Abstract
Bisphenol A (BPA), used primarily in the production of polycarbonates, is one of the most frequently detected synthetic chemicals in the environment. As an endocrine disruptor, it interferes with hormone systems, causing a range of health problems in humans and wildlife. Water treatment plants do not completely remove BPA, and targeted removal techniques for environmental application are not in use.Research into the removal of BPA from water using electrochemical oxidation is an established field. However, the processes typically reported (which rely on indirect oxidation) have been found to have incompatibilities with environmental application. This includes a susceptibility to radical scavenging, incompatibility with the pH of natural environments, and formation of harmful products due to oxidation of the chloride ions found in natural waters.
In this thesis, a bulk electrolysis process which uses low potentials to directly oxidise BPA was explored as an alternative method for environmental treatment. A method for carrying out this oxidation and quantifying the resultant removal was developed and found to be suitable for use at environmental pH.
A pyridine-alkoxide ligated iridium (IV) complex was investigated and found to be suitable for the catalysis of BPA oxidation under environmental conditions. Development of a method for isolating the catalyst onto the anode enabled heterogenous catalysis to be carried out. This catalysis was demonstrated to improve the removal efficiency of electrochemical oxidation for BPA by a factor of 1.92, exceeding the removal efficiency of reported processes under similar conditions.
This type of process has not been widely researched for use with BPA, due to electrode surface blocking, which occurs in direct phenolic oxidation and limits the activity of the electrodes. Use of the surface-bound catalyst was found to be beneficial in the development of a regeneration process. With catalysis an oxidative regeneration process enabled over 70 % of the initial electrode activity to be regained after surface passivation had occurred (where without the catalyst the improvement is negligible). This regeneration enabled a significant improvement in the removal of BPA achievable when running consecutive oxidation processes, demonstrating that with further process optimisation surface blocking may not be a limitation for the application of direct oxidation processes.
Assessment of product formation, at the anode and in the bulk solution, provided new information towards an understanding of reaction pathways. Additionally, this analysis indicated that chlorination does not occur in low-potential oxidation. This finding suggests that this process may be more appropriate for environmental use than typically reported processes, in which chlorination is a growing concern.
The process developed in this work was demonstrated to be applicable to analogues of BPA, which is promising for the future of pollutant remediation, as usage of bisphenols shifts with consumer concern and industrial regulation. Additionally, the process was found to be effective for removal of BPA across a range of environmental concentrations, from highly polluted waters to below the European Union’s predicted no effect concentration.
| Date of Award | 28 Jun 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Petra Cameron (Supervisor), Barbara Kasprzyk-Hordern (Supervisor), Mirella Di Lorenzo (Supervisor) & Peter Wilson (Supervisor) |
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