Abstract
Self-cleaning coatings that combine superhydrophobicity with photothermal properties offer an effective strategy to reduce soiling and icing on surfaces. However, conventional methods rely on surface roughness for hydrophobicity, and blackbody materials for photothermal heating, which reduce light transmittance and limit their suitability for photovoltaic applications. Two-dimensional materials such as graphene, borophene, and MXene are known for their reduced dimensionality and high surface-to-volume ratio. Among them, MXenes stand out due to their tuneable surface terminations that directly influence optical absorption, charge transport, band structure, and wettability.</p><p></p><p>Herein, relatively unexplored Ti<sub>2</sub>C MXene was prepared via hydrofluoric acid (HF) etching with an unmatched superior quality, while retaining its hexagonal crystal structure and intrinsic crystallinity. A comprehensive investigation using various characterisation techniques revealed a unique mechanism of light-to-heat conversion that deviates from conventional near infra-red (NIR) absorption-based pathways. Despite lacking significant NIR absorption, the synthesised MXene demonstrates extraordinary photothermal conversion to temperatures up to 85°C, primarily attributed to its electronic structure and broad ultraviolet light absorption, causing phonon induced inter band transitions. The introduction of various surface terminations imparts remarkable hydrophobic characteristics with an average contact angle of 149.8°. To the best of current knowledge, this is the first report of a Ti<sub>₂</sub>C MXene exhibiting such strong photothermal performance and hydrophobicity.</p><p></p><p>Safer molten-salt synthesis routes were explored enabling varied surface chemistry and higher yields, albeit lower photothermal response compared to HF etched MXene. Decoration of molten MXene with plasmonic metal nanoparticles broadened the absorption spectrum and boosted their photothermal performance. The comparison of synthesis methods and surface modification on the photothermal response of MXene suggested a dependence on thickness, morphology, aspect ratio, and surface chemistry. The findings indicate that surface properties of MXenes can be tailored according to the demand, significantly broadening their scope for photovoltaic, optoelectronic, automobile, and aerospace applications.