Surface reduction boosts free electron concentration in MXene for enhanced photothermal performance

The photothermal properties of MXenes originate from the localized surface plasmon resonance, which is attributed to their high free electron concentration. However, their intrinsic electron concentration is limited by suboptimal d-orbital occupancy and the electron-withdrawing effect from electronegative terminations. Herein, we report a sodium-mediated surface reduction strategy in molten salts, which optimizes the surface coordination environment via electronic modulation to mitigate the electron-withdrawing and electron-scattering effects, while simultaneously injecting electrons into the Ti-3d states for controlled state filling. This dual modulation enables the free electron concentration, carrier mobility, and electrical conductivity to reach 4.92, 2.63, and 12.96 times that of the pristine MXene, respectively. The optimized reduced Ti₃C₂ achieves a high photothermal conversion efficiency of 91.66% under 808-nanometer laser irradiation. A photothermal antibacterial woundplast with ultralow MXene content demonstrates a high bacterial kill rate. This work not only shows an effective method for tuning the photothermal properties of MXenes but also inspires applications that require tailored surface chemistry and high electron concentration.