| dc.description.abstract | The current study involved electrocatalytic reduction of the organochlorine pesticide
residues which are, (3aR,7aS)-2-[(trichloromethyl)sulfanyl]-3a,4,7,7a-tetrahydro-lHisoindole-
l,3(2H)-dione (Captan) and 1,1, I-trichloro-2,2-bis(p-methoxy phenyl) ethane
(Methoxychlor) pesticide residues in homogenous medium (acetonitrile/water 1:1) and
aqueous micellar solution of Sodium dodecyl sulfate (SDS) surfactant. The study
therefore involved the use of cyanocobalamin as a catalyst to lower the reduction
potentials. The studies were carried out by use of cyclic voltammetry method. A three
electrode system was used with Pyrolytic graphite and Glassy carbon as the working
electrodes, Platinum wire as the counter electrode and the Saturated Calomel Electrode
(SCE) as the reference electrode. Potassium ferricyanide was used as a standard for
instrument calibration. Preliminary work also involved cyclic voltammetric study of
cyanocobalamin. Direct reductions of (3aR,7aS)-2-[(trichloromethyl)sulfanyl]-3a,4,7,7atetrahydro-
lH-isoindole-l,3(2H)-dione (captan) and 1,1, I-trichloro-2,2-bis(p-methoxy
phenyl) ethane (methoxychlor) pesticides were carried out using glassy carbon and
pyrolytic graphite as working electrodes. The observed reduction potentials were
approximately -1.34 ± 0.07 V for captan and -1.31 ± 0.03 V for methoxychlor using
pyrolytic graphite electrode. The electrocatalytic reduction of the pesticide residues using
cyanocobalamin was then carried out. The obtained voltammograms gave lower
reduction potential of -0.800 ± 0.054 V for Captan and -0.88 V for methoxychlor in 0.1
M KN03 in acetonitrile/water, respectively. Therefore, a lowering of potential for
reduction of captan and methoxychlor of about 0.54 V and 0.43 V was achieved
respectively, which is an indication of energy saving. Captan and methoxychlor had low
solubility in the SDS solutions. This influenced the concentration of the substrate at the
surface of electrode. As a result the calculated current efficiency was lower than that of
the reduction in 0.1 M KN03 in acetonitrile/water (1: 1). The results of cyclic
voltammetry at glassy carbon and at pyrolytic graphite for catalytic electrode reduction of
captan were compared in order to establish the most suitable electrode with higher
current efficiency under the same conditions. The electrocatalytic reduction of captan by
cyanocobalamin in 0.1 M KN03 in acetonitrile/water (1: 1) using pyrolytic graphite
electrode gave current efficiency of 8.31 ± 0.19, while that obtained for glassy carbon in
the same solution medium and under the same reaction conditions gave lower values of
1.41 ± 0.046. The current efficiency at pyrolytic graphite was therefore higher suggesting
higher surface concentration and unhindered orientation of the substrate on the pyrolytic
graphite electrode. The pesticides were then decomposed in the presence of
cyanocobalamin by bulk electrolysis method for four hours each at constant potential of
1.0 V. The product yield was determined by UVNis Spectrophotometry. The UVNIS
spectrum for captan gave an intense absorption peak at 278 nm. The decomposed
substrate gave three peaks at 260.5 nm, 223.6 nm and 214.9 nm which indicated the
presence of decomposed products. The UVNIS spectrum for methoxychlor gave an
intense absorption peak at wave length of 283.440 nm. High performance liquid
chromatography (HPLC) was carried out for the pesticide standards and the decomposed
samples. The observed retention time of captan standard was 3.3 minutes and its
decomposed products had 4.0 minutes and 4.3 minutes, respectively. The chromatograms
for methoxychlor gave retention time of 3.8 minutes for the standard and the products,
3.2 minutes and 3.4 minutes, respectively. The captan sample after decomposition was
also analysed by Thin layer chromatography, which indicated the presence of two
decomposition products with different Rf values of 0.727 and 0.636 respectively, while
captan standard gave Rf value of 0.152. This confirmed the decomposition reaction. The
study demonstrated effective lowering of the reduction potentials of captan and
methoxychlor in the presence of cyanocobalamin. The method is therefore economical
and environmentally friendly and can greatly contribute in alleviating the levels of captan
and methoxychlor pesticide residues in the water bodies and in contaminated swimming
pools and improve their quality. | en_US |
