Abstract
Piezocatalysis based on piezoelectric materials offers new approaches to chemical transformations, such as the production of hydrogen from water or the production of hydrogen peroxide from oxygen. In this study, two materials namely (i) a purely organic graphitic carbon nitride (g-C3N4 in chapters 3 and 4), which is potentially piezoelectric, and (ii) a purely inorganic barium titanate (BaTiO3 in chapters 5 and 6) as a ferroelectric and piezoelectric material, are investigated. The synthesis and characterization of the two materials are reported, and the catalytic formation of hydrogen peroxide is studied. In this thesis, the main aims are (i)to develop an understanding of piezocatalytic processes in the production of hydrogen peroxide, (ii) employing biomass (using isopropanol as a model for biomass) in thepiezocatalytic process, and (iii) degrading model pollutants (indigo carmine and rhodamine B) in piezocatalytic processes. There are seven chapters.
Chapter 1 introduces piezo catalysis (contrasting to photocatalysis) and piezocatalytic materials. Chapter 2 provides background information about the experimental methods and tools employed in this study. In Chapter 3, a detailed investigation is presented of the photocatalytic ability of g-C3N4 to produce hydrogen peroxide from oxygen and water in the presence of a reducing agent (isopropanol). In contrast to the common approach of suspending the catalyst in water, here solid g-C3N4 (containing 2 wt% water) is employed directly for the formation of hydrogen peroxide in light. Once formed, the hydrogen peroxide can be stored essentially without any decomposition. Upon contact with water, the hydrogen peroxide is released from the g-C3N4 solid. The immobilization of g-C3N4 particles into a molecularly rigid microporous host (PIM-1) is demonstrated to recover and reuse the catalyst. The PIM-1 polymer allows embedding catalysts without capping surface sites and is therefore ideal for maintaining catalyst activity.
In Chapter 4, suspended g-C3N4 particles (typically micron-sized) in water are investigated under ultrasound irradiation (in a thermostatted ultrasound reactor). The degradation of indigo carmine (negatively charged) and rhodamine B (positively charged) are monitored. Products such as hydrogen are observed, and the mechanism is discussed for the case of different gases. Gases were chosen to clarify the possible catalytic process and to comprehend their function in the sonochemical synthesis of reactive nitrogen species (RNS) and reactive oxygen species (ROS).
In Chapter 5 barium titanate (BaTiO3 suspended in water; particle size typically 500 nm) is employed as a piezocatalyst for the degradation of rhodamine B. Stirring regimes are investigated to optimise piezocatalyst performance. Using simple mechanical stirring and BaTiO3 particles, rhodamine B dye molecules are removed from the solution. After evaluating a range of stirring parameters, it is demonstrated that there is an interplay between stirring speed, volume of liquid, catalyst structure, and rate of dye removal. The maximum degradation rate was 12.05 mg g−1 catalyst after 1 h of mechanical stirring at favorable conditions. This development provides a new insight into a low-energy physical technique that can be used in environmental remediation processes.
In Chapter 6, barium titanate catalyst particles are embedded into a molecularly rigid polyamine (PIM-EA-TB) to allow recovery and reuse of the catalyst in the production of hydrogen peroxide from oxygen and isopropanol. In this thermocatalytic process, the polymer host material is shown to accelerate the catalytic reaction. The hypothesis of a molecular cavity effect in the rigid polyamine host is discussed. Chapter 7 provides a summary and outlook on future work.
| Date of Award | 7 May 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Frank Marken (Supervisor) & Chris Bowen (Supervisor) |
Keywords
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