A Facile Reaction Strategy for the Synthesis of MOF-Based Pine-Needle-Like Nanocluster Hierarchical Structure for Efficient Overall Water Splitting.

Solvothermal reactions of Co(NO3)2·6H2O, 3-amino-1,2,4-triazole, and 1,2,4,5-benzenetetracarboxylic acid afforded a Co-MOF: {[Co2(Hatz)(bta)]·H2O}n. Furthermore, a unique metal-organic-framework-based pine-needle-like nanocluster hierarchical architecture has been rationally designed and prepared on a nickel foam skeleton via a simple solvothermal method based on the Co(OH)F intermediate and directly adopted as an optimum bifunctional electrocatalyst for overall water splitting. The Co-MOF/NF exhibited enhanced catalytic performance for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The optimized catalyst reveals the highest electrocatalytic characteristics, affording current densities of 50 mA cm-2 at an overpotential of 266 mV for the OER and 10 mA cm-2 at an overpotential of 115 mV forthe HER in 1 M KOH. Meanwhile, the catalyst exhibits an ultrastability in the OER process and long-term test at 20 mA cm-2 for 100 h led to only a 9.4% increase in overpotential. Furthermore, an electrolytic cell assembled from the bifunctional Co-MOF/NF delivers a current density of 10 mA cm-2 at a cell voltage of 1.548 V. This excellent performance is believed to be the result of the exotic pine-needle-like nanocluster structure with effective accessibility of dense catalytically active sites, as well as the high specific surface area and the promotion of reversible chemisorption for oxygen species due to the linkers interacting with Co ions. Further SEM, TEM, and XPS analyses of the catalyst after OER stability tests reveal that the formation of Co3O4 on the surface and unconsolidated architecture withinthe electrode materials are responsible for the high catalytic activity. This work extends the applications of MOFs in the field of electrocatalysis.

Exploring Reversible Thermochromic Behavior in a Rare Ni(II)-MOF System.

Thermochromic metal-organic frameworks (MOFs) are promising functional materials for a wide range of applications due to their ability to exhibit color variation under external temperature stimuli, yet the development of them with high cyclability and efficient regeneration processes remains challenging. Here, presented is a rare example of an ultrastable Ni(II)-MOF exhibiting an unprecedented reversible four-step color change between two complementary colors in a wide temperature range, which could be repeated for at least 500 cycles without losing crystallinity and thermochromic performance. Notably, the regeneration can be achieved within 1 min by simply letting the crystals cool naturally in the air, facilitated by the unique nature of the channels' inner surface. The reversible thermochromic behavior is owing to a series of reversible crystal structure changes with temperature, including the stepwise dehydration/rehydration process, and structural changes. This work facilitates the future development of more MOF-based reversible thermochromic materials with excellent performance and improved practical applicability.

Rational synthesis of an ultra-stable Zn(ii) coordination polymer based on a new tripodal pyrazole ligand for the highly sensitive and selective detection of Fe3+ and Cr2O72- in aqueous media.

A mixed-ligand strategy has been used to construct stable luminescent coordination polymers (CPs). An ultra-stable Zn(ii) coordination polymer, [Zn(H3tpb)(Hbtc)]n (1) was hydrothermally synthesized by employing a new tripodal pyrazole ligand H3tpb and a classical carboxylic ligand H3btc (H3tpb = 1,3,5-tris(pyrazolyl)benzene, H3btc = 1,3,5-benzenetricarboxylic acid). Complex 1 exhibits a 2D sql network. Importantly, 1 not only possesses excellent thermal stability but also shows superior chemical stability in terms of water resistance, acid/base aqueous solutions tolerance (pH = 2-12), and organic solvents resistance. This excellent structural stability was further illustrated from the perspective of thermal decomposition kinetics. The luminescence properties were investigated, showing that complex 1 displays high sensitivity and selectivity for detecting Fe3+ and Cr2O72- ions in aqueous solutions via luminescence quenching effects.

A water-stable La-MOF with high fluorescence sensing and supercapacitive performances.

A 3D lanthanide coordination polymer {[La(SIP)(H2O)3]·H2O}n (La-MOF) was synthesized successfully by the solvothermal reaction of La(NO3)3·6H2O and 5-sulfoisophthalic acid monosodium salt (NaH2SIP). In particular, two oxygen atoms of sulfate participate in the coordination, which is unusual in all the complexes. La-MOF was characterized by single-crystal X-ray diffraction, IR spectroscopy, powder X-ray diffraction, thermal-gravimetric analysis, and X-ray photoelectron spectroscopy. La-MOF shows excellent water stability and chemical stability in a broad pH range from 2 to 13. Moreover, the fluorescence and sensing properties of La-MOF were invsetigated in detail via its titration and cycling processes, revealing its highly efficient and selective quenching responses and good recyclability for the detection of Fe3+, Cr2O72- and CrO42- ions. In addition, La-MOF possesses an outstanding specific capacitance of 213 F g-1 at 0.5 A g-1. It still retains 92% of the original capacitance after 2000 cycles, exhibiting remarkable long-term cycling stability and reversibility; therefore, the electrode material based on La-MOF is a competitive and promising candidate for application in supercapacitors.

A Flexible and Stable Interpenetrated Indium Pyridylcarboxylate Framework with Breathing Behaviors and Highly Selective Adsorption of Cationic Dyes.

An interpenetrated indium pyridylcarboxylate framework, [NH2(CH3)2][In(L)2]·2.5DMF·5H2O (1), has been synthesized by employing a pyridylcarboxylate ligand, 4-(3-carboxylphenyl)picolinic acid (H2L), and an In3+ ion, with both chemical stability and framework flexibility. The desolvated 1 exhibits an uncommon breathing sorption behavior and shows highly selective adsorption for C2H2, C2H4, and CO2 over CH4. Furthermore, 1 shows rapid and higher adsorption efficiency for methylene blue and neutral red in aqueous solution.

Stable Indium-Pyridylcarboxylate Framework: Selective Gas Capture and Sensing of Fe3+ Ion in Water.

By employing a pyridyl-decorated dicarboxylic acid ligand, 3-(2',5'-dicarboxylphenyl)pyridine acid (H2dcpy), a three-dimensional In3+-based metal-organic framework, H3O[In3(dcpy)4(OH)2]·3DMF·4H2O (1), with a good chemical stability toward acid and base has been synthesized. The compound 1 shows an uncommon (3,8)-connected tfz-d; UO3 topological net based on linear In3(COO)4(OH)2 clusters and also contains one-dimensional open channels. Particularly, 1 contains two types of dcpy2- linkers, in which the pyridyl group in one participates in coordination with the In3+ ion, whereas that in the other is uncoordinated but hangs in the inner sides of the channels as functionalized sites. Gas adsorption experiments demonstrate that 1 is able to selectively adsorb C2H2, C2H4, and CO2 over CH4. Simultaneously, 1 shows a highly selective and sensitive fluorescence detection toward Fe3+ ion in water with good recyclability.

New amine-functionalized cobalt cluster-based frameworks with open metal sites and suitable pore sizes: multipoint interactions enhanced CO2 sorption.

By employing the mixed-linker synthetic strategy, two new cobalt(II) cluster-based frameworks, [Co(2.5)(btc)(atz)2(Hatz)(DMF)]·2DMF (1) and [Co(2.5)(btc)(Hbtc)0.5(atz)(CH3CN)(H2O)]·H2O (2), constructed from the same initial materials Co(NO3)2, 1,3,5-benzenetricarboxylic acid (H3btc) and 3-amino-1,2,4-triazole (Hatz), have been synthesized by solvothermal reactions. Crystal-structure analyses demonstrated that 1 and 2 are three-dimensional (3D) porous frameworks based on Co-triazolate chain/layer and tricarboxylate pillars. Thermogravimetric analysis (TGA) and power X-ray diffraction (PXRD) measurements showed that both of them have high thermal stability and good water stability. Remarkably, both the structures of desolvated 1 and 2 contain suitable pore sizes and highly polar channel systems functionalized by amino groups, open metal sites, carbonyl or free carboxylic acid sites and uncoordinated triazolate nitrogen atoms on the pore surfaces, exhibiting multipoint interactions between CO2 molecules and frameworks, resulting in high CO2 uptake and selectivity for CO2 over N2.