Controlled synthesis of hollow multishelled structures by sequential templating approach

Abstract

The hollow multi-shelled structure (HoMS) has at least two separated shells spatially ordered from outside to inside. This unique, temporal-spatial ordered structure endows an abundance of beneficial physicochemical properties, including high surface-to-volume ratios, short mass transport lengths and high loading capacities. Due to these favorable properties, the HoMS has been recognized as one of the most promising candidates for many potential applications, including electrochemical energy storage, solar energy conversion, electromagnetic wave absorption, catalysis, gas detection, and drug delivery. However, for a long time, achieving general and controllable synthesis of the HoMS, using conventional soft-templating or hierarchical self-assembly methods, has remained a great challenge, due to the complexity of the structure. This has limited the development and application of novel functional materials. Thus, in this article, we turn our heads to the development of the sequential templating approach (STA), which has greatly enriched both the compositional diversity and the geometrical diversity of the HoMS, leading to more controllable and applicable HoMS. Here, we first review the development process and characteristics of the STA for the synthesis of the HoMS. The STA, which was first reported by our research group and then further developed by others, has proven to be a universal and controllable technique to building HoMS with diverse compositions and structures. The essence of this approach is that the template can play a role of “multiple and sequential templating” during the removal process, and the precursors incorporating the template are then aggregated, solidified, and crystallized to gradually form rigid multiple shells. The STA has several attractive advantages: (1) There are no limitations on the composition or shape of the template. In addition to the most commonly used carbonaceous microspheres, other shapes and compositions such as polymers, metal-organic frameworks, and metal carbonates can also be used as the template for fabricating the HoMS. (2) The approach is universally applicable to the controlled synthesis of single, dual, multicomponent and heterogeneous HoMS with various compositions, such as metal oxides, non-metal oxides, metal carbonates, metal sulfides, metal phosphides, etc. (3) Templates can enrich precursors through many different methods, such as ion adsorption, ion exchange, precipitation reaction, and electrostatic spray. Remarkably, electrostatic spray, which indicates a simultaneous occurrence of template formation and precursor enrichment, is accessible for achieving large-scale HoMS production. Finally, we discuss the emerging challenges and future research directions of the HoMS. In-depth investigation on the basic reaction mechanism involved in the synthesis and manipulation of HoMS can guide researchers to develop improved designs and syntheses of the HoMS, in order to better fulfill the different requirements of specific applications.