Multilayered hollow transition metal nitride spheres made from single-source precursors for SERS analytics

Traditional high-temperature and high-pressure synthesis routes make transition metal nitride (TMN) grains prone to sintering and agglomeration, thus synthesis of architectures with high specific surface area and pore volume is an urgent problem to be solved for the applications of TMNs. Here, a general single-source precursor route is designed to synthesize cubic-phase γ-Mo₂N multilayered hollow spheres with high specific surface area (191.3 m² g^-1) and pore volume (0.69 cm³ g^-1) under relatively mild conditions. Furthermore, by changing the metal composition of the precursor through ion exchange, a series of TMN (WN, TiN, VN, NbN, MoN/WN, MoN/WN/TiN) multilayer hollow spheres with high specific surface area (178.6-193.7 m² g^-1) and pore volume (0.57-0.72 cm³ g^-1) are prepared. Particle size of precursor is found to be a key factor affecting the crystal phase and composition of molybdenum nitride nanostructures, and hexagonal-phase δ-MoN hierarchical hollow spheres composed of nanosheets are synthesized by adjusting the precursor particle size. The γ-Mo₂N multilayered hollow spheres exhibit enhanced Raman activity for applications in trace detection of polychlorophenol and microplastics.