Engineering of Solar-Energy Harvesting Quantum Dot Glasses for Photothermal and Photocatalytic Applications

This PhD investigated the engineering of quantum dot glasses, exploring their potential for solar-energy harvesting in both photocatalytic and photothermal applications. The study covers the fabrication and annealing of various Q-dot glasses and evaluates their characteristics using Raman, UV–visible spectroscopies, X-ray powder diffraction, transmission electron microscopy and photoluminescence. In the photocatalytic field, CdS quantum dots (Q-dots) and Tb3+-doped CdS Q-dots dispersed in a borosilicate glass matrix were studied for the photodissociation of hydrogen sulphide (H2S) into hydrogen gas (H2) and elemental sulphur, showing a substantial increase of 26.2% in hydrogen evolution rate under natural sunlight for Tb3+-doped CdS compared to undoped CdS Q-dot glass, both heat treated at 550 °C. Results from photoluminescence and lifetime showed that the Tb3+-CdS Q-dot glasses' photodissociation energy transfer is more efficient in the excited Q-dot states compared to the CdS-only Q-dot glasses. The photothermal studies investigated the structural and optical characterisation of various Q-dot glasses, including CdS, Tb3+-CdS, and Sm3+-CdS, embedded in a borosilicate glass matrix. The study provides profound insights into the effects of heat treatment, rare earth ion concentration, and remelting of Q-dot formation on electron-phonon coupling, radiation absorption capacity, specific heat capacity, and density. Results from this part revealed that annealing Q-dot glasses, increasing rare earth ion concentration, and remelting Q-dot glass improve the radiation absorption capacity of Q-dot glasses. As radiation absorption capacity increases, the light-to-heat conversion within the Q-dot glass samples rises. A photothermal heating and Newtonian cooling model, integrating specific heat capacity, convective heat transfer coefficient, and photothermal efficiency, was employed to understand temperature increments in the Q-dot glass system. Remarkably, borosilicate glass embedded with 1 wt.% Sm3+ and 2 wt.% CdS exhibited a photothermal efficiency of around 15.3%, whereas undoped borosilicate host glass had a photothermal efficiency of around 7.2%. The findings presented in this thesis highlight the potential of using CdS and rare earth ion-doped CdS Q-dots dispersed in glass matrices as efficient sunlight-to-heat conversion technologies. This interdisciplinary thesis not only advances the fundamental understanding of quantum dot glasses but also offers vital insights for the development of sustainable energy conversion and storage technologies. The multifaceted approach to solar-energy harvesting presented here contributes to the evolving landscape of materials engineering for renewable energy applications.