Development of Bismuth-Based Oxide Photocatalysts for Simultaneous Photo(electro)catalytic Reactions

<p dir="ltr">Toxic waste and the growing demand for renewable energy have driven research into sustainable solutions. Advanced oxidation processes (AOPs) are gaining attention for their reduced environmental impact compared to conventional technologies. Photoelectrocatalysis and photocatalysis are particularly studied for their low operational costs, minimal energy needs, and reduced by-products. Bismuth-based oxide photocatalysts are among the semiconductors that have received more attention due to visible-light harvesting capabilities and stability in driving chemical reactions. However, issues like poor charge transfer, high recombination rates, and wide band gaps limit their efficiency. The development of efficient and sustainable photocatalysts is crucial for addressing environmental and energy challenges. This thesis explores the development of bismuth-based oxide photo(electro)catalyst for organic substant synthesis and the simultaneous degradation of pollutant and hydrogen generation under visible light irradiation. The synthesized bismuth-based photocatalysts were systematically studied to enhance charge separation and improve overall efficiency.</p><p dir="ltr">Firstly, the study focuses on BiVO₄ with tuneable (110)/(010) facet ratios, synthesized via ethanolamine (ETA)-assisted hydrothermal synthesis for photocatalytic oxidative benzylamine coupling under visible light. The (110)-dominant BiVO₄ demonstrated superior photocatalytic activity at room temperature due to its highly exposed oxidative (110) facets and enhanced charge generation and migration. The catalyst achieved >85% selectivity in converting benzylamine derivatives to imines, showcasing its broad substrate applicability. Mechanistic insights suggest a superoxide radical-assisted (^•O₂⁻) oxidative coupling pathway. This work underscores ETA's role in tailoring BiVO₄ facets, directly impacting oxidative amine coupling, and offers a strategy for designing high-performance catalysts.</p><p dir="ltr">The second part of the study explores a novel Bi₂MoO₆-based photoelectrode (BMO/GO/CC), synthesized <i>via </i>solvothermal methods and supported on carbon cloth with graphene oxide (GO) as a binder. Physical and chemical characterisations confirmed that this composite exhibits the superior photoelectrocatalytic (PEC) performance for malachite green degradation compared to individual photocatalytic (PC) or electrocatalytic (EC) processes. The enhanced PEC performance is attributed to GO's role in improving conductivity and charge migration, reducing electron-hole recombination, and ensuring uniform catalyst deposition for better stability and recyclability. Mechanistic studies confirm that Bi₂MoO₆ facilitates the generation of various reactive oxygen species, driving efficient dye mineralization.</p><p dir="ltr">The final part of the thesis studies the development of p-CuBi₂O₄/n-Bi₂MoO₆ heterostructured photoanode for the PEC degradation of Rhodamine B (RhB) and simultaneous hydrogen (H₂) production in alkaline electrolyte and natural seawater. The heterostructured photoanode achieved higher RhB degradation and higher H₂ production than pristine CuBi₂O₄ and Bi₂MoO₆. The performance enhancement was attributed to the internal electric field, improving charge separation, electron migration, and suppressing recombination. In seawater, RhB degradation was further improved due to its high ionic conductivity, although H₂ production was limited due to competitive chloride oxidation and Mg(OH)₂/Ca(OH)₂ deposition at the Pt cathode. To the best of our knowledge, this study is among the first to demonstrate the PEC potential of the CuBi₂O₄/Bi₂MoO₆ heterostructure in seawater. Mechanistic investigations revealed that direct hole oxidation played a dominant role in RhB degradation, while RhB presence enhanced H₂ production.</p><p dir="ltr">This thesis demonstrates the potential of bismuth-based oxide photocatalysts for enhancing photo(electro)catalytic performance by various development strategies for environmental remediation and renewable energy production. The findings provide valuable insights for designing high-performance photocatalysts and advancing sustainable technologies.</p><p dir="ltr"><br></p>