Abstract
This thesis presents a comprehensive study on the synthesis, characterisation, and application of bismuth oxysulfide (Bi2O2S) and its engineered hetero-structured (Bi2O2S/ZnO, CeO2/Bi2O2S, Bi2O2S/NiTiO3, and BiOBr/Bi2O2S) photoanodes for the photoelectrochemical (PEC) degradation of emerging pharmauceutical pollutants in water which have been detected in aquatic bodies. This research addresses the challenge of recalcitrant nature of pharmaceutical compounds and their persistence against conventional methods, as well the fast rate of recombination associated with single photocatalyst. This work explored the unique properties, electronic properties and structural stability of Bi2O2S heterojunctions photoanode for the advanced, efficient and sustainable degradation process driven by PEC oxidation under visible light irradiation. The Bi2O2S heterojunctions photoanodes were prepared via in-situ hydrothermal method of synthesis to ensure strong contact and interactions between the semiconductors. The choice of semiconductors is based on band-structure alignment and charge transfer potential which mitigate electron-hole recombination which led to the Z-scheme, S-scheme and p-n heterojunction formation for enhanced degradation efficiency.
The synthesised nanomaterials were characterised using XRD, XPS, FE-SEM, TEM, FTIR, UV-Vis DRS, EIS, Photocurrent transient response, and Photoluminescence spectroscopy to elucidate the structural, optical and electrochemical properties. These analyses confirmed the heterojunction formation, visible light absorption, and efficient charge separation properties in the hetero-structured system. The PEC degradation experiments demonstrated that Bi2O2S heterojunctions photoanodes achieved a reasonable degradation of ciprofloxacin and sulfamethoxazole.
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Mechanism studies involving radical scavengers and reactive oxygen species quantification indicated that photoanodes generated sufficient photogenerated holes, hydroxyl radicals and superoxide anion radical, which plays a pivotal role in the degradation of the pollutants. The total organic carbon percentage removal was used to investigate the efficiency of the photoanodes in real wastewater. Furthermore, the heterojunction photoanodes were found to be stable with sustained photoelectrocatalytic performance over multiple pollutant treatment cycle.
The findings in this research shows the potential of Bi2O2S heterojunctions photoanodes as an efficient solution for water treatment application. Moreover, it provided more insights in the aspect of charge carrier dynamics and transfer mechanism. The systematic approach ranging from the synthesis method to the structural tuning to the in-depth characterisations into the extensive application for PEC water treatment establishes a framework for optimising semiconductor heterojunctions for environmental remediation. Therefore, the understanding gained through this thesis does not only demonstrate the viability of Bi2O2S heterojunctions photoanodes, but it also highlights ways of enhancing the properties of other semiconductor systems.