Transition Metal Chalcogenide (Cadmium Sulfide) Nanoparticles: (Bio)synthesis, Characterization and Photoelectrochemical Performance

Abstract

Cadmium sulfide (CdS) is one of the most commonly used and studied II/VI semiconductor materials due to its electron energy band structure with desirable band edges and direct band gap. CdS nanoparticles (NPs) are widely applied in different areas such as biosensing, antibacterial agents, photocatalytic hydrogen evolution, photoelectrochemical (PEC) energy conversion, and photovoltaic devices. Biosynthesis is an innovative, environmentally friendly route for the synthesis of CdS NPs. Specifically, bacterial precipitation of CdS NPs provides a simple, scalable production method. Our previous research shows that CdS NPs can be extracellularly precipitated with tunable CdS crystallite sizes ranging from 5 nm to over 15 nm in diameter. In this dissertation, I investigated the potential PEC application of bacterially precipitated NPs and the engineering of their band structure. The results show that i) bacterially precipitated CdS NPs and their devices performed competitively when compared to chemical bath deposited (CBD) CdS NPs and their devices; ii) the performance difference is likely due to a layer of organic ligands that cap the bacterially precipitated CdS NPs and changed the carrier dynamics; and iii) the band structure of bacterially precipitated CdS NPs can be tuned by using different capping ligands. Collectively, my research demonstrates a promising approach for the biosynthetic precipitation of CdS NPS with tunable electronic properties and their application potential in photoelectrochemical devices.