<p>This paper presents the construction of a type II heterostructure using a monolayer of Cu₃N (111) and MoS₂, and investigates its structural, electronic, and optical properties using first-principles methods. The study discusses the potential of the heterostructure for photocatalytic water decomposition. The results reveal that a staggered band alignment in the Cu₃N/MoS₂ heterojunction is conducive to the oxidation and reduction of water, thus meeting the requirements for photocatalytic water splitting. Under visible light irradiation, effective separation of photogenerated electrons and holes occurs, promoting the water oxidation of the MoS₂ layer and the water reduction of the Cu₃N layer. Charge transfer from the MoS₂ layer to the Cu₃N monolayer extends the lifetime of photogenerated charge carriers. Notably, the heterostructure exhibits significantly enhanced light absorption in the visible range compared to individual monolayers, highlighting its potential as a promising photocatalyst for water splitting applications.</p> Graphical Abstract <p></p>