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The structure and properties of materials are determined by a diverse range of chemical bond formation and breaking mechanisms, which greatly motivates the development of selectively controlling the chemical bonds in order to achieve materials with specific characteristics. Here, an orientational intervening bond-breaking strategy is demonstrated for synthesizing ultrathin metal-organic framework (MOF) nanosheets through balancing the process of thermal decomposition and liquid nitrogen exfoliation. In such approach, proper thermal treatment can weaken the interlayer bond while maintaining the stability of the intralayer bond in the layered MOFs. And the following liquid nitrogen treatment results in significant deformation and stress in the layered MOFs' structure due to the instant temperature drop and drastic expansion of liquid N2, leading to the curling, detachment, and separation of the MOF layers. The produced MOF nanosheets with five cycles of treatment are primarily composed of nanosheets that are less than 10â nm in thickness. The MOF nanosheets exhibit enhanced catalytic performance in oxygen evolution reactions owing to the ultrathin thickness without capping agents which provide improved charge transfer efficiency and dense exposed active sites. This strategy underscores the significance of orientational intervention in chemical bonds to engineer innovative materials.
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Pd/C catalysts have been widely applied in the debenzylation process due to their excellent ability of hydrogenolysis. However, they have been suffering from the problems of agglomeration and loss of active components, which lead to decreased and unstable activity. Thus, it is still a challenge to achieve Pd/C catalysts with high activity and stability. Herein, we propose a strategy for preparing Pd/C catalysts on porous carbon hollow spheres by a microwave discharge method. Due to the high-temperature property and reducibility of microwave discharge, Pd precursors can be rapidly reduced, resulting in well-dispersed Pd nanoparticles with a small size on the carbon carrier. Besides, the matched mesopores in the carbon hollow spheres can anchor Pd nanoparticles and effectively reduce the agglomeration and loss of Pd nanoparticles during the catalytic reaction. As a result, the as-prepared Pd/mesoporous carbon hollow spheres exhibit high and stable activity in the debenzylation reaction.
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Hydrogen spillover is the migration of activated hydrogen atoms from a metal particle onto the surface of catalyst support, which has made significant progress in heterogeneous catalysis. The phenomenon has been well researched on oxide supports, yet its occurrence, detection method and mechanism on non-oxide supports such as metal-organic frameworks (MOFs) remain controversial. Herein, we develop a facile strategy for efficiency enhancement of hydrogen spillover on various MOFs with the aid of water molecules. By encapsulating platinum (Pt) nanoparticles in MOF-801 for activating hydrogen and hydrogenation of C=C in the MOF ligand as activated hydrogen detector, a research platform is built with Pt@MOF-801 to measure the hydrogenation region for quantifying the efficiency and spatial extent of hydrogen spillover. A water-assisted hydrogen spillover path is found with lower migration energy barrier than the traditional spillover path via ligand. The synergy of the two paths explains a significant boost of hydrogen spillover in MOF-801 from imperceptible existence to spanning at least 100-nm-diameter region. Moreover, such strategy shows universality in different MOF and covalent organic framework materials for efficiency promotion of hydrogen spillover and improvement of catalytic activity and antitoxicity, opening up new horizons for catalyst design in porous crystalline materials.
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Building bridges among different types of catalysts to construct cascades is a highly worthwhile pursuit, such as chemo-, bio-, and chemo-bio cascade reactions. Cascade reactions can improve the reaction efficiency and selectivity while reducing steps of separation and purification, thereby promoting the development of "green chemistry". However, compatibility issues in cascade reactions pose significant constraints on the development of this field, particularly concerning the compatibility of diverse catalyst types, reaction conditions, and reaction rates. Metal-organic framework micro/nano reactors (MOF-MNRs) are porous crystalline materials formed by the self-assembly coordination of metal sites and organic ligands, possessing a periodic network structure. Due to the uniform pore size with the capability of controlling selective transfer of substances as well as protecting active substances and the organic-inorganic parts providing reactive microenvironment, MOF-MNRs have attracted significant attention in cascade reactions in recent years. In this Perspective, we first discuss how to address compatibility issues in cascade reactions using MOF-MNRs, including structural design and synthetic strategies. Then we summarize the research progress on MOF-MNRs in various cascade reactions. Finally, we analyze the challenges facing MOF-MNRs and potential breakthrough directions and opportunities for the future.
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The remarkable roles of metal promoters have been known for nearly a century, but it is still a challenge to find a suitable structure model to reveal the action mechanism behind metal promoters. Herein, a new function of metal-organic frameworks (MOFs) is developed as an ideal model to construct structurally ordered metal promoters by a targeted post-modification strategy. MOFs as model not only favor clearing the real action mechanism behind metal promoters, but also can anchor one or multiple kinds of metal promoters especially noble metal promoters. Typically, the as-prepared Pd/bpy-UiO-Cu catalysts show high selectivity (>99%) toward 4-nitrophenylethane in 4-nitrostyrene hydrogenation, mainly due to the enhanced interaction between Pd nanoparticles and MOF carriers induced by Cu promoters, thus inhibiting the hydrogenation of 4-nitrophenylethane. This strategy with flexibility and universality will open up a new route to synthesize efficient catalysts with structurally ordered metal promoters.
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The construction of metal-organic framework (MOF) films is a crucial step for integrating them into technical applications. However, due to the crystallization nature, it is difficult to grow most MOFs spontaneously or process them into films. Here, a convenient strategy is demonstrated for constructing MOF films by using modulators to achieve homogeneous assembly of MOF clusters. Small clusters in the early growth steps of MOFs can be stabilized by modulators to form fluidic precursors with good processibility. Then, simple removal of modulators will trigger the crosslinking of MOF clusters and lead to the formation of continuous films. This strategy is universal for the fabrication of several types of MOF films with large scale and controllable thickness, which can be deposited on a variety of substrates as well as can be patterned in micro/nano resolution. Additionally, versatile composite MOF films can be easily synthesized by introducing functional materials during the crosslinking process, which brings them broader application prospects.
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Herein, we report a stable catalyst with Ru single atoms anchored on a one-dimensional carbon fiber@graphitic carbon nitride hierarchy, by assembling wet wipes composed of fiber-derived carbon fiber (CF), melamine-derived graphitic carbon nitride (g-C3N4) and RuCl3 before NaBH4 reduction. The atomically dispersed Ru species (3.0 wt%) are tightly attached via N-coordination provided by exterior g-C3N4 nanosheets, and further stabilized by the interior mesoporous CF. The obtained CF@g-C3N4-Ru SAs catalyst can be cycled six times without notable leaching of Ru or loss of GVL yield in the acidic media. This catalyst is more stable than Ru nanoparticles supported on CF@g-C3N4, as well as Ru single atoms anchored on CF and g-C3N4, and proves to be one of the most efficient metal catalysts for aqueous LA hydrogenation to γ-valerolactone (GVL). The isolated Ru atoms by strong N-coordination, and their enhanced electron/mass transfer afforded by the one-dimensional hierarchy, can be responsible for the excellent durability of CF@g-C3N4-Ru SAs under harsh reaction conditions.
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The conversion of CO2 through CO2 reduction reaction (CO2 RR) into valuable products has potential to lessen the greenhouse effect caused by uncontrolled CO2 emissions. Challenges of CO2 RR reaction lie in the stabilization of the reaction intermediate and the activation of the inert chemical bond of CO2 , but the application of CO2 RR at large scale is limited by the high cost and structural instability of traditional catalysts. By applying CO2 RR catalyst with delicate structure of stable CO2 intermediate to industrial production, the problems such as high cost of CO2 conversion, low catalytic selectivity and poor catalytic efficiency can be effectively solved, showing better application value and significance than traditional catalysts. This review focuses on the defects, and metal-support interaction (MSI) effect to modify the catalyst and other strategies to enhance the effectiveness of CO2 reduction. The challenges and prospects from the three perspectives are also discussed to provide suggestions for the designing of efficient CO2 RR catalysts in the future. This review offers new insights and research perspectives of reducing CO2 emission through recycling CO2 , and neutralizing the carbon cycle.
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The one-pot combination of biocatalytic and chemocatalytic reactions represents an economically and ecologically attractive concept in the emerging cascade processes for manufacturing. The mutual incompatibility of biocatalysis and chemocatalysis, however, usually causes the deactivation of catalysts, the mismatching of reaction dynamic, and further challenges their integration into concurrent chemo-biocascades. Herein, we have developed a convenient strategy to construct versatile functional metal-organic framework micro-nanoreactors (MOF-MNRs), which can realize not only the encapsulation and protection of biocatalysts but also the controllable transmission of substances and the mutual communication of the incompatible chemo-biosystems. Importantly, the MOFs serving as the shell of MNRs have the capability of enriching the chemocatalysts on the surface and improving the activity of the chemocatalysts to sufficiently match the optimum aqueous reaction system of biocatalysts, which greatly increase the efficiency in the combined concurrent chemo-biocatalysis. Such strategy of constructing MOF-MNRs provides a unique platform for connecting the "two worlds" of chemocatalysis and biocatalysis.
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High-loading Pt/C catalysts play an important role in the practical application of metal-air batteries and fuel cells because of their superior activity, high conductivity, and commercial availability. It is well known that high loadings always lead to the agglomeration of Pt nanoparticles, resulting in a loss of catalytic activity and stability; thus, it still remains a challenge to prepare high-loading Pt/C catalysts with high dispersion and small particle sizes. Here, we introduce a surfactant-assisted microwave discharge method to prepare high-loading (>40 wt %) Pt/C electrocatalysts with ultrafine particle sizes (â¼3.19 nm) and good dispersion. Benefitting from the high-temperature property and reducibility of carbon-induced-arc, the surfactant and Pt precursors undergo rapid decomposition, reduction, and carbonization, generating the structure of Pt@C on carbon black. The carbon derived from the surfactant can not only inhibit the agglomeration of Pt nanoparticles but also prevent the Pt core from toxication, ensuring high activity and stability of the high-loading Pt/C catalyst. When evaluated in the oxygen reduction reaction, the as-prepared Pt/C catalyst demonstrates a comparable activity and better methanol resistance to commercial Pt/C.
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Combining the physical advantages of two-dimensional (2D) inorganic nanosheets and the modular design and programmed structure of metal-organic frameworks (MOFs), 2D MOFs remain at the forefront of functional material research. Despite tremendous efforts, precise control in the synthesis of 2D nonlayered MOFs with predesigned topology for desired applications remains challenging. Success in the bottom-up synthesis of 2D nonlayered MOFs via ligand exchange motivated us to incorporate partial BTC (BTC = 1,3,5-benzenetricarboxylate) ligand dissociation and CO2 capped coordination into the top-down treatment of bulk Cu-BTC MOF, leading to successful conversion of a 3D nonlayered network to a 2D Cu-based topological structure. Notably, a supercritical CO2-containing solvent mixture is employed to provide the desired defect and coordination engineering. Thus, our work introduces a new top-down concept based on modulated synthesis to fabricate high-quality 2D nonlayered MOFs for the first time.
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Shape-selective catalysis plays a key role in chemical synthesis. Porous nanomaterials with uniform pore structures are ideal supports for metal nanoparticles (MNPs) to generate efficient shape-selective catalysis. However, many commercial irregular porous nanomaterials face the challenge to realize satisfactory shape selectivity due to the lack of molecular sieving structures. Herein, we report a concept of creating shape selectivity in MNPs/porous nanomaterials through intentionally poisoning certain MNPs using suitable modifiers. The remaining MNPs within the substrates can cooperate with the channels to generate selectivity. Such a strategy not only applies to regular porous nanomaterials (such as MOFs, zeolites) but also extended to irregular porous nanomaterials (such as active carbon, P25). Potentially, the matching among different MNPs, corresponding modifiers, and porous nanomaterials makes our strategy promising in selective catalytic systems.
RESUMEN
To well address the problem of low stability for Ru-based catalysts against sintering and leaching during synthesis and aqueous levulinic acid (LA) hydrogenation to γ-valerolactone (GVL), herein we demonstrate an "inside-to-outside" synthetic strategy for robust yolk-structured nanospheres within a single Ru nanoparticle (NP, 4.2 nm) anchored inside the mesoporous shell (pore size, 4.0 nm), denoted as YS Ru@HMCS (yolk-structured Ru encapsulated into hollow mesoporous carbon sphere). Such a shell-supported-core configuration combines the merits of conventional yolk-structured and supported types, in which the active core is not only fully exposed, but also strongly anchored on the shell, based on the optimized interaction between oxidized Ru NP and N-doped mesoporous carbon shell. As a consequence, the resultant YS Ru@HMCS, delivers a high LA conversion (99.4%), a large selectivity to GVL (99.9%), and prolonged cycling life (up to 9 cycles) under water towards the LA hydrogenation, that exceeds conventional yolk-structured and supported analogues. Sintering-resistant, a single Ru NP is successfully encapsulated, and its leaching-resistant property is enhanced based on the improved metal-support contact, thus affording a highly stable Ru catalyst. Moreover, such a synthetic concept can be extended to the stabilization of other supported catalysts, providing a general approach to enhancing both the thermal and chemical stability of supported nanocatalysts.
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Constructing architectures with hierarchical porosity has been widely considered as the most efficient way to bypass the problems related to slow mass transfer and inaccessibility of internal space in MOFs. Now, a crystal-growth-dominated strategy is proposed to fabricate hierarchically porous MOFs (HP-MOFs). When the crystal growth is dominated by the monomer attachment, the aggregation of nonionic surfactant or polymer can be easily captured and released during the crystal growth process, resulting in the formation and ordering hierarchical pores along the radial direction. Owing to the accelerated mass diffusion and more exposed active sites of this design, HP-MOFs exhibited an enhanced catalytic efficiency in styrene oxidation.
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In the past decades, water tolerance has always been the long-pending key issue of sulfated solid superacids (SO42-/M xO y) toward industrial applications. Herein, we report a strategy for the facile coating of a thick tunable hydrophobic layer over SO42-/M xO y, which can significantly improve water tolerance, with negligible inhibition on the catalytic performance of SO42-/M xO y. Even after being directly immersed in water, the hydrophobic SO42-/M xO y can still maintain above 90% of original catalytic activity, whereas pristine SO42-/M xO y and control samples are almost completely deactivated. This strategy opens a new route to enhance the water tolerance of sulfated solid superacids.
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Nanoparticles@metal-organic frameworks (MOFs) composites have attracted considerable attention in recent years due to the prominent selective catalytic activity. However, it is highly desirable to develop a simple and universal way to settle the trade-off between the catalytic efficiency and selectivity. Herein, by employing the thermal instability of inherent defects, hierarchically porous Pt@UiO-66-NH2 , Pt@UiO-66, Pt@ZIF-8, and Au@ZIF-8 are successfully constructed after annealing at an appropriate temperature, respectively. The generated mesopores in the MOFs can be located around the external nanoparticle to retain the MOF shell for catalytic selectivity. Finally, when tested in olefin hydrogenation, Pt@UiO-66-NH2 shows significantly improved catalytic rate and enhanced dynamic selectivity.
RESUMEN
Metal-organic frameworks (MOFs) with an ordered channel and porosity show great promise for a myriad of purposes. Unfortunately, the coordination bond of metal ions and organic ligands easily weakens in unfavorable environments, which poses a key problem in expanding the application of MOFs. Herein, we report a general and efficient strategy to enhance the stability and preserve the porosity of MOFs by coating them with reduced graphene oxide (rGO). The prepared hybrid material consisted of MOFs and rGO, as the core and the protective shell, respectively. It is worth noting that the obtained MOFs@rGO composite material maintained a well-defined crystal structure and showed good catalytic activity as well as enhanced stability. Notably, this novel and general method of coating MOFs with a thin protective rGO shell will broaden the application fields of MOFs and open up a new avenue for the research of MOFs.
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Metal-organic framework (MOF)-based derivatives have attracted an increasing interest in various research fields. However, most of the reported papers mainly focus on pristine MOF-based derivatives, and research studies on functional MOF-based derivative composites are rare. Here, a simple strategy has been reported to design functional MOF-based derivative composites by the encapsulation of metal nanoparticle (MNP) in MOF matrixes (MNP@MOF) and the high-temperature calcination of MNP@MOF composites. The as-prepared MNP@metal oxide composites with a hierarchical pore structure exhibited excellent catalytic activity and high stability for the CO oxidation reaction.
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Functional organic molecules/metal-organic frameworks composites can be obtained by in situ crystalline structure transformation from ZIF-L to ZIF-8-L under double solvent conditions. Interestingly, the as-prepared molecules/ZIF-8-L composites with the leaf-like morphology exhibit good fluorescence properties and size selectivity in fluorescent quenchers due to the molecular sieving effect of the well-defined microporous ZIF-8-L.
RESUMEN
Visible-light-driven splitting of water using semiconductor photocatalysts is an excellent example of sustainable chemistry. The fabrication of mesoporous photocatalysts with a narrow bandgap into the sunlight region and a high specific surface area is crucial for efficient hydrogen evolution under visible light irradiation. Herein, we describe a facile one-pot hydrothermal approach toward uniform mesoporous microspheres of Cd1-xZnxS by adopting diethylenetriamine (DETA) as the structure-directing agent. The method is facile, reproducible and allows simultaneously control of the morphology, particle size, bandgaps, as well as the specific surface area of the mesoporous microspheres Cd1-xZnxS. The photocatalytic activity on H2 production through the splitting of water without noble metal loadingis highly enhanced by the mesoporous structure feature of the products. The optimized Cd0.2Zn0.8S mesoporous microspheres exhibit a specific surface area up to 98.09m(2)/g and a H2 production rate of 3.43mmol/hg (about 7.62 times higher than that of pure CdS powers) under visible light irradiation. Furthermore, apparent quantum efficiency (QE) of 16.2% was achieved in the as-fabricated Cd0.2Zn0.8S mesoporous microspheres under irradiation at 420nm. This study provides an effective route toward mesoporous microspheres photocatalysts for further investigations and practical applications.
