| dc.description.abstract | Adsorbents are applied in the removal of organic pollutants from wastewaters. One 0 f the
main adsorbents that have been widely used is activated carbon. However, activated carb on is
associated with high operational costs, hence the need to design. low cost alternatives.
Various materials such as magnetic nanoparticles and zeolites have been used in. the
purification of polluted waters with varied merits and demerits. Among the well-studied
water pollutants are pesticide residues. Considering the great potential of zeolites, this study
examined its utility for the removal of a model pesticide, malathion, from wastewaters, The
overall objective of this study was to explore the effects of physico-chemical properties of
sodium exchanged zeolites on the fate of malathion in fresh waters. The effects of Si/Al ratio,
diffusion dimensionality, pore/channel size and particle size of the zeolites mord enite
(MOR), ferrierite (FER), ZSM-5 (MFI) and USY (FAU) on the adsorption and degradation
kinetics of malathion were studied. Water samples for treatments were collected from
Monjolinho River in Brazil. The zeolites were characterized by XRD, FTIR, AAS, SEM, and
27Al-MAS-NMR, and then used to treat 500 mL of water sample in the ratio of one unit cell
of zeolite to one molecule of pesticide in triplicates in the laboratory and analyses done at
selected intervals up to 72 h. The concentrations of the remaining pesticides and their
metabolites in solutions were determined using a GC-MS while the means and standard
deviations were obtained by SPSS. Malathion degradation was enhanced in Na-zeolites with
half-life (tYz) in fresh water of 49.5 h. Additionally, the tYz of 16.5, 30.3, 24.8, and, 29 _7 h
were realized in faujasite, mordenite, ZSM and ferrierite, respectively. The degradation
kinetics of malathion in fresh water was pseudo-first order (R2
=0.996) with rate constant ofO.144±0.0IO h-I
compared to other zeolites. Na-faujasite had the highest percentage
degradation of malathion. High .SiiAI ratio encouraged degradation of malathion.
Effectiveness of dimensionality decreased in the order of 3D, 2D ID. Larger channeled
zeolites enhanced the dissipation of malathion in water. Major degradation products of
malathion in water were malathion mono and dicarboxylic acids and upon introduction of
zeolite were eliminated. Analysis of the zeolites after adsorption by XRD showed enhanced
stability and crystallinity of the zeolite structure. The decrease in weight below 500°C
observed from TGA curves was as a result of malathion thermal decomposition and
desorption. The FTIR, NMR, SEM and EDS detected interaction of malathion molecules
with the zeolite structure without formation of new chemical bonds between malathion and
zeolites | en_US |
