Technical Papers and Presentations

The mechanism of plasmonic photocatalytic systems is still debated as the two major mechanistic pathways, i.e., near-electric field and hot electron transfer for semiconductor photocatalytic systems coupled with small size (dia. < 25 nm) plasmon nanoparticles, are specific to the photocatalytic reaction[1–3]. In this work, we focus on elucidating the dominating mechanism of gold and silver plasmon-enhanced TiO2 photocatalysis using polymer spacer layers for application in photocatalytic oxidation of stearic acid and acetaldehyde. The designed plasmonic photocatalytic system is shown in Figure 1, in which the semiconductor photocatalyst and the plasmon nanoparticle are separated by either an insulating or conducting spacer layer. By using a thick enough insulating or conducting spacer layer, the near-electric field can be ruled out, whereas a thin spacer layer allows the beneficial effect of the near-electric field in reaction rate enhancement. The experimental results are compared with the near-electric field simulations by building FEM models of plasmonic photocatalysts using COMSOL Multiphysics. In the near-electric field modeling studies, Maxwell’s wave equations are solved with respect to the scattered electric field. 3D models of nanoparticles, and core-shell nanoparticles with varying polymer shell thickness, which acts as a spacer layer, were built in the wave optics physics in COMSOL Multiphysics (version 5.3). A plane wave polarized in the Z-axis direction and propagating along the X-axis direction was solved for the scattered field in a wavelength domain study. The normalized electric field enhancement is estimated using the formula |E|2/|E0|2, which emanates within a few nanometers from the surface of the plasmon nanoparticle[4]. The near-electric field simulation results shown in Figure 2 corroborate the experiments by providing crucial insight that near-field enhancements are vital for the photocatalytic reaction rate enhancement and has the highest benefit when the semiconductor photocatalyst and plasmon nanoparticle are in direct contact compared to interfacial contact.