title: Structural, Optical And Photo-Electrochemical Properties Of H:TiO<sub>2</sub> Nanoparticle, TiO<sub>2</sub>-MoS<sub>2</sub> Nanocomposite And TiO<sub>2</sub>-BiVO<sub>4</sub> Core-Shell Nanoparticle Structures
Creators: name: Mehta, Manan
Publisher: name: The Open University
Year: 2020

description: Photo-electrochemical decomposition of water into oxygen and hydrogen for fuel applications is one of the most important research areas because of the vital need to meet the ever-increasing global energy demands by sustainable and clean methods. For photoelectrochemical water splitting, semiconductor should possess properties of efficient absorption of photons, suitable energy band alignment, stability in the electrolyte and efficient carrier transport. In this work, surface treatment, core-shell nanoparticle synthesis and formation of 1D-2D nanocomposites have been used as the methodologies to achieve the above-mentioned material requirements using low cost methods. The central objective of the present study is to achieve improved visible light absorption and enhanced carrier separation in TiO<sub>2</sub> nanoparticles, which have a major drawback of very poor visible light absorption despite having good stability in the electrolyte and a favorable energy band alignment. <br><br> A detailed literature review has been done to have a comprehensive view of the background of the work done by other researchers to achieve similar objectives. Based on the experiments carried out in this thesis, hydrogen treatment of TiO<sub>2</sub> nanoparticle in mild hydrogen conditions have been observed to enhance photo-electrochemical performance which is related to the observed incease in optical absorption in the visible light and improved surface catalytic properties. The role of Ti<sup>3+</sup> defects for creating the energy states suitable of photon absorption and electronic transport has been established using experimental investigations and DFT based simulations. This is very important, as the nature of defects in terms of its energy position and localized/non-localized energy state is expected to influence the electronic properties of the resulting material. In another study, MoS<sub>2</sub> 2D nanoflakes have been used to form 2D nanocomposites with TiO<sub>2</sub> particles. On addition of MoS<sub>2</sub> nanoflakes with lower energy gap to TiO<sub>2</sub> nanoparticles, 1D-2D nanocomposite samples show increased optical absorption in the visible part of the spectrum along with large area interface between the two components. The present study has resulted in understanding the effect of varying MoS<sub>2</sub> concentration and about 7.5 % of MoS<sub>2</sub> has been found to be an optimal concentration for increasing visible light abosorption without screening the surface catalytic properties of TiO<sub>2</sub>. This is an important result of the present study. BiVO<sub>4</sub>-TiO<sub>2</sub> core shell nanoparticles have also been used for studying photo-electrochemical properties and the increased photo-electrochemical performance has been understood by comparing the structural, optical, photocatalytic properties of core-shell nanoparticles with BiVO<sub>4</sub> and TiO<sub>2</sub> nanoparticles. Changes in the anodic PEC response of pristine TiO<sub>2</sub> nanoparticle to cathodic response observed in BiVO<sub>4</sub>-TiO<sub>2</sub> nanoparticles is an interesting result. This has been explained on the basis of possible changes in semiconductor properties due to small thickness of the shell layer or due to its proximity with the electrolyte. Finally, summary of important results of the present thesis and scope for future research work in this area have been presented.