Production of silver-loaded zeolites and investigation of their antimicrobial activity
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Date
2008-12
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University of Wolverhampton
Abstract
The production of silver-loaded zeolites either by ion exchange method or by isomorphous
substitution of silver ions into zeolites frameworks and their antimicrobial activity is presented.
Silver-loaded zeolites produced by ion-exchange in this work include silver-exchanged zeolite X,
silver-exchanged zeolite A and silver-exchanged high-alumina Phillipsite. Silver-doped
Analcime was produced by isomorphous substitution of silver ions into the Analcime
framework. The silver-loaded zeolites were characterized by X-ray diffraction (XRD) analysis,
scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, particle size
analysis and Fourier transformed infrared (FTIR) spectroscopy.
Studies showed that the amount of silver ions loaded into the zeolites frameworks differed for
each zeolite. XRD analysis showed little or no changes in the phase purity of all zeolites before
and after ion exchange or before and after substitution of silver ions. SEM analysis and particle
size analysis showed that the morphology of each zeolite particles was closely related before and
after ion exchanged or before and after substitution of silver ions.
The antimicrobial activity of these silver-loaded zeolites was investigated by exposing
Escherichia coli K12W-T, Staphylococcus aureus NCIMB6571 and Pseudomonas aeruginosa
NCIMB8295 suspended in tryptone soya broth (TSB) to the silver-loaded zeolites. The first stage
of the investigation involved the exposure of the strains to silver-loaded zeolites in TSB for a
duration of 24 hours at different concentration of silver-loaded zeolites. The second stage
involved the exposure of the strains to silver-loaded zeolites in TSB over a period of two hours.
The persistency of antimicrobial activity of silver-loaded zeolites was investigated by retrieving
i
each silver-loaded zeolite from the first exposure cultures, washed copiously with de-ionised
water and adding to fresh bacterial suspensions. To understand the mode of antimicrobial activity
of the silver-loaded zeolites, the uptake of silver ions by the strains, composition of fatty acid, as
well as the DNA content of Escherichia coli K12W-T was studied.
The results obtained showed silver ions appeared to elute from the zeolites frameworks into the
TSB in anomalous trend. All three microorganisms were completely inhibited within one hour
with the silver-loaded zeolites retaining their antimicrobial activity. The release of silver ions
from the zeolites frameworks followed first-order kinetics with varying rate constants and halflives.
The fatty acid composition of all strains as well as the DNA content of Escherichia coli
K12W-T were affected by the action of silver ions.
Description
A thesis published by University of Wolverhampton