Adsorption of p-nitrothiophenol on mesostructured polyoxometalate–silicate–surfactant composites containing Au nanoparticles: study of surface-enhanced Raman scattering activity

Abstract

In this research, we fabricate thin-film shape-ordered mesostructured polyoxometalate–silica composites containing Au nanoparticles (NP) at the air–water interface. With three-dimensional (3D), densely packed Au NPs of 2.4 nm in size in the expanded polyoxometalate–silicate–surfactant (EPSS) template, we show that impressive surface-enhanced Raman scattering (SERS) results can be measured with p-nitrothiophenol (p-NTP) adsorbed onto Au-NPs@EPSS. The mesostructured Au-NP arrays demonstrate a SERS enhancement factor of up to 2 × 10⁷. This high level of SERS is beyond general expectations for such small Au NPs. The surface concentration allows us to estimate the adsorption isotherms of target molecules. Quantitative data for the relationship between SERS intensity and surface coverage of adsorbates on Au-NPs@EPSS provides a better understanding of the SERS activity of 3D substrates. Furthermore, we also use a Au-NPs@EPSS composite as a catalytic and analytical platform for chemical reactions performing conversions of p-NTP to p-p′-dimercaptoazobenzene (DMAB) with Au-NPs@EPSS. When DMAB-functionalized Au-NPs@EPSS acts as the SERS substrate, the detection sensitivity of p-NTP molecules increases by ∼6 times compared with as-synthesized Au-NPs@EPSS.