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

Constructing metal nanoparticle (MNP) composites from metal-organic framework (MOF) precursors has attracted extensive attention as the MOF precursors provide an excellent porous matrix for the generation of MNP composites, which enables the direct fabrication of well-dispersed MNP composites. In this work, a novel strategy is proposed to fabricate MNP composites by slow chemical reduction (SCR) of MOF precursors at room temperature. The reduction process is skillfully slowed via using ethanol as the solvent, and the formation of MNP composites is then realized by the SCR process. Briefly, BH4- slowly diffuses into an MOF precursor and in situ reduces metal ions to well-dispersed nanoscale MNP composites. Meanwhile, this SCR process breaks the coordination bonds from MOF precursors, leading to the generation of porous structures for the resulting composites. Interestingly, the composites inherit the morphology of MOF precursors well. Besides, this SCR strategy allows construction of MNP composites from different types of MOF precursors. The resulting Cu@HK-3 composites possess well-dispersed nanoscale Cu NPs and a porous architecture, which exhibit superior catalytic performance and stability in the Ullmann coupling reaction. This strategy provides a feasible, convenient, and energy-saving route to prepare MNP composites from MOF precursors with customizable morphology and well-dispersed MNPs.

Preparation of MOF Film/Aerogel Composite Catalysts via Substrate-Seeding Secondary-Growth for the Oxygen Evolution Reaction and CO2 Cycloaddition.

Substrate-supported metal-organic frameworks (MOFs) films are desired to realize their potential in practical applications. Herein, a novel substrate-seeding secondary-growth strategy is developed to prepare composites of uniform MOFs films on aerogel walls. Briefly, the organic ligand is "pre-seeded" onto the aerogel walls, and then a small amount of metal-ion solution is sprayed onto the prepared aerogel. The sprayed solution diffuses along the aerogel walls to form a continuous thin layer, which confines the nucleation reaction, promoting the formation of uniform MOFs films on the aerogel walls. The whole process is simple in operation, highly efficient, and eco-friendly. The resulting hierarchical MOFs/aerogel composites have abundant accessible active sites and enable excellent mass transfer, which endows the composite with outstanding catalytic activity and stability in both liquid-phase CO2 cycloaddition and electrochemical oxygen evolution reaction (OER) process.

Approach to Fabricating a Compact Gold Nanoparticle Film with the Assistance of a Surfactant.

We report a facile method to fabricate a compact Au nanoparticle film with the assistance of surfactants. First, the dodecanethiol-coated Au nanoparticles were floated on the surface of the toluene/acetonitrile solvent mixture and adjusted to an expanded dispersion by changing the mixture ratio. Silicone oil was then added as a surfactant to compress the floating nanoparticles from the original loose status to a closely packed arrangement that produced a compact nanoparticle film. The relationship of the compressed film area to the silicone oil concentration was plotted and compared to the surface tension curve of silicone oil. The results were quite consistent, suggesting that the surface location of the surfactant induced the nanoparticles' compression. The resulting nanoparticle film was uniform and sufficiently robust to be transferred to the solid substrate. Moreover, it could be applied to catalyze the reduction of 4-nitrophenol. Our study indicated that the utilization of surfactants to compress the well-dispersed nanoparticles on the liquid surface is a simple, fast, and adaptable method of fabricateing compact nanoparticle films with great promise for future applications.

Fabrication of Metal-Organic Framework and Infinite Coordination Polymer Nanosheets by the Spray Technique.

We have developed a rapid and convenient method for fabricating metal-organic framework (MOF) and infinite coordination polymer (ICP) nanosheets by spraying the atomized solution of metal ions onto the organic ligand solution. Nanosheet formation could be attributed to the anisotropic diffusion of metal ions in the ligand solution, which may give rise to a lateral interface of metal ions and organic ligands, where the crystals tend to grow laterally in the form of nanosheets. Three kinds of Zn- and Cu-based MOF nanosheets and two kinds of Co-based ICP nanosheets have been successfully obtained by spraying under mild conditions. The two-dimensional structures of nanosheets with a nanometer thickness and a homogeneous size can be evidenced by scanning electron microscopy, atomic force microscopy, X-ray diffraction, Brunauer-Emmett-Teller, and Fourier transform infrared spectroscopy measurements. Furthermore, the fabricated ICP nanosheets have exhibited efficient catalytic performance for the conversion of CO2 to high-value-added chemicals. This spray technique simplifies the nanosheet production process by industrialized means and enhances its controllability by the fast liquid-liquid interfacial fabrication, thus allowing access to the industrialized fabrication of MOF and ICP nanosheets.

Enabling long-distance hydrogen spillover in nonreducible metal-organic frameworks for catalytic reaction.

Hydrogen spillover is an extraordinary effect in heterogeneous catalysis and hydrogen storage, which refers to the surface migration of metal particle-activated hydrogen atoms over the solid supports. Historical studies on this phenomenon have mostly been limited to reducible metal oxides where the long-distance proton-electron coupled migration mechanism has been established, yet the key question remains on how to surmount short-distance and defect-dependent hydrogen migration on nonreducible supports. By demerging hydrogen migration and hydrogenation reaction, here we demonstrate that the hydrogen spillover in nonreducible metal-organic frameworks (MOFs) can be finely modulated by the ligand functional groups or embedded water molecules, enabling significant long-distance (exceed 50 nm) movement of activated hydrogen. Furthermore, using sandwich nanostructured MOFs@Pt@MOFs as catalysts, we achieve highly selective hydrogenation of N-heteroarenes via controllable hydrogen spillover from Pt to MOFs-shell. We anticipate that this work will enhance the understanding of hydrogen spillover and shed light on de novo design of MOFs supported catalysts for many important reactions involving hydrogen.

Preparation of Superhydrophobic Metal-Organic Framework/Polymer Composites as Stable and Efficient Catalysts.

Metal-organic frameworks (MOFs), as a chemical platform, combined with multifunctional polymers are of interest in catalytic applications, which can not only inherit the outstanding properties of the two components but also lead to unique synergistic effects. Nonetheless, most MOFs possess varying degrees of water instability, which limits their real application. Herein, we fabricated highly hydrophobic MOF/polymer composites via a universal post-synthetic polymerization strategy as efficient catalysts. Polyaniline (PANI) was first hybridized with MOFs by vapor deposition polymerization, and then, hydrophobic molecules were grafted to the PANI by a covalent linking process, thereby forming a superhydrophobic MOF/PANI hybrid material (MOF/PANI-shp). The resultant MOF/PANI-shp not only obtains superior moisture/water resistance without significantly disturbing the original features but also exhibits a novel catalytic selectivity in styrene oxidation because of the accessible sites and synergistic effects. Such a synthetic strategy for the MOF/polymer catalyst opens a new avenue for the design of a unique catalyst with outstanding catalytic efficiency, selectivity, and stability.

Fabrication of a robust MOF/aerogel composite via a covalent post-assembly method.

A covalent post-assembly strategy is developed to prepare a composite of dispersive MOF particles in an aerogel matrix. Briefly, the anhydride group-decorated MOF (UiO-66-NH2) particles covalently coupled with polyimide (PI) monomers through a one-pot amidation polymerization reaction, succeeding a process of gel-sol, freeze-drying and thermal-imidization to obtain the UiO-66-PI aerogel. The designed composite shows outstanding catalytic activity in CO2 cycloaddition and excellent adsorption capacity for dyes.

Construction of Zn/Ni Bimetallic Organic Framework Derived ZnO/NiO Heterostructure with Superior N-Propanol Sensing Performance.

Bimetallic organic frameworks (Bi-MOFs) have been recognized as one of the most ideal precursors to construct metal oxide semiconductor (MOS) composites, owing to their high surface area, various chemical structures, and easy removal of the sacrificial MOF scaffolds through calcination. Herein, we synthesized Zn/Ni Bi-MOF for the first time via a facile ion exchange postsynthetic strategy, formed a three-dimensional framework consisting of infinite one-dimensional chains that is unattainable through the direct solvothermal approach, and then transformed the Zn/Ni Bi-MOF into a unique ZnO/NiO heterostructure through calcination. Notably, the obtained sensor based on a ZnO/NiO heterostructure exhibits an ultrahigh response of 280.2 toward 500 ppm n-propanol at 275 °C (17.2-fold enhancement compared with that of ZnO), remarkable selectivity, and a limit of detection of 200 ppb with a notable response (2.51), which outperforms state-of-the-art n-propanol sensors. The enhanced n-propanol sensing properties may be attributed to the synergistic effects of several points including the heterojunction at the interface between the NiO and ZnO nanoparticles, especially a one-dimensional chain MOF template structure as well as the chemical sensitization effect of NiO. This work provides a promising strategy for the development of a novel Bi-MOF-derived MOS heterostructure or homostructure with well-defined morphology and composition that can be applied to the fields of gas sensing, energy storage, and catalysis.

Fabrication of 2D metal-organic framework nanosheet@fiber composites by spray technique.

A feasible and rapid one-step strategy has been developed to fabricate 2D metal-organic framework nanosheet (MOF-NS)@fiber composites at room temperature by spray technique, through which five kinds of MOF-NS@fiber were successfully prepared. The representative nanoscale CuBDC were synthesized on the surface of carbon fibers with homogeneous dispersion and high coverage.

Preparation of hierarchical trimetallic coordination polymer film as efficient electrocatalyst for oxygen evolution reaction.

A hierarchical trimetallic coordination polymer film was prepared using a spray-assisted interface synthetic strategy and in situ deposited onto Ni foam (denoted as Co0.5Ni0.3Fe0.2BDC-HCPF/Ni foam). The as-prepared material exhibits a 3D network hierarchical structure with 1D interconnected nanofibers and can be directly used as an efficient OER electrocatalyst.

Amorphous FeNi-bimetallic infinite coordination polymers as advanced electrocatalysts for the oxygen evolution reaction.

Amorphous bimetallic coordination polymers have been prepared by a mild room temperature solution phase method and utilized as an OER electrocatalyst. Their excellent performance with an overpotential of 228 mV at 10 mA cm-2 and a Tafel slope of 30.3 mV dec-1 exhibits their great potential in the field of the OER.

Fabrication of MOF Thin Films at Miscible Liquid-Liquid Interface by Spray Method.

Metal-organic frameworks (MOFs) are an intriguing class of porous crystalline inorganic-organic hybrid materials. The fabrication of oriented, crystalline thin film of MOFs is expected to open novel avenues to traditional applications and to serve myriad advanced technologies. Here, a facile spray-assisted miscible liquid-liquid interface (MLLI) synthetic strategy is carried out and reported under mild condition that utilizes miscible interface for the rapid and controllable fabrication of large-area free-standing MOF thin films. The methodology can employ various metal nodes and organic ligands to yield various high quality lamellar/granulous MOF thin films at MLLI, which indicates the universality of the MLLI strategy.