1. The application of voltammetric techniques for the detection and monitoring of the photocatalytic degradation of organic pollutants in water
- Author
-
McCormick, Wesley, Robertson, Peter, and Rooney, David
- Subjects
Photocatalysis ,Electrochemistry ,Water Treatment ,voltammetry ,sensor - Abstract
The aquaculture industry is the fastest growing food production system worldwide. Due to the expansion of this industry, concerns have arisen regarding the environmental impact of aquaculture development. The use of chemicals and drugs such as antibiotics, pesticides, insecticides, herbicides, antifoulants, anaesthetics and disinfectants are routinely employed to reduce disease occurrence with the goal of increased productivity. The overuse of these pollutants can have a negative effect on the surrounding ecosystem and be detrimental to aquatic life. The frequent monitoring of these pollutants is therefore necessary and is an essential step for assessing the potential harmful effects to the environment. Compared with other analytical techniques, electroanalysis is cost effective and delivers rapid results without the requirement for complicated operating procedures. The portability of the technique makes on-site and real-time monitoring an option if required. As an environmental remediation process, heterogeneous photocatalysis is a promising advanced oxidation process (AOP) and is extensively used for the treatment of water containing organic pollutants. Since there is no chemical consumption and no waste sludge generated during the reaction, photocatalysis is an appealing AOP in comparison with other technologies. In this thesis, the application of electroanalysis as a detection method was applied for monitoring different photocatalytic systems. Firstly, electrochemical analysis was utilised for the detection and monitoring of hydroxylated coumarin products when coumarin is used as a probe for indicating hydroxyl radical formation during a photocatalytic process. Compared to the established fluorescence detection method capable of monitoring only 7-hydroxycoumarin, the developed electroanalytical method was able to quantify all the mono-hydroxylated products providing a more accurate determination of hydroxyl radical formation. Secondly, electrochemical methods were developed for the determination of the insecticide, emamectin benzoate (EB) and the herbicide, MCPA, both widely used in Ireland and the UK. Both pollutants were electroanalytically evaluated using a three-electrode configuration consisting of a cathodically pre-treated boron doped diamond working electrode as the working electrode, a silver/silver chloride reference electrode and a platinum wire as the counter electrode. The developed electroanalytical methods were then employed for monitoring the photocatalytic degradation of EB and MCPA. The photocatalytic breakdown of EB and MCPA were performed in a suspension reactor using both TiO2 and ZnO as the photocatalysts. Different photocatalytst loadings, initial pollutant concentration, effect of pH and effect of scavengers were investigated. The degradation of the both EB and MCPA followed first-order kinetics according to Langmuir-Hinshelwood model. Under optimised conditions, complete photocatalytic degradation for EB was achieved in under 50 mins and approximately 70 mins for MCPA.Lastly, a novel immobilised photocatalytic reactor was designed for the degradation of MCPA as a model pollutant. TiO2 was coated on sections of nylon netting using a sol gel technique. The reactor was fabricated using 3D printed baffles to which the TiO2 coated net strips were attached with irradiation being provided by UV LED strip lighting (365 nm). The reactor was optimised in terms of light power, rotation speed and amount of catalyst and thereafter was scaled up to achieve the degradation of 2.5 L of MCPA (10 mg L-1) in approximately 120 mins. The photocatalytic coating-maintained stability over several runs with minimal loss of efficiency. The high photocatalytic activity and simple fabrication processes associated with this reactor make it a prospective method for the removal of contaminants such as MCPA from wastewater. The application of electroanalysis for the monitoring the photocatalytic reactions provided a simple, inexpensive and quick method for obtaining information occurring during the reaction. The added advantage of no sample preparation provided the ability to obtain results in close to real-time giving a truer representation of the processes occurring.
- Published
- 2023