Titanium Carbide MXenes Cocatalyst with Graphitic Carbon Nitride for Photocatalytic H₂ Production, CO₂ Reduction, and Reforming Applications: A Review on Fundamentals and Recent Advances

Two-dimensional (2D) titanium carbide (Ti₃C₂) MXenes have gained increasing attention in photocatalytic applications due to their prominent electrical conductivity, optical properties, and abundant surface functional groups. The unique layered microstructure characteristics of Ti₃C₂ provide a large surface area, interlayer spacing, and hydrophilic surface functional groups, contributing to their high photocatalytic efficiency. Graphitic carbon nitride is very promising among the semiconductors due to its layered structure and higher reduction potential. The present study discusses the recent advances in various Ti₃C₂ structures coupled with g-C₃N₄ for hydrogen evolution reactions (HER), photocatalytic CO₂ reduction reactions (CO₂ RR), and CO₂ reforming of methane (CO₂ RM). Initially, we provide an overview of the fundamental properties of Ti₃C₂-based composites and recent synthesis approaches, including structure development, of functional group formation, and various etching agents. We further explore using Ti₃C₂ in different structures coupled with g-C₃N₄ as a binary and ternary composite with the involvement of other semiconductors and sensitizers. The performance of various composites for water splitting to produce hydrogen and reforming systems, including CO₂ conversion with H₂O, CO₂ methanation, dry reforming of CH₄ (DRM), and bireforming of CH₄ (BRM), is discussed in detail. The hydrophilic surface functional groups and efficient electron transport pathways of Ti₃C₂ MXenes make them excellent candidates for catalysts with high yield rates and selectivity. Finally, this review provides valuable insights into the potential applications of Ti₃C₂-based composites, and future research directions in this field are proposed.