Ag-Au alloy nanoparticles: Synthesis and in situ monitoring SERS of plasmonic catalysis

Abstract

Noble metal nanostructures are currently of great interest for their unique plasmonic property and potential applications in catalysis and surface-enhanced spectroscopy. However, the application of plasmonic nanostructures for quantitatively in situ SERS monitoring of the catalytic reaction has been a great challenge for investigators because combining plasmonics with catalysis requires the same kind of noble metal nanoparticles (NPs) in two very different size regimes. Herein, We have demonstrated a facile wet chemical method to synthesize Au-Ag alloy plasmonic NPs that could combine the desired plasmonic and catalytic properties with same NPs. The catalytic activity of Au-Ag alloy NPs using the reduction of 4-nitrothiophenol (4-NTP) by sodium borohydride (NaBH 4) is chosen as a model reaction. The signals of the reaction processes are detected and identified through in situ SERS spectroscopy with high sensitivity. The insights gained by current study may serve as a promising and powerful technique for better investigation in the heterogeneous catalysis. Moreover, the reduction of aromatic nitro compounds with prepared Au-Ag alloy NPs also provides potential application in sewage treatment.

Silver Nanoprism-Loaded Eggshell Membrane: A Facile Platform for In Situ SERS Monitoring of Catalytic Reactions

“…Finally, the reduction of 4-NTP into 4-ATP was followed by real-time SERS after dropping a NaBH 4 solution on the membrane. Figure 7B shows the time-dependent SERS spectra of the 4-NTP-functionalized AgNP@ESM, which was recorded continuously for 270 s. The SERS spectra of 4-NTP exhibit four main characteristic peaks at 853, 1079, 1331 and 1568 cm -1 , attributed to C-H wagging, C-S stretching, O-N-O stretching, and phenyl ring stretching modes, respectively [19]. As the reaction progresses, new vibration Raman bands of an intermediate were observed 30 s later upon NaBH 4 addition, which can be assigned to the spectral features of 4,4 -dimercaptoazobenzene (4,4 -DMAB) at 1138, 1384, and 1428 cm -1 , ascribed to C-N symmetric stretching, N=N stretching and CH in-plane bending modes, respectively [16,19,43].…”

“…It seems that the single type of silver nanoparticles can hardly exhibit both excellent catalytic and SERS activity. Therefore, combining catalytically-responsive and SERS-active functionalities into an entire platform through suitable methods of core-shell [16], hybrid [17,18], alloy [19] or assembly [20] is the most popular strategy. However, it is difficult to achieve a balance between high catalytic efficiency and SERS enhancement, as the plasmonic near-field enhancement is distance-dependent and the surface coverage of catalytic nanoparticles (NPs) may also remarkably reduce the SERS enhancement.…”

Synthesis of Au doped Ag nanoclusters and the doping effect of Au atoms on their physical and optical properties

“…640 nm), which illustrates HOMO-LUMO transitions in the clusters. The enhancement of this peak caused by Localized Surface Plasmon Resonance (LSPR) [21]. That is also the manifestation of surface charges that have been produced on the clusters with the passage of time during synthesis.…”

“…The SPR band observed at 396 nm for Ag/Au alloy NCs clusters due to a high concentration of Ag. On the other hand, by increasing the concentration of Au, peak will shift towards 520 nm [16,21,29]. The SPR peak at 472 nm represents the exact composition of Ag/Au alloy NCs ( figure 1(a)) [1,21].…”

“…By changing the number of atoms, constituents, and surface to volume ratio, surface plasmon resonance (SPR) and other properties of NCs can be tuned due to quantum confinement effect [19,20]. Alloy NCs are more favorable than single metal NCs because of its synergistic effect and the easy tunability of its optical and physical properties by changing the number, size, structure, types and surrounding environment of its constituents [6,15,17,[21][22][23]. For the electronic and optical perspective, making the heteroatoms by doping it will be more prominent, if dopant can take place into the kernel of NCs, as the kernel dictates the HOMO-LUMO gap and optical properties of NCs [20].…”