Conspectus Metal–organic frameworks (MOFs) have been attracting tremendous attention owing to their great structural diversity and functional tunability. Despite numerous inherent merits and big ...progress in the fundamental research (synthesizing new compounds, discovering new structures, testing associated properties, etc.), poor chemical stability of most MOFs severely hinders their involvement in practical applications, which is the final goal for developing new materials. Therefore, constructing new stable MOFs or stabilizing extant labile MOFs is quite important. As with them, some “potential” applications would come true and a lot of new applications under harsh conditions can be explored. Efficient strategies are being pursued to solve the stability problem of MOFs and thereby achieve and expand their applications. In this Account, we summarize the research advance in the design and synthesis of chemically stable MOFs, particularly those stable in acidic, basic, and aqueous systems, as well as in the exploration of their applications in several expanding fields of environment, energy, and food safety, which have been dedicated in our lab over the past decade. The strategies for accessing stable MOFs can be classified into: (a) assembling high-valent metals (hard acid, such as Zr4+, Al3+) with carboxylate ligands (hard base) for acid-stable MOFs; (b) combining low-valent metals (soft acid, such as Co2+, Ni2+) and azolate ligands (soft base, such as pyrazolate) for alkali-resistant MOFs; (c) enhancing the connectivity of the building unit; (d) contracting or rigidifying the ligand; (e) increasing the hydrophobicity of the framework; and (f) substituting liable building units with stable ones (such as metal metathesis) to obtain robust MOFs. In addition, other factors, including the geometry and symmetry of building units, framework–framework interaction, and so forth, have also been taken into account in the design and synthesis of stable MOFs. On the basis of these approaches, the stability of resulting MOFs under corresponding conditions has been remarkably enhanced. With high chemical stability achieved, the MOFs have found many new and significant applications, aiming at addressing global challenges related to environmental pollution, energy shortage, and food safety. A series of stable MOFs have been constructed for detecting and eliminating contaminations. Various fluorescent MOFs were rationally customized to be powerful platforms for sensing hazardous targets in food and water, such as dioxins, antibiotics, veterinary drugs, and heavy metal ions. Some hydrophobic MOFs even showed effective and specific capture of low-concentration volatile organic compounds. Novel MOFs with record-breaking acid/base/nucleophilic regent resistance have expanded their application scope under harsh conditions. BUT-8(Cr)A, as the most acid-stable MOF yet, showed reserved structural integrity in concentrated H2SO4 and recorded high proton conductivity; the most alkali-resistant MOF, PCN-601, retained crystallinity even in boiling saturated NaOH aqueous solution, and such base-stable MOFs composed of non-noble metal clusters and poly pyrazolate ligands also demonstrated great potential in heterogeneous catalysis in alkaline/nucleophilic systems for the first time. It is believed that this Account will provide valuable references on stable MOFs’ construction as well as application expansion toward harsh conditions, thereby being helpful to promote MOF materials to step from fundamental research to practical applications.
Despite numerous inherent merits of metal–organic frameworks (MOFs), structural fragility has imposed great restrictions on their wider involvement in many applications, such as in catalysis. Herein, ...a strategy for enhancing stability and enabling functionality in a labile Zr(IV)‐MOF has been proposed by in situ porphyrin substitution. A size‐ and geometry‐matched robust linear porphyrin ligand 4,4′‐(porphyrin‐5,15‐diyl)dibenzolate (DCPP2−) is selected to replace the 4,4′‐(1,3,6,8‐tetraoxobenzolmn3,8phenanthroline‐2,7(1H,3H,6H,8H)‐diyl)dibenzoate (NDIDB2−) ligand in the synthesis of BUT‐109(Zr), affording BUT‐110 with varied porphyrin contents. Compared to BUT‐109(Zr), the chemical stability of BUT‐110 series is greatly improved. Metalloporphyrin incorporation endows BUT‐110 MOFs with high catalytic activity in the photoreduction of CO2, in the absence of photosensitizers. By tuning the metal species and porphyrin contents in BUT‐110, the resulting BUT‐110‐50%‐Co is demonstrated to be a good photocatalyst for selective CO2‐to‐CO reduction, via balancing the chemical stability, photocatalytic efficiency, and synthetic cost. This work highlights the advantages of in situ ligand substitution for MOF modification, by which uniform distribution and high content of the incoming ligand are accessible in the resulting MOFs. More importantly, it provides a promising approach to convert unstable MOFs, which mainly constitute the vast MOF database but have always been neglected, into robust functional materials.
The in situ porphyrin substitution strategy is developed for modifying labile interpenetrated BUT‐109(Zr), affording BUT‐110 with enhanced chemical stability and photocatalytic activity. By tuning the species and contents of metalloporphyrin in BUT‐110, some of the BUT‐110 MOFs may serve as potential photocatalysts for selective CO2‐to‐CO reduction, in the absence of photosensitizer.
Constructing stable palladium(II)-based metal–organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability ...is limited by synthetic challenges due to the inertness of the Pd–ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO2 reduction to CH4. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.
The application scope of metal–organic frameworks (MOFs) is severely restricted by their weak chemical stability and limited pore size. A robust MOF with large mesopores is highly desired, yet poses ...a great synthetic challenge. Herein, two chemically stable Ni(II)-pyrazolate MOFs, BUT-32 and -33, were constructed from a conformation-matched elongated pyrazolate ligand through the isoreticular expansion. The two MOFs share the same sodalite-type net, but have different pore sizes due to the network interpenetration in BUT-32. Controlled syntheses of the two MOFs have been achieved through precisely tuning reaction conditions, where the microporous BUT-32 was demonstrated to be a thermodynamically stable product while the mesoporous BUT-33 is kinetically favored. To date, BUT-32 represents the first example of Ni4-pyrazolate MOF whose structure was unambiguously determined by single-crystal X-ray diffraction. Interestingly, the kinetic product BUT-33 integrates 2.6 nm large mesopores with accessible Ni(II) active sites and remarkable chemical stability even in 4 M NaOH aqueous solution and 1 M Grignard reagent. This MOF thus demonstrated an excellent catalytic performance in carbon–carbon coupling reactions, superior to other Ni(II)-MOFs including BUT-32. These findings highlight the importance of kinetic control in the reticular synthesis of mesoporous MOFs, as well as their superiority in heterogeneous catalysis.
In principle, porous physisorbents are attractive candidates for the removal of volatile organic compounds such as benzene by virtue of their low energy for the capture and release of this pollutant. ...Unfortunately, many physisorbents exhibit weak sorbate-sorbent interactions, resulting in poor selectivity and low uptake when volatile organic compounds are present at trace concentrations. Herein, we report that a family of double-walled metal-dipyrazolate frameworks, BUT-53 to BUT-58, exhibit benzene uptakes at 298 K of 2.47-3.28 mmol g
at <10 Pa. Breakthrough experiments revealed that BUT-55, a supramolecular isomer of the metal-organic framework Co(BDP) (H
BDP = 1,4-di(1H-pyrazol-4-yl)benzene), captures trace levels of benzene, producing an air stream with benzene content below acceptable limits. Furthermore, BUT-55 can be regenerated with mild heating. Insight into the performance of BUT-55 comes from the crystal structure of the benzene-loaded phase (C
H
@BUT-55) and density functional theory calculations, which reveal that C-H···X interactions drive the tight binding of benzene. Our results demonstrate that BUT-55 is a recyclable physisorbent that exhibits high affinity and adsorption capacity towards benzene, making it a candidate for environmental remediation of benzene-contaminated gas mixtures.
Enhancing electrocatalytic water splitting performance by modulating the intrinsic electronic structure is of great importance. Here, porous bimetallic oxide and chalcogenide nanosheets grown on ...carbon paper denoted as NiCo
2
X
4
/CP (X = O, S, and Se) are prepared to demonstrate how the anion components affect the electronic structures and thereby disclose the correlation between their intermediates interaction and catalytic activities. The experimental characterization and theoretical calculation demonstrate that Se and S substitution can promote the ratio of Co
3+
/Co
2+
and thereby modulate the electronic structure accompanied with the upshift of d band centers, which not only enhance the inner conductivity but also regulate the interaction between the catalyst surface and intermediates, especially for the adsorption of absorbed H and hydroperoxy intermediates towards respective hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As a result, a full alkaline electrolyzer using NiCo
2
Se
4
/CP and NiCo
2
S
4
/CP as cathode and anode delivers a low voltage of 1.51 V at 10 mA·cm
−2
, which is comparable even superior to most transition metal-based electrolyzers.
Metal-organic frameworks (MOFs) have emerged as one of the most fascinating libraries of porous materials. In spite of their myriad merits, practical application of most MOFs is restricted due to ...their high preparation cost because of the complicated organic ligands involved. To address this limitation, we propose to use simple and cheap organic precursors to synthesize MOFs with complicated ligands
"one-pot"
reactions of these precursors along with the formation of new MOFs. In this work, we have carefully screened several organic reactions, through which target ligands were generated
from easily available reactants during the MOF construction. With this "one-pot" approach, the fabrication of a series of novel MOFs by integrating the organic covalent bond and the coordinate bond has thus been realized through the judicious selection of organic reactions, which effectively simplifies the MOF synthesis process and thus reduces the cost.
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•A facile mixed-ligand approach is adopted to functionalize IRMOF-74-IV with metalloporphyrin for multivariate mesoporous analogs.•Compared with IRMOF-74-IV, the functionalized ...analogs show improved stability and performance in photocatalytic CO2 reduction.•The photocatalytic performance of IRMOF-74-IV analogs could be optimized by tuning the contents and species of metalloporphyrin.
Metal-organic frameworks (MOFs) are widely employed as functional materials in various fields, while intriguing properties for specific applications have been pursued all along with their development. Herein, we adopt a ligand substitution strategy to functionalize the mesoporous IRMOF-74-IV for multivariate MOF catalysts. With similar size and geometry, the porphyrin ligand 4,4′-(porphyrin-5,15-diyl)bis(2-hydroxybenzolate) (PBHB2–) was mixed with the 3,3′″-dihydroxy-2′,2″,5′,5″-tetramethyl-1,1′:4′,1″:4″,1″′-quaterphenyl-4,4″′-dicarboxylate (L-IV2–) ligand in synthesis, giving porphyrin functionalized IRMOF-74-IV analogs. Compared with IRMOF-74-IV, the IRMOF-74-IV-PBHBX-M series show improved stability and performance in photocatalytic CO2 reduction. After tuning the contents of porphyrin ligand and the species of metal ion, IRMOF-74-IV-PBHB45%-Cu demonstrates to be the best as an efficient photocatalyst for the CO2-to-CO conversion. This work has achieved to tailor extant MOFs through a mixed-ligand approach, which would contribute to more multivariate materials and unlock new opportunities for their applications.
Metal–organic frameworks (MOFs) have shown great potential for application in various fields, including CO2 capture and proton conduction. For promoting their practical applications, both ...optimization of a given property and enhancement of chemical stability are crucial. In this work, three base‐stable isostructural MOFs, Ni8(OH)4(H2O)2(BDP‐X)6 (Ni–BDP‐X; H2BDP=1,4‐bis(4‐pyrazolyl)benzene, X=CHO, CN, COOH) with different functional groups, are designed, synthesized, and used in CO2 capture and proton conduction experiments. They possess face‐centered cubic topological structures with functional nanoscale cavities. Importantly, these MOFs are fairly stable to maintain their structures in boiling water and 4 M sodium hydroxide solution at room temperature. Functionalization endows them with tunable properties. In gas adsorption studies, these MOFs exhibit selective adsorption of CO2 over CH4 and N2, and in particular the introduction of COOH groups provides the highest selectivity. In addition, the COOH‐functionalized Ni–BDP exhibits a high proton conductivity of 2.22×10−3 S cm−1 at 80 °C and approximately 97 % relative humidity.
Pores for thought: Three highly base‐stable isostructural MOFs, Ni8(OH)4(H2O)2(BDP‐X)6 (Ni–BDP‐X; H2BDP=1,4‐bis(4‐pyrazolyl)benzene, X=CHO, CN, COOH), with pore surfaces lined by different functional groups are constructed, and used in CO2 capture and proton conduction experiments. The COOH‐functionalized MOF in particular exhibits selective adsorption of CO2 over CH4 or N2 and high proton conductivity.
Water adsorption of metal–organic frameworks (MOFs) is attracting intense interest because of their potential applications in atmospheric water harvesting, dehumidification, and adsorption-based ...heating and cooling. In this work, through using a hexacarboxylate ligand, four new isostructural Zr(IV)-MOFs (BUT-46F, -46A, -46W, and -46B) with rare low-symmetric 9-connected Zr6 clusters were synthesized and structurally characterized. These MOFs are highly stable in water, HCl aqueous solution (pH = 1), and NaOH aqueous solution (pH = 10) at room temperature, as well as in boiling water. Interestingly, the rational modification of the metal clusters in these MOFs with different functional groups (HCOO–, CH3COO–, H2O/OH, and PhCOO–) enables the precise tuning of their water adsorption properties, which is quite important for given application. Furthermore, all four MOFs show excellent regenerability under mild conditions and good cyclic performance in water adsorption.
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