Visible-light-mediated synergistic photocatalytic antimicrobial effects and mechanism of Ag-nanoparticles@chitosan-TiO2 organic-inorganic composites for water disinfection

By coupling chitosan bioaffinity adsorption, molecular imprinting, and nano TiO2 photocatalysis technologies, Ag nanoparticles@chitosan-TiO2 organic-inorganic composite (Ag-NPs@CTA) was prepared and found to be an efficient visible-light-mediated photocatalytic antimicrobial agent useful for water disinfection. Ag-NPs@CTA exhibited favorable antimicrobial activity for Escherichia coli, Staphylococcus aureus and Candida albicans, with the inactivation rate in excess of 99.0% in 2 h under visible light irradiation. Ag-NPs@CTA could be reused for five consecutive cycles directly without regeneration treatment and showed rather low cytotoxicity toward mammalian cells. Characterization of E. coli cells using TEM, AFM, Raman spectroscopy, FTIR and intracellular protein leakage illustrated that Ag-NPs@CTA could not only destroy the cell wall and membrane but also cause metabolic dysfunction. The synergistic antimicrobial mechanism was studied by Ag release evaluation, radical scavengers study, and Ag-NPs@CTA characterization by XPS and UV-vis absorption. The enhanced antimicrobial ability originated from the synergistic activities of the three components and the proposed mechanisms contained electrostatic interaction followed by two pathways: released Ag species and oxidative stress caused by photo-generated reactive radicals. The present work provided an efficient water disinfection technology of realistic potential and also opened a new idea in designing visible-light-mediated photocatalytic antimicrobial agents and in studying the antimicrobial mechanism. (C) 2015 Elsevier B.V. All rights reserved.