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

Samina Ghafoor; Sadia Ata; Nasir Mahmood; Salman Noshear Arshad

doi:10.1038/s41598-017-00366-7

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

Sci Rep. 2017 Mar 21;7(1):255. doi: 10.1038/s41598-017-00366-7.

Authors

Samina Ghafoor^{1

2}, Sadia Ata², Nasir Mahmood³, Salman Noshear Arshad⁴

Affiliations

¹ Department of Chemistry, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences, Lahore, 54792, Pakistan.
² Institute of Chemistry, University of the Punjab, P.O. Box 54590, Lahore, Pakistan.
³ Institute for Superconducting and Electronic Materials, Australian Institute for Innovative Materials, University of Wollongong, North Wollongong, 2500, Australia.
⁴ Department of Chemistry, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences, Lahore, 54792, Pakistan. salman.arshad@lums.edu.pk.

Abstract

TiO₂ nanofibers, with mean diameter ~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 UV-O₃ 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 ~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.