How linker's modification controls swelling properties of highly flexible iron(III) dicarboxylates MIL-88

A series of organically modified iron(III) terephthalate MIL-88B and iron(III) 4,4'-biphenyl dicarboxylate MIL-88D flexible solids have been synthesized and characterized through a combination of X-ray diffraction, IR spectroscopy, and thermal analysis (MIL stands for Material from Institut Lavoisier). The swelling amplitude of the highly flexible MOFs tuned by introducing functional groups onto the phenyl rings shows a clear dependence on the steric hindrance and on the number of groups per aromatic ring. For instance, while the introduction of four methyl groups per spacer in dried MIL-88B results in a large permanent porosity, introducing two or four methyl groups in MIL-88D allows an easier pore opening in the presence of liquids without drastically decreasing the swelling magnitude. The influence of the degree of saturation of the metal center and the nature of the solvent on the swelling is also discussed. Finally, a computationally assisted structure determination has led to a proposal of plausible structures for the closed (dried) and open forms of modified MIL-88B and MIL-88D and to evaluation of their framework energies subject to the nature of the functional groups.     

Adsorption of CO2 in metal organic frameworks of different metal centres: Grand Canonical Monte Carlo simulations compared to experiments

A Grand Canonical Monte Carlo study has been performed in order to compare the different CO₂ adsorption mechanisms between two members of the MIL-n family of hybrid metal-organic framework materials. The MIL-53 (Al) and MIL-47 (V) systems were considered. The results obtained confirm that there is a structural interchange between a large pore and narrow pore forms of MIL-53 (Al), not seen with the MIL-47 (V) material, which is a consequence of the presence of μ ₂-OH groups. The interactions between the CO₂ molecules and these μ ₂ OH groups mainly govern the adsorption mechanism in this MIL-53 (Al) material. The subsequent breaking of these adsorption geometries after the adsorbate loading increases past the point where no more preferred adsorption sites are available, are proposed as key features of the breathing phenomenon. After this, any new adsorbates introduced into the MIL-53 (Al) large pore structure experience a homogeneous adsorption environment with no preferential adsorption sites in a similar way to what occurs in MIL-47 (V).     

金属有机框架@介孔分子筛复合材料的构建和性质

通过蒸汽诱导内部水解法(VIH)在介孔分子筛SBA-15孔壁上引入Al_2O_3,合成得到Al_2O_3@SBA-15复合物,随后与对二苯甲酸配体反应,从而制备得到金属有机框架化合物(MIL-53)与介孔分子筛(SBA-15)复合材料(MIL-53@SBA-15)。采用粉末X射线衍射(PXRD)、N_2吸附-脱附测试、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等技术证明成功合成了MIL-53@SBA-15复合材料。染料吸附实验结果表明,MIL-53@SBA-15复合材料相比于SBA-15、MIL-53及其物理混合样品,表现出对丁基罗丹明染料更高效吸附特性。     

一个考虑沉积物孔径分布特征的水合物相平衡模型

天然气水合物的相平衡条件一直是水合物相关研究的重点和难点. 本文探讨了沉积物孔隙大小及其分布特征对水合物相平衡条件的影响机理, 提出了有效孔隙半径的概念, 并利用沉积物孔隙大小分布特征, 假设孔径分布呈正态分布, 建立了水合物饱和度和有效孔隙半径之间的定量关系; 与传统的van der Waals-Platteeuw相平衡模型相结合, 提出了一个考虑沉积物孔隙大小及其分布特征的相平衡模型. 相对于传统模型, 本模型所表达的相平衡条件不再是二维平面的p-T曲线, 而是温度、压力以及水合物饱和度之间的三维定量关系. 这一特征使得所建模型既能较为真实地反映水合物形成与分解机理, 又能有效地考虑孔隙大小分布对水合物相平衡条件的影响. 通过与实验数据对比, 证明了所建模型的预测结果优于其他模型. 本模型在温度和压力条件确定的情况下还可以预测沉积物中水合物的饱和度, 因此, 可用于地层中水合物储量计算.     

Synthesis and characterizations of hierarchical biomorphic titania oxide by a bio-inspired bottom-up assembly solution technique

As a representative semiconductor metal oxide, hierarchical biomorphic mesoporous TiO₂ with interwoven meshwork conformation was successfully prepared using eggshell membrane (ESM) as a biotemplate by an aqueous soakage technique followed by calcination treatment. The synthesis conditions were systematically investigated by controlling the concentration, the pH value of the precursor impregnant, and so on. The nucleation, growth, and assembly into ESM-biomorphic TiO₂ in our work depended more on the functions of ESM biomacromolecules as well as the processing conditions. As-prepared TiO₂ meshwork exhibiting hierarchical porous structure with the pore size from 2 nm up to 4 μm, was composed of intersectant fibers assembled by nanocrystallites at three dimensions. Based on the researches into the N₂ adsorption-desorption isothermal and corresponding BJH pore-size distribution, the biomorphic TiO₂ would arose interesting applications in some fields such as photocatalysis, gas sensors, antistatic coating, dye-sensitized solar cells, etc. This mild method and the relevant ideas offer a feasible path to synthesize a new family of functional materials by integrating material science, chemistry, and biotechnology.     

Very large swelling in hybrid frameworks: a combined computational and powder diffraction study

Using a combination of simulations and powder diffraction, we report here the study of the very large swelling of a three-dimensional nanoporous iron(III) carboxylate (MIL-88) which exhibits almost a reversible doubling (approximately 85%) of its cell volume while fully retaining its open-framework topology. The crystal structure of the open form of MIL-88 has been successfully refined and indicates that atomic displacements larger than 4 angstroms are observed when water or various alcohols are adsorbed in the porous structure, revealing an unusually flexible crystallized framework. X-ray thermodiffractometry shows that only a displacive transition occurs during the swelling phenomenon, ruling out any bond breaking.     

Copper-doped sulfonic acid-functionalized MIL-101(Cr) metal–organic framework for efficient aerobic oxidation reactions

A series of Cr-based metal–organic framework MIL-101-SO₃H bearing sulfonic acid functional groups were utilized for the immobilization of catalytically active copper species via a post-synthetic metalation method. The novel materials were fully characterized by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), the Brunauer–Emmett–Teller method, and thermogravimetric analysis. XPS and the EDX element map both suggested that Cu²⁺ is coordinately bonded to the MIL-101-SO₃H, which forms the MIL-101-SO₃@Cu structure. The obtained copper-doped MIL-101-SO₃@Cu-1, MIL-101-SO₃@Cu-2, and MIL-101-SO₃@Cu-3 catalysts were utilized in the selective oxidation of alcohols and epoxidation of olefins using molecular oxygen as an oxidant. Catalytic aerobic oxidation optimization showed that MIL-101-SO₃@Cu-1 is the optimal catalyst and it can be reused ten times without compromising the yield and selectivity.     

共价有机骨架的合成及其在气体吸附存储方面的应用

共价有机骨架(COFs)是一种新型的纳米结构材料,由于其独特的性质而受到人们的广泛关注.COFs的结晶.度高,孔径可调,比表面积大,具有良好的抗氧化性能和独特的分子结构,在能源、环境等方面得到了广泛的应用.COFs材料有较高的应用价值,促使人们不断努力研究其基本性质,并调控其结构和功能来提高性能.通过COFs的可设计性...     

乙二胺改性轻金属铝-金属有机骨架材料用于CO2/CH4分离

胺类分子在CO₂的捕获中可以起到选择性提升的作用,本文选择小尺寸的乙二胺分子对具有不饱和金属位点的轻金属铝基金属有机骨架（Al-MOFs）材料MIL-100Al进行改性,利用XRD、N₂吸附和FT-IR等对改性材料的结构进行表征,测试了不同浓度的乙二胺改性的MIL-100Al对CO₂和CH₄吸附性能。结果表明,与原始的MIL-100Al材料相比,改性后的材料对CO₂吸附量有明显提高,CH₄的吸附量却降低,从而进一步提高了材料的CO₂/CH₄吸附选择性,提升了吸附分离的效果。     

乙二胺改性轻金属铝-金属有机骨架材料用于CO_2/CH_4分离

胺类分子在CO_2的捕获中可以起到选择性提升的作用,本文选择小尺寸的乙二胺分子对具有不饱和金属位点的轻金属铝基金属有机骨架(Al-MOFs)材料MIL-100Al进行改性,利用XRD、N2吸附和FT-IR等对改性材料的结构进行表征,测试了不同浓度的乙二胺改性的MIL-100Al对CO_2和CH4吸附性能。结果表明,与原始的MIL-100Al材料相比,改性后的材料对CO_2吸附量有明显提高,CH4的吸附量却降低,从而进一步提高了材料的CO_2/CH4吸附选择性,提升了吸附分离的效果。     

In Situ Observation of Hot Carrier Transfer at Plasmonic Au/Metal-Organic Frameworks (MOFs) Interfaces

Constructing heterostructures have been demonstrated as an ideal strategy for boosting charge separation on plasmonic photocatalysts, but the detailed interface charge transfer mechanism remains elusive. Herein, that authors fabricate plasmonic Au and metal-organic frameworks (MOFs, NH₂−MIL-125 and MIL-125 used in this work) heterostructures and explore the interface charge transfer mechanism by in situ electron paramagnetic resonance (EPR) spectroscopy and electrochemical measurements. The plasmon-excited hot electrons on Au can transfer across the Au/MOF interface and be captured by the coordinatively unsaturated sites of secondary building units (Ti₈O₈(OH)₄ cluster) of the MOF structure, and the plasmon-excited hot holes on Au tend to transfer to and be trapped at the functionalized organic ligand (1,4-benzenedicarboxylate−NH₂). The spatially separated hot electrons and holes exhibit boosted the photocatalytic activity for chromium (VI) reduction and selective benzyl alcohol oxidation. This work illustrates the advantage of the versatile functionalization of MOF structures enabling molecular-level manipulation of interface charge transfer on plasmonic photocatalysts.     

铬-对苯二甲酸MOF的框架异构：MIL-88B(Cr)和MIL-101(Cr)

可以通过简单地控制乙酸浓度的方法,在相似的水热合成条件下合成2种同一家族的金属有机框架材料(MOFs):MIL-88B(Cr)和MIL-101(Cr)。在相对较低的乙酸浓度下,可以得到平均粒径为100 nm的MIL-101(Cr),并拥有很高的BET比表面积(3543 m^2·g^-1)。而在相对较高的乙酸浓度下,则可得到另一种具有“呼吸”特性结构的MOF——MIL-88B(Cr)。利用粉末X射线衍射、扫描电镜、N2吸附-脱附分析、热重分析等对它们的结构、形貌、孔隙率等性质做了详细的分析。     

MIL-101(Cr) Microporous Nanocrystals Intercalating Graphene Oxide Membrane for Efficient Hydrogen Purification

Graphene oxide (GO) is a promising two-dimensional building block for fabricating high-performance gas separation membranes. Whereas the tortuous transport pathway may increase the transport distance and lead to a low gas permeation rate, introducing spacers into GO laminates is an effective strategy to enlarge the interlayer channel for enhanced gas permeance. Herein, we propose to intercalate CO₂-philic MIL-101(Cr) metal-organic framework nanocrystals into the GO laminates to construct a 2D/3D hybrid structure for gas separation. The interlayer channels were partially opened up to accelerate gas permeation. Meanwhile, the intrinsic pores of MIL-101 provided additional transport pathways, and the affinity of MIL-101 to CO₂ molecules resulted in higher H₂/CO₂ diffusion selectivity, leading to a simultaneous enhancement in gas permeance and separation selectivity. The MIL-101(Cr)/GO membrane with optimal structures exhibited outstanding and stable mixed-gas separation performance with H₂ permeance of 67.5 GPU and H₂/CO₂ selectivity of 30.3 during the 120-h continuous test, demonstrating its potential in H₂ purification application.     

Hierarchical NiCo2O4 microspheres assembled by nanorods with p-type response for detection of triethylamine

The morphological and structural design provides an efficient protocol to optimize the performance of gas sensing materials. In this work, a gas sensor with high sensitivity for triethylamine (TEA) detection is developed based on p-type NiCo₂O₄ hierarchical microspheres. The NiCo₂O₄ microspheres, synthesized by a hydrothermal route, have a three-dimensional (3D) urchin-like structure assembled by nanorod building blocks. The structure-property correlation has been investigated by powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscope, scanning electron microscope, N₂ adsorption-desorption tests and comprehensive gas sensing experiments. The influence of calcination temperature on the morphological structure and sensing performances has been investigated. Results reveal that the material annealed at 300 °C has a very large specific surface area of 125.27 m²/g, thereby demonstrating the best TEA sensing properties including high response and low limit of detection (145 ppb), good selectivity and stability. The further increase of the calcination temperature leads to the collapse of the 3D hierarchical structure with significantly decreased surface area, which is found to decline the sensing performances. This work indicates the promise of ternary p-type metal oxide nanostructures for application in highly sensitive gas sensors.     

Breathing Effect via Solvent Inclusions on the Linker Rotational Dynamics of Functionalized MIL-53

The breathing effects of functionalized MIL-53-X (X=H, CH₃, NH₂, OH, and NO₂) induced by the inclusions of water, methanol, acetone, and N,N-dimethylformamide solvents were comprehensively investigated by solid-state NMR spectroscopy. 2D homo-nuclear correlation NMR provided direct experimental evidence for the host-guest interaction between the guest solvents and the MOF frameworks. The variations of the ¹H and ¹³C NMR chemical shifts in functionalized MIL-53 from the narrow pore phase transitions to large pore forms due to solvent inclusions were clearly identified. The influence of functionalized linkers and their host-guest interactions with the confined solvents on the rotational dynamics of the linkers was examined by separated-local-field MAS NMR experiments in conjunction with DFT theoretical calculations. It is found that the linker rotational dynamics of functionalized MIL-53 in narrow pore form is closely related to the computational rotational energy barrier. The BDC-NO₂ linker of activated MIL-53-NO₂ undergoes relatively faster rotation, whereas the BDC-NH₂ and BDC-OH linkers of activated MIL-53-NH₂ and MIL-53-OH exhibit relatively slower rotation. The host-guest interactions between confined solvents and MIL-53-NO₂, MIL-53-CH₃ would significantly induce an increase of the order parameters of unsubstituted carbon and reduce the rotational frequency of linkers. This study provides a spectroscopic approach for the investigation of linker rotation in functionalized MOFs at natural abundance with solvents inclusions.     

苯部分加氢制环己烯新型Ru-B/MOF催化剂

制备了多种金属-有机骨架(MOF)材料,采用浸渍-化学还原法制备了非晶态Ru-B/MOF催化剂,考察了它们在苯部分加氢反应中的催化性能.催化性能评价结果表明,这些催化剂的初始反应速率(r0)顺序为Ru-B/MIL-53(Al)Ru-B/MIL-53(Al)-NH2Ru-B/UIO-66(Zr)Ru-B/UIO-66(Zr)-NH2Ru-B/MIL-53(Cr)Ru-B/MIL-101(Cr)Ru-B/MIL-100(Fe),环己烯初始选择性(S0)顺序为Ru-B/MIL-53(Al)≈Ru-B/MIL-53(Cr)Ru-B/UIO-66(Zr)-NH2Ru-B/MIL-101(Cr)Ru-B/MIL-53(Al)-NH2Ru-B/UIO-66(Zr)≈Ru-B/MIL-100(Fe).催化性能最好的Ru-B/MIL-53(Al)催化剂上的r0和S0分别为23 mmol·min-1·g-1和72%.采用多种手段,对催化性能差异最为显著的Ru-B/MIL-53(Al)和Ru-B/MIL-100(Fe)催化剂的物理化学性质进行了表征.发现MIL-53(Al)载体能够更好地分散Ru-B纳米粒子,粒子的平均尺寸为3.2 nm,而MIL-100(Fe)载体上Ru-B纳米粒子团聚严重,粒径达46.6 nm.更小的粒径不仅能够提供更多的活性位,而且也有利于环己烯选择性的提高.对Ru-B/MIL-53(Al)催化剂的反应条件进行了优化,在180°C和5 MPa的H2压力下,环己烯得率可达24%,展示了MOF材料用作苯部分加氢催化剂载体的良好前景.     

Chromium-based metal–organic framework/mesoporous carbon composite: synthesis,characterization and CO<Subscript>2</Subscript> adsorption

New composites of a water-stable chromium-based metal organic framework MIL-101 and mesoporous carbon CMK-3 were in situ synthesized with different ratios of MIL-101 and CMK-3 using the hydrothermal method. The composites as well as the parent materials were characterized by X-ray diffraction, thermo gravimetric analysis, scanning electron microscope, transmission electron microscope and nitrogen/carbon dioxide adsorption isotherms. The hybrid material possesses the same crystal structure and morphology as its parent MIL-101, and exhibits an enhancement in CO₂ adsorption uptakes when compared to MIL-101 and CMK-3. The increase in CO₂ uptakes was attributed to the combined effect of the formation of additional micropores, the enhancement of micropore volume and the activation of unsaturated metal sites by CMK-3 incorporation.     

Conjugation of Disassembled Zincphthalocyanine-based Nanocomposites and the Synergistic Effect on Visible-light Photosensitive Activity

In this research, a conjugated Pc-MIL-88B(Fe) nanoplatform was constructed via a condensation process between modified zinc phthalocyanine and MIL-88B(Fe) for the removal of organic pollutants. The as-prepared material was fully characterized by TEM, XPS, ICP, FTIR, UV-Vis, N_2 adsorption-desorption isotherm,etc. The results indicate that Pc-MIL-88B(Fe) preserved the topological structure of MIL-88B(Fe), and the micropores of framework could effectively prevent the aggregation of Pc in water. Meanwhile, the conjugated Pc-MIL-88B(Fe) basically maintains the singlet oxygen quantum yield of Pc, and behaves a much higher photocurrent intensity compared to NH_2-MIL-88 B(Fe). Additionally, the photosensitive activity and reusability of Pc-MIL-88B(Fe) were evaluated by the degradation of methylene blue in aqueous solution under visible light irradiation, and the degradation mechanism was also investigated in detail.     

Microstructure and sensing properties of nanocrystalline indium oxide prepared using hydrothermal treatment

Nanocrystalline indium(III) oxide samples were prepared using soft chemistry. The microstructure (particle size and shape, specific surface area, pore-size distribution) and sensing properties of In₂O₃ were studied as functions of synthesis parameters. Indium oxide synthesis including hydrothermal treatment produces materials having high sensing sensitivity in NO₂ detection.