In this work, we present detailed investigations on the influence of binary ionic liquid (IL) mixtures on sol−gel syntheses of metastable metal oxide phases. The synthesis of the metastable TiO 2 bronze phase and anatase as well as the rutile modification is followed via in situ diffraction methods coupled with thermal gravimetric analysis. The variation of the composition of mixtures of ILs allows for the adjustment of TiO 2 phase composition at low temperatures. On the basis of these results, the synthesis of the hexagonal tungsten bronze-like titanium hydroxyl oxy fluoride was achieved. Our results pave the way for a deeper understanding of IL participation in the syntheses of inorganic nanomaterials, going further than treating them as solvents.
Particle resolved measurements of the phase behavior of hard colloidal ellipsoids with aspect ratios from 2 to 7 reveal that for intermediate aspect ratios the predicted nematic phase is absent and instead nematic precursors and domains are formed.
As reported previously, novel ZnO nanostructures can be grown by oxidation of [MeZnOtBu]4 “building blocks” with O3 in ionic liquids (ILs). In this study, we have explored the role of the IL during ZnO formation by in‐situ infrared reflection absorption spectroscopy (IRAS) in ultrahigh vacuum (UHV). [MeZnOtBu]4 and [C2C1Im][OTf] were (co‐)deposited as thin films by physical vapor deposition (PVD) onto Au(111), separately or simultaneously. The IR spectrum of [MeZnOtBu]4 was analyzed between 300 and 4000 cm–1 based on calculated spectra from density‐functional theory (DFT). Spectral changes in the IL‐related bands during the thermal treatment of [MeZnOtBu]4 in [C2C1Im][OTf] indicate the loss of the precursor ligands and the interaction of the IL with the growing ZnO aggregates. The films were treated with ozone (10–6 mbar) in UHV and the spectral changes were monitored in‐situ by IRAS. Slow ozonolysis of [C2C1Im][OTf] is observed. Spectroscopically we identify the primary ozonide formed by addition of O3 to [C2C1Im]+ and suggest a reaction mechanism, which leads to a biuret derivative. Upon ozone treatment of mixed [MeZnOtBu]4/[C2C1Im][OTf] films, ZnO aggregates are formed at the IL/vacuum interface. Ozonolysis of [C2C1Im][OTf] is suppressed. Upon annealing to 320 K, further ZnO aggregates are formed, leading to enclosure of [C2C1Im][OTf] in the ZnO film. At 380 K the IL is released from the mixed film. The pure [C2C1Im][OTf] desorbs at 420 K, leaving behind the ZnO phase.
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The majority of particle synthesis methods are based on nucleation and growth processes in solvents. Whereas the role of capping agents has been investigated extensively regarding control particle size and shape, the unique role of the solvent is understood to a much lesser extent. Compared to other polar solvents, e.g. water, ionic liquids (ILs) are unique because their properties can be fine‐tuned precisely by appropriate choice and modification of cation and anion. This makes ILs also interesting for particle synthesis. We present the generation of zinc oxide (ZnO) in imidazolium ILs starting from molecular precursors. A hydrolytic, sol‐gel based synthesis route is suitable to achieve nanocrystalline ZnO. We find by in‐situ synchrotron wide angle X‐ray diffraction that in ILs an unusual ZnO phase with α‐boron nitride structure acts as an intermediate prior to crystallization of the thermodynamically stable Wurtzite. This special mechanism leads to organic‐inorganic hybrid IL/ZnO nanoparticles with plate‐like morphology. Because of the large content of IL embedded in the ZnO matrix the novel particles gain ionogel properties, e.g. ion conductivity probed by impedance spectroscopy.
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