Abstract
This study explores the applications of nanomaterial modified on glassy carbon
electrode (GCE) in the electroanalysis of arsenic and selenium ions in water. GCE
was modified with gold nanoparticles and reduced graphene oxide. Gold
nanoparticle (AuNPs) modified GCE (GCE-AuNPs) was prepared by
electrochemical deposition of gold from 5 mM of HAuCl4 solutions by cycling the
potential from -400 mV to 1100 mV for 10 cycles at a scan rate of 50 mVs-1. GCEAuNPs
was electrochemically investigated using redox probes which are [Fe (CN)
6]3-/4- and Ru (NH3)62+/3+. The current and the reversibility of the redox probes were
enhanced in the presence of modifiers.
The electrochemical determination of selenium by square wave anodic stripping
voltammetry (SWASV) using GCE-AuNPs was carried out under the optimised
conditions: pH 1, deposition potential of -100 mV, deposition time of 60 s and 0.1 M
H2SO4 as supporting electrolyte. A detection limit of 0.64 μg L-1 was obtained. Cu
and Cd were the only significant interferences observed for the electrochemical
detection of selenium. Attempt was also made to sense selenium in tap water,
concentration of 8.86 (± 0.34) ppb Se, was calculated for the tap water. The
electrochemical method was validated with ICP-OES.
Furthermore, arsenic was detected on GCE-AuNPs by SWASV. The sensing of
arsenic was also optimised at different analytical conditions and a detection limit of
0.75 μgL-1 was obtained. Cu, Cd and Hg were the major interferences in arsenic
sensing. Ammonia, EDTA and G3 PPI were used as ligands to mask the
interference effect of copper on arsenic sensing in the bid to remove interference.
Graphene oxide was synthesised by using Hummer`s methods and was further
reduced to reduced graphene oxide using ascorbic acid. The reduced graphene
oxide was used to modify GCE, the modification of GCE with rGO-GCE resulted in
an increase in the electroactive surface area of the electrode which led to enhance
the redox peak of [Fe(CN)6]3-/4- in comparison to the bare GCE. SWASV was used
to detect Se (IV) in water at the following optimum conditions: 0.1 M HNO3 as
supporting electrolyte, deposition potential of -100 mV and pre-concentration time
of 240 s. The rGO-GCE sensor was able to detect Se (IV) to the limit of 2.2 ppb and
was not susceptible to many interfering cations except Cu (II) and Cd (II).
M.Sc. (Chemistry)