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.
Highlights
Enhanced photocatalytic activity of electrospun mesoporous TiO2 nanofibers was demonstrated by CO2 reduction to renewable hydrocarbon fuels[11]
Many attempts have been made to enhance the photocatalytic activity of TiO2 under illumination conditions similar to solar light[12, 13]
Enhanced simulated solar light driven photocatalytic performance was demonstrated by water splitting with hydrogen production at 708 μmolh−1 g−1 and photodegradation of methyl orange with pseudo-first order rate constant of 0.018 min−1 39
Summary
We previously reported enhanced photocatalytic activity under UV irradiation for TiO2 NPs (P25 Degussa) loaded polyacrylonitrile NFs due to excess Ti3+ surface defects and enhanced hydrophilicity induced by a UV-O3 surface treatment[55] These NFs showed stable performance when tested over 5 cycles of photodegradation as shown in the Fig. 6(b). The enhanced photocatalytic performance of 17 nm-Ag2S@TiO2 + UV-O3 sample is attributed to the synergistic effect of photosensitization by Ag2S NPs and excess surface Ti3+ states and oxygen vacancies. This facilitated the generated electrons transfer from CB of Ag2S to the CB of TiO2 to effectively inhibit the electron-hole recombination This photosensitization effect is further supplemented by the high Ti2O3 (Ti3+ state and oxygen vacancies) near the surface which leads to enhanced absorption of incident solar light below the bandgap of TiO2 (Ti4+ state) as shown in the Fig. 8(b) and reported in ref. These results demonstrate the potential of using these composite nanofibers for water remediation under sunlight
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