On the chemical synthesis of titanium nanoparticles from ionic liquids

Abstract We report on attempts towards the synthesis oftitanium nanoparticles using a wet chemical approach inimidazolium-based ionic liquids (ILs) under reducingconditions. Transmission electron microscopy finds nano-particles in all cases. UV/Vis spectroscopy confirms thenanoparticulate nature of the precipitate, as in all cases anabsorption band between ca. 280 and 300 nm is visible. IRspectroscopy shows that even after extensive washing anddrying, some IL remains adsorbed on the nanoparticles.Raman spectroscopy suggests the formation of anatasenanoparticles, but X-ray diffraction reveals that, possibly,amorphous titania forms or that the nanoparticles are sosmall that a clear structure assignment is not possible. Thereport thus shows that (possibly amorphous) titanium oxi-des even form under reducing conditions and that thechemical synthesis of titanium nanoparticles in ILs remainselusive.Keywords Ionic liquids Nanoparticles Titanium Titanium oxide Chemical reductionIntroductionNanoparticles are interesting owing to their optical, mag-netic, and catalytic properties and thus their resultingapplications in chemical technology, magnetic data stor-age, and sensing, to name a few examples [1]. As a result,an enormous number of studies have been devoted to thedevelopment of suitable protocols for the targeted andrational synthesis of inorganic nanoparticles, their stabil-ization, properties, processing, and application [2–8]. Themain issue very often is the synthesis and stabilization ofone specific particle size, particle morphology, or crystalphase. Besides aqueous and organic solvents [7–14], ionicliquids (ILs) have also recently been explored as reactionmedia and stabilizers for inorganic nanoparticle synthesis[15–26]. Many authors claim ILs to be green or environ-mentally friendly solvents, which explains some of theinterest. The more reasonable point for using ILs for(inorganic) nanomaterials synthesis is that the very largenumber of different ILs should in principle enable thespecific and targeted synthesis of interesting new materialswith advantageous properties. Moreover, ILs can in somecases enable the synthesis of materials that cannot be madevia conventional processes [21, 25, 27–34].Among others, metal nanoparticle formation in ILs andtheir application have attracted interest because manyILs efficiently stabilize nanoparticles under a variety ofexperimental conditions. The particular interest in ILs isthat they can also stabilize inorganics (not only nanopar-ticles) that cannot be stabilized otherwise. For example,Migowski et al. [35] have prepared nickel nanoparticles.