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Benign Synthesis of Black Microspheres of Anatase TiO 2 with Paramagnetic Oxygen Vacancies through NH 3 Treatment
Author(s) -
Maqbool Qysar,
Srivastava Aasheesh
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201702343
Subject(s) - anatase , electron paramagnetic resonance , materials science , raman spectroscopy , paramagnetism , x ray photoelectron spectroscopy , amorphous solid , oxygen , analytical chemistry (journal) , visible spectrum , photocatalysis , nuclear chemistry , photochemistry , crystallography , chemical engineering , chemistry , nuclear magnetic resonance , optics , catalysis , organic chemistry , physics , quantum mechanics , optoelectronics , engineering
Abstract Coloured TiO 2 is coveted for its ability to extract energy from the visible region of electromagnetic spectrum. Here a facile synthesis of black anatase titania microspheres ( B‐TiO 2 ) through a two‐step process is reported. In the first step, amorphous white TiO 2 microspheres ( W‐TiO 2 ) are obtained by hydrolysing titanium tetraisopropoxide by ammonia vapours in ethanol. In the second step, the W‐TiO 2 is thermally annealed at 500 °C to obtain B‐TiO 2 . The diffuse reflectance analysis showed that B‐TiO 2 absorbs across visible spectrum with absorption extending well into NIR region. Raman scattering together with EPR analysis showed compelling evidence of the existence of oxygen deficiency within the crystal in B‐TiO 2 that induces black colouration in the sample. The defects present in the black anatase sample were confirmed to be single‐electron‐trapped (or paramagnetic) oxygen vacancies (V o ⋅ ) by XPS and EPR studies. The magnetic susceptibility studies showed existence of antiferromagnetic interactions between these unpaired electron spins.