多孔MOFs(UiO-66和UiO-68)合成与表征的综合性大学化学实验*

结合科研工作设计了一个综合性大学化学实验--多孔MOFs(UiO-66,[Zr₆O₄(OH)₄(BDC)₄]_n (H₂BDC=对苯二甲酸)和UiO-68,[Zr₆O₄(OH)₄(ATDA)₄]_n (H₂ATDA=2′-氨基-[1,1′:4′,1″-三联苯]-4,4″-二羧酸))的合成、表征及相关性能研究。该设计实验选择具有不同长度的配体与锆离子组装得到晶态材料,整个实验过程包括有机合成、溶剂热合成、X射线单晶衍射和粉末衍射、红外光谱、热重分析等内容,综合了各大化学知识点于一身。经过此实验,学生不仅能有效了解并掌握MOFs材料的合成、性能测试与相关仪器的操作,还可做到理论结合实际、基础知识结合现代科研手段,培养学生的化学科研素养。     

UiO-66 and hcp UiO-66 Catalysts Synthesized from Ionic Liquids as Linker Precursors

Using ionic liquids (ILs) as linker precursors, the well-known metal-organic framework (MOF) UiO-66 (Universitetet i Oslo) and the recently reported MOF hcp UiO-66 (hexagonal closed packed) have been successfully synthesized and characterized. The advantage of the applied novel synthesis approach is an economically and environmentally benign work-up procedure, due to the better solubility of the IL. Additionally, the reactivity of the terephthalate anions is increased compared to terephthalic acid, resulting in faster MOF formation with an increased amount of defects in the MOF structure. In order to explore to the influence of defects on the catalytic performance, the cyclisation of citronellal to isopulegol was employed as test reaction. The activity of hcp UiO-66 and fcc UiO-66 (face centered cubic) is improved compared to other MOF or zeolite based catalysts, while the selectivity is similar.     

Exploiting parameter space in MOFs: a 20-fold enhancement of phosphate-ester hydrolysis with UiO-66-NH2

The hydrolysis of nerve agents is of primary concern due to the severe toxicity of these agents. Using a MOF-based catalyst (UiO-66), we have previously demonstrated that the hydrolysis can occur with relatively fast half-lives of 50 minutes. However, these rates are still prohibitively slow to be efficiently utilized for some practical applications (e.g., decontamination wipes used to clean exposed clothing/skin/vehicles). We thus turned our attention to derivatives of UiO-66 in order to probe the importance of functional groups on the hydrolysis rate. Three UiO-66 derivatives were explored; UiO-66-NO₂ and UiO-66-(OH)₂ showed little to no change in hydrolysis rate. However, UiO-66-NH₂ showed a 20 fold increase in hydrolysis rate over the parent UiO-66 MOF. Half-lives of 1 minute were observed with this MOF. In order to probe the role of the amino moiety, we turned our attention to UiO-67, UiO-67-NMe₂ and UiO-67-NH₂. In these MOFs, the amino moiety is in close proximity to the zirconium node. We observed that UiO-67-NH₂ is a faster catalyst than UiO-67 and UiO-67-NMe₂. We conclude that the role of the amino moiety is to act as a proton-transfer agent during the catalytic cycle and not to hydrogen bond or to form a phosphorane intermediate.     

Molecular dynamics simulation study of drugs adsorption in UiO-66

Metal-organic frameworks (MOFs) are novel porous materials that have been extensively used in sensors, catalysis, gas storage and separation, and drug deliver owing to their adjustable pore size, large surface area and high porosity. Among diverse MOFs, UiO-66 can be a promising carrier for drug delivery due to high porosity and chemical stability. However, the adsorption mechanism of drugs in UiO-66 has not been identified and need a further investigation. Hence, we utilized molecular dynamic (MD) simulation to investigate the adsorption mechanism of UiO-66 as drug carriers. The MD simulation of UiO-66 exhibits the busulfan loading of 80 %, ibuprofen of 20 % and 5-fluorouracil of 30 %, respectively. We also demonstrated that the host-guest interaction between UiO-66 and drugs is dominated by the Van der Waals force. UiO-66 shows the highest affinity for busulfan compared with ibuprofen and 5-fluorouracil. In addition, it is certified the linear relation between the adsorption atoms and the interaction energy, which could help us to predict the interaction energy between drugs and UiO-66 by the contact atoms.     

Preparation and photocatalytic performance research of Bi2WO6/UiO-66-NH2 composite

Bi₂WO₆/UiO-66-NH₂ photocatalysts were fabricated through solvothermal method using acetic acid as template. The photocatalytic performance of as-fabricated composites was highly improved under simulated visible light due to the addition of UiO-66-NH₂. The structural and chemical properties of the composites were characterized through FTIR, XRD, XPS, SEM, BET, UV–vis DRS and PL. After 90 min of visible light irradiation, the RhB at an initial concentration of 10 mg·L^?1 in the solution was degraded by 99.4% due to the addition of 10 mg of the composite. There was no significant decrease in the photocatalytic activity even after four rounds of cycles. The free radical capture experiments indicate that the photogenerated holes (h⁺) were the main active sites. The possible photocatalytic degradation mechanism was proposed as the specific surface area of the composite was enlarged due to the uniform distribution of UiO-66-NH₂ on the surface of Bi₂WO₆. The electron–hole pairs recombination rate was decreased due to the photogenerated electrons (e^?) on the CB of Bi₂WO₆ which can be rapidly transferred to the CB of UiO-66-NH₂ and the photogenerated holes of UiO-66-NH₂ transferred to the VB of Bi₂WO₆. Meanwhile, the RhB was directly oxidized to H₂O and CO₂ by h⁺ to achieve the purification effect.

     

高稳定性金属有机骨架UiO-66的合成与应用

金属有机骨架(metal-organic frameworks,MOFs)是一种由金属中心与有机配体自组装而成的、具有三维网状有序孔结构的新型多孔晶体材料,其具有超高的比表面积、种类和结构多样性、可化学功能化等特点,在多个研究领域显示出了潜在的应用前景,已成为当前化学、材料学科的研究热点之一。 然而大多数MOFs材料的稳定性较差,极大地束缚了MOFs材料的发展。 以Zr为金属中心,对苯二甲酸为有机配体的UiO-66具有较好的热稳定性,结构可在500 ℃保持稳定,并且其还具有很高的耐酸性和一定的耐碱性,引起了人们的关注。 本文主要综述了UiO-66在合成调控、功能化合成和后改性方面的研究现状,以及其在吸附和催化等领域的应用前景。     

Dynamic Interplay between Defective UiO-66 and Protic Solvents in Activated Processes

UiO-66, composed by Zr-oxide inorganic bricks [Zr₆(μ₃-O)₄(μ₃-OH)₄] and organic terephthalate linkers, is one of the most studied metal–organic frameworks (MOFs) due to its exceptional thermal, chemical, and mechanical stability. Thanks to its high connectivity, the material can withstand structural deformations during activation processes such as linker exchange, dehydration, and defect formation. These processes do alter the zirconium coordination number in a dynamic way, creating open metal sites for catalysis and thus are able to tune the catalytic properties. In this work, it is shown, by means of first-principle molecular-dynamics simulations at operating conditions, how protic solvents may facilitate such changes in the metal coordination. Solvent can induce structural rearrangements in the material that can lead to undercoordinated but also overcoordinated metal sites. This is demonstrated by simulating activation processes along well-chosen collective variables. Such enhanced MD simulations are able to track the intrinsic dynamics of the framework at realistic conditions.     

Fabrication of metal-organic framework Universitetet i Oslo-66 (UiO-66) and brown-rot fungus Gloeophyllum trabeum biocomposite (UiO-66@GT) and its application for reactive black 5 decolorization

Many various industries use synthetic dyes as their raw materials. These dyes have triggered environmental problems because of the occurring effluents, and one of the environmentally safe solutions for this problem is biodegradation through microorganisms. Reactive Black 5 (RB5) dye degradation was performed by utilizing a metal-organic framework Universitetet i Oslo-66 (UiO-66) and Gloeophyllum trabeum (GT) fungus biocomposite. The UiO-66@GT composite was fabricated by inoculating the fungal culture in flasks with the PDB medium that contained UiO-66. This biocomposite was applied to decolorize and degrade RB5 dye, while pure GT culture can decolorize about 36.47% in five days. The percentage of RB5 decolorization was shown to be increased with the addition of UiO-66; the composite could decolorize RB5 up to 72.55% after five days incubation period. Moreover, the optimum conditions for the 100% targeted rate of RB5 decolorization found by the Response Surface Methodology (RSM) are: initial RB5 concentration (72.54 mg L^-1), pH (6.53), and temperature (38.06 °C). Two novel metabolites from RB5 decolorization by the composite were detected based on LCMS-QTOF analysis and were used to propose a degradation pathway: 6-((1-amino-7,8-dihydroxy-6-sulfonaphthalen-2-yl) diazinyl) cyclohexa-2,4-dien-1-ide (m/z = 360) and 3,4-diamino-5,6-dihydroxy-1,2,7,8-tetrahydronaphthalene-2,7-disulfonic acid (m/z = 354).     

UiO-66-NH2 and Zeolite-Templated Carbon Composites for the Degradation and Adsorption of Nerve Agents

Composites of metal-organic frameworks and carbon materials have been suggested to be effective materials for the decomposition of chemical warfare agents. In this study, we synthesized UiO-66-NH₂/zeolite-templated carbon (ZTC) composites for the adsorption and decomposition of the nerve agents sarin and soman. UiO-66-NH₂/ZTC composites with good dispersion were prepared via a solvothermal method. Characterization studies showed that the composites had higher specific surface areas than pristine UiO-66-NH₂, with broad pore size distributions centered at 1–2 nm. Owing to their porous nature, the UiO-66-NH₂/ZTC composites could adsorb more water at 80% relative humidity. Among the UiO-66-NH₂/ZTC composites, U_0.8Z_0.2 showed the best degradation performance. Characterization and gas adsorption studies revealed that beta-ZTC in U_0.8Z_0.2 provided additional adsorption and degradation sites for nerve agents. Among the investigated materials, including the pristine materials, U_0.8Z_0.2 also exhibited the best protection performance against the nerve agents. These results demonstrate that U_0.8Z_0.2 has the optimal composition for exploiting the degradation performance of pristine UiO-66-NH₂ and the adsorption performance of pristine beta-ZTC.     

Metal-specific interactions of H2 adsorbed within isostructural metal-organic frameworks

Diffuse reflectance infrared (IR) spectroscopy performed over a wide temperature range (35-298 K) is used to study the dynamics of H(2) adsorbed within the isostructural metal-organic frameworks M(2)L (M = Mg, Mn, Co, Ni and Zn; L = 2,5-dioxidobenzene-1,4-dicarboxylate) referred to as MOF-74 and CPO-27. Spectra collected at H(2) concentrations ranging from 0.1 to 3.0 H(2) per metal cation reveal that strongly red-shifted vibrational modes arise from isolated H(2) bound to the available metal coordination site. The red shift of the bands associated with this site correlate with reported isosteric enthalpies of adsorption (at small surface coverage), which in turn depend on the identity of M. In contrast, the bands assigned to H(2) adsorbed at positions >3 ? from the metal site exhibit only minor differences among the five materials. Our results are consistent with previous models based on neutron diffraction data and independent IR studies, but they do not support a recently proposed adsorption mechanism that invokes strong H(2)···H(2) interactions (Nijem et al. J. Am. Chem. Soc.2010, 132, 14834-14848). Room temperature IR spectra comparable to those on which the recently proposed adsorption mechanism was based were only reproduced after contaminating the adsorbent with ambient air. Our interpretation that the uncontaminated spectral features result from stepwise adsorption at discrete framework sites is reinforced by systematic red shifts of adsorbed H(2) isotopologues and consistencies among overtone bands that are well-described by the Buckingham model of molecular interactions in vibrational spectroscopy.     

Facile Synthesis and Properties of UiO-66 Electrode Material for Supercapacitors

A block-like metal-organic framework UiO-66 was prepared by in-situ growth one-pot hydrothermal process. The as-synthesized material was characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The electrochemical properties used as a supercapacitor electrode material were evaluated by cyclic voltammetry(CV), galvanostatic charge-discharge measurement(GCD) and electrochemical impedance spectroscopy(EIS) in 2 M KOH solution, exhibiting a high specific capacitance(311 F·g~(-1) at 1 A·g~(-1)), suggesting its promising potential as a supercapacitor electrode material.     

UiO-67-Sal-CuCl2在空气中催化芳香醇的选择性氧化

利用水热法一步合成了金属有机骨架(MOFs)材料UiO-67-Sal, 并将3种铜盐固定在其表面, 研究了3种铜MOFs材料催化芳香醇选择性氧化的性能. 结果表明, UiO-67-Sal-CuCl₂催化剂对芳香醇选择性氧化反应具有良好的催化活性, 且在重复使用4次后, 依然保持较好的催化效果.     

The Carboxyl Functionalized UiO-66-(COOH)2 for Selective Adsorption of Sr2+

Efficient and selective removal of ⁹⁰Sr is an important process for the safe use of nuclear energy. Herein, we investigate and assess the Sr²⁺ adsorption properties of a metal-organic framework UiO-66-(COOH)₂ functionalized by non-bonded carboxylic groups. This MOF is an exciting class of free carboxylic functionalized MOFs that combine chemical stability with gas sorption, dye elimination, and conductivity. Specifically, we show that uniformly distributed carboxyl and water stability make it accessible for loading Sr²⁺ without structural changes. The FTIR spectroscopy, PXRD analysis, XPS, and SEM-EDS studies show excellent stability as well as the strong affinity between -COOH active site and Sr²⁺. This strong coordination interaction guarantees a high adsorption capacity of 114 mg g⁻¹ within 5 h (pH 5 and 298 K). Combined kinetic and thermodynamic studies show that the surface complexation is strong chemisorption and cost-effective spontaneous process (ΔG = −5.49 kJ mol⁻¹~−2.16 kJ mol⁻¹). The fact that UiO-66-(COOH)₂ not only possesses a high adsorption capacity, but also enables selectivity to Sr²⁺ in the presence of similar radius ions Na⁺ and K⁺, prefigures its great potential for the practical treatment of radioactive Sr²⁺ in polluted water.     

以UiO-66为前驱体的Fe-ZrO2的制备及其可见光降解性能研究

金属有机骨架（UiO-66）具有大的比表面积和强的吸附能力，且金属锆离子高度有序地排列在框架中.先采用UiO-66的结构特点使其吸附Fe³⁺，再通过煅烧前驱体Fe³⁺/UiO-66的方法成功制备出Fe掺杂的ZrO₂纳米光催化剂Fe-ZrO₂.通过扫描电子显微镜（SEM）、X射线衍射（XRD）、X射线光电子能谱（XPS）、N₂吸附-脱附、红外光谱（FT-IR）和紫外-可见光吸收光谱（UV-vis DRS）等方法对催化剂的形貌和结构进行表征，利用荧光（PL）和电化学阻抗对催化剂的电化学性能进行分析.最后，研究了催化剂对罗丹明B溶液的可见光降解作用，结果表明通过煅烧Fe³⁺/UiO-66前驱体的方法制备的Fe-ZrO₂催化剂，在可见光照射下对罗丹明B的降解率为83%，循环三次后降解率依然能够达到78%，稳定性好.     

螺吡喃功能化UiO-66光响应吸附剂的制备及其性能

将光响应分子甲基螺吡喃SP-CH₃引入UiO-66的非极性孔笼中,构筑吸附活性位可光控调节的光响应吸附剂。SP-CH₃功能化的吸附剂完好保留了载体UiO-66的骨架和孔道结构。以阴离子染料甲基橙为探针,研究了吸附剂在不同光照条件下的吸附和解吸性能。结果表明,经紫外光照后,吸附剂对甲基橙的吸附量为41.99 mg·g^-1,相较于可见光照后样品的吸附量提升57.56%,吸附作用增强;经可见光照后,甲基橙的脱附量为81.6%。本策略通过光照刺激改变UiO-66孔笼中SP-CH₃的构型及表面电荷性质,即对吸附活性位进行光控调节,在不同光照条件下实现对吸附质的高效吸附和有效脱附。     

Carbon Dioxide Capture Enhanced by Pre-Adsorption of Water and Methanol in UiO-66

The rapidly rising level of carbon dioxide in the atmosphere resulting from human activity is one of the greatest environmental problems facing our civilization today. Most technologies are not yet sufficiently developed to move existing infrastructure to cleaner alternatives. Therefore, techniques for capturing carbon dioxide from emission sources may play a key role at the moment. The structure of the UiO-66 material not only meets the requirement of high stability in contact with water vapor but through the water pre-adsorbed in the pores, the selectivity of carbon dioxide adsorption is increased. We successfully applied the recently developed methodology for water adsorption modelling. It allowed to elucidate the influence of water on CO₂ adsorption and study the mechanism of this effect. We showed that water is adsorbed in octahedral cage and stands for promotor for CO₂ adsorption in less favorable space than tetrahedral cages. Water plays a role of a mediator of adsorption, what is a general idea of improving affinity of adsorbate. On the basis of pre-adsorption of methanol as another polar solvent, we have shown that the adsorption sites play a key role here, and not, as previously thought, only the interaction between the solvent and quadrupole carbon dioxide. Overall, we explained the mechanism of increased CO₂ adsorption in the presence of water and methanol, as polar solvents, in the UiO-66 pores for a potential post-combustion carbon dioxide capture application.     

增强UiO-66-NH2光催化水分解制氢性能的研究进展

氢能是一种能量密度高、储量大、可再生、零污染的新能源。光催化水分解制氢是一种绿色、清洁的能源转换技术,被认为是一种有效的制氢方法。UiO-66-NH2是一种可见光响应、稳定性良好的金属有机骨架材料,但存在可见光响应范围有限、导电性差、载流子复合率高等问题。研究者们采用金属粒子掺杂、染料敏化、金属纳米粒子负载等多种方法对UiO-66-NH2进行改性,提升UiO-66-NH2在光催化水分解制氢反应中的性能,并报道了许多研究成果。因此,本文对近年来报道的有关增强UiO-66-NH2光催化水分解制氢性能的方法进行了综述,并对后续的发展提出了建议,以期为UiO-66-NH2在光催化水分解制氢中应用研究提供参考。     

High-Quality Thin Films of UiO-66-NH2 by Coordination Modulated Layer-by-Layer Liquid Phase Epitaxy

We report the fabrication of macroscopically and microscopically homogeneous, crack-free metal-organic framework (MOF) UiO-66-NH₂ (UiO: Universitetet i Oslo; [Zr₆O₄(OH)₄(bdc-NH₂)₆]; bdc-NH₂²⁻: 2-amino-1,4-benzene dicarboxylate) thin films on silicon oxide surfaces. A DMF-free, low-temperature coordination modulated (CM), layer-by-layer liquid phase epitaxy (LPE) using the controlled secondary building block approach (CSA). Efficient substrate activation was determined as a key factor to obtain dense and smooth coatings by comparing UiO-66-NH₂ thin films grown on ozone and piranha acid-activated substrates. Films of 2.60 μm thickness with a minimal surface roughness of 2 nm and a high sorption capacity of 3.53 mmol g⁻¹ MeOH (at 25 °C) were typically obtained in an 80-cycle experiment at mild conditions (70 °C, ambient pressure).     

螺吡喃功能化UiO-66光响应吸附剂的制备及其性能

将光响应分子甲基螺吡喃SP-CH₃引入UiO-66的非极性孔笼中,构筑吸附活性位可光控调节的光响应吸附剂。SP-CH₃功能化的吸附剂完好保留了载体UiO-66的骨架和孔道结构。以阴离子染料甲基橙为探针,研究了吸附剂在不同光照条件下的吸附和解吸性能。结果表明,经紫外光照后,吸附剂对甲基橙的吸附量为41.99 mg·g^-1,相较于可见光照后样品的吸附量提升57.56%,吸附作用增强;经可见光照后,甲基橙的脱附量为81.6%。本策略通过光照刺激改变UiO-66孔笼中SP-CH₃的构型及表面电荷性质,即对吸附活性位进行光控调节,在不同光照条件下实现对吸附质的高效吸附和有效脱附。