Sieland Melanie, Camus-Genot Valentine, Djerdj Igor, Smarsly Bernd M
Institute of Physical Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35392, Giessen, Germany.
Institut des Molécules et des Matériaux du Mans, UMR CNRS 6283, Le Mans Université, Avenue Olivier Messiaen, 72085, Le Mans Cedex 9, France.
ChemistryOpen. 2021 Feb;10(2):181-188. doi: 10.1002/open.202000256. Epub 2020 Nov 26.
The influence of the cation of imidazolium-derived ionic liquids (ILs) on a low-temperature solution-based synthesis of hexagonal tungsten bronze (HTB) type Ti(OH)OF ⋅ 0.66 H O and bronze-type TiO (B) is investigated. The IL (C mim BF ) acts as solvent and also as reaction partner with respect to the decomposition of [BF ] , releasing F . In the present study, the chain length of the alkyl chain side groups attached to the imidazolium ring was varied (C mim BF to C mim BF ), and the obtained solids were analyzed by Powder X-Ray diffraction (PXRD) followed by Rietveld refinement. As a main finding these analyses indicate a transformation of Ti(OH)OF ⋅ 0.66 H O into TiO (B), and upon prolonged reaction time finally also into anatase TiO . Rietveld analysis suggests that when using ILs with longer alkyl chains, the conversion of Ti(OH)OF ⋅ 0.66 H O is slower compared to syntheses performed with smaller alkyl chains. Hence, Ti(OH)OF ⋅ 0.66 H O appears to be metastable and is stabilized by long-chain ILs serving as surfactant attached to the crystallites' surface. In this view, the ILs shield the nanoparticles and thus slow down the conversion into the more stable compounds. This confirms previous findings that ILs act as both, solvent and reaction medium in this reaction, thus enabling the synthesis of peculiar Ti-oxides.
研究了咪唑衍生离子液体（ILs）的阳离子对基于低温溶液合成六方钨青铜（HTB）型Ti(OH)OF⋅0.66 H₂O和青铜型TiO₂（B）的影响。离子液体（C₄mim BF₄）既作为溶剂，又作为与[BF₄]⁻分解相关的反应伙伴，释放出F⁻。在本研究中，改变了连接在咪唑环上的烷基链侧基的链长（从C₄mim BF₄到C₈mim BF₄），并通过粉末X射线衍射（PXRD）对所得固体进行分析，随后进行Rietveld精修。这些分析的主要发现表明，Ti(OH)OF⋅0.66 H₂O会转变为TiO₂（B），并且在延长反应时间后最终还会转变为锐钛矿型TiO₂。Rietveld分析表明，与使用较短烷基链进行的合成相比，使用具有较长烷基链的离子液体时，Ti(OH)OF⋅0.66 H₂O的转化速度较慢。因此，Ti(OH)OF⋅0.66 H₂O似乎是亚稳态的，并通过作为表面活性剂附着在微晶表面的长链离子液体而得以稳定。从这个角度来看，离子液体屏蔽了纳米颗粒，从而减缓了向更稳定化合物的转化。这证实了先前的发现，即在该反应中离子液体既作为溶剂又作为反应介质，从而能够合成特殊的钛氧化物。
