Amorphous interface oxide formed due to high amount of Sm doping (5-20 mol%) stabilizes finer size anatase and lowers indirect band gap

In this study, we have synthesized Ti(1-x)SmxO2 (x = 0–20%) nanocomposites by adopting an aqueous sol-gel route. A two or multi-phase mixture of titania and samarium oxide could be expected as samarium added >5% may exceed its solubility limit in anatase. Surface and high-resolution characterization found Sm forming a predominantly thin amorphous layer that is not discernible in conventional transmission electron microscopy. The addition of Sm in such a high amount stabilizes formation of anatase phase of TiO2. Importantly, we observe that the incorporation of such high amount of Sm in titania leads to a grain growth inhibition of anatase. Sm can also be reduced from a trivalent state to a bivalent state. The addition of Sm thus results in very thin amorphous layer around the nanocrystalline anatase, inhibits the growth of this anatase and lowers the indirect band gap from 3.0 eV to 2.47 eV. That such lowering happens along with a lowering of size and a resulting increase in surface area means that doping of titania by more than 5% Sm can make better a photocatalyst either for the purpose of photodegradation of industrial organic water-pollutants and microorganisms under the visible light irradiation than a pristine anatase.