Facet engineering of MnO2: An important strategy for improving its efficiency

Due to its unique properties, manganese dioxide (MnO2) has been widely used in various environmental applications. However, its efficiency is not ideal, which limits its further applications. Fortunately, facet engineering has become an important strategy for improving its efficiency. This review aims to summarize the recent research progress in the facet engineering of MnO2. Firstly, the synthesis strategies of MnO2 with specific exposed facets are introduced in detail. Subsequently, the facet dependent properties of MnO2 crystals including surface energy, exposed atoms and electronic structure are concisely discussed. Furthermore, the applications of faceted MnO2 in terms of organic pollutant removal, air pollutant removal, heavy metal removal, energy production and storage are systematically reviewed. Finally, the remaining challenges are summarized and the perspectives for future research are stated. These are believed to provide guidelines for the development of facet engineering of MnO2 crystals.