Synthesis and Characterization of MOF-Derived Structures: Recent Advances and Future Perspectives

Due to their facile tunability, metal-organic frameworks (MOFs) are employed as precursors and templates to construct advanced functional materials with unique and desired chemical, physical, mechanical, and morphological properties. By tuning MOF precursor composition and manipulating conversion processes, various MOF-derived materials commonly known as MOF derivatives can be constructed. The possibility of controlled and predictable properties makes MOF derivatives a preferred choice for numerous advanced technological applications. The innovative synthetic designs besides the plethora of interdisciplinary characterization approaches applicable to MOF derivatives provide the opportunity to perform a myriad of experiments to explore the performance and offer key insight to develop the next generation of advanced materials. Though there are many published works of literature describing various synthesis and characterization techniques of MOF derivatives, it is still not clear how the synthesis mechanism works and what are the best techniques to characterize these materials to probe their properties accurately. In this review, the recent development in synthesis techniques and mechanisms for a variety of MOF derivates such as MOF-derived metal oxides, porous carbon, composites/hybrids, and sulfides is summarized. Furthermore, the details of characterization techniques and fundamental working principles are summarized to probe the structural, mechanical, physiochemical, electrochemical, and electronic properties of MOF and MOF derivatives. The future trends and some remaining challenges in the synthesis and characterization of MOF derivatives are also discussed.

Conceptual and Practical Aspects of Metal-Organic Frameworks for Solid-Gas Reactions

The presence of site-isolated and well-defined metal sites has enabled the use of metal-organic frameworks (MOFs) as catalysts that can be rationally modulated. Because MOFs can be addressed and manipulated through molecular synthetic pathways, they are chemically similar to molecular catalysts. They are, nevertheless, solid-state materials and therefore can be thought of as privileged solid molecular catalysts that excel in applications involving gas-phase reactions. This contrasts with homogeneous catalysts, which are overwhelmingly used in the solution phase. Herein, we review theories dictating gas phase reactivity within porous solids and discuss key catalytic gas-solid reactions. We further treat theoretical aspects of diffusion within confined pores, the enrichment of adsorbates, the types of solvation spheres that a MOF might impart on adsorbates, definitions of acidity/basicity in the absence of solvent, the stabilization of reactive intermediates, and the generation and characterization of defect sites. The key catalytic reactions we discuss broadly include reductive reactions (olefin hydrogenation, semihydrogenation, and selective catalytic reduction), oxidative reactions (oxygenation of hydrocarbons, oxidative dehydrogenation, and carbon monoxide oxidation), and C-C bond forming reactions (olefin dimerization/polymerization, isomerization, and carbonylation reactions).

MOF-on-MOF heterojunction-derived Co3O4-CuCo2O4 microflowers for low-temperature catalytic oxidation

Through the exchange-extended growth method (EEGM), MOF-on-MOF heteroarchitectures with distinct crystallography were produced and pyrolyzed into hybrid metal oxides. The strong exchange ability of organometallic compounds realized the component reconstruction of the MOF matrix and enhanced the interfacial forces between MOFs, showing an excellent performance in low-temperature catalytic oxidation.

Selective Hydrogenation of Furfural over the Co-Based Catalyst: A Subtle Synergy with Ni and Zn Dopants

A multimetal doping strategy has aroused extensive attention in promoting a non-noble catalyst for selective hydrogenation reaction. Herein, a multimetallic catalyst (NiCoZn@CN) with excellent catalytic performance for hydrogenation of furfural (FAL) to furfuryl alcohol (FOL) is prepared through a facile, inexpensive, and efficient pyrolysis method. Using H₂ as a H donor, extremely high selectivity (>99%) with 100% conversion is attained over the optimal NiCoZn@CN-600 catalyst. The subtle synergy between Co and Ni, Zn dopants, which remarkably promotes the performance of the Co-based catalyst, is revealed. In the NiCoZn@CN system, Co⁰ is proven to be the main active site, whose content is greatly improved by Ni and Co dopants. Additionally, the Ni dopant could also benefit activation of H₂ and the Zn dopant could enhance metal nanoparticle dispersion and the porous structure of the catalyst. In situ FTIR indicates that the vertical adsorption mode of FAL with the O_aldehyde terminal on NiCoZn@CN-600 ensures a selective hydrogenation process. With a N-doped carbon matrix, NiCoZn@CN-600 shows good cycling stability in five times run. NiCoZn@CN-600 is also competent in the catalytic transfer hydrogenation (CTH) of FOL, affording >99% yield with 2-propanol as a H donor. This study opens an avenue toward rational design of multimetallic doping catalysts with high selectivity for challenging reactions in the conversion of biomass-derived compounds.

Recent Progress on Metal-Organic Framework and Its Derivatives as Novel Fire Retardants to Polymeric Materials

High flammability of polymers has become a major issue which has restricted its applications. Recently, highly crystalline materials and metal-organic frameworks (MOFs), which consisted of metal ions and organic linkers, have been intensively employed as novel fire retardants (FRs) for a variety of polymers (MOF/polymer). The MOFs possessed abundant transition metal species, fire-retardant elements and potential carbon source accompanied with the facile tuning of the structure and property, making MOF, its derivatives and MOF hybrids promising for fire retardancy research. The recent progress and strategies to prepare MOF-based FRs are emphasized and summarized. The fire retardancy mechanisms of MOF/polymer composites are explained, which may guide the future design for efficient MOF-based FRs. Finally, the challenges and prospects related to different MOF-based FRs are also discussed and aim to provide a fast and holistic overview, which is beneficial for researchers to quickly get up to speed with the latest development in this field.

Leaf-like Co-ZIF-L derivatives embedded on Co2AlO4/Ni foam from hydrotalcites as monolithic catalysts for toluene abatement

Herein, a series of distinctively monolithic catalysts were first synthesized by decorating leaf-like Co-ZIF-L derivatives on Co₂AlO₄ coral-like microspheres from CoAl layered double hydroxides (LDHs), which were coated on three-dimensional porous Ni foam. As a proof of concept application, toluene was chosen as a probe molecule to evaluate their catalytic performances over the as-synthesized catalysts. As a result, the L-12 sample derived from Co₂AlO₄@Co-Co LDHs displayed an excellent catalytic performance, cycling stability and long-term stability for toluene oxidation (T₉₉ = 272 °C, 33 °C lower than that of Co₂AlO₄ sample), where leaf-like Co-ZIF-L served as a sacrificial template to synthesize Co-Co LDHs. The improved catalytic performance was attributed to its distinctive structure, in which leaf-like Co-ZIF-L derivatives on Co₂AlO₄ resulted in its higher specific surface area, lower-temperature reducibility, rich surface oxygen vacancy and high valence Co³⁺ species. This work thus demonstrates a feasible strategy for the design and fabrication of hybrid LDHs/ZIFs-derived composite architectures, which is expected to construct other novel monolithic catalysts with hierarchical structures for other potential applications.

MOF-derived metal oxide composite Mn2Co1Ox/CN for efficient formaldehyde oxidation at low temperature

A novel MOF-derived MnCoO_x nanoparticles embedded in porous N-doped carbon catalyst exhibits excellent catalytic activity for the low-temperature oxidation of formaldehyde.

Multicomponent metal-organic framework derivatives for optimizing the selective catalytic performance of styrene epoxidation reaction

Multicomponent metal-organic framework (MOF) derivatives have attracted strong interest in energy and environmental fields. However, most of the papers focus on single MOF derivatives; reports on multicomponent MOF derivatives and their catalytic studies are relatively few. Here, we report an easy-to-operate strategy to obtain multicomponent MOF derivatives by treating multicomponent MOFs under a suitable gas atmosphere and at high temperature. We used ZIF-67 as a template to introduce Zn and successfully obtained multicomponent MOFs. After carbonization, the multicomponent MOF derivatives with Co and CoO nanoparticles exhibit higher conversion of styrene (≈99%), higher selectivity (≈70%) and better stability compared to MOFs and single component MOF derivatives.

Vertically-aligned Co3O4 arrays on Ni foam as monolithic structured catalysts for CO oxidation: effects of morphological transformation

A generic hydrothermal synthesis route has been successfully designed and utilized to in situ grow highly ordered Co3O4 nanoarray (NA) precursors on Ni substrates, forming a series of Co3O4 nanoarray-based monolithic catalysts with subsequent calcination. The morphology evolution of Co3O4 nanostructures which depends upon the reaction time, with and without CTAB or NH4F is investigated in detail, which is used to further demonstrate the growth mechanism of Co3O4 nanoarrays with different morphologies. CO is chosen as a probe molecule to evaluate the catalytic performance over the synthesized Co-based oxide catalysts, and the effect of morphological transformation on the catalytic activity is further confirmed via using TEM, H2-TPR, XPS, Raman spectroscopy and in situ Raman spectroscopy. As a proof of concept application, core-shell Co3O4 NAs-8 presenting hierarchical nanosheets@nanoneedle arrays with a low density of nanoneedles exhibits the highest catalytic activity and long-term stability due to its low-temperature reducibility, the lattice distortion of the spinel structure and the abundance of surface-adsorbed oxygen (Oads). It is confirmed that CO oxidation on the surface of Co3O4 can proceed through the Langmuir-Hinshelwood mechanism via using in situ Raman spectroscopy. It is expected that the in situ synthesis of well-defined Co3O4 monolithic catalysts can be extended to the development of environmentally-friendly and highly active integral materials for practical industrial catalysis.

Effect of ultrasonic treatment of palygorskite on the catalytic performance of Pd-Cu/palygorskite catalyst for room temperature CO oxidation in humid circumstances

Pd-Cu/palygorskite catalysts were prepared by a wet impregnation method using palygorskite (PC/N-Pal) and ultrasonic-treated palygorskite (PC/U-Pal) as the support. Their catalytic activities toward CO oxidation at room temperature and in humid circumstances were investigated. PC/U-Pal exhibits much higher catalytic activity and stability than PC/N-Pal under the conditions of 1.0 vol.% CO and 3.3 vol.% H₂O in the feed gas. The X-ray diffraction results indicate that quartz impurities were eliminated from the Pal after the ultrasonic treatment, and more copper species exist in the form of Cu₂Cl(OH)₃ in PC/U-Pal. The temperature-programmed reduction results suggest that there is an enhanced reducibility of PC/U-Pal after ultrasonic treatment. Furthermore, the ultrasonic treatment can properly decrease the hydrophilicity of the support and catalyst, which may also contribute to the excellent catalytic performance.

Low-temperature CO oxidation over integrated penthorum chinense-like MnCo2O4 arrays anchored on three-dimensional Ni foam with enhanced moisture resistance

Advanced integrated nanoarray (NA) catalysts have been designed by growing metal-doped Co₃O₄ arrays on nickel foam with robust adhesion.

Co/Cu-MFF derived mesoporous ternary metal oxide microcubes for enhancing the catalytic activity of the CO oxidation reaction

Metal–organic framework (MOF)-based derivatives with uniform micro/mesoporous structures have attracted a great deal of interest in various research fields. Herein, we report a simple strategy to design functional mesoporous ternary metal oxides with controlled composition through direct pyrolysis of Co/Cu bimetal-formate frameworks (Co/Cu-MFFs), which were prepared by a facile one-step liquid-phase precipitation method, exhibiting uniform distribution of two different metal species and good structural integrity. The obtained mesoporous ternary metal oxide Cu_xCo_3−xO₄ (x = 0.5, 1) microcubes exhibit much better performance for CO oxidation than pure Co₃O₄, which can be mainly attributed to their larger specific surface areas, stronger reducibility, and the synergistic effect of two active metal oxide components.

The fabricated Cu_xCo_3−xO₄ microcubes with structure and component merits exhibit good performance for CO oxidation.

Fine Co Nanoparticles Encapsulated in a N-Doped Porous Carbon Matrix with Superficial N-Doped Porous Carbon Nanofibers for Efficient Oxygen Reduction

Herein, we develop a novel method to synthesize evenly dispersed fine Co nanoparticles (CoNPs) (particle size of ∼42 nm) encapsulated in a N-doped porous carbon matrix (NPCM) with superficial N-doped porous carbon nanofibers (NPCNF) (denoted as Co@NPCM/CNF-850) as an oxygen reduction reaction (ORR) electrocatalyst. Such an electrocatalyst is the direct pyrolysis product of the novel pine needle-like ZIF-67-based metal-organic framework nanowire array (MOFNWA) prepared using an inorganic cobalt carbonate hydroxide (Co(CO₃)_0.5(OH)·0.11H₂O) nanowire array as a linear sacrificial template, which is totally different from the traditional method, that is, using inorganic salts to synthesize MOF particles. Because of the high dispersibility of the effective fine N-doped carbon-wrapped CoNPs (rather than the overlarge CoNP aggregates); the unique linear MOF-derived assemblies, which are beneficial to electronic transmission; the high degree of graphitization, which is attributed to the superficial NPCNF and carbon layers wrapping the CoNPs; as well as the high porosity, our catalyst showed remarkable ORR activity (E_onset of 1.033 V vs the reversible hydrogen electrode) in alkaline solution. Besides, our catalyst revealed excellent stability and tolerance of methanol. Furthermore, on the basis of the X-ray absorption near-edge structure, extended X-ray absorption fine structure, and linear sweep voltammetry data, we first provided proof that a catalyst devoid of obvious Co-N_x can have superior ORR activity.

Metal organic framework-derived Co3O4 microcubes and their catalytic applications in CO oxidation

Porous Co₃O₄ catalysts were successfully synthesized via a one-step pyrolysis of Co-based metal-formate frameworks, which exhibit excellent catalytic activity for CO oxidation.

Catalytically active ceria-supported cobalt–manganese oxide nanocatalysts for oxidation of carbon monoxide

The crystallinity of the surface of the two-dimensional Co₃O₄ phase governs the catalytic performance of ceria-supported cobalt–manganese oxide nanostructures.

The Road to MOF-Related Functional Materials and Beyond: Desire, Design, Decoration, and Development

Metal-organic frameworks (MOFs), which are known as a class of porous coordination polymers, have proven to be of great significance to manifold applications, owing to their fascinating topology, ultrahigh porosity, enormous internal surface area, and the combination of being as rigid as inorganic materials and as flexible as organic materials . In this review, we give a concise history of the development of MOFs as functional materials prior to our entry into this area in 2006, then a summary of our road to participate in and extend the outline of the research in MOFs chemistry, as well as the challenge in further designing applicable functional materials. We describe not only the road of evolution from the past, present, and future of this chemistry, but also the road to finalize a functional material from the desire to the design, synthesis, and postmodification of a MOF. Throughout the review, we particularly emphasize the improvements in the application of MOFs as heterogeneous catalysts, such as employing MOFs as one component for the construction of composites, and their extended scope in tough catalytic reactions. Examples of applications in gas storage and separation, small molecular sensing, and our perspectives for future applications triggered by MOFs, are also introduced.

Cobalt nanoparticles embedded in porous N-doped carbon as long-life catalysts for hydrolysis of ammonia borane

Cobalt nanoparticles uniformly embedded in porous N-doped carbon prepared through the thermal decomposition of Co(salen) are promising catalysts for hydrolysis of ammonia borane.

Enhanced low temperature CO oxidation by pretreatment: specialty of the Au–Co3O4 oxide interfacial structures

The enhanced CO oxidation by Au deposition and particularly He- and in situ-pretreatments was elucidated in light of the structural specialties associated with the facets of Co₃O₄ substrates and the corresponding Au–Co₃O₄ interfaces.

Efficient and selective green oxidation of alcohols by MOF-derived magnetic nanoparticles as a recoverable catalyst

A magnetic Fe₃O₄@C heterogeneous catalyst derived from MOFs is highly efficient and selective in oxidation of alcohols with neat water and base-free conditions.

Design of Zeolitic Imidazolate Framework Derived Nitrogen-Doped Nanoporous Carbons Containing Metal Species for Carbon Dioxide Fixation Reactions

Various N-doped nanoporous carbons containing metal species were prepared by direct thermal conversion of zeolitic imidazolate frameworks (ZIFs; ZIF-7, -8, -9, and -67) at different temperatures (600, 800, and 1000 °C). These materials were utilized as bifunctional acid-base catalysts to promote the reaction of CO2 with epoxides to form cyclic carbonates under 0.6 MPa of CO2 at 80 °C. The catalyst generated by thermal conversion of ZIF-9 at 600 °C (C600-ZIF-9) was found to exhibit a higher catalytic activity than the other ZIFs, other conventional catalysts, and other metal-organic framework catalysts. The results of various characterization techniques including elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and transmission electron microscopy show that C600-ZIF-9 contains partly oxidized Co nanoparticles and N species. Temperature-programmed desorption measurements by using CO2 and NH3 as probe molecules revealed that C600-ZIF-9 has both Lewis acid and Lewis base catalytic sites. Finally, the substrate scope was extended to seven other kinds of epoxides.