Executive Summary : | Photocatalysis is an effective approach to fulfil multiple objectives of solar energy harvesting, driving chemical reactions to produce value added products and environmental pollution mitigation. Achieving higher efficiency in a photocatalysis process is therefore always desired. However, recombination of the photogenerated charges is one of the main bottlenecks that reduces overall efficiency of the process. This proposal aims to achieve higher photocatalytic efficiency in vertically aligned and ordered nanostructures by creating tailored metal vacancy defects that are known to create spin polarization, which, in turn, reduces the recombination of photogenerated charges. Based on this background, the proposal will investigate two fundamental and relevant questions: (i) can spin-polarization be achieved in ordered and aligned one-dimensional nanostructures such as TiO2 nanorod arrays? (ii) Can the density of metal vacancies be precisely controlled so that spin polarization can be tailored? To answer these, two metal oxide photocatalyst systems, binary TiO2 and ternary BiFeO3 will be explored in aligned nanostructure (nanorods) morphology for tailoring the metal vacancies. such highly ordered, vertically oriented nanorod arrays will be chosen to facilitate directional transport of charges, which in itself aids photocatalytic process by reduced scattering. In addition to employing the reported chemical protocol, we will explore low energy ion-beam irradiation (100 keV Ar ions) to create metal vacancies in a highly controlled manner, where low energy ensures minimal damage and inertness will keep the chemical nature unchanged. The extent of spin polarization will be measured through a host of measurements such as electron spin resonance spectroscopy, magnetic measurements, positron lifetime spectroscopy and time-resolved photoluminescence spectroscopy. In particular, a special lifetime measurement set-up will be built-up wherein, the lifetime of photogenerated electrons will be measured with and without magnetic field to investigate the field dependent enhancement of lifetime. The modified materials will be used for photoelectrochemical water splitting and photocatalytic CO2 reduction experiments and the quantified yield will be compared with values from pristine material to demonstrate the resultant change in efficiency. PI's previous experience and expertise with metal oxide nanostructures and ion-beam modification will greatly help towards fulfilling the objectives of the project. |