Zhao-Feng Wu

A magnesium MOF as a sensitive fluorescence sensor for CS2 and nitroaromatic compounds

Presented here are the hydrothermal synthesis, structural characterization, and luminescent and gas adsorption properties of a magnesium metal–organic framework compound, namely Mg5(OH)2(BTEC)2(H2O)4·11H2O (1, H4BTEC = 1,2,4,5-benzenetetracarboxylic acid). The structure of 1 features a three-dimensional network constructed from the linkage of BTEC ligands and rare pentanuclear magnesium clusters as secondary building units, giving rise to the 1D channels along the a axis. Luminescence studies revealed that compound 1 demonstrated high fluorescence sensing of carbon disulfide (CS2) and nitroaromatic compounds, that is, the fluorescence intensities were almost completely quenched only at the concentrations of 0.8 vol% of CS2 and 0.04 vol% of nitrobenzene.

Ionothermal syntheses, crystal structures and properties of three-dimensional rare earth metal–organic frameworks with 1,4-naphthalenedicarboxylic acid

Twelve isostructural rare earth metal-organic frameworks, namely, [Hmim][RE(2)Cl(1,4-NDC)(3)] (RE = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Y (12), Hmim = 1-hexyl-3-methylimidazolium, 1,4-NDCH(2) = 1,4-naphthalenedicarboxylic acid), have been ionothermally synthesized and structurally characterized. The structures feature three-dimensionally anionic frameworks of [RE(2)Cl(1,4-NDC)(3)](n)(n-) with channels in which the Hmim(+) cations are located. The current results are the first ionothermal synthesis of rare earth metal-organic frameworks based on 1,4-NDCH(2) which possess a previously unknown (4,7)-connected 3-nodal network with the Schläfli symbol of (3(2)·4(2)·5(2))(3(2)·4(9)·5(2)·6(8))(2)(4(3)·6(3))(2). Luminescent and magnetic properties of some of the title compounds have been studied. Thermogravimetric analyses indicated that all these compounds were thermally stable up to ca. 250 °C.

Ionothermal synthesis of microporous and mesoporous carbon aerogels from fructose as electrode materials for supercapacitors

The fabrication of hierarchical porous carbons with super-high surface areas from sustainable biomass is still challenging. Silica nanocasting and KOH activation are amenable to porosity introduction and therefore remain the most crucial pathways for porous carbon synthesis. However, these methods are multistep and rather energy-intensive processes. In the present work, a series of hierarchical porous carbon monoliths were prepared from fructose by a one-step ionothermal carbonization approach using an iron-based ionic liquid as solvent, and a porogenic agent. Importantly, the prepared carbon materials show narrow bi-modal pore distributions and possess super-high surface areas of ca. 1200 m2 g−1, which is the highest value in hydrothermal carbons as far as we know. The morphology of the monolithic carbons consists of interconnected carbon particles with fairly small particle sizes of ca. 30–50 nm. Moreover, the spent ionic liquids could be easily recovered by Soxhlet extraction, at above 98% for the cycle of ionothermal carbonization. Owing to their favorable textural properties, the impact of the porosity of the ionothermal carbons on their electrochemical capacitive performance was investigated. The ionothermal carbons exhibit a high specific capacitance of 245 F g−1 at a current density of 1 A g−1. The promising capacitive performance could be attributed to the high surface areas and well-controlled micro- and mesoporosities of the carbons. In addition, the hierarchical porosity and high surface area of the carbon lend it to highly efficient adsorption of methyl orange (qe = 240 mg g−1) and malachite green (qe = 170 mg g−1) from wastewater.

Solvent-assisted construction of diverse Mg-TDC coordination polymers

Upon alteration of selected solvents, the reactions of 2,5-thiophenedicarboxylic acid (H2TDC) and Mg(NO3)2·6H2O afforded four diverse coordination polymers, namely Mg2(TDC)2(EG)2.5·0.5EG (1), Mg(TDC)(DMSO) (2), (Me2NH2)[Mg2(TDC)2(Ac)]·1.5DMA·0.5H2O (3), and [Mg2(TDC)2(DMF)2(EtOH)(H2O)2]·DMF (4) (EG = ethylene glycol, DMSO = dimethyl sulfoxide, Ac = acetate anion, DMA = N,N′-dimethylacetamide, DMF = N,N′-dimethylformamide, EtOH = ethanol). Single-crystal X-ray diffraction analyses indicated that compounds 1–3 possessed a three-dimensional (3D) network while 4 adopted a two-dimensional (2D) layered structure. Noticeably, the coordinated solvent molecules adopt distinct coordination modes which play a vital role in constructing the Mg-TDC structures. In 1, the solvent EG molecules as bi-dentate bridging ligands help in interconnecting the Mg-TDC layers to a 3D framework, whereas the solvent DMSO molecules in 2 and the Ac− anions generated from decomposition of DMA in 3 are coordinated in a μ2-fashion and in a (k2-k2)-μ3 mode, respectively, leading to infinite chains as secondary building units. In the layered structure of 4, the collaboration of coordinated DMF, EtOH and H2O molecules assists in inducing the noncentrosymmetric structure. The compounds were fully characterized by PXRD, TGA, EA, and IR. The luminescence properties of 1–3 and the second-harmonic generation (SHG) properties of 4 were studied. 3 emitted bright green light upon the excitation of 365 nm UV light, while 4 displayed sound SHG response.

A Mg-CP with in Situ Encapsulated Photochromic Guest as Sensitive Fluorescence Sensor for Fe3+/Cr3+ Ions and Nitro-Explosives

Here we report a fluorescent magnesium coordination polymer (Mg-CP), namely, [CH3-dpb]2[Mg3(1,4-NDC)4(μ-H2O)2(CH3OH)(H2O)]·1.5H2O (1, 1,4-H2NDC = 1,4-naphthalene dicarboxylic acid, dpb = 1,4-bis(pyrid-4-yl)benzene). Compound 1 possesses a three-dimensional (3D) host-guest structure constructed by the 1,4-NDC linkers bridging the linear trinuclear secondary building units of [Mg3(COO)8(μ-H2O)2]. The dpb molecules were in situ reacted with CH3OH resulting in photochromic cations of [CH3-dpb]+ that acted as guests located in the channels parallel to the b-axis. Photoluminescence (PL) studies indicated that 1 showed a strong green emission demonstrating sensitive fluorescence sensing of Fe3+/Cr3+ metal ions and nitro-explosive compounds. Compound 1 represents the first PL Mg-CP as a fluorescent probe for detecting metal ions. Moreover, because of the in situ encapsulation of photochromic [CH3-dpb]+ guests, 1 exhibited reversible photochromic behavior.

Dual-Emission Luminescence of Magnesium Coordination Polymers Based on Mixed Organic Ligands.

Presented herein are two luminescent magnesium coordination polymers (Mg-CPs), namely [Mg2 (H2O)2 (2-NDC)4 (1,10-phen)2] (1) and [Mg2 (H2O)(1,4-NDC)2 (1,10-phen)] (2), in which 2-NDCH=2-naphthalenecarboxylic acid, 1,4-NDCH2 =1,4-naphthalene dicarboxylic acid, and 1,10-phen=1,10-phenanthroline. Based on the mixed ligands, the title compounds exhibit linker-based photoluminescence (PL) properties thanks to the unique configuration of the Mg(2+) ions. The two compounds show interesting dual emission on excitation of the different luminophores of the mixed linkers. In particular, the emissions of compound 2 could be tuned from green to yellow simply by varying the excitation energies. Furthermore, 2 could be excited by using a commercial λ=450 nm blue LED chip to generate white-light emission, which allows the fabrication of a white-light-emitting diode (WLED) with 20 lm W(-1) luminous efficacy. This work may provide a new method for designing tunable PL CPs by using the low-cost and abundant magnesium ion.

An ionothermally synthesized Mg-based coordination polymer as a precursor for preparing porous carbons

A new magnesium coordination polymer (Mg-CP), namely [Bmim]2[Mg6(NDC)5(HNDC)2(HCOO)2] (1, H2NDC = 1, 4-naphthalenedicarboxylic acid, [Bmim] = 1-butyl-3-methyl-imidazolium ion), has been ionothermally synthesized and structurally characterized. Single-crystal X-ray structural determination indicated that the title compound possessed an anionic three-dimensional (3D) framework constructed by the interconnections of unprecedented hexanuclear magnesium-carboxylate clusters as secondary building units (SBUs) via bridging NDC ligands. Compound 1 exhibited blue luminescence emission at 440 nm when excited at 360 nm. Significantly, the title non-porous Mg-CP could be utilized as a precursor for preparing porous carbons through thermal decomposition in optimized conditions. Different from the reported high decomposition temperature (>1000 °C) mostly based on porous Zn-CP precursors, the optimum decomposition temperature for 1 was only 700 °C, and the resulting porous carbons showed 465 cm3 g−1 adsorption volume for N2. The as-prepared carbon exhibited finely selective N2 adsorption ability over H2 and CO2. This work may provide a certain guiding significance for exploiting ionothermally synthesized Mg-CPs as a new type of precursor towards porous carbons.

A photochromic dual-functional Mg-CP exhibits white-emission after modification with CuI

A new 3D host–guest Mg-CP shows tuneable dual emission and ultimately achieves direct white emission after being post-modified with CuI, which also represents the first photochromic Mg-CP based on a non-photochromic organic linker that exhibits reversible colour changes.

Mg1−xCoxLi2(3,5-pdcH)2(DMF)2 (x = 0, 0.285, 0.575, 1): a series of heterometallic coordination polymers doped with magnetic Co2+ ions

The introduction of heterometal ions into coordination polymers (CPs) could yield novel structural types and thus unprecedented properties. This work reports on the syntheses, characterizations and magnetic properties of a series of heterometallic CPs (HCPs), namely Mg1−xCoxLi2(3,5-pdcH)2(DMF)2 (x = 0 (1), 0.285 (2), 0.575 (3) and 1 (4); 3,5-pdcH3 = pyrazole-3,5-dicarboxylic). The CPs are isostructural to each other with a three dimensional neutral framework of apo type topology, which is constructed by 3,5-pdcH2− ligands interconnecting infinite chain-like SBUs of [MLi2(COO)4(DMF)2]n (M = Mg (1), Mg0.715Co0.285 (2), Mg0.425Co0.575 (3) and Co (4)). Compound 1 represents a rare example of an s–s block HCP based on lightweight Mg2+ and Li+ ions. Compound 1 is magnetically inactive, while the successful doping of Co2+ ions into Mg2+ sites endows the resulting heterometallic compounds with antiferromagnetic behaviour. The magnetic behaviour of compounds 2–4 was analyzed and was shown to come from the zero field split or the spin–orbit coupling of the high-spin mononuclear Co2+ ions. Compounds 2 and 3 represent a rare type of HCP which simultaneously contains independent metal ions (Li+) and co-occupied ones (Mg2+ and Co2+) in different crystallographic sites.

An easily synthesized microporous framework material for the selective capture of radioactive Cs+ and Sr2+ ions

It is of vital importance to capture 137Cs+ and 90Sr2+ from solutions for radionuclide remediation due to their hazardous nature and long half-life. Although metal organic framework (MOF) materials have been greatly developed, the studies of their application in the capture of radioactive cations remain rare. Especially, the capture mechanism has not been clarified. Here, we present a new In-MOF material with the potential for remediation of radioactive Cs+ and Sr2+ ions by ion exchange, namely, [Me2NH2][In(TDC)2]·1.5DMA·1.5H2O (FJSM-InMOF; H2TDC = 2,5-thiophenedicarboxylic acid and DMA = N,N′-dimethylacetamide). It possesses an anionic framework of [In(TDC)2]nn− charge balanced by dimethylammonium cations. It could be easily synthesized via a one-pot solvothermal route. Remarkably, it showed excellent β and α radiation-resistances, high exchange capacities (qCsm = 198.63 mg g−1; qSrm = 43.83 mg g−1), impressive selectivity (KCsd = 7.50 × 104 mL g−1; KSrd = 9.49 × 105 mL g−1), high ion-exchange efficiency (RSr = 99.89%; RCs = 99.63%) and the ability of convenient elution with low cost. In particular, the ion exchange mechanism was illuminated by an unprecedented observation of the single-crystal to single-crystal structural transformation in the Cs+-exchange process. This work paves the way to develop highly efficient and environmentally friendly MOFs for the selective capture of radionuclides.