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1. NATURAL SCIENCES, Inorganic and nuclear chemistry, Physical chemistry, Colloid chemistry, Analytical chemistry

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Inorganic Chemistry 2012, 51, 7164−7173

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Highly visible light active S, N co-doped anatase-rutile heterojunctions is 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 Ti4+-thiourea complex upon reaction between peroxo-titania complex and thiourea. Decomposition of the Ti4+-thiourea complex and formation of visible light active S, N co-doped TiO2 heterojunctions are confirmed using X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and UV/Vis spectroscopic studies. Existence of sulfur as sulfate ions (S6+) 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 co-doped heterojunctions proved the fact that the formation of isolated S 3p, N 2p and П* N-O states between the valence and conduction bands are responsible for the visible light absorption. Titanium dioxide obtained from the un-doped 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 co-doped anatase-rutile heterojunctions at a temperature as low as 500 °C. The most active S, N co-doped heterojunction (0.2 SN-TiO2) obtained at 600 °C exhibits a two-fold and eight-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 exceptionally high visible light photocatalytic activities of S, N co-doped heterojunctions.



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