Di-Ming Chen

Template-directed synthesis of a luminescent Tb-MOF material for highly selective Fe3+ and Al3+ ion detection and VOC vapor sensing

A flexible bidentate polyaromatic acid ligand 4,4′-oxybis(benzoic acid) (H2oba) was used for the construction of a novel luminescent Tb(III)-based metal–organic framework (MOF), namely {(Me2NH2)[Tb(OBA)2]·(Hatz)·(H2O)1.5}n, with 3-amino-1,2,4-triazole (Hatz) as the template reagent. In the structure of the Tb-MOF, there co-exist single-stranded and double-stranded helical chains along the c axis, and the overall network shows a three-fold interpenetrated qtz net. This MOF is capable of selectively sensing Fe3+ and Al3+ ions in water via quenching the luminescence and tuning the emission ratio between the ligand-based and metal-based luminescence, respectively. More importantly, this MOF can realize fast detection for p-xylene (PX) vapor with a response time of less than 10 s and 40% fluorescence enhancement, while nitrobenzene (NB) vapor could lead to a quenching effect in 10 min with a 75% quenching efficiency. Remarkably, this is the first example of a multi-responsive luminescent Tb-MOF sensor for Fe3+ and Al3+ ions and VOC vapor detection. In connection to these, the probable sensing mechanisms were also discussed in this paper.

Charge Control in Two Isostructural Anionic/Cationic CoII Coordination Frameworks for Enhanced Acetylene Capture

Two isostructural CoII -based metal-organic frameworks (MOFs) with the opposite framework charges have been constructed, which can be simply controlled by changing the tetrazolyl or triazolyl terminal in two bifunctional ligands. Notably, the cationic MOF 2 can adsorb much more C2 H2 than the anionic MOF 1 with an increase of 88 % for C2 H2 uptake at 298 K in spite of more active nitrogen sites in 1. Theoretical calculations indicate that both nitrate and triazolyl play vital roles in C2 H2 binding and the C2 H2 adsorption isotherm confirms that the enhanced C2 H2 uptake for 2 (225 and 163 cm3 g-1 at 273 and 298 K) is exceptionally high for MOF materials without open metal sites or uncoordinated polar atom groups on the frameworks.

Two isomeric Zn(II)-based metal–organic frameworks constructed from a bifunctional triazolate–carboxylate tecton exhibiting distinct gas sorption behaviors

Two isomeric Zn(II)-based metal–organic frameworks, {[Zn(CPT)2](NMF)3}n (1) and {[Zn(CPT)2](DMF)0.75}n (2) (HCPT = 4-(4-carboxyphenyl)-1,2,4-triazole, NMF = N-methylformamide, DMF = N,N-dimethylformamide), with the same 4-fold interpenetrated dia topological network have been prepared under solvothermal conditions by employing a bifunctional triazolate–carboxylate organic linker, which show very similar voids but different pore shapes. Thermogravimetry, powder X-ray diffraction, molecular mechanics calculation, and gas sorption studies revealed their different framework stabilities and flexibilities, in which desolvated 1 exhibits temperature-dependent stepwise and hysteretic selective sorption of CO2 over N2 at 195 K, whereas desolvated 2 could adsorb neither CO2 nor N2. Furthermore, the luminescence properties of 1 and 2 were investigated.

Pore modulation of metal-organic frameworks towards enhanced hydrothermal stability and acetylene uptake via incorporation of different functional brackets

Metal–organic frameworks (MOFs), as a class of adjustable porous crystalline materials, have received considerable attention in recent years. In this study, starting from an unstable MIL-88 type Co(II)-MOF as the prototype structure, two isoreticular stabilized MOFs with similar structural features but different water/thermal stabilities and acetylene sorption behaviors were prepared, which can be modulated by incorporating different functional brackets in the pores. MOF 1 equipped with open metal sites (OMSs) decomposed quickly in water solution, while the free N-donor functionalized MOF 2 could be stable in water with improved thermostability. The gas sorption study reveals that activated material 2 has a significantly enhanced acetylene uptake capacity with a lower Qst value than those of activated 1, showing a 79% increase (242 vs. 135 cm3 g−1) at 273 K and 91% increase (165 vs. 86 cm3 g−1) at 298 K. The acetylene uptake capacity of activated material 2 is extraordinarily high among MOFs without OMSs, and is even comparable to some famous MOFs with much stronger C2H2 binding ability which however require considerably higher energy for regeneration. The experimental results were further confirmed by the molecular mechanics (MM) calculations, grand canonical Monte Carlo (GCMC) simulations and density functional theory (DFT) studies.

A Mixed-Cluster Approach for Building a Highly Porous Cobalt(II) Isonicotinic Acid Framework: Gas Sorption Properties and Computational Analyses

A unique channel-type metal-organic framework (MOF) built up from mixed square-planar Co4(μ2-OH)4(μ4-OH) and cuboidal Co4(μ3-OH)4 clusters with an isonicotinic acid ligand has been successfully fabricated that demonstrates the highest specific surface area and high H2 uptake capacities among all of the cobalt(II) isonicotinic acid frameworks reported so far.

Quest for the Ncb-type Metal–Organic Framework Platform: A Bifunctional Ligand Approach Meets Net Topology Needs

A custom-designed bifunctional ligand was used to connect an in situ formed Co3(OH) cluster affording a porous metal-organic framework, which represents the first case of ncb-type networks constructed from a single kind of ditopic ligand. Noticeably, the activated MOF shows high volumetric C2H2 uptake and excellent adsorption selectivity for C2H2/CO2 separation at room temperature with a low sorption heat.

A CoII-based metal–organic framework based on [Co6(μ3-OH)4] units exhibiting selective sorption of C2H2 over CO2 and CH4

By virtue of unique planar [Co6(μ3-OH)4] cluster units, a new microporous isonicotinate-based framework with high thermal and framework stabilities was achieved. The guest-free framework demonstrates high capacity and selectivity for C2H2 relative to CO2 and CH4 at room temperature, which was further understood by GCMC simulation.

Microporous Cobalt(II)–Organic Framework with Open O-Donor Sites for Effective C2H2 Storage and C2H2/CO2 Separation at Room Temperature

The self-assembly of a bifunctional organic ligand with a formate-bridged rod-shaped secondary building unit leads to a new microporous metal-organic framework (MOF). This MOF shows a moderately high C2H2 storage capacity (145 cm3/g) and an excellent adsorption selectivity for C2H2/CO2 (11) at room temperature. Furthermore, its discriminatory sorption behavior toward C2H2 and CO2 was probed by computational analysis in detail.

Aptamer-Embedded Zirconium-Based Metal–Organic Framework Composites Prepared by De Novo Bio-Inspired Approach with Enhanced Biosensing for Detecting Trace Analytes

A series of Zr-based metal-organic framework (MOF) composites embedded with three kinds of aptamer strands (509-MOF@Apt) were achieved by a one-step de novo synthetic approach. A platform for ultrasensitive detection of analytes, namely, thrombin, kanamycin, and carcinoembryonic antigen (CEA), was also established. Considering the conformational changes caused by the binding interactions between aptamer strands and targeted molecules, the label-free electrochemical aptasensors based on 509-MOF@Apt composites could be developed to detect various target molecules. By comparing the common fabrication approaches of aptasensors, a distinct determination mechanism was presented through analysis of the electrochemical measurements on different interaction behaviors between probe aptamer strands and 509-MOF materials. The optimized aptasensors based on 509-MOFs@Apt demonstrated excellent sensitivity (with the detection limit of 0.40, 0.37, and 0.21 pg mL-1 for CEA, thrombin, and kanamycin, respectively), stability, repeatability, and applicability. This work will provide a new platform for direct and feasible detection in biosensing related to clinical diagnostics and therapeutics, and further, extend the scope of potential applications for MOF materials.

A flexible doubly interpenetrated metal–organic framework with gate opening effect for highly selective C2H2/C2H4 separation at room temperature

A flexible metal–organic framework, {[Cu2(TPPB)2](DMF)8}n (1, H2TPPB = 4,4′-((5-(4-(4H-1,2,4-triazol-4-yl)phenoxy)-1,3-phenylene)bis(oxy))dibenzoic acid, DMF = N,N-dimethylformamide), with a doubly interpenetrated network was solvothermally prepared by employing a flexible bifunctional triazolcarboxylate ligand. This MOF shows a dynamic structure with its network displaying different configurations by accommodating different solvents. More importantly, due to the synergistic effect of its suitable pore size and flexible structural feature, its activated phase demonstrates a significant C2H2 uptake capacity with stepwise and hysteretic sorption behavior, but only limited C2H4 is absorbed; this enables the discriminatory adsorption of C2H2 over C2H4. The separation potential of this flexible MOF towards C2H2/C2H4 is further established using IAST calculations of mixture adsorption equilibrium.