261 J. Indian Chem. Soc., Vol. 95, March 2018, pp. 261-268 Photocatalytic action of silver-titanium dioxide nanocomposite against pathogenic bacteria Sharda Bharti a , Soumyo Mukherji b and Suparna Mukherji a * a Centre for Environmental Science and Engineering, b Department of Bioscience and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India E-mail : sbharti05@iitb.ac.in, mukherji@iitb.ac.in, mitras@iitb.ac.in Manuscript received 15 November 2017, accepted 26 February 2018 Abstract : Various waterborne disease outbreaks have been reported even after disinfection with conventional techniques due to development of resistance in microorganism. Moreover, generation of carcinogenic disin- fection by-products (DBPs) poses additional problems. This has prompted an exploration of alternative anti- microbial agents for disinfection of water. Over the last few decades, photocatalysis has been widely applied for degradation of various pollutants and inactivation of waterborne microbial pathogens. The present study was focused on the synthesis and characterization of Ag-TiO 2 nanocomposite by doping of TiO 2 nanoparticles (NPs) with silver (Ag). Water disinfection studies were conducted in a photochemical reactor in batch mode using UV and visible light irradiated Ag-TiO 2 nanocomposite (NC). Studies conducted using four opportu- nistic bacterial pathogens, i.e. Escherichia coli (MTCC 443), Pseudomonas aeruginosa (RS1), Burkholderia cepacia (ES1) and Acinetobacter baumanii (RS4) revealed effective disinfection of 10 3 CFU/mL of bacteria within 30 min even for visible light irradiated nanocomposite (5 mg/100 mL). Keywords : Disinfection by-products, nanocomposite, pathogens, photocatalysis, water disinfection. I. Introduction Water disinfection is a crucial step for control of waterborne infectious diseases. Various conventional disinfection techniques, including chlorination and ozonation are associated with formation of carcino- genic disinfection-byproducts (DBPs) 1 . Other disin- fection approaches, such as, UV based disinfection is unable to provide residual disinfectant for long term effectiveness 2 . Moreover, various microbial pathogens, such as, Cryptosporidium and Giardia are found difficult to inactivate effectively with con- ventional methods. These limitations have prompted research on alternative antimicrobial agents. Over the past few decades, photocatalysis using metal ox- ide nanoparticles and nanocomposites has been ap- plied for degradation of various pollutants and inac- tivation of waterborne pathogens. Among these, TiO 2 is the most extensively used photocatalyst due to its low cost, availability and effectiveness. Since TiO 2 is a semiconductor with a bandgap of 3.2 eV (ana- tase phase), UV irradiation (at  < 380 nm) of TiO 2 excites electrons from the valence band to the con- duction band, thereby generating electron hole (e – -h + ) pairs. These electrons and holes further re- act with dissolved oxygen and water and subsequently, generates a series of reactive oxygen species (ROS), which are found to be responsible for oxidative deg- radation of organic pollutants and microbial inacti- vation 2–5 . However, a few limitations of TiO 2 based photocatalysis limits its widespread application. These include high probability of electron hole recombina- tion and dependence on UV irradiation. Dependence on UV irradiation not only increases the overall cost of treatment, it also increases the risk of UV expo- sure during handling of the UV source. Moreover, disinfection using photocatalysis relying on ROS