Photosensitization of TiO nanofibers by AgS with the synergistic effect of excess surface Ti states for enhanced photocatalytic activity under simulated sunlight.

TiO nanofibers, with mean diameter ~200 nm, were fabricated by electrospinning and successfully photosensitized with low bandgap AgS nanoparticles of 11, 17, 23 and 40 nm mean sizes, with corresponding loading of 4, 10, 18 and 29 wt.% AgS, respectively. 17 nm AgS@TiO nanofibers exhibited optimal activity in the photodegradation of methylene blue under simulated sunlight with pseudo-first order rate constant of 0.019 min compared to 0.009 min for pure TiO nanofibers. In spite of greater visible-light absorption and reduced bandgap, larger than 17 nm AgS nanoparticles exhibited sluggish photodegradation kinetics probably due to less photo-induced carriers generation in TiO and reduced electron injection rates from the larger sized AgS into TiO. Furthermore, a UV-O surface treatment induced excess Ti surface states and oxygen vacancies which synergistically enhanced the photodegradation rate constant to 0.030 min for 17 nm AgS@TiO sample which is ~70% better than the previously reported for AgS/TiO hierarchical spheres. This was attributed to the efficient charge separation and transfer driven by increased visible-light absorption, bandgap narrowing and reduced electron-hole recombination rates. The present study demonstrate the potential utilization of AgS@TiO nanofibers in filtration membranes for removal of organic pollutants from wastewater.