Photo-reduction of heavy metal ions and photo-disinfection of pathogenic bacteria under simulated solar light using photosensitized TiO2 nanofibers

Abstract

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 Ag₂S/TiO₂ nanofibers showed 90% photocatalytic reduction of Cr(VI) at pH of 3 with a pseudo-first order rate constant of 0.016 min⁻¹ which is significantly better than the previously reported for Ag–Ag₂S/TiO₂ composite particles. The antibacterial capability of the Ag₂S/TiO₂ nanofibers was evaluated via photo-disinfection of the Gram-positive and Gram-negative bacterial strains. The smallest sized 11 nm Ag₂S/TiO₂ nanofiber showed the best bactericidal efficiency of 100% and 90.6% against Gram-negative E. coli and Gram-positive S. aureus after 1 h of irradiation, respectively, whereas, only 50% E. coli and 41% S. aureus were found to be inactivated in dark. Furthermore, a UV–O₃ treatment of the 11 nm Ag₂S/TiO₂ nanofibers remarkably enhanced the antibacterial activity where 89% E. coli and 81% S. aureus 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 TiO₂ and the optimally sized Ag₂S nanoparticles. The disinfection nature of the Ag₂S 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 TiO₂ nanofibers for water remediation.