Metal Organic Framework HKUST-1 Research Articles

Metal–organic frameworks HKUST-1 embedded in amino-functionalized SBA-15: Efficient catalytic reduction of 4-nitrophenol to 4-aminophenol

The amino-functionalized SBA-15 silicon carrier (PMO-pr-NH2) was prepared by the one-pot method, and then HKUST-1 functional composites were synthesized by adsorption combined with in-situ preparation technology (HKUST-1@PMO-pr-NH2). A series of characterization techniques were used to analyze composites, such as BET, FTIR, TEM, XPS, TG, SEM, and XRD. The analysis showed that HKUST-1 was successfully prepared in the pores of the PMO-pr-NH2 silicon-based carrier. The catalytic reduction activity and thermal stability of the composite material were investigated using the reaction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). After 4 cycles, the catalytic performance of the composites was maintained without any obvious change.

A bio-platform TCN@HKUST-1 with admirable biocompatibility was applied to the antibacterial field

Antibiotics are powerful weapons against bacteria and the unique porous structure makes metal–organic frameworks be good choices for antibiotic delivery. In this work, metal–organic framework HKUST-1 with excellent biocompatibility was synthesized to entrap the antibacterial tetracycline hydrate (TCN) obtaining TCN@HKUST-1 system. The drug loading amount of the system was 54.90 wt%. TCN@HKUST-1 showed excellent antibacterial effects against both Staphylococcus aureus and Escherichia coli due to the antibacterial Cu2+ and TCN, revealing utilizable potentiality in the field of antibacterial application.

Insights into structure and reactivity of MOFs by ambient pressure soft X-ray absorption spectroscopy

Metal–Organic Frameworks (MOFs) are nanostructured porous materials made up by metal cations and organic linkers forming three-dimensional structures. Since their discovery, the local properties of metal centers in MOFs have often been studied with hard X-ray absorption spectroscopy that is not a surface sensitive technique. Here, we employ the ambient-pressure soft X-ray absorption spectroscopy, using a newly developed experimental setup, to unveil the formation mechanism of surface defective sites in the prototypical Cu(II)-based MOF HKUST-1, as well as the reactivity and selectivity of these sites towards CO2 from the analysis of the Cu L3-edge near edge X-ray absorption spectroscopy (NEXAFS) data. We observe that, upon thermal heating, Cu(I) defects are formed more abundantly on the surface of the material as compared to the bulk, a process that is almost fully reversed when the MOF is exposed to CO2, even when mixed with H2. Additionally, we propose a structure and a formation mechanism for such defective sites, supported by theoretical DFT-based calculations.

Facile adsorption of organophosphate pesticides over HKUST-1 MOFs.

The recovery of organophosphate pesticides (OPPs) from aqueous solutions is imperative considering their agricultural and environmental implications. Among various mitigation approaches used for OPPs' removal, adsorption offers many advantageous features for OPPs abatement owing to its benign nature, cost-effective processing, and non-requirement of excessive equipment. This research describes the adsorptive removal of three organophosphate pesticides (OPPs) namely chlorpyrifos (CPF), methyl parathion (MP), and malathion (MAL) by HKUST-1 (HKUST = Hong Kong University of Science and Technology) metal-organic framework (MOF). The synthesis of HKUST-1 MOFs was confirmed by various spectroscopic and microscopic techniques. The adsorption kinetics was systematically investigated by varying three parameters to include solution pH, contact time, and initial pesticide concentration. Among all the three pesticides, HKUST-1 showed enhanced removal of CPF in terms of pH, resulting in an adsorption capacity of 1.82mg·g-1. However, under the effect of contact time at 60min, the adsorption capacity of HKUST-1 for PM, MAL, and CPF were computed to be 1.83, 1.79, and 0.44mg·g-1, respectively. Besides, HKUST-1 showed a remarkable performance towards adsorptive removal of MAL (14.01mg·g-1 at 10mg·L-1 concentration) with linear increase in adsorption capacity as the function of initial pesticide concentration. The MOFs were also able to retain ca. 50% of their adsorption efficiency over the course of five cycles of adsorptive removal of CP. In the future, a comprehensive data table showing the performance of various MOFs against various OPPs can be constructed on the basis of parameters used in this study.

Cellulose acetate/MOF film-based colorimetric ammonia sensor for non-destructive remote monitoring of meat product spoilage

Herein, we designed an on-site and portable colorimetric assay using cellulose acetate polymeric films incorporated with HKUST-1 metal-organic framework while immersed in a solution of methyl red and brilliant cresyl blue organic dyes as an indicator for monitoring ammonia levels. Ammonia serves as a significant biomarker of food spoilage which falls under the category of volatile organic compounds (VOCs). The designed colorimetric solid-state sensor was comprehensively characterized using FE-SEM, EDS-mapping, XRD, FTIR, and contact angle analyses. The results confirmed the superior stability, water permeability, good crystallinity and desirable morphology of the prepared sensor platform. Additionally, customized smartphone was developed and applied for online signaling and colorimetric analysis. The findings demonstrated two linear ranges: 1–100 ppb and 0.1–1340 ppm with a detection limit of 0.02 ppm. The solid-state sensor exhibited high selectivity in the presence of other VOCs such as methanol, ethanol, acetone, 2-propanol, toluene, humidity, and hexane. It displayed acceptable repeatability in both inter-day (RSD = 3.38 %) and intraday (RSD = 3.86 %), long-term stability over 4 days as well as reusability over 3 cycles. We successfully applied this sensing platform for ammonia monitoring in spoiled meat foods including veal, fish and chicken. The results indicated favorable percentage recovery and repeatability, confirming the feasibility and potential applicability of this intelligent packaging system for monitoring freshness. The platform allows for real-time monitoring and data analysis via smartphone-based online signaling, providing a convenient and effective method for ensuring food quality.

Specific separation of flavonoids isomers by defect modulated metal-organic framework HKUST-1: Experiment and density functional theory analysis

Discovering and separating active monomers from natural products is an efficient way to develop new drugs, but faces the difficulty in complex and time-consuming separation process. Metal-organic frameworks (MOFs) are considered a promising separation strategy due to their molecular recognition properties, but their microporous nature poses challenges for capturing most natural compounds with molecule sizes larger than 20 Å. For the first time, this study proposed a simple and efficient approach to separate active monomeric components with larger diameters from structurally similar natural compounds by defect modulation strategy. In this study, defective HKUST-1 with hierarchical microporous/ mesoporous structures and Cu1+/Cu2+ mixed-valence sites was rapidly synthesized. The defective MOF demonstrated specific loading of silibinin A&B from silymarin containing seven structurally similar flavonoids within 5 min, and high separation capacity with the purity of ∼91.2% after primary separation. FTIR, XPS, and DFT calculation revealed the site competition mechanism for specific recognition and loading, where silibinin A&B preferentially acted on Cu2+ and Cu1+ clusters with the highest binding energy via hydrogen and coordination bonds, respectively. Compared to traditional separation techniques, the separation approach via defective MOF shows multiple advantages including high specificity, high separation efficiency, and easy to operate.

Peroxidase-like biomimetic epoxidation and subsequent alcoholysis of olefins by Fe(III)tetrakis(4-sulphonatophenyl) porphyrin (Fe4SP) encapsulated in the metal-organic framework HKUST-1

The efficiency and diverse functionality of biological catalysts has inspired the synthetic design of systems to mimic the stabilizing and catalytic properties of enzyme substrate binding protein pockets. One such system is the Fe4SP@HKUST-1 metal organic framework (MOF) system, also known as MOMzyme-1, in which Fe(III)tetrakis(4-sulphonatophenyl)porphyrin (Fe4SP) is encapsulated within the cuboctahedral cavities of the HKUST-1 MOF. Within this system the Fe4SP heme active site is encapsulated in a pseudo protein pocket within the MOF. Here, the ability of the Fe4SP@HKUST-1 to catalyze the tandem epoxidation of olefins followed by selective alcoholysis is examined. It is observed that encapsulation of Fe4SP within the MOF framework significantly enhances the turnover number (TON) of peroxide-driven epoxidation of styrene while greatly reducing metalloporphyrin degradation and maintaining stereoisomer selectivity. The Fe4SP@HKUST-1 catalyzes both the olefin epoxidation and the subsequent ring opening through the addition of CH3OH. The epoxidation of styrene occurs through the hydrogen peroxide generated high valent Fe(IV) = O of the encapsulated Fe4SP while the corresponding ring opening and methanolysis takes place at the Cu metallo building blocks of the HKUST-1 framework. These results provide a framework through which to develop a more extensive library of bio-inspired heme-based MOF catalysts.

Pyrolysis Kinetics of Lignin-Based Flame Retardants Containing MOFs Structure for Epoxy Resins

This study describes the preparation of a lignin-based expandable flame retardant (Lignin-N-DOPO) using grafting melamine and covering 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) using the Mannich reaction. Then, through in situ growth, a metal-organic framework (MOF) HKUST-1 (e.g., Cu3(BTC)2, BTC = benzene-1,3,5-tricarboxylate)/lignin-based expandable flame retardant (F-lignin@HKUST-1) was created. Before that, lignin epoxy resin containing phosphorus (P) and nitrogen (N) components had been created by combining epoxy resin (EP) with F-lignin@HKUST-1. Thermogravimetric analysis was used to examine the thermal characteristics of epoxy resin (EP) composite. The findings indicate that the thermal stability of EP is significantly affected by the presence of F-lignin@HKUST-1. Last but not least, the activation energy (E) of EP/15% F-lignin@HKUST-1 was examined using four different techniques, including the Kissinger-SY iteration method, the Ozawa-SY iteration method, the Lee-Beck approximation-iteration method, and the Gorbatchev approximation-iteration method. It was discovered that the activation energy was significantly higher than that of lignin. Higher activation energy suggests that F-lignin@HKUST-1 pyrolysis requires more energy from the environment, which will be significant about the application of lignin-based flame retardants.

Guiding Metal Organic Framework Morphology via Monolayer Artificial Defect-Induced Preferential Facet Selection.

Guiding metal organic framework (MOF) morphology, especially without the need for chemical additives, still remains a challenge. For the first time, we report a unique surface guiding approach in controlling the crystal morphology formation of zeolitic imidazole framework-8 (ZIF-8) and HKUST-1 MOFs on disrupted alkanethiol self-assembled monolayer (SAM)-covered Au substrates. Selective molecule removal is applied to generate diverse SAM matrices rich in artificial molecular defects in a monolayer to direct the dynamic crystal growth process. When a 11-mercaptoundecanol alkanethiol monolayer is ruptured, the hydroxyl tail groups of surface residue molecules act as nucleating sites by coordination with precursor metal ions. Meanwhile, the exposed alkane chain backbones stabilize a particular facet of MOF nuclei in the dynamic growth by slowing down their crystal growth rates along a specific direction. The competitive formation between the [110] and [100] planes of ZIF-8 ultimately regulates the crystal shapes from rhombic dodecahedron, truncated rhombic dodecahedron, and truncated cube to cube. Similarly, changeable morphologies of HKUST-1 crystals are also achieved from cube and tetrakaidekahedron to octahedron, originating from the competitive selection between the [100] and [111] planes. In addition to the artificial matrix preferred orientation of initial nucleation, parameters such as temperature also play a crucial role in the resulting crystal morphology. Standing on the additive-free MOF crystal morphology growth control, porous architectures prepared in this approach can act as templates for ligand-free metal (Au, Ag, and Cu) nanocluster synthesis. The nanocluster-embedded MOF structures represent distinct crystal morphology-dependent optical properties, and interestingly, their fluorescence emission can be highly enhanced by facet-induced nanocluster packing alignments. These findings not only provide a unique thought on MOF crystal morphology guidance but also pave a new route for the accompanied property investigation and further application.

Synthesis of magnetic Fe3O4-HKUST-1 nanocomposites for azo dye adsorption

The magnetic Fe3O4-HKUST-1 nanocomposites were synthesized using a simple and green hydrothermal technique, utilizing Fe3O4 and the chemically stable metal–organic framework HKUST-1. The Fe3O4-HKUST-1 nanocomposites were synthesized with a varied proportion of Fe3O4 and subjected to advanced characterization, which included XRD, IR, BET, TG, SEM, TEM, EDS, and VSM. The magnetic nanocomposite 0.4 Fe3O4-HKUST-1 (FH4) had a rough surface with spherical morphology and a good proportion of micro and mesopores. The magnetic nanocomposite had a mean pore size of 2.58 nm, with pore volume of 0.35 cm3/g, having excellent magnetic saturation performance (26.39 emu/g). The adsorption isotherm and adsorption kinetics of magnetic nanocomposites on azo dye neutral red (NR) wastewater were assessed in detail. In contrast to the Freundlich model, the Langmuir model better described the adsorption isotherms, while the pseudo-second-order kinetic model better captured the adsorption kinetics. The FH4 magnetic nanocomposite was the most effective adsorbent with the highest adsorption capacity for NR separation.

Methane storage in metal-organic framework HKUST-1 with enhanced heat management using 3D printed metal lattices

The adsorbed natural gas (ANG) concept uses a high-capacity adsorbent packed in the fuel tank allowing high-density fuel storage at a reduced pressure (30–60 bar). One major problem of ANG is during a fast tank filling: generation of heat of adsorption is not released fast, increasing the temperature of the adsorbent and reducing its storage capacity. In this work, we have evaluated the temperature evolution of a storage tank packed with HKUST-1 and subjected to a fast filling of methane under different external heat transfer conditions. When the tank is operated in adiabatic regime, the sudden temperature excursion damaged the HKUST-1 adsorbent with a reduction of 10% of its surface area. To enhance heat transfer and protect the integrity of the adsorbent, the MOF was packed inside 3D printed metal lattices with different lengths. The experiments showed a significant enhancement of the heat transfer which can be particularly beneficial for larger storage tanks.

Effects of Missing Linker Defects on the Elastic Properties and Mechanical Stability of the Metal–Organic Framework HKUST-1

The defects can naturally exist or be artificially designed in metal–organic frameworks (MOFs), which could significantly affect their mechanical properties. In this paper, the elastic properties of HKUST-1 with randomly distributed missing linker defects are investigated by reactive molecular dynamics simulations together with the strain-fluctuation method. Although all elastic constants of HKUST-1 are found to reduce due to the linker missing, the cubic symmetry is retained in the defective HKUST-1, indicating that the simplified Born stability criterion is still applicable in determining its mechanical stability. On the basis of the simplified Born stability criterion together with direct compression simulations, the critical pressure of instability of HKUST-1 with randomly distributed defects is found to almost linearly decrease as the defect concentration grows. The mechanical instability is similarly attributed to the compression mode in both pristine and defective HKUST-1. Moreover, the direct compression simulations indicate an obvious intermediate transition process existing during the structural collapse of the defective HKUST-1, which is absent in its pristine counterpart. Overall, this work is expected to provide a more precise understanding of the mechanical properties of realistic MOFs.

Using Metal-Organic Framework HKUST-1 for the Preparation of High-Conductive Hybrid Membranes Based on Multiblock Copolymers for Fuel Cells.

Novel proton-conducting hybrid membranes consisting of sulfonated multiblock copolymer of polysulfone and polyphenylsulfone (SPES) reinforced with a HKUST-1 metal-organic framework (MOF) (5, 10, and 20 wt. %) were prepared and characterized for fuel cell applications. The presence of the MOF in the copolymer was confirmed by means of FE-SEM and EDS. The hybrid membranes show a lower contact angle value than the pure SPES, in agreement with the water uptake (WU%), i.e., by adding 5 wt. % of the MOF, this parameter increases by 20% and 40% at 30 °C and 60 °C, respectively. Additionally, the presence of the MOF increases the ion exchange capacity (IEC) from 1.62 to 1.93 mequivH+ g−1. Thermogravimetric analysis reveals that the hybrid membranes demonstrate high thermal stability in the fuel cell operation temperature range (<100 °C). The addition of the MOF maintains the mechanical stability of the membranes (TS > 85 MPa in the Na+ form). Proton conductivity was analyzed using EIS, achieving the highest value with a 5 wt. % load of the HKUST-1. This value is lower than that observed for the HKUST-1/Nafion system. However, polarization and power density curves show a remarkably better performance of the hybrid membranes in comparison to both the pure SPES and the pure Nafion membranes.

Dual-Amplifying Electrochemiluminescence Sensor Based on CdS QDs@HKUST-1/MWCNTs Composite for Sensitive Catechol Assay

Herein, a novel electrochemiluminescence (ECL) sensor was developed using a dual signal amplification mechanism based on a typical HKUST-1 metal-organic framework, [Cu3(BTC)2(H2O)3, BTC=1,3,5-benzene tricarboxylate], CdS quantum dots (QDs) and multi-walled carbon nanotubes (MWCNTs) for ultrasensitive determination of catechol. HKUST-1 not only has a dispersion effect to carry more CdS QDs for enhancing stability, but also acts as effective catalyzer to accelerate the transformation of persulfate ion (S2O8 2−) for generating more sulfate radical anions (SO4 •−), therefore amplifying the signal of the ECL sensor. Meanwhile, the introduction of MWCNTs to the ECL process could promote the electron transfer rate and accelerate the kinetics of the electro-catalytic reaction attributing to its stronger conductivity, achieving dual-amplifying effect, which could obviously increase the sensitivity of the ECL sensor. The proposed sensor displayed a wide linear range of 1 × 10−7 − 1 × 10−3 M and a low detection limit of 3.8 × 10−8 M with excellent stability, high repeatability and outstanding anti-interference ability under the optimal conditions. Impressively, the sensor possessed commendable feedback when detecting catechol in real samples. Therefore, this research provided a new strategy combining the advantages of MOFs, QDs and MWCNTs materials for phenolic pollutants detection.

Vapor-Assisted Powder Synthesis and Oriented MOF-CVD Thin Films of the Metal-Organic Framework HKUST-1.

A vapor-assisted synthesis method was developed for the metal-organic framework (MOF) HKUST-1 in both powder and film format. The use of a solvent template supplied from the vapor phase is essential to form the framework under these conditions. Chemical vapor deposition of HKUST-1 films (MOF-CVD) results in smooth films that show the expected adsorption behavior. Interestingly, the HKUST-1 films obtained this way show a (111) preferred crystallographic orientation.

Encapsulation of Imazalil in HKUST-1 with Versatile Antimicrobial Activity.

Based on high surface areas, adjustable porosity and microbicide activity, metal-organic frameworks (MOFs) HKUST-1 are widely used as drug release carriers for their slow degradation characteristics under slightly acidic conditions. In this work, porous HKUST-1 was reacted rapidly by cholinium salt (as the deprotonation agent and template) in an aqueous solution at room temperature. A novel antimicrobial system based on an imazalil encapsulated metal organic framework (imazalil IL-3@HKUST-1) was established. Imazalil IL-3@HKUST-1 could achieve synergism in inhibiting pathogenic fungi and bacteria. Moreover, six days after treatment, the slow and constant release of imazalil from imazalil IL@HKUST-1 exhibited better sustainability and microbicidal activity than imazalil. We believe that the method may provide a new strategy for related plant diseases caused by bacteria or fungi.

Synthesis of core-double-shell structured Fe3O4@PDA/HKUST-1: Characterization analysis and adsorption performance on cationic MB dyes

Organic dyes have complex and relatively stable molecular structures that are not easily removed in aqueous solutions. Methylene blue (MB) is a common toxic cationic organic dye. Therefore, in order to remove the excessive MB in wastewater, a novel magnetic core-double-shell structure of Fe3O4@PDA/HKUST-1 metal-organic framework material (MOF) using a two-step solvothermal method as an efficient adsorbent for MB. Various characterization techniques analyzed its morphology structure, porosity, magnetic stability, and thermal stability. The effects of initial pH, pollutant concentration, reaction time, and temperature on MB adsorption were investigated in detail by batch experiments. The results showed that the maximum adsorption capacity was up to 34 mg/g under the optimum adsorption conditions. The removal of MB followed the Langmuir isotherm and the pseudo-second-order model, which represented a thermodynamically spontaneous heat absorption process. Fe3O4@PDA/HKUST-1 had a good cyclic regeneration capacity. The results suggest that the adsorbent has wide application prospects.

Solar-radiation-induced adsorption/desorption system for carbon dioxide capture

Solid-adsorbent-based temperature swing adsorption (TSA) technology is intriguing in CO2 capture, and the predominant energy consumption lies in the temperature swing process. Inspired by the self-regulation of lizards, here, we design a solar-radiation-induced adsorption/desorption system, avoiding additional energy supply for the temperature swing process. In this system, adsorbents filled in a reversible quartz device are covered by radiative cooling coating. With the demand of adsorption and desorption, the temperature of adsorbents can be regulated by radiative cooling and solar heating, respectively. Adsorption tests for over 1 year using the metal-organic framework HKUST-1 as an adsorbent demonstrate that the CO2 working capacity of our system is higher than most industrial TSA with various adsorbents. Furthermore, our system can save more than 80% of the energy input for industrial TSA technologies.

Effective adsorption of chlorpyrifos pesticides by HKUST-1 metal-organic framework

Effective adsorption of chlorpyrifos pesticides by HKUST-1 metal-organic framework

A novel photocatalytic and photoelectrocatalytic system for oxidative desulfurization of model fuel using BiVO4@HKUST-1 composite in powder and deposited on fluorine-doped tin oxide

In this study, photocatalytic oxidative desulfurization (PODS), as well as a photoelectrocatalytic oxidative desulfurization (PEODS) process was used for ultra-desulfurization of a model fuel using BiVO4@HKUST-1 composite as the catalyst in powder and deposited form on a fluorine tin oxide glass. Accordingly, the metal–organic framework HKUST-1 was synthesized and modified by the addition of BiVO4 to form the BiVO4@HKUST-1 photocatalyst. The composite, as well as pristine BiVO4 and HKSUT-1 samples were used for oxidative desulfurization under catalytic, photocatalytic, and eletrophotocatalytic conditions. The best results were observed for the BiVO4@HKUST-1 composite under photocatalytic desulfurization. The effect of different parameters such as reaction time, temperature, oxidizing agent, extractant solvent, catalyst amount, and solvents was investigated. Under optimal conditions, the dibenzothiophene (DBT) removal reached 95% in the PODS system. In comparison between photocatalytic and photoelectrocatalytic systems, PEODS gave the same results at the lower time and lower amounts of oxidant and catalyst. The catalyst could be recycled and reused six times without a significant change in DBT removal.