Hongming He

Metal-Organic Frameworks for CO2 Chemical Transformations

Carbon dioxide (CO2 ), as the primary greenhouse gas in the atmosphere, triggers a series of environmental and energy related problems in the world. Therefore, there is an urgent need to develop multiple methods to capture and convert CO2 into useful chemical products, which can significantly improve the environment and promote sustainable development. Over the past several decades, metal-organic frameworks (MOFs) have shown outstanding heterogeneous catalytic activity due in part to their high internal surface area and chemical functionalities. These properties and the ability to synthesize MOF platforms allow experiments to test structure-function relationships for transforming CO2 into useful chemicals. Herein, recent developments are highlighted for MOFs participating as catalysts for the chemical fixation and photochemical reduction of CO2 . Finally, opportunities and challenges facing MOF catalysts are discussed in this ongoing research area.

A porous metal–organic framework formed by a V-shaped ligand and Zn(II) ion with highly selective sensing for nitroaromatic explosives

A V-shaped aromatic ligand 1,3-di(4-carboxyphenyl)benzene (H2DCPB), retaining only one branch of the H6TDCPB ligand, was utilized. The assembly of this ligand with Zn(II) ions forms a two-fold interpenetrated porous MOF with pcu topology (JUC-135). The N2 adsorption isotherm of the activated sample at 77 K revealed type-I microporous characteristics. The BET and Langmuir surface areas are calculated to be 503.7 m2 g−1 and 718.9 m2 g−1, respectively. Notably, by the fluorescence technique, JUC-135 can be used to detect nitroaromatic explosives. In particular, it is one of the most efficient porous material-based sensors for TNP (KSV = 3.7 × 104 M−1). Furthermore, JUC-135 also can distinguish TNP (blue-shift) from NB, 1,3-DNB and 2,4-DNT (red-shift) by virtue of the shift direction of fluorescence spectra.

Construction of Thermophilic Lipase-Embedded Metal–Organic Frameworks via Biomimetic Mineralization: A Biocatalyst for Ester Hydrolysis and Kinetic Resolution

Enhancing the activity and stability of enzymes and improving their reusability are critical challenges in the field of enzyme immobilization. Here we report a facile and efficient biomimetic mineralization to embed thermophilic lipase QLM in zeolite imidazolate framework-8 (ZIF-8). Systematic characterization indicated that the entrapment of lipase molecules was successfully achieved during the crystal growth of ZIF-8 with an enzyme loading of ∼72.2 ± 1.88 mg/g lipase@ZIF-8, and the enzymes could facilitate the construction of framework building blocks. Then the composite lipase@ZIF-8 was observed to possess favorable catalytic activity and stability in the ester hydrolysis, using the hydrolysis of p-nitrophenyl caprylate as a model. Finally, the composite was successfully applied in the kinetic resolution of (R,S)-2-octanol, with favorable catalytic activity and enantioselectivity during 10 cycle reactions. Thus, the biomimetic mineralization process can be potentially used as an effective technique for realizing the entrapment of biomacromolecules and constructing efficient catalysts for industrial biocatalysis.

Imparting amphiphobicity on single-crystalline porous materials

The sophisticated control of surface wettability for target-specific applications has attracted widespread interest for use in a plethora of applications. Despite the recent advances in modification of non-porous materials, surface wettability control of porous materials, particularly single crystalline, remains undeveloped. Here we contribute a general method to impart amphiphobicity on single-crystalline porous materials as demonstrated by chemically coating the exterior of metal-organic framework (MOF) crystals with an amphiphobic surface. As amphiphobic porous materials, the resultant MOF crystals exhibit both superhydrophobicity and oleophobicity in addition to retaining high crystallinity and intact porosity. The chemical shielding effect resulting from the amphiphobicity of the MOFs is illustrated by their performances in water/organic vapour adsorption, as well as long-term ultrastability under highly humidified CO2 environments and exceptional chemical stability in acid/base aqueous solutions. Our work thereby pioneers a perspective to protect crystalline porous materials under various chemical environments for numerous applications.

A luminescent metal–organic framework for sensing methanol in ethanol solution

A new luminescent Zn-MOF has been synthesized under hydrothermal condition using a semi-rigid ligand H3pcoip (4-(2-carboxyphenoxy)isophthalic acid) is reported. The luminescence properties of 1 in methanol, ethanol, and water have been investigated. Interestingly, compound 1 has a unique response to methanol compared to ethanol and water. Moreover, 1 displays a turn-on switching property triggered by methanol solvent molecules and a high sensitivity towards methanol concentration as low as 2 × 10(-7) (V(MeOH)/V(total)) in ethanol solution. The results indicate that the Zn-MOF has potential application as a sensor for detecting methanol in ethanol solution with excellent selectivity and high sensitivity.

Syntheses, structures and luminescence properties of three metal–organic frameworks based on 5-(4-(2H-tetrazol-5-yl)phenoxy)isophthalic acid

Three metal–organic frameworks (MOFs), namely [Zn2(TPIA)(OH)(H2O)]·H2O (JUC-114), [Cd2(TPIA)(OH)(H2O)2]·H2O (JUC-115), and [Co2(TPIA)(OH)(H2O)2]·H2O (JUC-116) (JUC = Jilin University China), based on a new ligand, 5-(4-(2H-tetrazol-5-yl)phenoxy)isophthalic acid (H3TPIA), were synthesized under hydrothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis, IR spectroscopy, TGA analysis and powder X-ray diffraction. JUC-114, JUC-115 and JUC-116 all possess 3D frameworks with (4,8)-connected fluorite (flu) topology based on similar tetranuclear metal centers as secondary building unit (SBU). Furthermore, the luminescence of the ligand H3TPIA and compounds was measured at room temperature.

A bifunctional metal–organic framework featuring the combination of open metal sites and Lewis basic sites for selective gas adsorption and heterogeneous cascade catalysis

A bifunctional MOF (JUC-199) featuring dual functionality, open metal sites (Zn2+) and Lewis basic sites (–NH2), has been successfully synthesized using a custom-designed ligand. JUC-199 demonstrated good selective gas sorption behaviours with IAST selectivity values of 9, 30, 37 and 64 at 298 K and 101 kPa for CO2/CH4, CO2/N2, C2H6/CH4 and C2H4/CH4 respectively; surpassing those of most MOFs reported thus far. Moreover, JUC-199 can serve as a heterogeneous cascade catalyst to efficiently catalyse the tandem one-pot deacatalization-Knoevenagel condensation reaction.

Reticular Synthesis of a Series of HKUST-like MOFs with Carbon Dioxide Capture and Separation

We reported a series of HKUST-like MOFs based on multiple copper-containing secondary building units (SBUs). Compound 1 is constructed by two SBUs: Cu2(CO2)4 paddle-wheel SBUs and Cu2I2 dimer SBUs. Compound 2 has Cu2(CO2)4 paddle-wheel SBUs and Cu4I4 SBUs. Furthermore, compound 3 possesses Cu2(CO2)4 paddle-wheel SBUs, Cu2I2 dimer SBUs, and Cu(CO2)4 SBUs. These compounds are promising materials for CO2 capture and separation, because they all display commendable adsorption of CO2 and high selectivity for CO2 over CH4 and N2. It is worthy to note that compound 1 exhibits the highest Brunauer-Emmett-Teller surface area (ca. 901 m(2) g(-1)) among the MOF materials based on CuxIy SBUs. In addition, compound 3 is the first case that three copper SBUs coexist in MOFs.

Four new metal–organic frameworks based on bi-, tetra-, penta-, and hexa-nuclear clusters derived from 5-(phenyldiazenyl)isophthalic acid: syntheses, structures and properties

Four new metal–organic frameworks (MOFs), namely, [Cu(PDIA)(DMA)]n (JUC-126), [Mn4(PDIA)4(DMF)6]n·nDMF·2nH2O (JUC-127), [Zn23(PDIA)18(μ4-O)2(μ3-OH)6DMA6]n·10nDMA·6nH2O (JUC-128), [Co3(PDIA)2(HCOO)(μ3-OH)(H2O)(DMA)2]n·nDMA·nH2O (JUC-129) (JUC = Jilin University, China), based on a new rigid ligand 5-(phenyldiazenyl)isophthalic acid (H2PDIA) with azobenzene were synthesized under solvothermal conditions. The ligand is connected to different metals to form bi-, tetra-, penta- and hexa-nuclear cores with distinctive coordination modes to generate different structures. Moreover, π–π stacking interactions between arene cores of the ligands also exist to affect the structural assembly process. JUC-126 displays a three-dimensional (3D) NbO topology with the point symbol (64·82) based on Cu2(COO)4 as secondary building units (SBUs), JUC-127 shows a two-dimensional (2D) sql topology with the point symbol (44·62) based on Mn2(COO)4 as SBUs, JUC-128 has a new 3D topology with the point symbol (33·46·56)2(36·48·510·64)3 based on Zn4O(COO)6 and Zn5(μ3-OH)2(COO)8 as SBUs and JUC-129 exhibits a 2D sql topology with the point symbol (44·62) based on Co6(μ3-OH)2(COO)10 as SBUs. In addition, JUC-126, JUC-128 and JUC-129 are achiral frameworks; however, JUC-127 shows a chiral framework from an achiral ligand. Furthermore, the luminescent property of JUC-128 and the magnetic properties of JUC-127 and JUC-129 have been studied and discussed.

Three novel zinc(II) metal–organic frameworks based on three tetrazolate ligands: synthesis, structures and photoluminescence

Three metal–organic frameworks (MOFs), namely [Zn(BPT)H2O] (JUC-121), [Zn5(IBT)6]·8[H2N(CH3)2]·DMA (JUC-122) and [Zn(TPD)(H2O)2]·0.5H2O (JUC-123) (JUC = Jilin University, China), H2BPT = (5-bromo-1,3-phenylene)bis(tetrazole), H3IBT = 4,5-bis(tetrazol-5-yl)imidazole and H2TPD = 3,5-di(tetrazol-5-yl)pyridine, were obtained by the reactions of Zn(NO3)2·6H2O and three tetrazolate ligands, which were characterized by single crystal X-ray diffraction, thermal gravimetric analyses (TGA), Fourier-transform infrared spectra (FT-IR), elemental analysis (CHN) and powder X-ray diffraction (PXRD). From the crystal structures of these complexes and the coordination modes of the ligands, we can see that the tetrazolate ligands have multi-connectivity abilities to obtain intriguing varieties of molecular architectures. JUC-121 displays a three-dimensional (3D) network with the point symbol (4·65)2(42·84)(64·82). JUC-122 shows a two-dimensional (2D) framework with the point symbol (243)2(24)9 and JUC-123 has a 2D bimodal (3, 3)-connected net with the point symbol (4·82). The solid-state fluorescent spectra of JUC-121, JUC-122, JUC-123 and the free ligands were measured at room temperature.