Abstract
M.Sc.
The contamination of water by toxic compounds is one of the most serious
environmental problems today. These toxic compounds mostly originate from
industrial effluents, agriculture runoff, natural sources (e.g. heavy metals in water
from rocks and soil erosion) and human waste. The contamination, which is both
“organic” and “inorganic” has an impact on the environment and human health.
The demand for water and the pressure to re-use this valuable resource has
increased the need for improved techniques and materials to remove pollutants
from water. The Nanomaterials Science research group at the University of
Johannesburg has focused on developing synthetic polymers that can be
employed in water treatment and pollutant monitoring. Recently, cyclodextrins
(CD) and carbon nanotubes (CNTs) have been included in polymers for this
application. For example, CD-co-hexamethylene-/toluene-diisocyanate
polyurethanes and CNT-modified equivalents have been developed and have
been successfully applied in removing organic contaminants from water to very
low levels.1
Calixarenes are synthetic analogues of cyclodextrins that can be exploited via
chemical modification to express a range of properties. In the present study,
calixarenes, thiacalixarenes and carbon nanotube-based polymeric materials
incorporating these molecules have been synthesised, characterised and tested
for removing both organic pollutants (such as p-nitrophenol) and inorganic
pollutants (Cd2+, Pb2+) from water. Lead(II) and Cadmium(II) are a threat in South
Africa because of their toxicity, and while p-nitrophenol is much less of a problem it
represents a useful model organic pollutant. The absorption capacity of the
polymers towards heavy metals and organic contaminants was tested by mixing
the polymer with synthetic water containing known concentration of the
contaminants at about 10 mg/L. Atomic absorption spectrometry (AAS) and
ultraviolet-visible spectrometry (UV-vis) were used to determine the levels of
heavy metals and organic contaminants, respectively. The target pollutants (Cd2+,
1 see KL Salipira MTech dissertation, University of Johannesburg 2008
Pb2+ and p-nitrophenol) were all successfully removed from water by the various
polymers, however the degree of removal and loading capacities of the polymers
differed. This information gives some insight into what functional components are
needed for making successful adsorbents. It was observed, for example, that ptert-
butylcalix[8]arene/hexamethylene diisocyanate (C8A/HMDI) had a higher
adsorption capacity towards p-nitrophenol and Pb2+ than towards Cd2+, and also a
higher capacity than the corresponding calix[4]arene polymers with smaller
calixarene cavities.