Abstract
Phosphate is a valuable commodity with its widespread use in fertilisers to improve crop yields, because it is an essential nutrient in plant and animal cell functions. In contrast, in wastewater phosphate is treated as a contaminant to be removed, because of its negative effects when in high concentrations on waterbodies. Metal-organic frameworks (MOFs) are porous materials that are promising for a variety of adsorption-based applications; thus, this thesis explores using MOFs as adsorption materials for the removal of phosphate from wastewater.Chapter 1 introduces the key background, context and aims for this work. Phosphate reserves are predicted to run out in 100 – 300 years, but reserves of phosphate are not distributed evenly across different countries. The reserves in China and The US are both predicted to run out at in approximately 40 years which will then put pressure on other exporters. Phosphate is currently removed from wastewater via chemical dosing. Adsorption via MOFs could be a suitable alternative to achieve low phosphate concentrations, as there is the potential to recover phosphate from these materials.
Chapter 2 lays out the general experimental and simulation methods that have been utilised throughout this work. Chapters 3 – 5 explore the phosphate removal ability from solution of a wide range of MOFs. The effects of functionalisation, defectivity and topology of MOFs on phosphate uptake are systematically investigated. Ring electron donating functionalised groups are shown to result in improved MOF – phosphate interaction energies and higher experimental phosphate uptake. Defective MOFs were shown to have the highest phosphate uptake of the MOFs investigated. Lastly, to reuse the adsorbent the materials need to remain stable, an underlying theme throughout this thesis is the lack of MOF structural stability after exposure to water and phosphate.
Chapter 6 draws Chapters 3 – 5 together so overarching themes across different MOFs are discussed. Throughout this work molecular dynamic simulations have been used to gain insight into the interactions between the MOFs and phosphate. In this chapter the consistency between simulations and experimental results is explored to address whether simulations can be used to screen MOFs computationally for this application. The initial results are promising, especially for MOFs with low experimental phosphate uptake. However, consistency between simulation and experiment for the highest uptake materials is difficult due to the more complex mechanisms that MD simulations do not consider.
Lastly, current methods used in water recycling centres to remove phosphorus from wastewater, include chemical dosing and wetlands. In Chapter 7 these methods have been analysed in terms of running costs and the load of phosphorus removed, in order to understand the phosphorus removal performance required for adsorption materials to compete with the current removal techniques.
| Date of Award | 11 Oct 2023 |
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| Original language | English |
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| Supervisor | Andrew Burrows (Supervisor) & Tina Düren (Supervisor) |