Femtosecond Laser Carburization of WS2 Flakes to W2C for Enhanced Photothermal Conversion Efficiency

Photothermal therapy is a new, promising approach for treating cancer in a noninvasive way. Herein, a photothermally efficient nanomaterial is synthesized by exposing bulk WS₂ powder, dispersed in carbon-rich acetonitrile, to high-intensity femtosecond laser pulses. The photothermal measurements show a significantly higher rise in temperature and enhance photothermal efficiency for the laser-treated material. The attribution is on the enhancement to the formation of tungsten semi-carbide (W₂C), which is verified by morphological and structural characterization. The tungsten semi-carbide is formed by laser-induced carburization; intense laser pulses knock S atoms out of the WS₂ lattice and dissociate the acetonitrile molecules, resulting in the formation of W₂C. Interestingly, the hexagonal W₂C has a two-dimensional (2D) layered morphology like that of the WS₂, suggesting its morphology is not random and might be determined by the morphology of the parent material. The study provides a simple route to transform a 2D transition-metal dichalcogenide into a 2D transition-metal carbide, which is useful for applications including photothermal therapy.