Theoretical study on the optical properties of a Pd–TiO2 core-shell nanoparticle as a highly active heterogeneous structure for photocatalytic applications

The influence of TiO₂ shell on both the optical response and associated nearfield intensity of a spherical Pd core has been investigated theoretically by employing the Finite-Difference Time-Domain (FDTD) simulation tool. By devoting the concept of the effective dielectric medium, a theoretical analysis is introduced to provide a better understanding of how combined materials (shell material and host medium) can impact the spectral response of the core-shell nanoparticles and the correlated sensing capability. From the results of the numerical simulations, it is found that the sensing competence of the considered core-shell system is decreased significantly with increasing the shell thickness (t). This implies that a thicker shell acts as a shield, allowing the complex dielectric function of the TiO₂ to dominate the resonance condition and progressively reducing the influence of the surrounding host matrix on the resonance phenomenon. Additionally, independent of the material types, the current study provides a scaling model to properly connect the impact of both the shell thickness and the core size (r) to the related sensing performance, such that t/r should be smaller than a factor of two for the successful usage of such nanoparticles for sensing applications. The current findings provide some detailed guidelines to properly and accurately design plasmon-based sensing platforms constructed from heterogeneous core-shell nanostructures.