Photo-reduction of heavy metal ions and photo-disinfection of pathogenic bacteria under simulated solar light using photosensitized TiO nanofibers.

We report the photosensitization of electrospun titania nanofibers, with a mean diameter of 195 nm, by low bandgap silver sulfide nanoparticles of 11-23 nm mean size with the aim of treating heavy metal ions and pathogenic bacteria simultaneously under simulated solar light irradiation. The 17 nm AgS/TiO nanofibers showed 90% photocatalytic reduction of Cr(vi) at pH of 3 with a pseudo-first order rate constant of 0.016 min which is significantly better than the previously reported for Ag-AgS/TiO composite particles. The antibacterial capability of the AgS/TiO nanofibers was evaluated photo-disinfection of the Gram-positive and Gram-negative bacterial strains. The smallest sized 11 nm AgS/TiO nanofiber showed the best bactericidal efficiency of 100% and 90.6% against Gram-negative and Gram-positive after 1 h of irradiation, respectively, whereas, only 50% and 41% were found to be inactivated in dark. Furthermore, a UV-O treatment of the 11 nm AgS/TiO nanofibers remarkably enhanced the antibacterial activity where 89% and 81% were inactivated in just 10 min of the irradiation. Enhanced photocatalytic activity is attributed to the efficient charge separation and transfer and reduced electron-hole recombination induced by the effective heterojunction formation between TiO and the optimally sized AgS nanoparticles. The disinfection nature of the AgS nanoparticles, role of the generated hydroxyl species under irradiation, and the cell wall damage mechanism is also discussed. This study demonstrates the potential use of these multifunctional composite TiO nanofibers for water remediation.