Metal Organic Framework HKUST-1 Research Articles

3D monolithic composites TiO2/HKUST-1/RGO@melamine foam with improved surface mass transfer for efficient photocatalytic degradation of toluene gas

Currently, photocatalytic technology mostly uses powdered TiO2 catalysts, which are not conducive to recycling, limit the contact between volatile organic compounds (VOCs) and the photocatalyst, and result in lower mass transfer efficiency in gas-solid reactions. Meanwhile, TiO2 catalysts including the electrospun TiO2 nanofibers with hydrophilic surfaces are not favorable for the infiltration and adsorption of non-polar VOCs. To solve these problems, in this work, the monolithic composites TiO2/HKUST-1/RGO@melamine foam (named MRTH) with improved surface mass transfer composed of metal-organic framework (HKUST-1), graphene oxide (GO) and electrospun TiO2 nanofibers was designed. The metal-organic framework HKUST-1 plays a role in promoting the adsorption of toluene, while the reduced graphene oxide (RGO) facilitates the infiltration of non-polar molecules on the surface of the composite and has better electron transport capability. A type II heterojunction between the electrospun TiO2 nanofibers and HKUST-1 formed in the monolithic composites suppresses the recombination of electron-hole pairs and extends their lifespan. Comparing with the bare electrospun TiO2 nanofibers, the MRTH foam composites exhibit a wider light absorption range, hydrophilic and oleophobic properties and a higher separation efficiency of photogenerated carriers. In 90 min of dark adsorption, the removal rate of toluene over MRTH-8 was 52.32 %, while under irradiation by xenon lamp for 150 min, the removal rate over MRTH-8 reached 90.15 %. The amount of monolithic foam composites can also be easily adjusted in the reactor to achieve the best possible removal of the contaminant. The prepared composite materials have been characterized in detail, and the possible mechanisms have also been discussed. The foam composites prepared in this work have high catalytic activity and gas-solid reaction mass transfer efficiency, so they have wide practical application prospects in the field of VOCs abatement.

Synthesis and Characteristics of Ionic Liquid-Implanted HKUST-1 Metal–Organic Frameworks for Transforming Heat into Extraordinary Water Transfer

Synthesis and Characteristics of Ionic Liquid-Implanted HKUST-1 Metal–Organic Frameworks for Transforming Heat into Extraordinary Water Transfer

Carbon (IV) oxide adsorption efficiency of functionalized HKUST-1, IRMF-1, and UiO-66 metal organic frameworks

The ever-increasing consumption of fossil fuels to meet up with the global economic and industrial energy needs has led to climatic change due to uncontrollable emission of a major greenhouse gas (CO2). As a way of mitigating the amount of CO2 in the atmosphere, search for effective and efficient solid adsorbent has been at the front burner of current scientific research. A class of solid adsorbent known as metal organic frameworks (MOFs) have demonstrated immense potentials for CO2 adsorption due to its porous, high thermal and chemical stability, high versatility and ease of production. Upon functionalization, the adsorption efficiency of this class of materials was found to improve tremendously. In this review, the CO2 capture and sequestration potentials of three MOFs (UiO-66, HKUST-1, and MOF-5) and their composites were investigated in the search for economical, stable, and highly selective novel adsorbents for CO2 adsorption.

Miniature Optical Fiber Fabry-Perot Interferometer Based on a Single-Crystal Metal-Organic Framework for the Detection and Quantification of Benzene and Ethanol at Low Concentrations in Nitrogen Gas.

This study reports for the first time, to the best of our knowledge, a real-time detection of ultralow-concentration chemical gases using fiber-optic technology, combining a miniaturized Fabry-Perot interferometer (FPI) with metal-organic frameworks (MOFs). The sensor consists of a short and thick-walled silica capillary segment spliced to a lead-in single-mode fiber (SMF), housing a tiny single crystal of HKUST-1 MOF, imparting chemoselectivity features. Ethanol and benzene gases were tested, resulting in a shift in the FPI interference signal. The sensor demonstrated high sensitivity, detecting ethanol gas concentrations (EGCs) with a sensitivity of 0.428 nm/ppm between 24.9 and 40.11 ppm and benzene gas concentrations (BGCs) with a sensitivity of 0.15 nm/ppm between 99 and 124 ppm. The selectivity study involved a combination of three ultralow concentrations of ethanol, benzene, and toluene gases, revealing an enhancement factor of 436% for benzene and 140% for toluene, attributed to the improved miscibility of these conjugated ring molecules with the alkane chains of the ethanol-modified HKUST-1. Experimental tests confirmed the sensor's viability, demonstrating significantly improved response time and spectral characteristics through crystal polishing, indicating its potential for quantifying and detecting chemical gases at ultralow concentrations. This technology may prevent energy resource losses, and the sensor's small size and robust construction make it applicable in confined and hazardous locations.

Effect of HKUST-1 metal–organic framework in root and shoot systems, as well as seed germination

The seed germination, as well as root and shoot growth effect of HKUST-1 MOF, and its derived linear polymer ([Cu2(OH)(BTC)(H2O)]n·2nH2O) were herein examined. These effects were studied for seven higher plant species: sweet corn (Zea mays L.), black bean (Phaseolus vulgaris L.), tomato (Solanum lycopersicum L.), lettuce (Lactuca sativa L.), celosia (Celosia argentea L.), Aztec marigold (Tagetes erecta L.), and gypsophila (Gypsophila paniculata L.). The studied concentrations of MOFs were 10, 100, 500, or 1000 mg/L, enhancing the percentage of germination and growth of plants in most species. In general, the growth of the root is lower compared to the controls due to the capacity of the MOF to adsorb water and provide micronutrients such as C, O, and Cu, acting as a reserve for the plant. Shoot system growths are more pronounced with HKUST-1 compared with control, and linear polymer, due to the 3D structure adsorbs major water contents. It was found that all studied species are tolerant not only to Cu released from the material, but more evident to Cu structured in MOFs, and this occurs at high concentrations compared to many other systems. Finally, copper fixation was not present, studied by EDX mapping, banning the possibility of metallic phytotoxicity to the tested cultivars.

Spray synthesis of hierarchical porous metal-organic framework HKUST-1 with soft templates and methylene blue adsorption performance

We synthesize hierarchical porous HKUST-1 (HP-HKUST-1) with micropores, mesopores, and macropores using the spray synthesis and soft template methods. We utilize two types of structure-directing agents (SDAs), namely cetyltrimethylammonium bromide and citric acid for C-HKUST-1 and triblock copolymer P123 for P-HKUST-1. Paq-HKUST-1 is successfully synthesized using only water as the solvent. The volumes of the mesopores and macropores are changed by the amounts of SDAs. The highest values are: 0.78 and 0.30 cm3/g for C-HKUST-1; 0.44 and 0.38 cm3/g for P-HKUST-1; and 0.30 and 0.23 cm3/g for Paq-HKUST-1, respectively. HP-HKUST-1 shows high methylene blue (MB) adsorption rates and capacities of over 700 mg/g owing to its HP structure. In particular, C-HKUST-1 exhibits a rate constant of 19.7 mg/mg min for MB adsorption based on the pseudo-second-order adsorption kinetic model. This rate constant is 10 times higher than that of batch-synthesized HKUST-1. Furthermore, HP-HKUST-1 exhibits good stability for reuse as an MB adsorbent.

Test Bench Development and Application to a Parametric Experimental Study on the Dynamic Adsorption Capacity of Noble Gases (Kr, Xe) in the Metal–Organic Framework HKUST-1

Test Bench Development and Application to a Parametric Experimental Study on the Dynamic Adsorption Capacity of Noble Gases (Kr, Xe) in the Metal–Organic Framework HKUST-1

An all-glass based micro gas chromatographic column for light hydrocarbon separation with HKUST-1 as stationary phase

BackgroundThe gas chromatography column is one of the key components of the gas chromatograph and typically be miniaturized using micro-electro-mechanical system (MEMS) technology. Due to the limited area of the Si wafer, the column length of micro gas chromatographic column (μGCC) is usually much smaller than that of commercial chromatographic columns. Therefore, it is always difficult to use μGCCs to separate small molecule gas components such as light hydrocarbons. More importantly, the heterogeneous microchannel surface formed by silicon glass bonding causes uneven stationary phase coating, further preventing the improvement of separation performance. ResultsIn this paper, a novel all-glass based μGCC with 2 m length for the separation of light hydrocarbons is proposed. The microchannels of the μGCC were directly prepared in the glass substrate by ultrafast laser assisted chemical etching (ULAE). The all-glass microchannels make the coating of the hydrophilic metal-organic frameworks (MOFs) stationary phase continuously because of the homogeneous material composition. Therefore, a widely used copper based hydrophilic MOFs HKUST-1 was used as stationary phase for coating and testing. The test results show that the μGCC which is an open tubular column can realize the baseline separation of light hydrocarbons at 100 °C. And the resolution of difficult separated compounds, methane and ethane, can reach 12.98, which is 201.86 % higher than the silica-based monolithic capillary column in the relevant research. The resolution of ethane and ethylene reaches 6.81 at 120 °C. SignificanceThe μGCC fabricated by ULAE method is composed of all-glass and has the uniform stationary phase coating because of the homogeneous microchannel surface which greatly improve the separation performance, resulting in a large resolution for methane and ethane. The all-glass μGCC has broad application prospects in light hydrocarbon separation.

Adsorption of methane and ethane on HKUST-1 metal–organic framework and mesoporous silica composites

Composite materials HKUST-1@MCM-41 and HKUST-1@ BPS based on metal–organic framework HKUST-1 [Cu3(btc)2, btc = benzene-1,3,5-tricarboxylate] and silicas, i.e., mesoporous MCM-41 and biporous BPS with a bimodal mesopore size distribution, were prepared by one-step direct growth technique. Methane and ethane adsorption isotherms were measured for the HKUST-1@MCM-41 and HKUST-1@BPS composites in a wide pressure range for the first time. The silica porous structure significantly affects the content and location of HKUST-1 crystallites in these host matrices, and thereby the adsorption selectivities of the composites.

Electrochemical Sensors Based on Metal-Organic Framework and Conductive Polymer HKUST-1@PANI for High-Performance Detection of Lead Ions

In this research a highly microporous Cu-BTC (denoted as HKUST-1) was synthesized using a simple and rapid synthesis room temperature method. The as-prepared HKUST-1 obtained at room temperature for 10 min exhibited a very high Brunauer–Emmett–Teller (BET) surface area of 1875 m2/g, pore volume (Vp) of 0.789 cm3/g, and average micropore size of 7.84 Å. Based on this product, we successfully fabricated a conductive electrochemical sensor HKUST-1@PANI by polymerizing a conductive polyaniline polymer (PANI) around the metal-organic framework HKUST-1. Fourier transform infrared (FTIR) spectra, X-ray diffraction pattern (XRD) support the formation of HKUST-1@PANI. Furthermore, scanning electron microscopy (SEM) studies confirmed that PANI uniformly covered the surface of HKUST-1. We used the resulting material to build a new electrochemical sensor for the reliable detection of lead ions. The electrochemical response of the developed sensor towards ions was evaluated using differential pulse voltammetry (DPV). Under optimized conditions, linear detection was reproducible over the Pb2+ concentration range from 0.005 to 50 μM with a minimum detection limit of 5 nM. The sensor is practically usable in a wide variety of environments, as it is virtually immune to interference from other coexisting ions.

Pd@HKUST-1@Cu(II)/CMC composite bead as an efficient synergistic bimetallic catalyst for Sonogashira cross-coupling reactions

We fabricated an efficient Pd@HKUST-1@Cu(II)/CMC composite bead catalyst through an innovative strategy based on the unique properties of metal-organic frameworks (MOFs) and carboxymethylcellulose (CMC). In this strategy, HKUST-1 MOFs were grown in-situ on the surface of micrometer-sized Cu-based CMC beads (Cu(II)/CMC), then Pd(II) ions were incorporated into the pores of the MOF and further be partially reduced to Pd(0) NPs, which is an active species for oxidative addition with aryl halides in Sonogashira reactions. The micron-sized Cu(II)/CMC beads were formed through inter/intramolecularly crosslinking facilitated by Cu(II) ions, which was achieved by the metathesis of Cu(II) with numerous carboxylic groups of CMC. Such Cu(II)/CMC bead offers many Cu(II) ions as interaction sites for in-situ nucleation and growth of HKUST-1 MOFs. The architecture and composition of the prepared Pd@HKUST-1@Cu(II)/CMC composite were fully verified by various techniques such as FTIR, XRD, TGA, BET, XPS, SEM, TEM, EDX, and elemental mapping analysis. This novel composite bead was applied as an efficient and reusable heterogeneous Pd/Cu bimetallic catalyst for Sonogashira reactions, decarbonylative Sonogashira reaction, and Sonogashira cyclization tandem reactions. The catalyst is readily isolated by simple filtration, and can be reused for five consecutive runs with retaining its activity and structural integrity.

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.