Multifunctional nanomaterials designed for the detection and removal of priority contaminant substances from waste and drinking water

Frost, Mark Stuart (2015) Multifunctional nanomaterials designed for the detection and removal of priority contaminant substances from waste and drinking water. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Heavy metal pollution in waste water and drinking water is a growing concern, with the European Commission producing the Water Framework Directive (WFD) and Drinking Water Directive (DWD) to set ‘acceptable’ levels for priority chemicals in water systems. Taking into account the innovative work being carried out in the area of nanosensors, this research has produced several methods for the quantitative analysis of some aqueous metal ions. This study explored the use of citrate functionalised Au and Ag NPs and CuS nanoclusters Citrate functionalised Au and Ag NPs were synthesised to develop for a localised surface plasmon absorption spectroscopy analysis technique, to determine the concentration of a Pb and Hg, respectively. This study concentrated on the molecular interactions of the surface-bound citrate molecules with the nanomaterial surface, and the metal ions in solution. Computational simulations into these interactions were also carried out as a comparison. The citrate speciation for the AuNPs and AgNPs was significantly different, showing single and double carboxylate coordinated molecules respectively. There were also differences in the heavy metal/citrate interaction. Notably, Pb2+ ions produced a rapid coagulation of the AuNPs, which was not observed when using AgNPs, demonstrating that the noble metal used for the fabrication of the nanomaterial has an effect on the nature of the metal/citrate bonding interactions. This coagulation produced a unique, very broad UV-Vis absorption spectrum, due to plasmon coupling. The Hg2+/AgNP sample also produced localised surface plasmon absorption spectra that were unique when compared to all of the other metal ion/NP solutions. The citrate functionalised AuNP were also incorporated into a SERS-based technique for the detection of Pb. This technique provided good results, with a low limit of detection (~25 ng/l) and a low relative standard deviation of 0.147%, over a wide range of practical concentrations (~25 ng/l to 25000 ng/l). Although this method is non-selective, this technique would be highly useful for analysis of solutions after a Pb2+ ion-selective preconcentration step has been employed. The most useful and impressive results, for any of the nanomaterial based chemical sensors produced in this study, were those obtained for the CuS cation-exchange nanosensor. The material was found to not only be sensitive to the concentration of Hg2+ ions in aqueous form, but also highly selective to Hg2+ ions in a solution containing several different metal ions commonly found in water samples (comparing the results from a solution containing just Hg2+ ions and the CuS nanoclusters, and the mixed metal solution containing the CuS nanoclusters produced a correlation coefficient of 0.9985). The data clearly shows that CuS cation-exchange nanosensor is extremely useful for the selective detection and accurate quantification of Hg2+ ions at low concentrations between 525 ng/l to 5250 ng/l. Therefore, this method is exceptionally suitable for the detection of Hg2+ ions at levels set by the DWD as ‘acceptable’. Ultimately, this method entirely achieves the aims and objectives set for this research project, for the DWD.