCo-LDH/g-C3N4 photocatalysts with direct Z-scheme heterojunction were successfully prepared.•NiCo-LDH/g-C3N4 heterojunction showed boosting photocatalytic H2 evolution performance.•Direct Z-scheme heterojunction improved the electron utilization efficiency of the photocatalyst.•Possible photocatalytic H2 evolution mechanism of NiCo-LDH/g-C3N4 heterojunction was proposed. The photocatalytic decomposition of water to produce hydrogen (H2) is considered to be an effective method to mitigate the influence of greenhouse effect. In this work, NiCo-LDH/g-C3N4 (NCH/SCN) photocatalysts with direct Z-scheme heterojunction for photocatalytic H2 evolution are synthesized by in situ hydrothermal growth method. It is worth mentioning that the optimized NCH/SCN heterojunction with strong light response exhibits the best H2 evolution performance of 3125 μmol·g−1·h−1, and the apparent quantum yield (AQY) reaches 7.35％ at 420 nm. Smoke-like g-C3N4 (SCN) prepared by supramolecular self-assembly method shows a wide triazine ring spacing, which improves electron transfer performance and enhances stability. In addition, the porous structure of SCN is conducive to closely binding with flower-like NiCo-LDH (NCH) to construct direct Z-scheme heterojunction. The reduction of electron transport distance and the presence of internal electric field (IEF) in heterojunction promote the separation of photo-generated carriers. At the same time, NCH/SCN still shows good photocatalytic performance after five cyclic experiments. Characterizations such as valence-band spectrum, work function and density of states were used to analyze the energy band and electronic structure of NCH/SCN, the electron migration path and photocatalytic mechanism were also deduced. This study provides useful strategy for constructing Z-scheme heterojunctions between g-C3N4 and layered double hydroxides (LDHs) to improve photocatalytic H2 evolution performance.