Two highly stable metal-organic frameworks (MOFs) with suitable hydrophobic pores have been constructed, and they show great potential for application in the capture of trace aromatic volatile organic compounds in ambient air. One of the MOF adsorbents even retains single crystallinity after the adsorption of aromatic hydrocarbons together with water, allowing precise structure determination of its guest-loaded phases. These results could offer important guidance for the development of new adsorbents for the capture of harmful air pollutants.

Metal–organic frameworks (MOFs) have been developing at an unexpected rate over the last two decades. However, the unsatisfactory chemical stability of most MOFs hinders some of the fundamental studies in this field and the implementation of these materials for practical applications. The stability in a MOF framework is mostly believed to rely upon the robustness of the M–L (M = metal ion, L = ligand) coordination bonds. However, the role of organic linkers as agents of stability to the framework, particularly the linker rigidity/flexibility, has been mostly overlooked. In this work, we demonstrate that a ligand-rigidification strategy can enhance the stability of MOFs. Three series of ligand rotamers with the same connectivity but different flexibility were prepared. Thirteen Zr-based MOFs were constructed with the Zr6O4(OH4)­(−CO2) n units (n = 8 or 12) and corresponding ligands. These MOFs allow us to evaluate the influence of ligand rigidity, connectivities, and structure on the stability of the resulting materials. It was found that the rigidity of the ligands in the framework strongly contributes to the stability of corresponding MOFs. Furthermore, water adsorption was performed on some chemically stable MOFs, showing excellent performance. It is expected that more MOFs with excellent stability could be designed and constructed by utilizing this strategy, ultimately promoting the development of MOFs with higher stability for synthetic chemistry and practical applications.

Dichromate is known for severe health impairments to organisms. New and valid strategies have been developed to rapidly detect and efficiently remove this pollutant. Constructing stable luminescent metal-organic frameworks (MOFs) for dichromate recognition and removal from aqueous solution could provide a feasible resolution to this problem. Herein, a new luminescent Zr(IV)-MOF, ZrO(OH)(HO)(BTBA) (BUT-39, BUT = Beijing University of Technology) was constructed through the reaction of a newly designed functionalized T-shaped ligand 4,4',4″-(1 H-benzo[ d]imidazole-2,4,7-triyl)tribenzoic acid (HBTBA) with zirconium salt. BUT-39 has a unique porous framework structure, in which Zr cluster acts as a rare low-symmetric 9-connected node and BTBA as a T-shaped 3-connected linker. As far as we know, this represents the first case of a (3,9)-connected Zr(IV)-MOF. BUT-39 could retain its framework integrity in boiling water, 2 M HCl aqueous solution, and pH 12 NaOH aqueous solution. Due to its good water stability and strong fluorescent emission, BUT-39 is then employed in fluorescence sensing for various ions in aqueous solution and shows good performance toward CrO selectively, at a low concentration and a short response time (<1 min). Simultaneously, it also exhibits excellent capacity to rapidly capture CrO (within 1 min) with a high uptake up to 1 mmol g. Taking advantage of its excellent stability, sensitive and selective sensing, as well as rapid and high adsorption, BUT-39 is expected to be useful in CrO detection in and removal from water.

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 i...

Nanodiamond particles produced by detonation synthesis and having ∼5 nm diameter possess unique properties, including low cell toxicity, biocompatibility, stable structure, and highly tailorable surface chemistry, which render them an attractive material for developing drug delivery systems. Although the potential for nanodiamonds in delivery and sustained release of anticancer drugs has been recently demonstrated, very little is known about the details of adsorption/desorption equilibria of these and other drugs on/from nanodiamonds with different purity, surface chemistry, and agglomeration state. Since adsorption is the basic mechanism most commonly used for the loading of drugs onto nanodiamond, the fundamental studies into the details of adsorption and desorption on nanodiamond are critically important for the rational design of the nanodiamond drug delivery systems capable of targeted delivery and triggered release, while minimizing potential leaks of dangerous drugs. In this paper we report on a physical-chemical study of the adsorption of doxorubicin and polymyxin B on nanodiamonds, analyzing the role of purification and surface chemistry of the adsorbent.

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−1 at <10 Pa. Breakthrough experiments revealed that BUT-55, a supramolecular isomer of the metal–organic framework Co(BDP) (H2BDP = 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 (C6H6@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.

A metal-free novel, simple, and highly efficient method for the direct C2-alkylation of azoles with alcohols and ethers has been developed on the basis of an oxidative C-H activation process. The dehydrogenative C-C cross-coupling reactions of α-position sp(3) C-H in alcohols and ethers with the 2-position sp(2) C-H in azoles proceeded smoothly in the presence of tert-butyl hydroperoxide (TBHP) under neat reaction conditions, which generated the corresponding products in good yields.