Nacre-mimetic PVA/MXene/CNTs films via covalent crosslinking: Synergistic mechanics, photothermal conversion, and radiative cooling for sustainable energy applications

Efficient utilization of clean solar thermal energy remains for addressing the global energy challenges. Ti₃C₂T_x MXene exhibits exceptional thermal conductivity and mechanical strength, however, its incorporation into polymer composites is hindered by weak interfacial interactions and poor dispersion. This study presents a covalent engineering strategy to construct MXene/carbon nanotube (CNT) hybrid fillers through esterification crosslinking, where polyacrylic acid (PAA) bridges hydroxyl-rich polydopamine-coated CNTs and MXene nanosheets. The resulting polyvinyl alcohol/MXene/CNTs (PMC) composite films fabricated through solution casting exhibit a unique gradient deposition architecture. The optimized PMC-10 film has excellent mechanical properties with a tensile strength of 216 MPa and a Young's modulus of 3.07 GPa, which are 2.8 and 5.1 times higher than those of the original PVA, respectively. Meanwhile, the composite simultaneously exhibits dual-mode thermal regulation capabilities: daytime photothermal heating enhancement of 45.43 °C and nighttime radiative cooling reduction of 7.47 °C. This diurnal thermal gradient enables continuous 24-h thermoelectric generation. Furthermore, the PMC films display rapid ice-melting capabilities, efficient heat dissipation, and improved flame retardancy. This work establishes a paradigm for designing 1D/2D covalent hybrid fillers in polymer composites that simultaneously enhance mechanical properties and multifunctional performance, significantly expanding their potential for sustainable energy applications.