Study on adsorption of kaolinite and gold thiosulfate.

The adsorption behavior of gold thiosulfate ions on the surface of kaolinite was studied using a combination of experimental research and quantum chemical calculations. Under the condition of a stirring time of 30 min, a stirring speed of 500 r·min-1, and a mass ratio of 30% kaolinite in the slurry, when the initial gold concentration of 56.50 mg·L-1,the adsorption rate of gold-thiosulfate ions from a kaolinite-containing solution was 7.44%. The results of Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS) showed that the physical and chemical adsorption of kaolinite and gold thiosulfate occurred in solution. Quantum chemical calculations were performed using the CASTEP module in Materials Studio. The adsorption energy of gold thiosulfate on the surface of kaolinite (001) was calculated as - 438.01 kJ·mol-1.The calculated H76-O289 distance was 1.615 Å. Mulliken Charge population analysis and bond population analysis showed that gold thiosulfate ions form relatively stable bonds on the kaolinite surface (001). In the process of thiosulfate immersion, part of gold is adsorbed by kaolinite, which affects the extraction of gold. These results indicate that during the leaching process of gold thiosulfate, kaolinite has the ability to "catch" gold, which affects the leaching efficiency.

Zero- to One-Dimensional Zn24 Supraclusters: Synthesis, Structures and Detection Wavelength.

A zinc supracluster [Zn24(ATZ)18(AcO)30(H2O)1.5]·(H2O)3.5 (Zn24), and a 1D zinc supracluster chain {[Zn24(ATZ)18(AcO)30(C2H5OH)2(H2O)3]·(H2O)2.5}n (1-D⊂Zn24) with molecular diameters of 2 nm were synthesized under regulatory solvothermal conditions or the micro bottle method. In an N,N-dimethylformamide solution of Zn24, Fe3+, Ni2+, Cu2+, Cr2+ and Co2+ ions exhibited fluorescence-quenching effects, while the rare earth ions Ce3+, Dy3+, Er3+, Eu3+, Gd3+, Ho3+, La3+, Nd3+, Sm3+, and Tb3+showed no obvious fluorescence quenching. In ethanol solution, the Zn24 supracluster can be used to selectively detect Ce3+ ions with excellent efficiency (limit of detection (LOD) = 8.51 × 10-7 mol/L). The Zn24 supracluster can also detect wavelengths between 302 and 332 nm using the intensity of the emitted light.

Selective and Rapid Detection of 4-Nitrophenol in River and Treated Industrial Wastewater by a Luminescent Lanthanide Metal-Organic Framework Sensor.

Phenolic organic compounds are widely used industrial chemicals that exist extensively in the environment and have a significant impact on human health. 4-Nitrophenol (4-NP) is a typical phenolic organic compound found in aqueous environments. Efficient detection of 4-NP in wastewater is highly challenging due to the complexity of testing environmental samples. Herein, a luminescent lanthanide metal-organic framework (MOF) sensor based on the Eu3+ ion {[Eu(HL)(L)(H2O)]·2H2O}n (EuMOF; H2L = 5-(4H-1,2,4-triazol-4-yl)benzene-1,3-dicarboxylic acid) was successfully synthesized for efficient 4-NP detection in wastewater. Fluorescence sensing experiments revealed that 4-NP could greatly quench the EuMOF fluorescence. Subsequently, EuMOF was applied to 4-NP detection in distilled water, tap water, river water, and treated industrial wastewater, exhibiting high sensitivity, a fast response within 30 s, high selectivity, excellent reusability, and a low detection limit. Finally, the fluorescence quenching mechanism was explored and attributed to competitive absorption of irradiated light between 4-NP and the ligand.

Promoted Photocatalytic Hydrogen Evolution by Tuning the Electronic State of Copper Sites in Metal-Organic Supramolecular Assemblies.

The electronic state in terms of charge and spin of metal sites is fundamental to govern the catalytic activity of a photocatalyst. Herein, we show that modulation of the electronic states of Cu sites, without changing the coordination environments, of two metal-organic supramolecular assemblies based on π⋅⋅⋅π stacking can significantly improve photocatalytic activity. The use of these heterogeneous photocatalysts, without using noble metal cocatalysts, resulted in an increase of the hydrogen production rate from 522 to 3620 µmol h-1 g-1 . A systematical analysis revealed that the charge density and spin density of the metal centers are efficiently modulated via the modulation of the coordination fields around active copper (II) centers by the variation of the non-coordination groups of terminal ligands, leading to the significant enhancement of photocatalytic activity. This work provides an insight into the electronic state of active metal centers for designing high-performance photocatalysts.

Hydrogen-bonded Complex-based Frameworks for Stable Lithium Storage.

Metal-complex-based materials for lithium storage have attracted great interest due to their highly designable structures with multiple active sites and well-defined lithium transport pathways. Their cycling and rate performances, however, are still constrained by structural stability and electrical conductivity. Herein, we present two hydrogen-bonded complex-based frameworks with excellent lithium storage capability. Multiple hydrogen bonds among the mononuclear molecules result in three-dimensional frameworks that are stable in electrolyte. The origin of the remarkable lithium storage performance of this family was revealed through kinetic analysis and DFT calculations.

High-Efficiency Lithium-Ion Transport in a Porous Coordination Chain-Based Hydrogen-Bonded Framework.

Fast and selective Li+ transport in solid plays a key role for the development of high-performance solid-state electrolytes (SSEs) of lithium metal batteries. Porous compounds with tunable Li+ transport pathways are promising SSEs, but the comprehensive performances in terms of Li+ transport kinetics, electrochemical stability window, and interfacial compatibility are difficult to be achieved simultaneously. Herein, we report a porous coordination chain-based hydrogen-bonded framework (NKU-1000) containing arrayed electronegative sites for Li+ transport, exhibiting a superior Li+ conductivity of 1.13 × 10-3 S cm-1, a high Li+ transfer number of 0.87, and a wide electrochemical window of 5.0 V. The assembled solid-state battery with NKU-1000-based SSE shows a high discharge capacity with 94.4% retention after 500 cycles and can work over a wide temperature range without formation of lithium dendrites, which derives from the linear hopping sites that promote a uniformly high-rate Li+ flux and the flexible structure that can buffer the structural variation during Li+ transport.

Efficient Recognition and Removal of Persistent Organic Pollutants by a Bifunctional Molecular Material.

Persistent organic pollutants (POPs) exist widely in the environment and place significant impact on human health by bioaccumulation. Efficient recognition of POPs and their removal are highly challenging tasks because their specific structures interact often very weakly with the capture materials. Herein, a molecular nanocage (1) is studied as an efficient sensing and sorbent material for POPs, which is demonstrated by a representative and stable perfluorooctane sulfonate (PFOS) substrate containing a hydrophilic sulfonic group and a hydrophobic fluoroalkyl chain. A highly sensitive and unusual turn-on fluorescence response within 10 s and a 97% total removal of PFOS from water in 20 min have been achieved owing to the strong host-guest interactions between 1 and PFOS. The binding constant of 1 to PFOS is 2 orders of magnitude higher than state-of-the-art adsorbents for PFOS and thus represents a new benchmark material for the recognition and removal of PFOS. The host-guest interaction has been elucidated by solid-state NMR spectroscopy and single-crystal X-ray diffraction, which provide key insights at a molecular level for the design of new advanced sensing/sorbent materials for POPs.

Bimetallic Cage-Based Metal-Organic Frameworks for Electrochemical Hydrogen Evolution Reaction with Enhanced Activity.

A cage-based metal-organic framework (Ni-NKU-101) with biphenyl-3,3',5,5'-tetracarboxylic acid was synthesized via solvothermal method. Ni-NKU-101 contains two types of cages based on trinuclear and octa-nuclear nickel-clusters that are connected with each other by the 4-connected ligands, to form a 3D framework with a new topology. A mixed-metal strategy was used to synthesize isostructural bimetallic MOFs of Mx Ni1-x -NKU-101 (M=Mn, Co, Cu, Zn). The electrocatalytic studies showed that the hydrogen evolution reaction (HER) activity of Cux Ni1-x -NKU-101 is much higher than that of other Mx Ni1-x -NKU-101 catalysts in acidic aqueous solution, owing to the synergistic effect of the bimetallic centers. The optimized Cu0.19 Ni0.81 -NKU-101 has an overpotential of 324 mV at 10 mA cm-2 and a Tafel slope of 131 mV dec-1 . The mechanism of HER activity over these bimetallic MOF-based electrocatalysts are discussed in detail.

Detection of the UV-vis silent biomarker trimethylamine-N-oxide via outer-sphere interactions in a lanthanide metal-organic framework.

Trimethylamine-N-oxide (TMAO) is a biomarker of the cardiovascular disease that is one of the leading causes of worldwide death. Facile detection of TMAO can significantly improve the survival rate of this disease by allowing early prevention. However, the UV-vis silent nature of TMAO makes it intricated to be detected by conventional sensing materials or analytical instruments. Here we show a bilanthanide metal-organic framework functionalized by borono group for the recognition of TMAO. Superior sensitivity, selectivity and anti-interference ability were achieved by the inverse emission intensity changes of the two lanthanide centers. The limit of detection is 15.6 µM, covering the clinical urinary concentration range of TMAO. A smartphone application was developed based on the change in R-G-B chromaticity. The sensing mechanism via a well-matched outer-sphere interaction governing the sensing function was studied in detail, providing fundamentals in molecular level for the design of advanced sensing materials for UV-Vis silent molecules.

Fast Detection of Entacapone by a Lanthanide-Organic Framework with Rhombic Channels.

Entacapone (ENT) is a powerful catechol-O-methyl transferase inhibitor that is used for the diagnosis and treatment of Parkinson's syndrome, but the amount used must be well controlled to avoid overtreatment and side effect. Fast and selective detection of ENT needs well-matched energy levels and well-designed sensor-ENT interaction which is highly challenging. In this work, a water stable europium-based metal-organic framework (Eu-TDA) was synthesized to detect ENT by luminescence with excellent reusability and selectivity in the presence of main coexisting and interference species of plasma with a limit of detection of 5.01 µM. The experimental results showed that the luminescence of Eu-TDA can be effectively quenched by ENT via well-designed photoinduced electron transfer mechanism and internal filtration effect mechanism in the system.

A Europium-Organic Framework Sensing Material for 2-Aminoacetophenone, a Bacterial Biomarker in Water.

2-Aminoacetophenone (2-AA) is a metabolite produced in large quantities by the pathogenic bacteria Pseudomonas aeruginosa (PA), which is a biomarker for PA in water. State-of-the-art analytical techniques to detect PA usually require expensive instruments and a long analysis time which are not suitable for real-time water quality monitoring, especially for high-quality drinking water. Herein, we reported the application of a europium metal-organic framework (Eu-MOF) as a luminescent sensing material, which provides a facile, environmentally friendly and low-cost way for the fast detection of PA in water. Eu-MOF shows a high sensitivity toward 2-AA with a KSV value of 3.563 × 104 M-1, rapid luminescence response in 12 s and high-selectivity and anti-interference ability with the existence of common detection indexes in drinking water owing to the good match of the energy levels of Eu-MOF and 2-AA. A systematical optimization of the sensing conditions to enhance the sensing function of Eu-MOF for 2-AA was discussed in detail, to give fundamentals for the rational design of MOF-based sensing materials.

Water Stable Heterometallic Zn-Tb Coordination Polymer for Rapid Detection of the Ultraviolet Filter Benzophenone.

Benzophenone (BP) is an ultraviolet filter (UVF) widely used in personal care products such as sunscreens and cosmetics. Excessive exposure to BP-type UVFs is a potential threat to human's health because of their endocrine-disrupting activity. Water stability of lanthanide compounds is crucial when they serve as luminescent sensors because of the practicality and recyclability. In this study, a water-stable luminescent Zn-Tb heterometallic coordination polymer was rationally designed and synthesized for rapid detection of BP. This material showed a high quenching effect, excellent selectivity, and fast response toward BP.

Cadmium-Based Coordination Polymers from 1D to 3D: Synthesis, Structures, and Photoluminescent and Electrochemiluminescent Properties.

Cadmium-based coordination polymers, namely, {[Cd(HL)(L)] ⋅ HN(Et)3 }n (1), [Cd2 (L)2 (H2 O)5 ]n (2), [Cd(L)(phen)]n (3), [Cd(L)(2,2'-bpy)]n (4), [Cd(L)(4,4'-bpy)]n (5), [Cd(L)(bpp)]n (6), [Cd(L)(dpa)]n (7), {[Cd(L)(dpa)] ⋅ H2 O}n (8) (H2 L=4,4'-((p-tolylazanediyl)bis(methylene))dibenzoic acid, phen=1,10-phenanthroline, 2,2'-bpy=2,2'-bipyridine, 4,4'-bpy=4,4'-bipyridine, bpp=1,3-bis(4-pyridyl)propane, dpa=bis(4-pyridyl)amine) have been synthesized in hydro/solvothermal reactions. 1 is a 4-connect 3D network with an eightfold interpenetrating diamond topology. The 1D ladder chain structure of 2 was composed of the dinuclear [Cd2 (CO2 )4 ] subunit bridged with two L2- ligands. 3 shows a 1D double-chain with a channel formed by edging out the coordination water with the rigid co-ligand phen. Polymer 4 displays a 2D lamellar structure based on superseding the coordination water molecules by the rigid chelating auxiliary ligands 2,2'-bpy. By substituting the small molecules with a rigid bridging ligand 4,4'-bpy, a 2D undulating structure of 5 was built. Compounds 6 and 7 exhibit a 2D layer structure with a 4-connect (44 ⋅ 62 ) sql-net. Compound 8 presents a 3D architecture with a sixfold interpenetrating diamond topology. Through our construction strategy, versatile structures from 1D-3D have been rationally designed by controlling the process condition and rigid/flexible of N-donor spacers. Additionally, the photoluminescence, charge transfer, and electrochemical luminescence (ECL) properties of 1-8 have been demonstrated.