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Ternary heterojunction CN/TiO 2 -Ti 3 C 2 constructed by CN and partially oxidized Ti 3 C 2 MXene exhibits excellent performance for visible-light photocatalystic NOx removal. [Display omitted] • Ti 3 C 2 MXene can be turned to TiO 2 -Ti 3 C 2 nanosheet by partially oxidation. • Ternary heterojunction catalyst was formed by g-C 3 N 4 and partially oxidized Ti 3 C 2. • NO conversion on the catalyst is inferred to S-scheme heterojunction mechanism. • NO removal efficiency of the photocatalyst reaches up to 66.3% under visible light. Highly efficient composite photocatalysts were prepared through annealing partially oxidized Ti 3 C 2 MXene with melamine under N 2 flow. The two-dimensional Ti 3 C 2 MXene was aforehand partially oxidized to form TiO 2 -Ti 3 C 2 nanosheet by precisely controlling the oxidation conditions. Ternary g-C 3 N 4 /TiO 2 /Ti 3 C 2 MXene photocatalyst was constructed by coating melamine derived g-C 3 N 4 on TiO 2 -Ti 3 C 2 nanosheet. The photogenerated electron-hole separation was significantly enhanced by the S-scheme heterojunction. Ti 3 C 2 tightly bonded with TiO 2 benefits transfer and aggregation of photo-induced holes. The composite material has an interconnected nanosheet structure, which increases the absorption of light and the reaction interface between gaseous reactant and photocatalysts. When evaluated as NOx purification photocatalysts, the fabricated composites get the high NO removal efficiency and low NO 2 generation. Under visible light, NO removal efficiency of the composite photocatalyst can reach up to 66.3%, which is significantly better than the g-C 3 N 4 or TiO 2 -Ti 3 C 2. This work demonstrates that moderately oxidized Ti 3 C 2 MXene is a good candidate for the construction of high-performance air purification photocatalysts. [ABSTRACT FROM AUTHOR]