The encapsulation of noble-metal nanoparticles (NPs) in metal-organic frameworks (MOFs) with carboxylic acid ligands, the most extensive branch of the MOF family, gives NP/MOF composites that exhibit excellent shape-selective catalytic performance in olefin hydrogenation, aqueous reaction in the reduction of 4-nitrophenol, and faster molecular diffusion in CO oxidation. The strategy of using functionalized cavities of MOFs as hosts for different metal NPs looks promising for the development of high-performance heterogeneous catalysts.

limits the diffusion of chemical species and their interactions with active sites in MOFs. [ 10 ] One of successful strategy from zeolites, silica, and carbon is the fabrication of mesopore structure which has expanded a large variety of potential and existing commercial applications. [1][2][3] Hence, it is worthwhile to develop methods to fabricate MOFs with mesopores so as to enhance the molecular diffusion while preserving their molecular sieve properties.To date, two major synthetic strategies have been explored to synthesize mesoporous-MOFs (meso-MOFs). [ 11 ] One is through ligand extension, either to increase the length of organic ligands [ 12 ] or to use bulky organic scaffolds [ 13 ] to form mesopores inside MOFs. In this case, the largest pore size reported is 9.8 nm in MOF-74 by increasing the length of organic linker to 5 nm. [ 14 ] Besides the diffi culties in complex ligands synthesis, interpenetration, disintegration, and instability of frameworks almost inevitably occur in MOFs with extended organic linkers, which prevent this functionalization method from being generally adopted in the formation of meso-MOFs. Another approach, the surfactanttemplate method, [ 4d , 15 ] has been introduced to increase the pore size in MOFs. For example, the Zhou group has successfully used cetyltrimethylammonium bromide (CTAB) as soft template to build meso-MOFs. [ 16 ] In this system, surfactant mole cules fi rst self-assembled into micelles serving as a soft template for MOFs growth and were subsequently removed to generate mesopores. The pore diameter of the resulting MOFs could be tuned from 3.8 to 31.0 nm. Nevertheless, as is well known, small molecular micelles are usually unstable under the synthesis conditions of most MOFs, so that only a few series of MOFs (such as carboxylic acid ligands) can be obtained by the surfactant-template method. Recently, some new methods have been successively developed to prepare the meso-MOFs, such as the gelation process, [ 17 ] and switchable solvent. [ 18 ] Moreover, the above methods are suitable for preparation of intrinsic meso-MOFs, but lack of control over the shape, position, and space distribution of mesopores in MOFs makes it hard to meet the demand for the growing applications of MOFs. It is well known that the potential applications of MOFs can be further developed and extended by encapsulating various nanoparticles (NPs) within the frameworks matrix so that the functionalized MOFs can exhibit the novel chemical and physical properties endowed by NPs. [ 7b , 19 ] Thus, to the best of our knowledge, general and versatile strategies of synthesizing functionalized MOFs with size-, shape-, and space-distribution-controlled mesopores have been rarely reported, in spite of the need and the signifi cance in application of functionalized meso-MOFs.Herein, we report a facile strategy of crafting mesopores inside MOFs through encapsulation of NPs followed by etching. Especially, the mesopore morphology, hierarchical structure, and space Porous materials, such as sili...

Controllable integration of nanoparticles (NPs) and metal−organic frameworks (MOFs) is crucial for expanding the applications of MOF-based materials. In this study, we demonstrate the facile encapsulation of presynthesized NPs into carboxylic acid based MOFs using NPs@metal oxide core−shell nanostructures as the self-template. The shell dissolved gradually in the mildly acidic growth solution created by dissociation of the ligands and thus directing the growth of the MOF crystals by providing metal ions. With protection of the metal oxide shell, various NPs (Au NPs, Au nanorods, Pd nanocubes, and Pt-on-Au dendritic NPs) could be encapsulated easily without being aggregated or dissolved in the reaction mixture. Importantly, instead of forming the exact replicate of the self-template, the obtained NP@MOF heterostructures exhibited a yolk−shell morphology with a central cavity and a certain degree of mesoporosity. The formation of the well-defined yolk−shell structure was demonstrated to be dependent on both the choice of the solvent and the dissolution behavior of the metal oxide shell. Finally, the obtained heterostructures were employed for heterogeneous catalysis, in which the size selectivity of the MOF shell was perfectly retained.

Self-assembly of monodispersed objects with sizes ranging from nanometers to millimeters offers a useful route to new functional materials and devices featuring two-dimensional (2D) or three-dimensional (3D) ordered structures that are not easily achieved with conventional photolithographybased microfabrication techniques. [1] Beyond classic spheres, [2] non-spherical building blocks [3] such as ellipsoids, [4] dumbbells, [5] rods, [6] stars, [7] octapods, [8] and polyhedrons [9][10][11][12] have attracted increasing interest due to advances in colloidal synthesis that enable the precise control over the size and shape of colloidal particles. In particular, selfassembly of polyhedrons made of crystalline materials such as metals, [9] oxides, [10] and semiconductors [11] has been extensively investigated from both the theoretical [12] and experimental viewpoints in recent years.Metal-organic frameworks (MOFs), a new class of crystalline materials, are synthesized by assembly of metal ions or clusters with organic linkers. [13] MOFs display permanent microporous structures with large surface areas, regular but tunable cavity sizes, and tailorable chemistry, and thus show great promise for wide applications including gas storage, [14] molecule separation, [15] heterogeneous catalysis, [16] chemical sensing, [17] and drug delivery. [18] In the past few years, many efforts have been undertaken in MOF synthesis to control the size [19][20][21][22] and shape [23] of MOF crystals since these parameters can significantly impact certain properties of bulk materials, for example, gas sorption, [19] and indeed are critical for biological applications. [18,20] Meanwhile, MOF crystals with small sizes can be processed easily into thin films and membranes through dip-coating [24] or spin-coating, [25] and further, oriented MOF films can also be prepared with crystals of regular shapes and with the aid of the Langmuir-Blodgett (LB) technique. [26] In this regard, MOF crystals with uniform size and shape will facilitate not only the control over the thickness of oriented films but also the formation of 2D or 3D ordered structures by bottom-up self-assembly. Nevertheless, relevant work is just beginning, and only 2D self-assembly of MOF microcrystals has been realized recently. [27] Challenges in this emerging area are the synthesis of monodispersed MOF crystals with uniform sizes and shapes as well as the exploration of appropriate assembly techniques.Here, we report 1) the acetic acid-modulated synthesis of monodispersed octahedral microcrystals of a zirconium-carboxylate MOF material, UiO-66 (UiO stands for University of Oslo), 2) the preparation of oriented MOF films with controlled thickness based on the assembly of large-area 2D monolayers of a microcrystal, and 3) the formation of longrange 3D superlattices of MOF microcrystals through a sedimentation technique (Scheme 1). UiO-66 is a chemically robust and thermally stable MOF material and was first synthesized in intergrown crystal form by Lillerud et al. [28] Subsequen...

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