Nian Zhao

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.

Ionothermal synthesis and proton-conductive properties of NH2-MIL-53 MOF nanomaterials

It is a big challenge to construct proton-conductive materials for practical applications operating at high temperatures and low humidity. Herein, we propose an ionothermal strategy for the preparation of highly stable NH2-MIL-53(Al)it nanomaterials with high proton conductivity. The crystalline structure and the direct incorporation of the 1-ethyl-3-methyl-imidazolium ionic liquid within NH2-MIL-53(Al)it are identified by XRD, TG/DTA and IR techniques. The as-prepared NH2-MIL-53(Al)it exhibits a high proton conductivity of 3.0 × 10−5 S cm−1 at 80 °C and low relative humidity of ∼26%.

An Amino-Coordinated Metal–Organic Framework for Selective Gas Adsorption

A novel 3D porous metal organic framework, JUC-141, constructed by 5-aminoisophthalic acid and Cu(NO3)2, has been synthesized successfully. The carboxyl groups in the ligand coordinate to Cu2+ to form the classic Cu2(COO)4 paddle wheel SBU, and the assembly of the SBUs with the isophthalic acid moieties leads to a kagome lattice. Interestingly, the amino groups in the ligand also take part in the coordination and link to the dipole of the paddle wheel as pillars, thus forming a 3D porous framework with eea topology. The sizes of the channels are 5.2 Å in the direction of [111] and 10.9 Å in the direction of [001]. Gas sorption tests show that the CO2 adsorption capacities of JUC-141 are 79.94 and 51.39 cm3 g-1 at 273 and 298 K under 1 atm pressure, respectively. However, the N2 adsorption capacities of JUC-141 are 13.90 and 6.76 cm3 g-1 at 273 and 298 K under 1 atm pressure, respectively. IAST calculations indicate that the selectivity values of CO2/N2 are 21.62 at 273 K and 27.60 at 298 K under 101 kPa, respectively. Good selective adsorption of CO2 over N2 makes JUC-141 possible for CO2 storage and separation.

Deprotonation-Triggered Stokes Shift Fluorescence of an Unexpected Basic-Stable Metal–Organic Framework

A new three-dimensional porous metal-organic framework, JUC-119, constructed by a pyrene-based dendritic organic linker, H8TIAPy (H8TIAPy = 1,3,6,8-tetrakis(3,5-isophthalic acid)pyrene), and Eu(III) has been synthesized successfully. JUC-119 shows unexpected stability under a wide range of basic conditions from 0 to 0.01 M NaOH. Furthermore, with two carboxyl groups uncoordinated in each ligand, the crystals of JUC-119 show deprotonation-triggered Stokes shift fluorescence under basic conditions. As the concentration of base increases from 0 to 0.01 M NaOH, the luminescence emission of JUC-119 becomes gradually red shifted from 455 to 485 nm. In addition, the Stokes shift shows a good linear relationship to -log[OH(-)], which makes JUC-119 promising for base sensing.

An acid-stable hexaphosphate ester based metal–organic framework and its polymer composite as proton exchange membrane

Use of a proton exchange membrane (PEM) is a key technique in proton exchange membrane fuel cells (PEMFCs) for clean energy applications. Recently, use of metal–organic frameworks (MOFs) as well as their composite membranes with polymers as PEM have been one research focus in this area. In this paper, the synthesis and proton conductive properties of a novel hexaphosphate ester-based MOF, JUC-200, prepared by the reaction of the inositol hexaphosphoric ligand (phytic acid) and Zn(II) is described. JUC-200 shows excellent water tolerance and acid resistance in a solution of pH = 2.0, and exhibits a proton conductivity of 1.62 × 10−3 S cm−1 at 80 °C. Furthermore, the polymer composite membranes of poly(vinyl alcohol) (PVA) and JUC-200 were fabricated for use as fillers with different mass percentages (X%, the membrane denoted as JUC-200@PVA-X). The measurement of proton conductivity of these membranes shows that JUC-200@PVA-10 has the advantage of a good proton conductivity of 1.25 × 10−3 S cm−1 at 50 °C. As far as is known, this is the first water-stable and acid-stable composite made of MOFs and polymers as proton exchange membranes. This research may make some contribution to the further development of MOFs in the field of the PEMFCs.

Synthesis and Catalytic Properties of New Metalloporphyrin-Based Porous Organic Framework Materials with Single and Accessible Sites

It is a big challenge to homogenize heterogeneous catalysts with molecular catalytic performance. With this target in mind, herein, we describe a facile strategy for direct incorporation of single catalytic sites in 3D open porous aromatic frameworks (PAFs). The synthesis of the PAF (denoted as PAF‐76) as well as its derivatives (PAF‐76‐M, M=Fe, Mn, Zn) was achieved by the use of tetrakis(4‐bromophenyl)methane as tetrahedral nodes and tetrakis(4‐bromophenyl)porphyrin as planar nodes. The connection of monomers into an extended network of PAF‐76 was monitored by 13C NMR and FTIR spectroscopies. The prepared PAF‐76s showed 3D porous structures with surface areas of 450–700 m2 g−1, pore volumes of 0.3–0.4 cm3 g−1, and pore sizes around 1.2 nm. The direct incorporation of metalloporphyrin components into the PAF‐76‐M frameworks has allowed the uniform distribution of metal ionic sites throughout the PAF‐76‐M particles. The combined merits of isolated metal sites and suitable pore size make PAF‐76 a good candidate for heterogeneous catalysis. The catalytic performances of the porphyrin/metalloporphyrin‐based active sites in the PAF‐76s were evaluated by aerobic oxidation reactions of styrene, which are usually carried out with homogeneous systems. Metal‐functionalized PAF‐76s (PAF‐76‐M) exhibit enhanced turnover frequencies for styrene conversion (16.9–50.9 mol mol(M)−1 h−1) compared with molecular catalysts (0–35.0 mol mol(M)−1 h−1), and improved selectivity toward phenylacetaldehyde (85.7–99 %) in contrast to their corresponding monomers (0–75.5 %). The robustness of PAF‐76 in terms of high thermal stability, good recyclability, and excellent solvent resistance showed that these PAF‐76 materials hold great promise for developing heterogeneous catalysts.

Synthesis of an ultra-stable metal–organic framework for proton conduction

A new ultra-stable metal–organic framework of Zn3(IBT)2(H2O)2 is synthesized. This MOF not only exhibits good thermal stability but also shows superior chemical stability in terms of water resistance, acid/base tolerance and solvent anticorrosion. In addition, it shows moderate proton-conductive properties with a conductivity of 1.98 × 10−5 S cm−1 at ∼30 °C and 97% RH.

A nanosized metal–organic framework with small pores for kinetic xenon separation

Nanosizing of crystals can bring superior properties into materials, particularly for facilitating mass transport in porous materials. Herein, we report the synthesis of CaSDB metal–organic framework (MOF) nanocrystals using additives; two types of additives (ammonia and lauric acid) are adopted to effectively control the crystal size down to 400–700 nm. In individual synthesis systems, ammonia acts as a nucleation promoter and lauric acid serves as a growth inhibiter during crystallization. The CaSDB crystals can be easily engineered from nanoscale (600 nm) to macroscale (35 μm) by adjusting the ammonia content in the synthetic solutions. The CaSDB nanocrystals prepared using both additives have the same porosity including the same pore size (5.0 A), similar surface areas (140–157 m2 g−1), and ultramicropore volumes (0.02–0.027 cm3 g−1), probed by N2 sorption measurements. Xe and Kr adsorptions show that the CaSDB nanomaterials exhibit a good thermodynamic selectivity of 20.5 for Xe over Kr owing to the optimized interactions between Xe molecules (4.1 A) and CaSDB pores (5.0 A). Breakthrough measurements show that the dynamic selectivity for Xe over Kr is close to the thermodynamic selectivity. More importantly, nanosized CaSDB MOF crystals exhibit a very fast rate for xenon adsorption that is demonstrated by a significantly higher rate constant of nanocrystals (1.8 × 10−2 min−1) than those of micro- (5.53 × 10−3 min−1) and macrocrystals (1.65 × 10−3 min−1). The enhanced adsorption rate is due to the high external surface area of CaSDB nanocrystals. Repetitive tests reveal that the CaSDB nanomaterials are robust and reproducible in terms of Xe/Kr selectivity and Xe uptake and hold great promise for application in adsorption-based xenon separation and capture.

A Homochiral Multifunctional Metal-Organic Framework with Rod-Shaped Secondary Building Units

A new homochiral multifunctional metal-organic framework, [Zn2(CTBA)2·H2O] (JUC-112), was synthesized under solvothermal conditions, through the design of chiral ligand 4-(3-carboxy-2,2,3-trimethylcyclopentanecarboxamido) benzoic acid (H2CTBA) based on camphoric acid as building block. The crystal structure of the new material is a 2-dimensional (2D) chiral layer packed with infinite rod-shaped secondary building units (SBUs). The homochiral framework was identified by circular dichroism (CD) spectrum. Thermogravimetric measurement indicates its high thermal stability up to 450 °C. In addition, JUC-112 exhibits the capability of separating water from alcohols, second-order nonlinear optical effect, and photoluminescence.

A new approach to construct bulk and size-dependent continuous binary solution phase diagrams of alloys

The construction of bulk and size-dependent temperature–composition phase diagrams of alloys is critical for their industrial applications. However, the nano-phase diagrams are difficult to be determined accurately by experiments since the nano-phase equilibrium is metastable. In this work, a new approach was developed to construct both bulk and size-dependent continuous binary solution phase diagrams with three steps: (1) determining bulk atomic interaction energy by using ab initio molecular dynamics simulation; (2) calculating size-dependent melting enthalpy, melting temperature, and atomic interaction energy using a unified nanothermodynamics model; and (3) constructing phase diagrams with the above parameters, where a typical Au–Ag alloy was studied here as an example. It is found that (i) the simulated bulk atomic interaction energy is consistent with experimental data; (ii) the melting enthalpy, melting temperature, and atomic interaction energy decrease with decreasing material size for isolated nanocrystals; and (iii) the temperatures of the solidus and liquidus curves drop and the two-phase zone becomes small for the Au–Ag nanoalloy. The general approach developed here can be used to investigate other continuous binary alloy systems and can be extended to construct other phase diagrams, for example, the eutectic phase diagram.