Soft chemistry of ion-exchangeable layered metal oxides
Soft chemical reactions such as ion-exchange and acid–base reactions have been extensively investigated to synthesize novel metastable layered inorganic solids, to exfoliate them into individual nanosheets, and to re-assemble them as thin films and nanocomposite materials. These reactions proceed at relatively low temperature and enable the synthesis of a rich variety of structures by stepwise reactions. In recent years, the toolbox of soft chemical reactions has been utilized to rationally design and tailor the properties of functional layered transition metal oxides. Layer-by-layer assembly and intercalation chemistry have provided insight into covalent interactions that stabilize oxide-supported nanoparticle catalysts. In addition, topochemical reactions have been utilized to tune the compositions of layered perovskite oxides in order to break inversion symmetry, resulting in piezoelectric and ferroelectric properties. This review focuses on the use of soft chemical approaches to design functional layered transition metal oxides with tunable properties. Soft chemical reactions enable the design of functional materials for diverse applications that include artificial photosynthesis, catalysis, energy storage, fuel cells, optical sensors, ferroics, and high-k dielectrics.