Construction of a Stable Two-Dimensional MAX Supported Protonated Graphitic Carbon Nitride (pg-C₃N₄)/Ti₃AlC₃/TiO₃Z-Scheme Multiheterojunction System for Efficient Photocatalytic CO₃Reduction through Dry Reforming of Methanol

In situ construction of two-dimensional (2D)/2D pg-C₃N₄Ti₃AlC₃ MAX heterojunction was achieved using a protonated assisted sonication approach, while TiO3 nanoparticles were embedded over the layered heterostructure using a sol?gel method. This multiheterojunction system exhibits proficient charge transfer and superior activity toward photocatalytic reduction of CO3 through dry reforming of methanol (DRM). Using pg-C₃N₄)/Ti₃AlC₃/TiO₃ composite, H2 and CO production rates at 91.9 and 4.97 mmol (g of cat.)?1 h?1 were achieved, which are 18- and 6-fold higher than using pristine pg-C3N4, respectively. The enhancement in photocatalytic activity is mainly attributed to intimate interfacial contact due to the formation of a multiheterojunction for better light absorption, boosted electron separation, and stronger photoreductive potential. More importantly, CO₃ reduction with H₂O produces CO-rich syngas; however, the methanol/water mixture promoted hydrogen-rich syngas production. Higher quantum yield and prolonged stability are further achieved over the composite catalyst, attributed to the exfoliated 2D Ti3AlC3 MAX structure with strong metal/support interaction. This work demonstrates DRM as a potential approach to get hydrogen-rich syngas and provides a new pathway for the construction of highly stable 2D MAX based structured composite for water splitting and CO3 reforming applications.