Photothermal Boost of Laser-Synthesized TiC Colloidal Variants with Engineered Solid-State Interfaces and Nitridation

Colloids are vital in many fields, including optics, energy conversion, and photothermal therapy. TiC colloids and their variants are synthesized in acetonitrile using a "green" femtosecond laser fragmentation method under varying laser-power conditions. Three distinct types of TiC colloids are produced: i) pure TiC spherical nanoparticles at low laser power (<0.5 W) through thermodynamically driven spheroidization; ii) TiC nanoparticles with a multilayer graphene shell at moderate laser power (0.5-1 W) via carbon nucleation from acetonitrile decomposition; and iii) nitridated TiC nanoparticles with a multilayer graphene shell at high laser power (1.5-2 W), achieved through nitrogen incorporation facilitated by the breakdown of strong C≡N bonds in acetonitrile. The structural integrity of TiC in all three types of nanoparticles is maintained. The nanoparticle formation mechanisms are investigated, along with the effects of the interfaces and nitridation of TiC on its light-to-heat conversion. Photothermal measurements show a significant improvement in light-to-heat conversion for TiC nanoparticles with shells compared to pure TiC. This enhancement is attributed to light trapping within the colloidal solution, caused by the refractive index mismatch between TiC and graphene. Comparative scattering, absorption, and extinction efficiencies calculations based on Mie theory confirm this effect. Further photothermal enhancement is observed in the nitridated nanoparticles attributed to superior absorption in the NIR region. This study presents a sustainable approach for synthesizing photothermally efficient TiC-based colloids with nanoscale interface engineering and doping, enabling applications in energy and biomedical technologies.