Abstract
M.Sc.
The prevalence of toxic contaminants in water remains a huge challenge for water supplying companies and municipalities. Both organic and inorganic contaminants (especially heavy metals) pollutants are often present in water distribution networks. Organic and inorganic pollutants often co-occur in drinking water networks. However, at present there is no water treatment intervention that simultaneously removes organic and inorganic pollutants from water. Additionally, current water treatment technologies fail to remove these contaminants to parts per billion (ppb or µg.L-1) levels. Methods that can simultaneously remove organic and inorganic pollutants to desired levels need to be developed.
In our laboratories, both functionalised and unfunctionalised cyclodextrin (CD) polymers have demonstrated the ability to effectively remove organic species from water at low (ppb) concentrations. Cyclodextrins (CDs), which are cyclic oligomers consisting of glucopyranosyl units linked together through α-1,4-glycosidic linkages, behave like molecular hosts. They are capable of interacting with a range of guest molecules within their cylindrical hydrophobic cavities thereby forming the so-called inclusion complexes. Their solubility in water, however, precludes their application in the removal of organic pollutants from water. This limitation is easily dealt with by polymerizing the CDs into water insoluble polymers with suitable bifunctional linkers. On the other hand, ionic liquids (ILs) have been reported to “absorb” heavy metal ions from aqueous media. ILs are low melting point molten salts that are composed of organic cations (e.g. imidazolium and pyridinium ions) and mostly inorganic anions like Cl–, Br–, [PF6]– and [BF4]–.
In this study, the two systems were combined by an initial attachment of the imidazolium or pyridinium rings to the cyclodextrin moiety. Polymerisation of the resulting cyclodextrin-ionic liquid (CD-IL) complexes with a suitable linker produced the corresponding water insoluble CD-IL polymers. This dual system has shown excellent capabilities for the removal of model pollutants such as p-nitrophenol (PNP) and 2,4,6-trichlorophenol (TCP) and chromium (Cr6+) from aqueous media. However, the CD-IL polymers showed very little affinity for the absorption of cadmium from water. TGA and DSC studies showed that these polymers are stable over a wide range of temperatures (100-400 C).