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

**Sourav Das 1, Neha Ranjana 1, Ananyo Jyoti Misra 1, Mrutyunjay Suar 1, Amrita Mishra 1, Ashok J. Tamhankar 1,2,\* , Cecilia Stålsby Lundborg <sup>2</sup> and Suraj K. Tripathy 1,3,\***


Academic Editor: Paul B. Tchounwou Received: 3 May 2017; Accepted: 5 July 2017; Published: 10 July 2017

**Abstract:** 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.

**Keywords:** core-shell; disinfection; *Escherichia coli*; nanoparticles; pathogens; silver; solar-photocatalysis; *Staphylococcus aureus*; water; zinc oxide
