Tin(II) Doped Anatase (TiO₂) Nanoparticles: A Potential Route to “Greener” Yellow Pigments

Benign by design : Tin(II) doped anatase TiO 2 nanoparticles, a potential candidate as environmentally benign yellow pigments, have been synthesized. The presence of Sn 2+ in anatase structure has been confirmed by various analytical techniques including optical and 119 Sn Mössbauer spectroscopy. magnified image During our exploration of compounds in the Sn II ‐Ti IV ‐O system, we discovered that hydrolysis of titanium alkoxide solution in the presence of Sn II salts resulted in stable deep‐yellow colored anatase nanoparticles. The samples were characterized by X‐ray powder diffraction, electron microprobe, thermal analysis, transmission electron microscopy, and 119 Sn Mössbauer spectroscopy. Mössbauer data of the yellow colored samples showed the presence of both Sn II and Sn IV in a distorted environment as expected in the anatase structure. It is suggested that the cationic charge imbalance is compensated by oxygen vacancies and/or hydroxyl groups as evidenced by Mössbauer data which show two types of Sn II environments. When heated in air to 300 °C the samples changed color to completely white and 119 Sn Mössbauer data of these samples showed only the presence of Sn IV . These observations indicate that the origin of the yellow color in our Sn doped anatase nanoparticles arises from filled Sn 5s states just above the O 2p band, thus decreasing the band gap. The Sn II doped anatase TiO 2 nanoparticles reported here can potentially lead to environmentally benign yellow pigments. The simplistic nature of the synthetic procedure could easily be adapted to large‐scale industrial manufacture.