Polypyrrole(PPy)/titania(TiO 2) nanocomposites were prepared by an in situ oxidative polymerization method with two different oxidants, namely ammonium persulfate (APS) and ferric chloride. The effects of oxidant type and TiO 2 particle loading level on the physiochemical properties of the PPy/TiO 2 nanocomposites were investigated in details. The intermolecular interactions within the polymer nanocomposites were explored by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). While scanning electron microscopy (SEM) was used to characterize surface morphology, transmission electron microscopy (TEM) revealed the well-dispersed TiO 2 nanoparticles in the PPy matrix. The thermogravimetric analysis (TGA) revealed improved thermal stability of PPy with addition of the nanofillers. The nanocomposites prepared by APS oxidation exhibited lower electrical conductivity at room temperature than that of the PPy nanocomposites from FeCl 3 oxidation polymerization. Both nanocomposites and pure PPy follow the three-dimensional variable range hopping (VRH) electron conduction mechanism. The frequency dependent dielectric constants of PPy/TiO 2 nanocomposites were measured in the range of 20 Hz-2 MHz.

The major mechanism responsible for plasmonic enhancement of titanium dioxide photocatalysis using gold nanoparticles is still under contention. This work introduces an experimental strategy to disentangle the significance of the charge transfer and near-field mechanisms in plasmonic photocatalysis. By controlling the thickness and conductive nature of a nanoparticle shell that acts as a spacer layer separating the plasmonic metal core from the TiO2 surface, field enhancement or charge transfer effects can be selectively repressed or evoked. Layer-by-layer and in situ polymerization methods are used to synthesize gold core–polymer shell nanoparticles with shell thickness control up to the sub-nanometer level. Detailed optical and electrical characterization supported by near-field simulation models corroborate the trends in photocatalytic activity of the different systems. This approach mainly points at an important contribution of the enhanced near field.

Graphical abstractHighlights  Ag-polymer-TiO2 composites show ultrastable photocatalytic activity in the long term  Ag-polymer core-shell nanoparticles prepared using affordable layer-by-layer method  Thin polymer shell prevents oxidation and clustering of the silver nanoparticles  Finite element simulations show retention of plasmonic near-field enhancement 3 ABSTRACT Affordable silver-polymer core-shell nanoparticles are prepared using the layer-by-layer (LbL) technique. The metallic silver core is encapsulated with an ultra-thin protective shell that prevents oxidation and clustering without compromising the plasmonic properties. The core-shell nanoparticles retain their plasmonic near field enhancement effect, as studied from finite element numerical simulations. Control over the shell thickness up to the sub-nanometer level is there for key. The particles are used to prepare a plasmonic Ag-TiO2 photocatalyst of which the gas phase photocatalytic activity is monitored over a period of four months. The described system outperforms pristine TiO2 and retains its plasmonic enhancement in contrast to TiO2 modified with bare silver nanoparticles. With this an important step is made toward the development of longterm stable plasmonic (photocatalytic) applications.

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Silver nanoparticles are widely used in the field of plasmonics because of their unique optical properties. The wavelength-dependent surface plasmon resonance gives rise to a strongly enhanced electromagnetic field, especially at so-called hot spots located in the nanogap in-between metal nanoparticle assemblies. Therefore, the interparticle distance is a decisive factor in plasmonic applications, such as surface-enhanced Raman spectroscopy (SERS). In this study, the aim is to engineer this interparticle distance for silver nanospheres using a convenient wet-chemical approach and to predict and quantify the corresponding enhancement factor using both theoretical and experimental tools. This was done by building a tunable ultrathin polymer shell around the nanoparticles using the layer-by-layer method, in which the polymer shell acts as the separating interparticle spacer layer. Comparison of different theoretical approaches and corroborating the results with SERS analytical experiments using silver and silver-polymer core-shell nanoparticle clusters as SERS substrates was also done. Herewith, an approach is provided to estimate the extent of plasmonic near-field enhancement both theoretically as well as experimentally.