Recent trends in two-dimensional nanocomposites as photoelectrocatalysts for water treatment and hydrogen production: A comprehensive review

Two-dimensional (2D) materials have attracted significant attention as advanced photoelectrocatalysts for environmental remediation and sustainable hydrogen production. This review critically discusses recent advances in various 2D layered materials, including MXenes, graphene and its derivatives, hexagonal boron nitride (h-BN), layered double hydroxides (LDHs), graphitic carbon nitride (g-C 3 N 4 ), and metal chalcogenides-based materials in photoelectrocatalytic degradation of pharmaceuticals and personal care products (PPCPs) and solar-driven hydrogen (H 2 ) production. The preparation methods governing the surface, electronic, structural and optical properties have been discussed, highlighting their influence on photoelectrocatalytic activity. The fundamental principles of photoelectrocatalysis are also examined, including light absorption, electron-hole pair generation, charge-carrier separation, interfacial charge transfer, reactive oxygen species formation, and surface redox reactions. Furthermore, the application of 2D materials in photoelectrocatalytic removal of pharmaceuticals in terms of reaction mechanisms and kinetics are discussed in detail. In addition, H 2 production using 2D material-based composites, along with the associated mechanistic pathways and kinetic parameters, has been comprehensively analyzed. Despite these advances, several challenges remain, including incomplete mechanistic understanding, nanosheet restacking, defect control, photocorrosion, catalyst leaching, long-term stability, real-wastewater performance, and scalable electrode fabrication. Thus, this review not only consolidates existing knowledge but also explores key research directions to address these challenges associated with both photoelectrocatalysis and 2D material-based composites.