Dual‐plasmonic Ag/MoO _{3− <i>x</i>} nanoflowers for ultrasensitive SERS sensing of aldehyde VOCs gas

Abstract The electromagnetic field coupling between two kinds of noble metal nanoparticles endows high surface‐enhanced Raman scattering (SERS) activity but is accompanied by uneven hot spots. Using two‐dimensional semiconductors with localized surface plasmon resonance (LSPR) effects instead of one of the noble metal components can effectively improve uniformity. Hence, the Ag nanoparticles (Ag NPs) loaded MoO 3− x nanoflowers (Ag/MoO 3− x ) were engineered to exploit dual‐plasmonic coupling and realize the trace detection of aldehyde volatile organic compounds (VOCs) gas. The finite‐difference time‐domain (FDTD) simulation results proved that there is an obvious electromagnetic field coupling effect between Ag NPs and MoO 3− x semiconductors, which can amplify the molecular dipole moment significantly. The chemical enhancement mechanism in the Ag/MoO 3− x substrate was clarified by band structure analysis, in which the free electrons accumulated at the bottom of the conduction band of the MoO 3− x semiconductor can promote the charge transfer process between Ag/MoO 3− x and the 4‐aminothiophenol (4‐ATP) molecule. Moreover, the electron delocalization of 4‐ATP molecule was enhanced after being absorbed on Ag/MoO 3− x nanoflowers, facilitating the charge transfer between 4‐ATP and Ag/MoO 3− x substrate effectively. Importantly, using the 4‐ATP molecule as a probe, the trace detection of a variety of aldehyde VOCs gas was realized by Ag/MoO 3− x substrate with a low limit of detection (LOD) of 10 ppb. This work provided a new idea for the design of noble metal‐plasmonic semiconductor heterostructure substrates.