Wen-Wen He

A fluorescent sensor for highly selective detection of nitroaromatic explosives based on a 2D, extremely stable, metal-organic framework.

A 2D, extremely stable, metal-organic framework (MOF), NENU-503, was successfully constructed. It displays highly selective and recyclable properties in detection of nitroaromatic explosives as a fluorescent sensor. This is the first MOF that can distinguish between nitroaromatic molecules with different numbers of NO2 groups.

Stable Luminescent Metal–Organic Frameworks as Dual-Functional Materials To Encapsulate Ln3+ Ions for White-Light Emission and To Detect Nitroaromatic Explosives

A stable porous carbazole-based luminescent metal-organic framework, NENU-522, was successfully constructed. It is extremely stable in air and acidic/basic aqueous solutions, which provides the strategy for luminescent material encapsulation of Ln(3+) ions with tunable luminescence for application in light emission. More importantly, Ln(3+)@NENU-522 can emit white light by encapsulating different molar ratios of Eu(3+) and Tb(3+) ions. Additionally, Tb(3+)@NENU-522 is found to be useful as a fluorescent indicator for the qualitative and quantitative detection of nitroaromatic explosives with different numbers of -NO2 groups, and the concentrations of complete quenching are about 2000, 1000, and 80 ppm for nitrobenzene, 1,3-dinitrobenzene, and 2,4,6-trinitrophenol, respectively. Meanwhile, Tb(3+)@NENU-522 displays high selectivity and recyclability in the detection of nitroaromatic explosives.

A multifunctional microporous anionic metal–organic framework for column-chromatographic dye separation and selective detection and adsorption of Cr3+

In this work, a novel microporous anionic metal–organic framework (MOF), [Zn(ABTC)0.5(NO3)][(CH3)2NH2]·DMA·3H2O (NENU-505; NENU = Northeast Normal University; H4ABTC = 3,3′,5,5′-azobenzenetetracarboxylic acid; DMA = N,N-dimethylacetamide), has been rationally synthesized under solvothermal conditions. Single-crystal X-ray analysis reveals that NENU-505 is a (4,4)-connected 3D network with pts topology. Charge neutrality is achieved by [(CH3)2NH2]+ ions. It is noteworthy that NENU-505 displays high stability in air for more than two months. In particular, the adsorption ability of NENU-505 toward ionic dyes has been also investigated. According to the UV/vis spectroscopy analysis and the colour variance of NENU-505, we found that the cationic dyes could be efficiently adsorbed over a period of time, while the neutral and anionic dyes could not be adsorbed. Therefore, NENU-505 exhibits selective adsorption toward cationic dyes and can potentially serve as a column-chromatographic filler for the separation of dye molecules. Furthermore, the cationic dyes can be gradually released in the presence of NaCl. More interestingly, when NENU-505 was immersed in different metal ion DMA solutions, it performs as a rare example of a highly selective and sensitive sensor for Cr3+ ions. In connection to this, the probable sensing mechanism was also further investigated in detail in this paper. Remarkably, this is the first MOF to exhibit an excellent ability for the detection and adsorption of Cr3+ ions in a convenient, economical, and environmentally friendly manner.

Self‐Assembly versus Stepwise Synthesis: Heterometal–Organic Frameworks Based on Metalloligands with Tunable Luminescence Properties

A new family of heterometal-organic frameworks has been prepared by two synthesis strategies, in which IFMC-26 and IFMC-27 are constructed by self-assembly and IFMC-28 is obtained by stepwise synthesis based on the metalloligand (IFMC=Institute of Functional Material Chemistry). IFMC-26 is a (3,6)-connected net and IFMC-27 is a (4,8)-connected 3D framework. The metalloligands {Ni(H4 L)}(NO3 )2 are connected by binuclear lanthanide clusters giving rise to a 2D sheet structure in IFMC-28. Notably, IFMC-26-Eux Tby and IFMC-28-Eux Tby have been obtained by changing the molar ratios of raw materials. Owing to the porosity of IFMC-26, Tb(3+) @IFMC-26-Eu and Eu(3+) @IFMC-26-Tb are obtained by postencapsulating Tb(III) and Eu(III) ions into the pores, respectively. Tunable luminescence in metal-organic frameworks is achieved by the two kinds of doping methods. In particular, the quantum yields of heterometal-organic frameworks are apparently enhanced by postencapsulation of Ln(III) ions.

A stable metal–organic framework with suitable pore sizes and rich uncoordinated nitrogen atoms on the internal surface of micropores for highly efficient CO2 capture

An air-stable tetrazolate-containing framework, [Zn2L2]·2DMF (NENU-520, H2L = 4-(1H-tetrazole-5-yl)biphenyl-4-carboxylic acid), with uncoordinated N atoms on its internal surface was solvothermally synthesized and structurally characterized. This metal–organic framework (MOF) exhibited high CO2 uptake of 79.9 cm3 cm−3 at 298 K and 100 kPa, as well as excellent adsorption selectivity for CO2 over CH4 and N2. Particularly, its exceptionally high selectivity of CO2 over N2 at 298 K has ranked NENU-520 among the highest MOFs for selective CO2 separation. Furthermore, the potential application of NENU-520 for the fixed bed pressure swing adsorption (PSA) separation of CO2 from CH4 and N2 has been validated via simulated breakthrough experiments. The small channel with the size of 3.6 A, combined with CO2-accessible free nitrogen atoms directed toward the inner surface, is believed to contribute to its high CO2 uptake capacity and selectivity. Thus, this work represents a unique way to target MOF materials for highly selective CO2 separation by incorporating CO2-philic functional sites on pore surfaces, and at the same time optimizing pore sizes.

Controllable synthesis of microporous, nanotubular and mesocage-like metal–organic frameworks by adjusting the reactant ratio and modulated luminescence properties of Alq3@MOF composites

Three metal–organic frameworks (MOFs) comprising micropore, mesocage and nanotube structures have been prepared based on the same ligands and binuclear zinc secondary building units. We have successfully achieved flexible modulation of pore size from micropore to mesopore in a binary system by adjusting the reactant ratio. With the merit of a nanoscale channel, IFMC-8 can be applied as the host material for encapsulating Alq3 chromophores to exhibit tunable luminescence. The fluorescence emission of composite material Alq3@IFMC-8 has changed from green to blue. More importantly, the inclusion of IFMC-8 effectively prolonged the excited-state lifetime of Alq3 in ethanol. To the best of our knowledge, it is the first time that a MOF was studied as the host material for modulating the fluorescence properties of Alq3 chromophores.

Solid-state structural transformation doubly triggered by reaction temperature and time in 3D metal-organic frameworks: great enhancement of stability and gas adsorption

In this work, we have demonstrated an unprecedented single-crystal-to-single-crystal (SCSC) transformation between two 3D metal-organic frameworks (MOFs). The centrosymmetric IFMC-68 ([(Zn4O)2(L)3]·10H2O·46DMA) transforms into a chiral IFMC-69 ([(Zn4O)2(L)3H2O]·H2O·4DMA) doubly triggered by reaction temperature and time simultaneously in the presence or absence of solvent. To our knowledge, this is the first representative that the non-interpenetrated structure transforms into self-penetrated structure in MOFs. For the first time, we have studied the influence of reaction temperature and time on SCSC transformation, simultaneously, and get the transformation relationship among IFMC-68, IFMC-69 and the intermediate coming from the direct synthesis method and stepwise synthesis method at different temperatures and for different times. Meanwhile, we have achieved the conversion from an air-unstable to air-stable structure. Air-stable IFMC-69 exhibits the selective CO2 uptake over N2 and more excellent gas adsorption ability than IFMC-68. In addition, IFMC-69 shows an efficient capability in reversible adsorption of iodine. The electrical conductivity value (σ) of I2@IFMC-69 is much higher than the pristine MOF and thus is promising for potential semiconductor materials in the future.

An anionic interpenetrated zeolite-like metal-organic framework composite as a tunable dual-emission luminescent switch for detecting volatile organic molecules

The luminescent MOF [(CH3 )2 NH2 ]2 [(Zn2 O)L]⋅5 DMF (NENU-519, NENU=Northeast Normal University) with a zeolite BCT topology was successfully synthesized. It is a rare example of a two-fold interpenetrated framework with a zeolite topology. NENU-519 demonstrates the ability to selectively adsorb cationic dyes. Furthermore we developed Rh6@NENU-519 (Rh6=Rhodamine 6G) as a dual-emitting sensor for probing different volatile organic molecules (VOMs) due to an energy transfer between L and the dye. The composite can be used to distinguish the isomers of o-, m-, and p-xylene and ethylbenzene using the emission-peak-height ratios of L to the dye as detectable signals, in which the readout signals are involved in the interactions between the dye@MOF composite and the guest analytes. Moreover, Rh6@NENU-519 can serve as a luminescent switch for the detection of different aromatic compounds, like benzene, benzene substituted with different groups, and pyridine. In other words, the Rh6@NENU-519 composite can be used as molecular decoder of the structural information of different VOMs into recognizable luminescent signals. Hopefully this work will open a new corridor to develop luminescent guest@MOF composites as sensors for practical applications.

Multipoint interactions enhanced H2 storage and organosulfur removal in a microporous metal–organic framework

A novel microporous metal–organic framework, IFMC-16, has been successfully constructed by using mixed ligands. IFMC-16 has multipoint interaction sites and exhibits high hydrogen storage capacity not only at ambient pressure, but also at lower pressure in a high pressure region, and displays high adsorptive efficiency in the removal of organosulfur compounds.

Phenyl Groups Result in the Highest Benzene Storage and Most Efficient Desulfurization in a Series of Isostructural Metal–Organic Frameworks

A series of isoreticular metal-organic frameworks (MOFs; NENU-511-NENU-514), which all have high surface areas and strong adsorption capacities, have been successfully constructed by using mixed ligands. NENU-513 has the highest benzene capacity of 1687 mg g(-1) at 298 K, which ranks as the top MOF material among those reported up to now. This NENU series has been used for adsorptive desulfurization because of its permanent porosity. The results indicate that this series has a higher adsorptive efficiency in the removal of organosulfur compounds than other MOF materials, especially NENU-511, which has the highest adsorptive efficiency in the ambient atmosphere. This study proves that the design and synthesis of targeted MOFs with higher surface areas and with functional groups present is an efficient method to enhance benzene-storage capacity and the adsorption of organosulfur compounds.