An-Najah Staff

Abstract Several procedures are commonly used for water disinfection from bacteria. Unfortunately each procedure has its shortcomings. The most important shortcoming is the formation of disinfection by-products. Photo-degradation of microorganisms using photo catalysts (such as ZnO) could be a good alternative. However, ZnO is a wide band gap (3.2 eV) semiconductor, and demands UV irradiations for excitation. Therefore, sensitization of ZnO is necessary here to make use of the solar light for the photo-catalyst excitation. In this work, ZnO semiconductor particles, combined with safe low cost sensitizer (the natural dye anthocyanin) were used to disinfect water from bacteria by photo degrading it with solar simulator light. Both nano- and micro-sized ZnO particles were investigated here. The natural dye can sensitize ZnO to the visible light, as the dye has smaller band gap and absorbs in the visible region. More than 90% degradation percent was achieved in 90 minutes under solar simulator, with improvement ~10% than the naked ZnO. Control experiments that were conducted in absence of catalyst or light showed only small loss in bacteria concentration. Sensitized ZnO catalyst worked well under purely visible light. Using a cut-off filter (eliminating 400 nm and shorter wavelengths) confirmed that. The sensitized catalyst activity was almost not affected by eliminating UV from the solar simulator light. ZnO nano-particles (with average size 20 nm) were prepared and used for water disinfection. They were characterized using UV-Visible absorption spectrophotometry, photoluminescence spectrometry, XRD and SEM techniques. Sensitized ZnO nano-particles showed higher catalytic activity than the sensitized ZnO with large particle size (micro-size). Complete degradation was achieved with Nano-particles under the same conditions. Some factors affecting photo-degradation reaction and catalyst efficiency, such as illumination time, temperature, pH, catalyst concentration, contaminant concentration and dissolved organic and inorganic impurities, were studied. Changing temperature didn’t significantly affect the catalyst efficiency. The amphoteric nature of ZnO decreased the effect of changing pH value for the reaction medium on the catalyst efficiency. The nominal amount of the used catalyst affected the degradation, and there was an optimum weight that should be used for maximum benefit. Increasing the initial concentration of contaminants enhanced the catalyst activity. The presence of impurities (organic and inorganic) affected the catalyst activity in different manners. Catalyst recovery after reaction completion was achieved by simple means, and the recovered catalyst showed good sound activity on reuse. Re-dying the re-used catalyst restored its efficiency under solar simulator.