Highly sensitive hydrazine detection through a novel Raman scattering quenching mechanism enabled by a crystalline and noble metal-free polyoxometalate substrate

In the field of Raman spectroscopy detection, the quest for a non-noble metal, recyclable, and highly sensitive detection substrate is of utmost importance. In this work, a new crystalline and noble metal-free substrate of [Bi(DMF)8][PMo12O40] (Bi-PMo12) is designed, which is composed of [PMo12O40]3− and solvated [Bi(DMF)8]3+ cations. Mechanistic studies have revealed that Raman scattering quenching phenomenon arises from two main factors. Firstly, it arises from the absorption of the scattered light due to the transition of a single electron in the reduced state of MoV between 4d orbitals. Secondly, after the interaction between the substrate and hydrazine, the surface undergoes varying degrees of roughening, leading to an impact on the scattered light intensity. These two effects collectively contribute to the detection of low concentrations of N2H4. As a result, Bi-PMo12 opens up a novel Raman scattering quenching mechanism to realize the detection of reduced N2H4 small molecules. A remarkably low detection limit of 4.5 × 10−9 ppm for N2H4 is achieved on the Bi-PMo12 substrate. This detection has a lower concentration than the currently known SERS detection of N2H4. Moreover, Bi-PMo12 can be recovered and reused through recrystallization, achieving a recovery rate of up to ca. 51%. This study reveals the underlying potential of crystalline polyoxometalate materials in the field of Raman detection, thus opening up new avenues for highly sensitive analysis using Raman techniques.