Understanding Mode of Action of Nanoparticles in Water Disinfection: ZnO in Bacteria Killing vs. Complete Photo-degradation

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Type: 
Thesis
Year: 
2013
Students: 
Jumana Fayez Mohammad Ishtaiwa
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Understanding Mode of Action of Nanoparticles in Water Disinfection: ZnO in Bacteria Killing vs. Complete Photo-degradation1.7 MB
Abstract: 
ZnO nanoparticles have been considered to possess potential biological application as efficient antimicrobial agent. In this work, ZnO semiconductor particles were used to disinfect water from bacteria by photo-degrading it with solar sun light. The catalyst 0.1 g was added to 50 mL distilled water pre-contaminated with bacteria. Four different water beakers were prepared each one has 50 mL of ~5 x 105 cfu/mL of bacteria. The solutions were magnetically stirred in a 100 mL glass beaker. The first beaker was exposed to the light source for 60 minutes at 30 °C. In the second one, ZnO nano-catalyst was used in the dark to know if it affects bacteria growth. The third sample was also exposed to light without addition of catalyst to examine light effect on bacteria degradation. The fourth beaker was prepared without catalyst under dark condition. ZnO is known to kill bacteria in the dark, without totally degrading it into mineral species. This has been confirmed in this work, as ZnO nanoparticles killed the bacteria in the dark and the organic contents remained therein. It may also photo-catalyze removal of bacteria under light irradiation. This study aims at investigating mode of action of ZnO nanoparticles in disinfecting water. It is assumed that ZnO nanoparticles would totally degrade Escherichia coli and Pseudomonas aeruginosa under light and convert it into CO2 gas and other minerals. This work showed evidence in this activity, and the bacteria were totally degraded into mineral species. Results of E. coli degradation showed 100 % activity. In the dark, using ZnO nanoparticles, there was some decline in bacteria concentration 20.21%. Under sun light using ZnO nanoparticles, 100% loss of E. coli concentration was observed. These results proved that the activity of catalyst in light conditions better than under dark condition. TOC analysis showed that the concentration of TOC is very low 7.27 ppm for E. coli experiment after using ZnO nanoparticles under sun light condition. This concentration of carbon led to the conclusion that the catalyst and the sun light killed and degraded E. coli. ZnO nanoparticles killed P. aeruginosa under solar sun light 100 %. In the dark condition, the ZnO nanoparticles catalyst killed 50% of bacteria, this result indicates that the activity of the catalyst under sun light condition was better than under dark condition. In P. aeruginosa experiments, the concentration of TOC was very low when the catalyst was used under sun light (8.8 ppm). This result proved that the catalyst has great activity under sun light to kill and degrade P. aeruginosa to gases and other minerals. On the other hand, the concentration of TOC was increased when the catalyst was used without sun light (36.2 ppm). Some factors affecting photo-degradation reaction of P. aeruginosa and catalyst efficiency, such as illumination time, temperature, pH, catalyst amount and bacteria concentration, were studied; All such factors had no effect on P. aeruginosa degradation. This shows the wide applicability of the method described there for water disinfection. The study comes out with an important recommendation that "ZnO nanoparticles can be used as a photo-catalyst for complete mineralization of E. coli and P. aeruginosa under light in different working conditions". More investigations in this direction are therefore needed.