Abstract
Ionic liquids (ILs) and deep eutectic solvents (DESs) have proven to be suitable solvents and reactants for low-temperature reactions. To date, several attempts were made to apply this promising class of materials to metal oxide chemistry, which, conventionally, is performed at high temperatures. This review gives an overview about the scientific approaches of the synthesis as well as the dissolution of metal oxides in ILs and DESs. A wide range of metal oxides along with numerous ILs and DESs are covered by this research. With ILs and DESs being involved, many metal oxide phases as well as different particle morphologies were obtained by means of relatively simple reactions paths. By the development of acidic task-specific ILs and DESs, even difficultly soluble metal oxides were dissolved and, hence, made accessible for downstream chemistry. Especially the role of ILs in these reactions is in the focus of discussion.
Highlights
Metal oxide materials are of great scientific as well as economic interest because of their versatile utilisation and potential new applications
Investigating the heating method, sonochemical and ionothermal (170 ◦ C, 2 h) heating gave anatase particles varying morphologies, a microwave-heated (2.45 GHz, 80 ◦ C, 10 min) sample contained significant amounts of brookite alongside [40]. This extensive study shows that the control of phase and morphology of metal oxides in Ionic liquids (ILs) depends on various factors
Another approach for the synthesis of metal oxides in ILs or deep eutectic solvents (DESs) is their utilisation for an efficient synthesis of the respective metal hydroxide in a desired morphology followed by an annealing step
Summary
Metal oxide materials are of great scientific as well as economic interest because of their versatile utilisation and potential new applications. Block-copolymers as a structure-directing template for mesostructured materials have already previously been applied to the synthesis of a large number of metal oxides including Al2 O3 , HfO2 , Nb2 O5 , SnO2 , Ta2 O5 , TiO2 , WO3 and ZrO2 , as well as the mixed oxides Al2 TiOx , SiAlOx , SiTiOx , ZrTiOx and ZrW2 Ox [6] Rare earths, such as CeO2 , are of increasing interest for a wide range of applications, e.g., as catalysts, oxygen sensors, and UV absorbers [7]. ILs, by definition, are salts with a melting point below 100 ◦ C Their favourable properties, such as a negligible vapour pressure, a wide liquid range, good thermal and chemical stability as well as the ability to dissolve a large number of substances, make them an interesting reaction medium for low-temperature synthesis [19]. The focus is on metal oxide chemistry, metalloids mostly are neglected
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