Anisotropic Plasmon Resonance in Ti₃C₂T_x MXene Enables Site-Selective Plasmonic Catalysis

The ever-growing interest in MXenes has been driven by their distinct electrical, thermal, mechanical, and optical properties. In this context, further revealing their physicochemical attributes remains the key frontier of MXene materials. Herein, we report the anisotropic localized surface plasmon resonance (LSPR) features in Ti₃C₂T_x MXene as well as site-selective photocatalysis enabled by the photophysical anisotropy. Both experimental and theoretical studies provide direct evidence of the occurrence of transverse and longitudinal dipolar plasmon resonance modes, respectively, driven by in-plane and out-of-plane vibrations of the two-dimensional (2D) MXene nanoflakes. Wavelength-controlled excitation of the two LSPR modes is demonstrated to activate either the on-edge or the in-plane active sites for plasmonic charge carrier-induced site-selective catalysis. Our findings uncover the presence as well as the mechanism of the anisotropic plasmon resonance in nonmetallic 2D nanomaterials and provide intriguing design principles for next-generation plasmonic nanocatalysts.