Photosensitization of TiO2 nanofibers by Ag2S with the synergistic effect of excess surface Ti3+ states for enhanced photocatalytic activity under simulated sunlight

TiO2 nanofibers, with mean diameter similar to 200 nm, were fabricated by electrospinning and successfully photosensitized with low bandgap Ag2S nanoparticles of 11, 17, 23 and 40 nm mean sizes, with corresponding loading of 4, 10, 18 and 29 wt.% Ag2S, respectively. 17 nm Ag2S@ TiO2 nanofibers exhibited optimal activity in the photodegradation of methylene blue under simulated sunlight with pseudo-first order rate constant of 0.019 min(-1) compared to 0.009 min(-1) for pure TiO2 nanofibers. In spite of greater visible-light absorption and reduced bandgap, larger than 17 nm Ag2S nanoparticles exhibited sluggish photodegradation kinetics probably due to less photo-induced carriers generation in TiO2 and reduced electron injection rates from the larger sized Ag2S into TiO2. Furthermore, a UVO3 surface treatment induced excess Ti3+ surface states and oxygen vacancies which synergistically enhanced the photodegradation rate constant to 0.030 min(-1) for 17 nm Ag2S@ TiO2 sample which is similar to 70% better than the previously reported for Ag2S/TiO2 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 Ag2S@ TiO2 nanofibers in filtration membranes for removal of organic pollutants from wastewater.