Quasi-metal Microwave Route to MoN and Mo2C Ultrafine Nanocrystalline Hollow Spheres as Surface-Enhanced Raman Scattering Substrates

MoN and Mo₂C are important functional materials; however, due to the high activation energy barrier in their nucleation, their synthesis generally requires harsh conditions such as high temperature (>1000 °C) and high pressure (several GPa). The extreme conditions also hinder the acquisition of their ultrafine nanostructures. Herein, we report that MoN and Mo₂C hollow spheres with large surface area (108.7-125.6 m² g^-1) and ultrafine nanoparticles (2-5 nm) are prepared by a quasi-metal-based microwave route under mild conditions. MoO₂ hollow spheres are used as a quasi-metallic microwave absorbing medium as well as a molybdenum source and template simultaneously. The MoN and Mo₂C ultrafine nanocrystalline hollow spheres exhibit strong localized surface plasmon resonance, high photothermal conversion efficiency, and strong surface-enhanced Raman scattering effects. Highly crystalline MoS₂ nanosheet hollow spheres can also be obtained by this method, indicating its universality. The present work provides an effective strategy for the rapid and mild preparation of ultrafine nanocrystalline transition metal nitrides and carbides with ultrahigh activation energy.