Complete Mineralization of Enterococcus and Proteus mirabilis Bacteria in Water Using ZnO Nanoparticles Photocatalysts

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يوسف, أميمة خضر محمود
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An-Najah National University
Semiconductors have been widely used in water disinfection and also used in photodegradation of water-organic contaminants. Zinc oxide (ZnO) semiconductor has a band gap (3.2 eV). This wide energy gap makes it very effective on microorganisms under sunlight. The ZnO can be activated with the small fraction of UV solar light. It is cheap, stable and safe. In earlier studies, ZnO particles were assessed in killing gram negative bacteria (E. coli) and (P. aeruginosa) followed by complete mineralization. In this research, ZnO was used in photodegradation reaction as a catalyst for water disinfection from Enterococcus (gram-positive bacteria) and Proteus mirabilis (gram-negative bacteria). Killing and complete mineralization of these two bacteria have not been examined before by photocatalytic systems, to our knowledge. The photodegradation reaction was conducted under solar simulator light. Zinc oxide was lab prepared from the reaction of zinc chloride with sodium hydroxide; the prepared ZnO was characterized using XRD, SEM, photoluminescence (PL) spectra, and electronic absorption spectra. The energy gap was calculated and found to be 3.23 eV. The efficiency of catalyst was assessed based on a bacterial killing percentage; turn over frequency and quantum yield. Effect of different parameters on reaction was studied at different periods of time for both Enterococcus and Proteus mirabilis. About 100% degradation percent was achieved in 30 minutes under a light. Control experiments showed that using light and using ZnO separately promote only small percentage of killing. Other factors that affect photodegradation reaction and catalyst efficiency such as pH, catalyst concentration, contaminant concentration and temperature were studied and discussed. High-performance liquid chromatography (HPLC) was used to determine organic content in water. For both bacteria under photo-the HPLC results confirm the complete photodegradation of bacteria.