Defect-engineered Ga-K-PCN/Ti3C2 MXene@TiO2-X ternary heterojunction via spontaneous MXene oxidation for enhanced photocatalytic hydrogen evolution

The development of ternary heterojunction photocatalysts that simultaneously address sluggish charge separation kinetics, narrow spectral response, and interfacial instability remains a formidable bottleneck for efficient solar-driven hydrogen evolution. Herein, we report a defect-engineered Ga/K co-doped polymeric carbon nitride (Ga-K-PCN) coupled with Ti 3 C 2 MXene-derived TiO 2-X via spontaneous oxidation, constructing a ternary heterojunction for superior photocatalytic hydrogen production. The Ti 3 C 2 MXene serves as both a structural template and a reducing agent, enabling the in situ formation of oxygen-deficient TiO 2-X through controlled oxidation while maintaining interfacial Ti-O-C bonding with the Ga-K-PCN matrix. Density functional theory (DFT) calculations and spectroscopic analyses reveal that Ga/K co-doping induces mid-gap states in PCN, broadening visible-light absorption, while TiO 2-X acts as electron trap to suppress carrier recombination. The synergistic interplay between the ternary components establishes a unique charge transfer mechanism, accelerating carrier separation and enhancing redox potentials. The optimized photocatalyst achieves a remarkable hydrogen evolution rate of 925 μmol·g −1 ·h −1 under visible light, 7.1-fold higher than pristine PCN, with an apparent quantum efficiency of 1.085% at 420 nm. Furthermore, the heterojunction exhibits excellent stability over 480 min of cycling, attributed to the robust interfacial coupling and defect-mediated self-healing properties. This work provides a novel strategy for leveraging MXene oxidation dynamics and defect engineering to construct high-performance ternary photocatalysts for sustainable energy applications. • Ga-K-PCN/Ti 3 C 2 MXene@TiO 2-X heterojunction was built via spontaneous MXene oxidation. • In-situ defective TiO 2-X bridges components for synergistic charge separation. • Ga/K co-doping accelerated charge transfer within π-conjugation of PCN. • Superior H 2 -yield of 1850 μmol·g -1 at 420 nm visible light irradiation was achieved. • Defect-mediated and interfacial synergy drive enhanced photocatalytic activity.