A study of plasmonic systems using Layer-by-Layer synthesized core-shell nanoparticles
18 September 2018
Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerpen (route: UAntwerpen, Campus Middelheim
Organization / co-organization:
Department of Bioscience Engineering
Silvia Lenaerts & Sammy Verbruggen
PhD defence Ramesh Asapu - Faculty of Science, Department of Bioscience Engineering
The application of plasmonic nanoparticles has found its way in multiple domains of research such as solar cells, plasmonic photocatalysis, Raman spectroscopy and biophotonics. Plasmonic materials possess a unique property called surface plasmon resonance (SPR), which is an oscillation of electron cloud generated in the close vicinity of nanoparticle, when in resonance with the incident electromagnetic radiation. Among the noble metals that exhibit surface plasmon resonance, gold and silver are most commonly investigated as they display SPR over a wide wavelength range and their SPR properties can be fine-tuned to utilize the visible light spectrum of the abundant solar radiation. The application of plasmonic nanoparticles in photocatalysis has found wide applications in the field of pollution control and alternative energy and has helped in overcoming the long existing problem to utilize the photocatalysts in a wide light spectrum and overcome the drawbacks associated with conventional UV light TiO2 photocatalysis. The major mechanisms responsible for enhancement of photocatalytic efficiency by plasmonic nanoparticle are near-electric field, electron transfer and enhanced photon absorption.
The objective of this thesis is to study the major mechanisms responsible for Ag-TiO2 and Au-TiO2 plasmonic photocatalytic systems. To accomplish this, a system was fabricated in such a way that Ag/Au and TiO2 nanoparticles are in contact through a spacer layer. The insulating spacer layer thickness was increased to rule out the near-electric field whereas a conductive spacer layer thick enough to exclude near-electric field allows the electron transfer. The space layer was built around the plasmonic nanoparticle to create (Ag/Au)-polymer core-shell nanoparticles using colloidal layer-by-layer (LbL) method. Comparison of the photocatalytic degradation of model pollutants using Ag-TiO2 and Au-TiO2 plasmonic photocatalytic systems provided a hypothesis to clarify on different mechanisms. Electromagnetic modelling and near-field simulations performed using COMSOL Multiphysics® program acted as a vital mechanistic tool for this study. Raman spectroscopy was used as an experimental evidence to support the near-field simulations explaining the concept that near-field enhancement is only available within the vicinity of few nanometres from the surface of plasmonic nanoparticle. This study provides crucial insights about the properties of noble metal nanoparticles that can be used for optimal design of plasmonic systems.