Single-crystal-ordered-mesoporous metal nitrides without intrinsic Raman signals for highly sensitive SERS detection

The formation of transition metal nitrides (TMNs) necessitates overcoming extremely high reaction barriers, which renders the precise synthesis of TMN materials with tailored structures a significant challenge. Herein, we propose a molten-salt/template strategy for the accurate customization of TMNs featuring a rare single-crystal ordered mesoporous (SCOM) structure. By leveraging this strategy, 5 types of SCOM-structured TMNs-including WN, MoN, TiN, VN, and CoN were synthesized. Hydroxylation of templates and the subsequent formation of SCOM-structured metal oxides were identified as the key factors governing the formation of SCOM-TMNs. Interestingly, these SCOM-structured WN lack the intrinsic Raman signals typically possessed by non-metallic materials, effectively resolving the long-standing issue of background interference in non-metallic surface-enhanced Raman scattering (SERS) substrates. The WN substrate achieves an ultrahigh Raman enhancement factor of up to 7.5 × 10⁷ and an ultralow detection limit of 1 × 10^-12 M.