Charge separation and transfer are the dominating factors in achieving high activity of solar energy-based photocatalysis. Here, a plasmonic transition metal nitride, Ni3N, nanosheet was fabricated and employed as an efficient cocatalyst to couple with Cd0.9Zn0.1S (CZS) solid solution via a self-assembly method to form a novel Ni3N/CZS heterojunction with an intimate interface. On one hand, localized surface plasmon resonance of the Ni3N nanosheets endowed the fabricated Ni3N/CZS composite with a wide-spectrum light absorption capacity, even to the near-infrared range. On the other hand, Ni3N as a cocatalyst can not only effectively induce the directional electron transfer from CZS to Ni3N active sites but also enhance the surface charge separation efficiency of the Ni3N/CZS heterojunction by 4.1 times compared to that of pure CZS. Plasmonic Ni3N also provided a photothermal effect to enhance the surface temperature of the composite for boosting the catalytic reaction kinetics. As a result, under visible light irradiation, the optimal Ni3N/CZS composite exhibited simultaneous H2 generation and benzaldehyde formation rates of 35.08 and 16.44 mmol g-1 h-1, which were 9.4 and 5.9 times those of CZS, respectively; and the composite also demonstrated a strong antibacterial ability with a sterilization rate of 99.7% toward Escherichia coli. Besides that, under NIR light, plasmonic Ni3N offered extra hot electrons that can transfer back to CZS to take part in the photocatalytic reaction, leading to the Ni3N/CZS composite still having a high H2 production of 179.6 μmol g-1 h-1. This work focuses on developing and applying novel plasmonic cocatalysts in photocatalysis for achieving adjustable electron transfer and fast charge separation for extensive practical application.