Nanostructured Ti(1-x)S(x)O(2-y)N(y) heterojunctions for efficient visible-light-induced photocatalysis.
Highly visible-light-active S,N-codoped anatase-rutile heterojunctions are reported for the first time. The formation of heterojunctions at a relatively low temperature and visible-light activity are achieved through thiourea modification of the peroxo-titania complex. FT-IR spectroscopic studies indicated the formation of a Ti(4+)-thiourea complex upon reaction between peroxo-titania complex and thiourea. Decomposition of the Ti(4+)-thiourea complex and formation of visible-light-active S,N-codoped TiO(2) heterojunctions are confirmed using X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and UV/vis spectroscopic studies. Existence of sulfur as sulfate ions (S(6+)) and nitrogen as lattice  (N-Ti-N) and interstitial  (Ti-N-O) species in heterojunctions are identified using X-ray photoelectron spectroscopy (XPS) and FT-IR spectroscopic techniques. UV-vis and valence band XPS studies of these S,N-codoped heterojunctions proved the fact that the formation of isolated S 3p, N 2p, and Π* N-O states between the valence and conduction bands are responsible for the visible-light absorption. Titanium dioxide obtained from the peroxo-titania complex exists as pure anatase up to a calcination temperature as high as 900 °C. Whereas, thiourea-modified samples are converted to S,N-codoped anatase-rutile heterojunctions at a temperature as low as 500 °C. The most active S,N-codoped  heterojunction 0.2 TU-TiO(2) calcined at 600 °C exhibits a  2-fold and   8-fold increase in visible-light photocatalytic activities in contrast to the control sample and the commercial photocatalyst Degussa P-25, respectively. It is proposed that the efficient electron-hole separation due to anatase to rutile electron transfer is responsible for the superior visible-light-induced photocatalytic activities of S,N-codoped  heterojunctions.
Centre for Research in Engineering Surface Technology (CREST), and School of Chemical and Pharmaceutical Sciences, Dublin Institute of Technology, Kevin Street, Dublin 8, Ireland.
Vinodkumar
V
Etacheri
Michael K
MK
Seery
Steven J
SJ
Hinder
Suresh C
SC
Pillai
D002384:Catalysis; D008027:Light; D049329:Nanostructures / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010316:Particle Size; D052817:Phototrophic Processes; D013455:Sulfur / Q000737:chemistry*; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
D013455:Sulfur; D014025:Titanium; D009584:Nitrogen; D010100:Oxygen