Ionic liquid-assisted hydrothermal synthesis of TiO 2 nanoparticles and its application in photocatalysis G. Nagaraju • K. Manjunath • T. N. Ravishankar • B. S. Ravikumar • H. Nagabhushan • G. Ebeling • J. Dupont Received: 26 April 2013 / Accepted: 6 August 2013 / Published online: 23 August 2013 Ó Springer Science+Business Media New York 2013 Abstract Anatase TiO 2 nanoparticles have been suc- cessfully synthesized at 130 °C for 2 days via ionic liquid- assisted hydrothermal method. The obtained products are characterized using various techniques. The X-ray dif- fraction data reveal that the nanoparticles are anatase TiO 2 . FTIR spectrum shows that the presence of ionic liquid and indicates Ti–O–Ti peak at around 398 cm -1 , and the bands at 1500 and 1600 cm -1 indicates C–H in-plane vibrations and stretching of imidazolium ring. Raman spectroscopy show bands at 142, 393, 513, and 636 cm -1 reveal crys- talline anatase phase. UV–Vis spectroscopy shows the k max at 355 nm corresponding to a band gap of 3.49 eV. TEM images reveal that the average diameters of anatase TiO 2 nanoparticles are in the range 50–100 nm. Anatase TiO 2 exhibited excellent photocatalysis for the degradation of organic dye. Introduction Nanoparticles have gained interest due to their novel, optical, magnetic, and catalytic properties, and thus their resulting applications in chemical technology, magnetic data storage, battery materials, and sensing [1]. As a result, enormous studies have been devoted to the development of suitable protocols for the targeted and rational synthesis of inorganic nanoparticles, their stabilization, properties, processing, and application [2–8]. Titanium oxide (TiO 2 ) nanoparticles have received significant attention because of their numerous applications, such as photocatalysts, lith- ium-ion batteries, pigments, photovoltaic cells, gas sensors, and so on [9] . TiO 2 occurs mainly in three different poly- morphs, namely anatase, rutile, and brookite, and it was reported that the phase composition of TiO 2 has an effect on its photocatalytic property. Although, the photocatalytic activity of rutile was considered to be indistinct, several groups found that the rutile phase shows higher photocat- alytic activity than anatase. A lot of experimental evi- dences supported the existence of a synergistic effect between the anatase and rutile phases. This effect is ben- eficial for reducing the recombination of photogenerated electrons and holes, which usually results in an enhanced photocatalytic activity [10–14]. However, it is known that the anatase modification of TiO 2 can be obtained first in all solution synthesis pathways and it is even believed that anatase with particle size of 10–20 nm is a thermody- namically stable modification of TiO 2 , with respect to surface energy [15–17]. The physical and chemical prop- erties of TiO 2 can be controlled by its particle size, mor- phology, and crystallinity. Many synthetical methods were used to obtain TiO 2 nanoparticles, such as sol–gel, hydrothermal, solvothermal, sonochemical, chemical vapor deposition, electrodeposition etc. [18–23]. As an alterna- tive, ionothermal synthesis is one of the soft solution routes benefitted from the other method using ionic liquid (IL) as solvent. Over the past two decades, ILs have received extensive attention because of their unique properties, such as extremely low volatility, wide liquid temperature range, good thermal stability, good dissolving ability, tailorable G. Nagaraju (&)  K. Manjunath  T. N. Ravishankar Centre for Nano and Material Sciences, Jain University, Jakkasandra, Karnataka, India e-mail: nagarajugn@rediffmail.com G. Nagaraju  G. Ebeling  J. Dupont Laboratory of Molecular Catalysis, Institute of Chemistry, UFRGS, Porto Alegre, RS, Brazil B. S. Ravikumar  H. Nagabhushan Department of Physics, University College of Science, Tumkur University, Tumkur, India 123 J Mater Sci (2013) 48:8420–8426 DOI 10.1007/s10853-013-7654-5