M.Sc. / Water that is free from toxic organic pollutants is essential to human health and the environment at large. Organic contaminants may affect the endocrine system of animals and humans, even when present in very low concentrations (i.e. levels ppb). Current technologies fail to remove these organic compounds efficiently from water at ppb levels. So, the development of new technologies that are capable of removing and degrading organic pollutants from water is crucial. Hence, recently in our laboratories cyclodextrin (CD) polymers have demonstrated that they are capable of removing organic pollutants from water at ppb levels. The research has also demonstrated that both functionalized and unfunctionalized CD polymers can remove organic species to as low as parts per billion (ppb) from water. In this project, Si and Ti based compounds which have been reported to degrade organic compounds through photocatalysis in an aqueous media were incorporated. Firstly, attempts were made to attach the silicon (Si) and titanium (Ti) pendent chains onto the CD moiety to form silicon-based cyclodextrin (Si-CD) and titanium based cyclodextrin (Ti-CD) precursors. The Si-CD precursor was synthesized by attaching the 3-(triethoxysilyl)propyl isocyanate onto the native b-CD moiety. The synthesis of the Si-CD precursor was successful and high yields (80%) of the product were obtained. A hydrolysis of this Si-CD precursor in an inert atmosphere led to the formation of silanol. This was followed by curing the silanol in air, after adding TiO2 nanoparticles, and the Ti-CD precursor was formed. The polymerization of Si-CD with suitable bifunctional linkers was a success and water-insoluble polymers were produced. An attempt to polymerize the Ti-CD precursor failed, because the precursor was decomposed. The Si-CD polymers were tested for their capabilities to encapsulate and destroy organic pollutants from water. 1H NMR, FT-IR and EDX spectroscopic techniques were used to prove the formation of the Si-CD and Ti-CD precursors and their corresponding polymers. The Si-CD polymers showed capabilities of being able to remove organic pollutants (33-55%) from water. Unfortunately, the removal is slightly less efficient than the corresponding native CD polymers. However, their efficiency in removing organic pollutants improved when exposed to light. Moreover, the polymers formed display good thermal stabilities, since they decompose at about 300- 400°C. This is observed from the thermograms obtain ed from DSC and TGA. Their morphological studies showed that most of the Si-CD polymers formed were crystalline. This was observed from the SEM images obtained. Based on the information provided by the FT-IR spectroscopy, the synthesis of the Ti-CD precursor was success. However, the challenge was the fact that it decomposed after a while. Hence, it was difficult polymerize it into a water insoluble polymer. The explanation of this phenomenon is not yet established.

D.Phil. (Chemistry) / The problem of maintaining good quality of water for domestic use and for aquatic life remains a challenge. Water sources are often contaminated with pollutants from natural sources such as volcanic eruptions and by human activities such as manufacturing industries, mining, water-purification processes, agricultural activities and a vast number of other activities. Water-purification processes used by municipal authorities are designed to remove most of the pollutants but some trace amounts will always remain and have been detected in drinking water and treated waste water reservoirs. These trace amounts pose a threat to human health and the well-being of aquatic life. The detection of these trace amounts of pollutants is often carried out by laboratory-based techniques that require sophisticated, expensive instruments and often require extensive sample preparation and pre-concentration. Simple, quick and in-field detection methods are necessary especially for remote small communities with limited or no access to laboratories. Optical detection systems offer hope as a solution to this problem. In this work newly developed fluorescence-based molecular sensors for the detection of pollutants in water were developed, characterised and tested for their sensing abilities towards organic and inorganic pollutants. The fluorescent probes for organic pollutants were designed based on the host-guest chemistry of the cyclodextrin molecule. Azo dye-modified β-cyclodextrins were synthesised and linked via ethylene glycol and epichlorohydrin to produce the sensors that were then tested for their sensing response towards chlorophenols and small aliphatic chlorinated alkanes which are often formed during the disinfection of water in the purification process. The sensor molecules were characterised by UV-Vis, FT-IR and 1D and 2D NMR spectroscopy. The amount of cyclodextrin in each sensor molecule was quantified using the anthrone method (67%) as well as by 1H-NMR spectroscopy (72%). To demonstrate the host-guest interaction of the sensor molecules, isothermal titration calorimetry (ITC) was used. ITC measurements showed that modifying β-cyclodextrin and using linkers did not alter its host-guest interaction with guest molecules as demonstrated by the stoichiometry, n, stability (or binding or association) constant (K) and thermodynamic parameters of the interaction. The sensor molecule linked via ethylene glycol showed selectivity towards 4- chlorophenol among the chlorophenols investigated and has the potential to be used in a sensor for the detection of 4-chlorophenol. The sensor molecule linked via epichlorohydrin showed sensitivity towards chloroform, a typical disinfection by-product. These experimental results showed that the sensor molecules could be used for quick on-field detection of chlorinated organic compounds in water. Sensor molecules for inorganic pollutants were based on the complex formation of crown ethers with metal ions. The sensor was formed by modifying a dibenzo-18- crown-6 ether molecule with an azo dye. The sensor was then characterised using UV-Vis spectrophotmetry, FT-IR and NMR spectroscopies as well as mass spectrometry and CHNS elemental analysis. The sensor molecule was then subjected to different metal ions and the fluorescence change of the probe observed. Interestingly, the sensor was highly sensitive and selective to mercury (II) and Cu (II) ions in water. Mercury (II) is one of the most hazardous heavy metals among the heavy-metal ions found in environmental waters and its early detection in water sources is important. The synthesised molecular sensor can therefore be incorporated into a simple hand-held gadget with a light source and be used for on-field detection of mercury (II) ions in remote areas.