Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Due to the adverse human health effects associated with mercury (Hg) toxicity, an
innovative method for inorganic mercury (Hg2+) determination in aqueous solutions
was investigated. The method of Hg2+ determination involved the use of a Hg2+
selective chemosensor immobilised onto an indium tin oxide (ITO) coated electrode
in a photoelectrochemical cell. Upon light activation and in the presence of Hg2+ the
fluorescent chemosensor absorbed a photon, and charge separation would occur
according to the nature of the semiconductive material coated onto the ITO substrate.
The charge separators and semiconductors investigated were an n-type carrier TiO2,
polyaniline (PANI) and copolymers of polyaniline and 2-bromoaniline (P[A-co-2-
BrA]s) with different monomer ratios.
The polymer and copolymer coated ITO working electrodes used in the Hg2+ sensitive
photoelectrochemical cell were electrochemically evaluated. The results demonstrated
that the ITO coated with PANI had superior conductive and semiconductive
properties compared to ITO coated with P[A-co-2-BrA]s. The ITO glass substrates
were coated with TiO2, PANI or P[A-co-2-BrA]s, followed by the fluorescent
chemosensor, a rhodamine 6G derivative (RS). The electrodes were subsequently
photoelectrochemically evaluated in a photoelectrochemical cell in the presence of
Hg2+. The PANI-RS coated electrode behaved as a photocathode in the presence of
Hg2+ under illumination. The PANI-RS photoresponse increased with increasing Hg2+
concentration in the range 10 to 150 μg L-1, with a limit of detection of 6 μg L-1.
ITO coated with TiO2 (ITO/TiO2) followed by a composite of PANI and RS had a
linear photoanodic response in the Hg2+ concentration range of 10 to 200 μg L-1 and a
limit of detection of 5 μg L-1. ITO and ITO/TiO2 coated with the P[A-co-2-BrA]s and
RS had considerably lower photoresponses towards Hg2+ in aqueous solutions
compared to PANI-RS. The photoresponses decreased with increasing 2-bromoaniline
content.
The PANI and P[A-co-2-BrA]s coated ITO and ITO/TiO2 electrodes were then also
coated with another rhodamine 6G derivative with a thiolactone moiety (RT). The
PANI coated electrode yielded a photocathodic response in the Hg2+ concentration range 0.2 to 5 μg L-1. ITO coated with TiO2 had no photoresponse towards Hg2+ due
to repulsive forces between TiO2 and the RT molecules.
The photoresponses of the working photoelectrodes towards Hg2+ were further
evaluated in a custom photoelectrochemical Hg2+ detector. The photoresponses of
PANI-RS and PANI-RT gave qualitative results for the presence of Hg2+ in aqueous
solutions in concentrations as low as 2 μg L-1. / AFRIKAANSE OPSOMMING: Weens die negatiewe gesondheids aspekte toegeskryf aan Hg2+ vergiftiging is ‘n nuwe
innoveerende metode van Hg2+ deteksie in wateroplossings ondersoek. Die
voorgestelde metode van Hg2+ deteksie behels die gebruik van ‘n Hg2+ selektiewe
chemosensor geimmobiliseer op ITO elektrodes in ‘n fotoelektrochemiese sel.
Met lig aktivering en in die teenwoordigheid van Hg2+, absorbeer die fluoreseerende
chemosensor ‘n foton, gevolg deur lading skeiding, soos bepaal deur die aard van die
halfgeleidende material wat op die ITO platjies bedek is. Die halfgeleiers wat
ondersoek was, was TiO2, PANI en ko-polimere van PANI met 2-bromoanilien.
Die polimeer en kopolimeer bedekte ITO werkende elektrodes wat in die Hg2+
sensitiewe fotoelektrochemiese sel gebruik is, is elektrochemies geevalueer. Daaruit is
gevind dat ITO bedek met PANI superieure geleier en halfgeleier eienskappe het in
vergelyking met die ITO wat bedek is met P[A-co-2-BrA] kopolimere. Die ITO glas
plaatjies is bedek met TiO2, PANI en die P[A-co-2-BrA] kopolimere gevolg deur die
fluoresseerende chemosensor, RS. Die elektrodes is onderskeidelik
fotoelektrochemies getoets in ‘n fotoelektrochemiese sel in die teenwoordigheid van
Hg2+. Die PANI-RS elektrode het soos ‘n fotokatode opgetree in die teewoordigheid
van Hg2+ onder beligting. Die foto-reaksie van die PANI-RS elektrode teeonoor Hg2+
het liniêr toegeneem van 10 μg L-1 tot 150 μg.L-1 met ‘n limiet van deteksie op 6 μg
L-1.
ITO/TiO2 wat bedek is met ‘n samestelling van PANI en RS het ‘n fotoanodiese
reaksie gehad teenoor Hg2+ in die liniêre reeks van 10 tot 200 μg L-1 met ‘n deteksie limiet van 5 μg L-1. ITO en ITO/TiO2 bedek met die P[A-co-2-BrA] kopolimere het
heelwat laer fotoreaksies getoon teenoor Hg2+ in waterige oplossings Die fotoreaksie
het afgeneem met toeneemende 2-bromoanilien inhoud van die kopolimeer.
Die PANI en P[A-co-2-BrA] kopolimere bedekte ITO en ITO/TiO2 elektrodes is
verder bedek met ‘n tweede rhodamine 6G afgeleide, RT. Die ITO/PANI bedek met
RT het weer ‘n fotokatodiese reaksie gehad teenoor Hg2+ in die konsentrasie interval
0.2 tot 5 μg L-1. Die ITO/TiO2 elektrode bedek met die PANI-RT samestelling het
geen fotoreaksie gehad teenoor Hg2+ weens afstotende kragte tussen die TiO2 and RT
molekules.
Die fotoreaksies van die verskeie werkende elektrodes teenoor Hg2+ is verder getoets
in ‘n tuisgemaakte fotoelektrochemiese Hg2+ detektor. Die fotoreaksies van die PANIRS
en PANI-RT samestellings op ITO het kwalitatiewe resultate gelewer vir die
teenwoordigheid van Hg2+ in waterige oplossings in konsentrasies tot so laag soos 2 μg L-1.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5213 |
| Date | 12 1900 |
| Creators | Chamier, Jessica |
| Contributors | Crouch, Andrew M., Leaner, Joy J., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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