Metal oxide mesocrystals with tailored structures and properties for energy conversion and storage applications

Abstract

Mesocrystals (MCs) are superstructures with a crystallographically ordered alignment of nanoparticles. Owing to their organized structures, MCs posses some unique characteristics such as a high surface area, pore accessibility, and good electronic conductivity and thermal stability; thus, MCs could be beneficial for many areas of research and application. This review begins with a description of the common synthesis strategies for, and characterization and fundamental properties of metal oxide MCs. Newly developed analytical methods (that is, photoconductive atomic force microscopy and single-molecule, single-particle fluorescence microscopy) for unraveling the charge transport and photocatalytic properties of individual MCs are then introduced. Further, recent developments in the applications of various metal oxide MCs, especially in the fields of energy conversion and storage, are also reviewed. Finally, several perspectives in terms of future research on MCs are highlighted. NPG Asia Materials (2014) 6, e100; doi:10.1038/am.2014.21; published online 16 May 2014 Keywords: energy storage; mesocrystal; metal oxide; photocatalysis; solar energy conversion; superstructure INTRODUCTIONThe self-assembly of nanoparticle building blocks into highly ordered superstructures is one of the actively pursued research topics in materials science and technology. 1-4 Such hierarchical architectures have potentially tunable electronic, optical and magnetic properties, which promise various applications ranging from catalysis to optoelectronics. A mesocrystal (MC), which was first introduced by Cölfen in the early years of 2000s, is defined as a superstructure consisting of nanoparticles on the scale of several hundred nanometers to micrometers. [5][6][7][8][9][10][11] In contrast to the classical mechanism of atom/ ion-mediated growth of a single crystal, the particle-mediated growth mechanisms of MCs are termed as non-classical crystallization (Figure 1). This definition has been developed in recent years, where MCs are defined entirely according to their structures rather than their formation mechanism. 12 In this decade, a variety of MCs of metal oxides (for example, TiO 2 , 13-23 ZnO, [24][25][26][27][28][29][30][31][32][33][34] Among metal oxides, TiO 2 is used in many applications that deal with environmental and energy problems (for example, photodegradation of pollutants, 67 water splitting for H 2 evolution, 68 dyesensitized solar cells 68 and lithium-ion batteries 69 ) owing to its

Nanoparticle Clusters: Assembly and Control Over Internal Order, Current Capabilities, and Future Potential

“…This approach has been used to increase the photocatalytic efficiency of spherical TiO 2 , [128] ZnO, [129] and CeO 2 [130] NPCs in various catalytic applications, ranging from dye degradation to CO oxidation. The experiments demonstrate that a highly ordered structure of the NPs in the NPCs, referred to as mesocrystals in these cases, [131] is particularly effective for charge separation due to the presence of efficient transport pathways resulting in notable photocatalytic performance. [132] This demonstrates that, with careful design of the NPC composition and internal structure, substantial improvements in the photocatalytic efficiency can be achieved.…”

“…[131] Using NPs as building blocks prevents fracture due to expansion or contraction following lithiation or delithiation, while the interparticle spaces within the NPCs provide some space for expansion. In addition, the enclosure of the particles in the cluster allows for minimization of the contact with the electrolyte, which is needed to ensure good cyclability.…”

Tuning the functionalities of a mesocrystal via structural coupling

“…This kind of superstructures has stimulated wide interests in the research fields of condensed matter physics and solid state chemistry for their unique properties that are different from bulk single crystals and randomly assembled nanocrystals1234. Current methods to prepare the mesocrystals are mostly based on the chemical synthesis, starting from colloidal nanoparticles and then naturally assembled by means of organic matrices, physical fields, mineral bridges, etc 2.…”

TiO2 mesocrystal with nitrogen and fluorine codoping during topochemical transformation: Efficient visible light induced photocatalyst with the codopants

“…It is inferred that the anisotropic dissolution of NH 4 TiOF 3 can chemically convert to TiO 2 mesocrystal (TMC) during the topochemical transformation, accompanying with N and F releasing [13][14][15][16]. As a new class of porous building blocks oriented assembly of nanocrystals, the obtained TMC with a well-defined crystal shape significantly enhances the charge separation with remarkably long-lived charges and exhibits excellent photocatalytic activities http compared with TiO 2 nanocrystals and commercial P25 [17][18][19][20]. It is a great of significance to introduce the dopant simultaneously from the original precursors or intermedium during the synthesis, without affecting the nucleation and growth of TMC.…”