Sunlight Assisted Photocatalytic Degradation of Ciprofloxacin in Water Using Fe Doped ZnO Nanoparticles for Potential Public Health Applications.

Antibiotic residues in the aquatic environment have the potential to induce resistance in environmental bacteria, which ultimately might get transferred to pathogens making treatment of diseases difficult and poses a serious threat to public health. If antibiotic residues in the environment could be eliminated or reduced, it could contribute to minimizing antibiotic resistance. Towards this objective, water containing ciprofloxacin was treated by sunlight-assisted photocatalysis using Fe- doped ZnO nanoparticles for assessing the degradation potential of this system. Parameters like pH, temperature, catalytic dosage were assessed for the optimum performance of the system. To evaluate degradation of ciprofloxacin, both spectrophotometric as well as microbiological (loss of antibiotic activity) methods were employed. 100 mg/L Fe-doped ZnO nanoparticle catalyst and sunlight intensity of 120,000⁻135,000 lux system gave optimum performance at pH 9 at 30 °C and 40 °C. Under these conditions spectrophotometric analysis showed complete degradation of ciprofloxacin (10 mg/L) at 210 min. Microbiological studies showed loss of antibacterial activity of the photocatalytically treated ciprofloxacin-containing water against Staphylococcus aureus (108 CFU) in 60 min and for Escherichia coli (108 CFU) in 75 min. The developed system, thus possess a potential for treatment of antibiotic contaminated waters for eliminating/reducing antibiotic residues from environment.

Doped ZnO nanoparticles impregnated on Kaolinite (Clay): A reusable nanocomposite for photocatalytic disinfection of multidrug resistant Enterobacter sp. under visible light.

Water contamination by multidrug resistant (MDR) enteric bacteria can be considered as the foremost cause of gastrointestinal infections and poses a threat to global public health. Therefore, there is an urgent need to pursue unorthodox techniques with potential of community scale applications for purging of water borne pathogenic bacteria. We communicate visible-light assisted photocatalytic disinfection (PCD) of an enteric MDR bacterium; Enterobacter sp. using Fe-doped ZnO nanoparticles impregnated on Kaolinite (Clay) (ZnO/K). ZnO/K was synthesized by co-precipitation technique and was found to be more effective than Fe-doped ZnO (ZnO) and Kaolinite for PCD process. Analysis from fluorescence microscopy and electron microscopy (FESEM) proposed complete bacterial cell death via PCD due to damage of bacterial cell membrane. Experimental evidences indicated that O2- could be acting as the most significant component in disinfection of MDR Enterobacter sp. in visible-light assisted PCD process in presence of ZnO/K. Considering the experimental data of Resazurin assay, it is proposed that reactive oxygen species (ROS) generated during PCD might have impeded the oxido-reductase enzyme system of the bacteria and hence trammeling its metabolic activity. Crystal structure and particle size of ZnO/K was found to be unaltered during the photocatalytic process indicating its potential for reusability. When ZnO/K was exposed to HCT-116 Human Colorectal Carcinoma cell lines, about 79% cell survivability was noticed. The synthesized material was successful in completely disinfecting the target microorganism in Zebra Fish model, without producing any adverse effects on the Fish itself, further reinforcing its biocompatibility factor. High effectiveness of PCD process using ZnO/K under visible light in disinfecting enteric MDR bacteria, might have promising outcome as an alternative water disinfection technology to prevent the spread of infectious and resistant bacteria without producing any adverse effect on non-specific flora and fauna.

Disinfection of the Water Borne Pathogens Escherichia coli and Staphylococcus aureus by Solar Photocatalysis Using Sonochemically Synthesized Reusable Ag@ZnO Core-Shell Nanoparticles.

Water borne pathogens present a threat to human health and their disinfection from water poses a challenge, prompting the search for newer methods and newer materials. Disinfection of the Gram-negative bacterium Escherichia coli and the Gram-positive coccal bacterium Staphylococcus aureus in an aqueous matrix was achieved within 60 and 90 min, respectively, at 35 °C using solar-photocatalysis mediated by sonochemically synthesized Ag@ZnO core-shell nanoparticles. The efficiency of the process increased with the increase in temperature and at 55 °C the disinfection for the two bacteria could be achieved in 45 and 60 min, respectively. A new ultrasound-assisted chemical precipitation technique was used for the synthesis of Ag@ZnO core-shell nanoparticles. The characteristics of the synthesized material were established using physical techniques. The material remained stable even at 400 °C. Disinfection efficiency of the Ag@ZnO core-shell nanoparticles was confirmed in the case of real world samples of pond, river, municipal tap water and was found to be better than that of pure ZnO and TiO2 (Degussa P25). When the nanoparticle- based catalyst was recycled and reused for subsequent disinfection experiments, its efficiency did not change remarkably, even after three cycles. The sonochemically synthesized Ag@ZnO core-shell nanoparticles thus have a good potential for application in solar photocatalytic disinfection of water borne pathogens.