Fabrication of Metal Nanoparticle Composites by Slow Chemical Reduction of Metal-Organic Frameworks

Nanoparticle/metal-organic framework hybrid catalysts: elucidating the role of the MOF

Hybrid materials of metal-organic frameworks (MOFs) and nanoparticles (NPs) have attracted significant attention because of the wide variety of attractive properties derived from the two components. In the last decade, the development of synthesis techniques for NP/MOF composites was particularly significant. In the field of catalysis in particular, various synergistic effects that make the composites attractive catalysts have been reported. However, the role of MOFs in the composite catalysts is still not well understood and is being elucidated. In this feature article, we focus on recent progress in NP/MOF composite catalysts, concentrating on the analysis of the interaction between NPs and MOFs and the reaction mechanisms, together with the synthetic techniques used for NP/MOF hybrid materials.

Construction of a Hierarchical Structure of Bimetallic Oxide Derived from Metal-Organic Frameworks

Bimetallic oxides are a class of promising advanced functional metal nanomaterials, especially in terms of the sophisticated hierarchical structure of bimetallic oxide, which not only is in favor of enhancing their intrinsic physiochemical properties because of more accessible actives sites but also is capable of integrating the synergistic effect between two metals. Herein, we report a novel strategy to controllably construct bimetallic CuO/ZnO nanomaterials with sophisticated hierarchical structure through a pseudomorphic transformation and subsequent calcination process. The resulting unique hierarchical structure of ZnO/CuO is primarily constituted of a nanosphere and a rod grafted in a microscale cube with multidimensional size, which thus results in excellent dispersion, superior charge-transport capability, and abundant accessible active sites. Impressively, the optimized hierarchical structure product of CuO/ZnO (4:1) demonstrates an excellent glucose detection performance with a rapid response time, a wide linear range, a low detection limit, and strong antiinterference ability, realizing more advantages than commercial CuO or ZnO materials and shedding light on the positive correlation of the structure and performance. This study provides a new strategy for the controllable fabrication of the sophisticated hierarchical structure of bimetallic oxide nanomaterials.

Fabrication of Hierarchical Quaternary Architectures of Metal-Organic Frameworks through Programmed Transformation

A new method to construct hierarchical architectures has been developed by programmed transformation of metal-organic frameworks (MOFs). A MOF precursor was fabricated by reaction of Cu(OAC)₂ and 2,5-dihydroxyterephthalic acid (H₄DOBDC), which could perform transformation in pure methanol solvent and the sodium dodecyl benzene sulfonate (SDBS) solution of methanol, respectively. Interestingly, two kinds of immersion solutions could induce the transformation of the MOF precursor into MOF-74, which resulted in different morphologies: nanoneedles for the methanol and nanosheets for the SDBS. Herein, nanosheets-mesorods-microcuboid hierarchical quaternary architectures of MOF have been successfully achieved by sequential immersion of the precursor in two kinds of transformation solutions, which demonstrates well-defined hierarchy from the nanoscale to mesoscale to microscale. A unique hierarchical architecture could be recognized as quaternary structures, taking the MOF unit cell as the primary structure, the nanosheets as the secondary structure, the mesorods as the tertiary structure, and the microcuboid as the quaternary structure. Our study indicated the potential of programmed transformation between MOFs in the construction of hierarchical architectures, offering a new approach to sophisticated materials.

Preparation of Hierarchically Porous Metal-Organic Frameworks via Slow Chemical Vapor Etching for CO2 Cycloaddition

Hierarchically porous metal-organic frameworks (HP-MOFs) are a class of promising functional material with micropores, mesopores, and/or macropores, which can address the issue of slow mass transfer and less exposed active sites for primitive microporous MOFs. Despite many attempts that have been achieved through a variety of techniques to date, there is still a myriad of spaces that urgently need to be exploited. In this work, we report the novel synthesis of HP-MOFs via slow chemical steam etching. The preparation process can be subtly achieved using water vapor as an etchant; meanwhile, the addition of ethanol into the vapor atmosphere is carried out because it can stabilize the MOF framework well with its hydrophobic alkane tails, thereby slowing the etching rate toward MOFs, successfully realizing the controllable etching manner of MOF components. Furthermore, the joint influence of the water content and etching temperature on the MOF backbone structure etched has thus been investigated in detail. Impressively, we can harvest desired HP-MOFs with the retained crystalline structure at a water content of 50% and an etching temperature of 120 °C. The resulting HK-120/50 product etched exhibits excellent catalytic activity and stability in [2 + 3] cycloaddition of CO₂ than pristine MOF, which can be attributed to the more exposure of active sites and the acceleration of mass transportation across the entire MOF skeleton. Noteworthy, the strategy proposed in this study may be extended to other HP-MOF construction systems due to the lability of most MOFs toward the chemical water vapor.