UiO-66的制备、功能化及膜分离研究进展

UiO-66是一种具有优异物理化学稳定性的金属有机骨架（MOFs）材料,近年来引起了研究者们的强烈关注。本文详细介绍了UiO-66的结构,重点探讨了溶剂热法过程中的一系列影响因素,包括使用不同的金属前体,改变合成温度、溶剂、各组分配比以及模板剂等,制备各种性能的UiO-66。针对溶剂热法合成效率较低的问题,介绍了微波合成法、微流控、连续流和无溶剂法等其它UiO-66的制备方法。为了扩大UiO-66的应用范围,对其有机配体进行功能化改性或与其他材料复合改性,具体介绍了改性后UiO-66在气体吸附、水处理、催化、电化学和化学传感等方面的应用。最后综述了利用UiO-66具有多孔特性构建分离膜方面的研究进展,具体阐述了纯UiO-66膜和UiO-66复合膜在气体分离和水处理方面的应用。     

功能化Zr-MOF强化混合基质膜CO2分离

混合基质膜（MMMs）在气体分离领域具有良好的应用前景,金属有机框架（MOFs）由于具有高孔隙率和有机连接基团,常被用作填料制备MMMs。但由于MOFs与聚合物的界面相容性问题,MMMs的气体分离性能提升受到限制。本文合成了功能化的Zr-MOF（UiO-66-AC）,并利用其与聚醚共聚酰胺（Pebax）共同制备了混合基质膜。填料中引入的羰基和羧基等基团提供了MOFs与聚合物基质之间较强的界面相互作用。与纯Pebax膜相比,UiO-66-AC/Pebax MMMs的气体渗透性能得到了显著提高。当填料质量分数为6%时,膜的CO₂渗透系数为102.4 Barrer,CO₂/N₂和CO₂/CH₄选择性分别为90.6和26.0,CO₂/N₂分离性能突破了Robeson上限(2008),表明该混合基质膜在CO₂的分离应用上具有潜力。     

Fabrication of in-situ polymerized UiO-66/PVDF supramolecular membranes with high anti-fouling performance

The composite membrane with the advantages of high separation efficiency and wide application, has been widely concerned in the field of water purification and molecular separation. However, the common composite membrane cannot achieve continuity, or the grafting process is complex, which significantly hinders its further development. In this work, the in-situ polymerization of UiO-66/PVDF supramolecular flat membranes as the continuous and high-performance composite membrane can be easily synthesized using the supramolecular force, (such as, hydrogen bond, etc.). These supramolecular membranes exhibit good hydrophilic (61°) and anti-fouling performance for bovine serum albumin (BSA) solution with rejection rate 97.79% than the original membrane. Moreover, this membrane can achieve more MOF doping based on maintaining the membrane performance, which undoubtedly greatly improves its hydrophilicity and mechanical properties. In addition, we also characterized the porous microstructure of the UiO-66/PVDF supramolecular membrane to analyze the influence of different doping amounts on the membrane structure. This supramolecular membrane has the advantages of simple synthesis, good hydrophilicity and water separation performance, which provides a more convenient and effective way for the preparation of MOFs/polymer flat membrane, and also provides a new method and new idea for expanding the application of MOFs/polymer ultrafiltration membrane in water treatment.     

A universal strategy for efficient synthesis of Zr-based MOF nanoparticles for enhanced water adsorption

Zr-based metal-organic framework (Zr-MOF) nanoparticles (NPs) have attracted extensive research thanks to their outstanding thermal and chemical stability, but their efficient synthesis is still challenging. Here, high-quality Zr-MOF NPs with tunable and uniform particle sizes can be successfully fabricated within 30 min by high-gravity technology with high yields. Significantly, the rapidly milder preparation of UiO-66 NPs can also be achieved at 90 or 70°C. This strategy has been extended to the synthesis of other Zr-MOF NPs. Furthermore, the water vapor adsorption properties of obtained UiO-66 NPs display a size-dependent effect. The 70 nm UiO-66 NPs have the highest adsorption capacity of 625 mg g⁻¹ among unmodified UiO-66 reported so far, and manifest 2.0–2.8 times faster water adsorption rate than the micron ones. This study provides a feasible method for the efficient and mild preparation of MOFs nanoparticles, which may promote the synthesis and applications of nano-sized MOFs.     

Hybridization of metal–organic framework and monodisperse spherical silica for chromatographic separation of xylene isomers

Metal–organic frameworks(MOFs) packed in the column have been a promising candidate as the stationary phase for high performance liquid chromatography(HPLC). However, the direct packing of irregular MOF powder could raise some problems like high back pressure and low column efficiency in the HPLC separation. In this work, UiO-66 capable of separating xylenes was supported effectively on the surface of the monodisperse spherical silica microspheres by one-pot method. The hybridization of Ui O-66 and silica microspheres(termed UiO-66@SiO_2 shell–core composite) was prepared by stirring the suspension of the precursors of Ui O-66 and\\COOH terminated silica in the N,N-dimethylformamide with heating. The shell–core composite material UiO66@SiO_2 was characterized by SEM, TEM, PXRD and FTIR. Then, it was used as a packing material for the chromatographic separation of xylene isomers. Xylene isomers including o-xylene, m-xylene and p-xylene were efficiently separated on the column with high resolution and good reproducibility. Moreover, the Ui O-66@SiO_2 shell–core composites packed column still remained reverse shape selectivity as Ui O-66 possessed, and the retention of xylenes was probably ascribed to the hydrophobic effect between analytes and the aromatic rings of the Ui O-66 shell. The Ui O-66@SiO_2 shell–core composites obtained in this study have some potential for the separation of structural isomers in HPLC.     

金属有机骨架UiO-66在催化领域的应用

金属有机骨架（MOFs）经过二十多年的快速发展,已经合成了成千上万种,然而MOFs材料普遍具有较低的稳定性,在一定程度上限制了MOFs的发展。UiO-66的合成是MOFs材料稳定性的一个突破,其在催化领域的发展尤为迅速。本文首先介绍了理想及实际状态下UiO-66的结构特征,并说明了配体缺失导致的节点空位处的元素组成。然后综述了利用UiO-66特殊的结构特征或将其功能化用于催化反应的研究,包括节点空位、功能化节点空位、负载金属纳米颗粒、功能化配体等。最后,考虑到可以综合利用UiO-66的特殊结构,对UiO-66在未来多功能催化剂的设计合成领域所能发挥的作用进行展望。     

A computational study of water in UiO-66 Zr-MOFs: Diffusion,hydrogen bonding network,and confinement effect

For chemical warfare agent removal, the humidity emerges as an unavoidable challenge that significantly affects the performance of metal–organic frameworks. In this work, via density functional theory calculations, ab initio molecular dynamics and classical molecular dynamics simulations, we investigate the structural and diffusion properties of water in the pristine defect-free UiO-66, one Zr-based metal–organic framework. Through the detailed analyses of the distribution probability of water in two different cages of UiO-66, the binding interaction between water and UiO-66, the hydrogen bonding networks and resulted localized water clusters, we gain a fundamental understanding of structural and dynamics properties as well as the concentration dependence of water in UiO-66. We anticipate those theoretical results could provide insight to the competitive adsorption of water and chemical warfare agents, which eventually shows the utmost importance for the design and development of the next generation porous materials with appropriate water properties in real-life applications.     

Enhanced CO2 selectivity of polyimide membranes through dispersion of polyethyleneimine decorated UiO-66 particles

Branched polyethyleneimine (PEI) functionalized UiO-66 were synthesized and used as fillers to fabricated mixed-matrix membranes (MMMs) for CO₂/CH₄ separation. The purpose of introducing amino-functional groups in the filler is to improve the interfacial compatibility of the filler with the polymer through the formation of hydrogen bonds with the carbonyl group of 6FDA-ODA. Additionally, the amino group can facilitate CO₂ transport through a reversible reaction, enhancing the CO₂/CH₄ separation properties of MMM. The chemical structure and morphology of fillers and membranes were characterized by employing X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), thermogravimetric (TGA), Derivative thermogravimetry (DTG) and scanning electron microscope (SEM). Furthermore, the effects of filler loading and feed pressure on CO₂ permeability and CO₂/CH₄ selectivity have been investigated. MMMs present higher gas separation performance than pure 6FDA-ODA due to the presence of amino groups and the improvement of interface morphology. In particular, the MMM with 15 wt% loading of UiO-66-PEI shows optimum CO₂ permeability of 28.23 Barrer and CO₂/CH₄ selectivity of 56.49. Therefore, post-synthetic modification of UiO-66 particle with PEI is a promising alternative to improved membrane performance.     

Flow synthesis of a novel zirconium-based UiO-66 nanofiltration membrane and its performance in the removal of p-nitrophenol from water

In this work, a thin zirconium-based UiO-66 membrane was successfully prepared on an alumina hollow fiber tube by flow synthesis, and was used in an attempt to remove p-nitrophenol from water through a nanofiltration process. Two main factors, including flow rate and synthesis time, were investigated to optimize the conditions for membrane growth. Under optimal synthesis conditions, a thin UiO-66 membrane of approximately 2 µm in thickness was fabricated at a flow rate of 4 mL·h⁻¹ for 30 h. The p-nitrophenol rejection rate for the as-prepared UiO-66 membrane applied in the removal of p-nitrophenol from water was only 78.1% due to the existence of membrane defects caused by coordinative defects during membrane formation. Post-synthetic modification of the UiO-66 membrane was carried out using organic linkers with the same flow approach to further improve the nanofiltration performance. The result showed that the p-nitrophenol rejection for the post-modified membrane was greatly improved and reached over 95%. Moreover, the post-modified UiO-66 membrane exhibited remarkable long-term operational stability, which is vital for practical application.     

雪花状Cu2S/缺陷型UiO-66 p-n异质结用于光催化还原Cr(VI)

为了解决金属-有机骨架材料Ui O-66可见光响应差、电子-空穴复合快的问题，以雪花状Cu₂S为基材，对Ui O-66进行缺陷调控，采用溶剂热法制得Cu₂S/缺陷型Ui O-66 p-n异质结型复合光催化剂。以K₂Cr₂O₇溶液为目标污染物，分析其对Cr(Ⅵ)的光催化还原能力。SEM、XRD和XPS结果证明，缺陷型UiO-66在雪花状Cu₂S上均匀生长。莫特-肖特基曲线证明，在Cu₂S与缺陷型UiO-66界面处形成了紧密的p-n异质结，提高了材料对可见光的利用率，促进了光生电子-空穴对的有效分离。在模拟可见光照射下，20 mg 50%Cu₂S/缺陷型Ui O-66复合光催化剂(50%为缺陷型UiO-66的负载量，以生成的Cu₂S质量计)对50 mL质量浓度为20 mg/L的K₂Cr₂O₇溶液的还原率高达98.92%，且循环5次...     

缺陷UiO-66对水中塑化剂的吸附

金属有机骨架材料（metal-organic frameworks,MOFs）是一种具有骨架结构的新型多孔材料。本研究合成了金属有机框架化合物UiO-66和有缺陷的UiO-66（UiO-66-1）,并研究了其作为吸附剂吸附塑化剂邻苯二甲酸二甲酯（DMP）的性能及其吸附动力学,最后通过拟合吸附等温线和吸附动力学模型拟合了吸附剂的最大吸附量和最快吸附时间。实验结果表明,UiO-66-1对DMP有更好的吸附性能,在5~10min内快速达到吸附平衡,pH在3~10吸附率仍可保持稳定;分析测试结果表明,引入缺陷的UiO-66-1的比表面积比UiO-66大,达到了1438m²/g,孔容为0.58cm³/g,晶体的尺寸也明显增大,吸附量增大了近一倍,最大吸附量可达到404mg/g,且循环利用率高;通过吸附等温线模型和吸附动力学模型的拟合研究表明,UiO-66-1的吸附过程比较符合Langmuir模型和拟二级动力学模型。     

3,4-二羟基苯甲醛改性UiO-66-NH2及其对U(Ⅵ)的吸附性能研究

本文通过在120℃条件下在DMF中回流用ZrCl4和2-氨基对苯二甲酸合成了金属-有机骨架化合物UiO-66-NH2,再在氮气保护下在乙醇中回流用3,4-二羟基苯甲醛对UiO-66-NH2进行了功能化修饰,获得了UiO-66-OHBA。通过红外光谱、元素分析以及X射线粉末衍射实验证明了3,4-二羟基苯甲醛成功修饰了UiO-66-NH2,且修饰后获得的UiO-66-OHBA骨架结构并未发生改变。以UiO-66-NH2和UiO-66-OHBA为吸附剂吸附U(Ⅵ)并研究了pH、固液比、反应温度、离子强度、平衡时间等对吸附行为的影响,并对结果进行了分析。实验结果表明UiO-66-NH2和UiO-66-OHBA均对U(Ⅵ)表现出比较良好的吸附能力,并且经修饰后的吸附剂吸附性能得到了提升。pH值对吸附性能有较大影响,两者均在pH为4.5处吸附速率最大。温度对UiO-66-OHBA吸附性能的影响要小于UiO-66-NH2,它们的吸附模型与Freundlich等温吸附模型吻合良好。     

高稳定铪金属-有机骨架材料的合成及二氧化碳捕获性能

采用高温高浓度的溶剂热方法,合成了具有高结晶度的一种金属-有机骨架（metal-organic framework,MOF）材料UiO-66（Hf）,并发现该材料在沸水、酸碱等苛刻条件下具有非常好的化学稳定性。为了提高其对气体的吸附分离性能,进一步采用具有不同官能团的有机配体--氨基对苯二甲酸（H₂BDC-NH₂）、硝基对苯二甲酸（H₂BDC-NO₂）、溴对苯二甲酸（H₂BDC-Br）,设计合成了孔道表面具有不同化学性质的三种新型铪MOF材料,且这些材料与UiO-66（Hf）具有相同的拓扑结构。同时,气体吸附实验结果表明,极性基团的引入,尤其是氨基的引入,能极大提高材料对CO₂/N₂以及CO₂/CH₄体系的分离性能。这为以后应用于化工体系分离的新型多孔材料合成提供了理论指导。     

锆基金属有机骨架UiO-66的合成及在化学防护领域中的研究进展

UiO-66除了具备其他MOFs材料的比表面积大、孔隙率高及孔道易调、易功能化等特点外，与大多数MOFs 材料不同，还具有优异的化学稳定性、机械稳定性、热稳定性和抗水性能，使其在吸附及催化领域具有巨大的应用前景。本文详细介绍了UiO-66的合成方法最新研究进展，包括溶剂热法、机械研磨法、微波辅助法、持续流法及干胶转化法，同时指出干胶转化法产品收率高，纯化、活化过程简单且不产生有机废液，是UiO-66合成及未来工业化生产的发展方向。同时综述了改性UiO-66材料近年来在有毒工业化学品吸附及化学战剂催化降解领域中的研究进展，展望了静电纺纳米纤维负载UiO-66在化学防护领域应用的发展趋势。     

PVP-assisted synthesis of monodisperse UiO-66 crystals with tunable sizes

A polyvinylpyrrolidone (PVP)-assisted synthesis method was reported to prepare monodisperse UiO-66 octahedral crystals with tunable sizes. In this acetic acid/PVP co-modulated synthesis system, the relatively weak coordination of PVP to Zr(IV) played an important role in manipulating the sizes of UiO-66 crystals instead of their shapes. With the optimized PVP concentrations, sizes of the monodisperse UiO-66 crystals could be effectively tuned from ~ 1900 nm to ~ 700 nm. These uniform MOF crystals could be assembled into monolayers on water surface and further transferred onto a solid substrate to yield MOF films with preferential orientation and controlled thicknesses.     

Investigation on the enhancement of solvent-resistant nanofiltration membrane performance utilizing PDA-UiO-66@CNT as an interlayer

With the growing complexity of separation systems, the application of thin film composite nanofiltration (TFN) membranes in organic solvent separation faces numerous challenges. To augment its solvent stability, an in-situ constructed dopamine hydrogel doped with UiO-66@CNT was developed as an intermediate layer on a polyetherimide (PEI) ultrafiltration membrane. Subsequent interfacial polymerization on this interlayer led to the formation of a solvent-resistant nanofiltration membrane with a vast covalent bond structure, large specific surface area, and enhanced hydrophilicity. Our findings revealed that when the CNT loading in the UiO-66@CNT composite nanoparticles was 2 wt%, the TFN-U₂C₂ membrane exhibited a maximum pure water flux of 126.32 L/(m²·h) and a methanol flux of 45.45 L/(m²·h). The rejection rates for Congo red aqueous and methanol solutions were 96.88% and 92.14%, respectively. The membrane also demonstrated commendable anti-fouling properties. Remarkably, even after 48 h of immersion in various organic solvents, the membrane retained its morphology and separation efficiency. Compared to the TFN-U₂ membrane without CNT addition, the enhancement in separation performance was considerably significant. Hence, this membrane has significant potential for application in treatment of wastewater containing organic solvents and is promising in related fields.     

Integrating of metal-organic framework UiO-66-NH2 and cellulose nanofibers mat for high-performance adsorption of dye rose bengal

UiO-66-NH₂ is an efficient material for removing pollutants from wastewater due to its high specific surface area, high porosity and water stability. However, recycling them from wastewater is difficult. In this study, the cellulose nanofibers mat deacetylated from cellulose acetate nanofibers were used to combine with UiO-66-NH₂ by the method of in-situ growth to remove the toxic dye, rose bengal. Compared to previous work, the prepared composite could not only provide ease of separation of UiO-66-NH₂ from the water after adsorption but also demonstrate better adsorption capacity (683 mg∙g^‒1 (T = 25 °C, pH = 3)) than that of the simple UiO-66-NH₂ (309.6 mg∙g^‒1 (T = 25 °C, pH = 3)). Through the analysis of adsorption kinetics and isotherms, the adsorption for rose bengal is mainly suitable for the pseudo-second-order kinetic model and Freundlich model. Furthermore, the relevant research revealed that the main adsorption mechanism of the composite was electrostatic interaction, hydrogen bonding and π–π interaction. Overall, the approach depicts an efficient model for integrating metal-organic frameworks on cellulose nanofibers to improve metal-organic framework recovery performance with potentially broad applications.     

Immobilization Horseradish Peroxidase onto UiO-66-NH2 for Biodegradation of Organic Dyes

Enzymes are extensively used as catalyst in several fields of production such as chemistry, and pharmaceuticals owing to their selectivity, efficiency and environmentally friendliness. However, their applications are often hindered due to their insufficient stability and difficulties in re-use. As a member of porous crystalline materials, metal organic frameworks are a promising enzyme carrier due to their multi-functional pore surfaces and robustness in variety of harsh conditions. In this study, the horseradish peroxidase (HRP) enzyme was immobilized onto UiO-66-NH₂ (Universitetet i Oslo) by a facile incubation method at the room temperature to improve the stability and reusability of enzyme. The prepared HRP@UiO-66-NH₂ bio-composite was characterized by using FT-IR, XRD and SEM. The crystal structure of MOF was well-preserved after enzyme immobilization. A colorimetric assay for enzyme activity after released from UiO-66-NH₂ has been employed based on the catalytic oxidation of phenol coupled with 4-aminoantipyrine. The robustness and activity of immobilized enzyme after released from UiO-66-NH₂ were investigated by biodegradation of methyl orange (MO) and methylene blue (MB) with several parameters such as pH, temperature, the dosage of H₂O₂ and the dye concentration with comparison to its free form. The optimum condition for dye degradation was obtained at basic conditions. The immobilized enzyme maintained its activity at elevated temperature while free enzyme lost its activity at the same conditions, attributed to the armoring effect of UiO-66-NH₂. According to the results of studied various parameters, MO and MB were biodegraded to 60% and 45%, respectively, within 60 min with the optimum conditions at pH 9 and 50 °C at a H₂O₂ dosage of 3%. The superior pH tolerance and stability suggest potential of UiO-66-NH₂ immobilized peroxidase enzyme in industrial applications.

     

Performance-Enhanced and Washable Triboelectric Air Filter Based on Polyvinylidene Fluoride/UiO-66 Composite Nanofiber Membrane

Applying triboelectric nanogenerators (TENGs) in air filtration systems to generate electric charges through friction is a major advancement in air cleaning technology. The performance of triboelectric air filter strongly depends on the properties of triboelectric materials. In this work, a better triboelectric material, polyvinylidene fluoride (PVDF)/UiO-66 composite nanofiber membrane (P6-NFM), is designed and fabricated through electrospinning technology by doping UiO-66 into PVDF matrix. As the weight ratio of UiO-66 increases to 1%, PVDF/UiO-66 composite nanofiber-based TENG (P6-TENG) achieves the maximum current, voltage, and triboelectric charge of 4.29 µA, 52.8 V, and 22.02 nC, which are 6.5 times, 5.1 times, and 8.0 times as large as those of pure PVDF-based TENG (P-TENG). Therefore, the triboelectric air filter based on P6-NFM can be easily charged by slapping the fiber membrane and spun-bond fabric. After charging, the removal efficiency of P6-NFM is 92% for PM_0.5 and 98% for PM_2.5, which are 2.8 and 1.2 times those of the uncharged one. More importantly, the filtration efficiency of this air filter keeps stable after the membrane is washed four times. This method of loading UiO-66 on the triboelectric fiber material shows tremendous potential in self-charging and reusable air purification applications.     

Assembling Ag/UiO-66-NH2 Composites for Photocatalytic Dye Degradation

The water pollution currently constitutes a severe threat to our living life, and MOF (metal–organic framework)-based photocatalysts offer an efficient route to clean various water pollutants in an eco-friendly manner. Integration of metal nanoparticles (MNPs) with photoactive MOFs has proven an effective way to further boost the photocatalytic performance. In this work, Ag/UiO-66-NH₂ composites (UiO?=?University of Oslo) have been facilely assembled in two steps involving first wet impregnation of AgNO₃ into UiO-66-NH₂ followed by chemical reduction with NaBH₄. Benefited from the built-in heterostructure that can promote both the electron–hole separation, and the absorption of the visible-light, Ag/UiO-66-NH₂ composites exhibited an enhanced photocatalytic performance than the pristine UiO-66-NH₂ towards photodegradation of RhB (Rhodamine B) dye under the irradiation of UV–Visible light. About 96% of RhB can be degraded by Ag/UiO-66-NH₂ in a period of 40 min. Besides, Ag/UiO-66-NH₂ demonstrated a good recycling stability which showed an only slight drop in the dye photodegradation efficiency after three consecutive runs. The current work suggests that Ag/UiO-66-NH₂ composites have a great potential in practical application toward water remediation.