Abstract
Ph.D. (Chemistry)
One of the main challenges in heavy metal adsorption is the lack of selectivity (or specificity) for a pollutant by an adsorbent. This lack of selectivity may compromise the adsorption efficiency and the effectiveness of the adsorbent for the adsorption of a target pollutant. The solution to this problem lies in imprinting a memory for the target pollutant on the adsorbent so that when the adsorbent is required for adsorption it will choose to bind with the target pollutant even in the presence of other pollutants. In this study, ion-imprinted polymers (IIPs) were synthesized for the selective removal of Cr(VI) and Hg(II) from aqueous solutions. Furthermore, sulphur-containing ion imprinted polymers (S-IIPs) were used in the selective adsorption of Hg(II) and in the electrochemical detection of Hg(II) from water. The ion-imprinted polymers were derived from sodium carboxymethyl cellulose and synthesized via a surface imprinting method.
In the first part of this thesis, IIPs were applied for Cr(VI) adsorption. The ligand, ethylenediamine was used for complexation with the Cr(VI). For comparative purposes, non-ion imprinted polymers (NIPs) were also synthesized. The obtained IIPs and NIPs were characterized by various techniques such as X-ray photoelectron spectroscopy (XPS), 13C Nuclear magnetic resonance (13C NMR) analysis, Energy dispersive X-ray spectroscopy (EDS) and Brunauer-Emmet-Teller (BET) surface area analysis. EDS and XPS spectrums showed the presence of nitrogen in the IIPs and NIPs. The surface area of the IIPs was larger than that of NIPs an aspect which had a significance in the adsorption performances for the Cr(VI). The adsorption of Cr(VI) was favourable at low pH, while the desorption process was best at high pH. The kinetics of adsorption followed a pseudo-second-order model while the Langmuir adsorption isotherm provided the best fit with a maximum adsorption capacity of 177.62 mg g−1 at 25 oC. The Langmuir adsorption capacity for the non-imprinted polymers (NIPs) at 25 oC was 149.93 mg g−1. Thermodynamic parameters indicated an endothermic process and spontaneous adsorption of Cr(VI) on the polymers. The selectivity of the IIPs was remarkable compared to the NIPs. Furthermore, the IIPs adsorbent was successfully recycled 5 times using 0.1 M NaOH as a leachate; 98% Cr(VI) was desorbed during the last adsorption-desorption cycle.
In the second part of the study, sulphur containing ion imprinted polymers (S-IIPs) were applied for the uptake of Hg(II) from aqueous solution. Cysteamine, which was used as the...