Cu-BTC Metal Organic Framework Research Articles

Metal-organic framework on porous TiO2 thin film-coated alumina beads for fractional distillation of plant essential oils.

Fractionation of essential oils is technically challenging due to enormous scaffold diversities and structural complexities as well as difficulties in the implementation of the fractionation in the gas phase. Packing beads with multi-dimensional hierarchical nanostructures have been developed herein to pack fractional columns for atmospheric distillations. Activated alumina beads were coated with a porous TiO2 thin film. Growth of Cu-BTC (benzene-1,3,5-tricarboxylate) crystals in resultant porous surfaces leads to the generation of new nanopores and increased metal centers for differential coordination with diverse components of essential oils. The TiO2 thin film is not only an integral part of the composites but also induces the oriented growth of Cu-BTC metal organic framework (MOF) crystals through coordinative interactions. These Al2O3@TiO2@Cu-BTC MOF beads show very strong absorptive capability for major components of essential oils, except for a single cyclic ether eucalyptol with steric hindrances. The eucalyptol was fractionated by using the column packed with those modified alumina beads from raw materials of Artemisia argyi, and Rosmarinus officinalis with high purities up to 96% and 93%, respectively.

Role of Bimetallic Solutions in the Growth and Functionality of Cu-BTC Metal-Organic Framework.

Bimetallic solutions play a vital role in the growth and functionality of copper trimesate (Cu-BTC) metal–organic frameworks (MOFs). The effect of Ag+, Ca2+, Mn2+, Co2+, and Zn2+ on the growth of Cu-BTC was studied by fabricating M-Cu-BTC MOFs at room temperature using bimetallic M-Cu solutions. While Ag+ in the MOF had a rod-like morphology and surface properties, divalent cations deteriorated it. Moreover, unconventional Cu+ presence in the MOF formed a new building unit, which was confirmed in all the MOFs. Apart from Ag and Mn, no other MOF showed any presence of secondary cations in the structure. While Ag-Cu-BTC showed an improved H2S uptake capacity, other M-Cu-BTC MOFs had superior organic pollutant adsorption behavior. Thus, we have demonstrated that the physicochemical properties of Cu-BTC could be modified by growing it in bimetallic solutions.

Adsorption behavior of methylene blue on regenerable composite Cu-BTC@AG

The application of metal-organic frameworks (MOFs) Cu-BTC with good adsorption performance in wastewater treatment is limited due to its powder form. The high crystallinity Cu-BTC was compounded with agarose (AG) to obtain a porous foam-like composite Cu-BTC@agarose (Cu-BTC@AG). The Cu-BTC@AG is easy to recycle, the problem of difficult recovery when Cu-BTC is used in water treatment is well solved. In this paper, the influence of contact time, methylene blue (MB) initial concentration, adsorbent dosage, Na+ concentration, pH and temperature on the adsorption of MB by Cu-BTC@AG were studied systematically. Results showed that the adsorption amount of MB by Cu-BTC@AG increased with increasing of MB initial concentration, and the adsorption equilibrium was reached in 120 ​min. The solution pH ​= ​7 is favorable for Cu-BTC@AG to adsorb MB. In addition, the adsorption mechanism of MB on Cu-BTC@AG was further explored by isothermal adsorption model and adsorption kinetics model. The adsorption of MB on Cu-BTC@AG was well fitted with Langmuir isotherm and pseudo-second-order model. Maximum adsorption capacities of MB was 282.466 ​mg/g. The adsorption of MB was carried out through formation of a monolayer adsorption onto the homogeneous surface of Cu-BTC@AG. The adsorption behavior of MB on Cu-BTC@AG was analyzed by adsorption thermodynamics.

Application of nanosecond laser to a direct and rapid growth of Cu-BTC metal-organic framework thin films on copper substrate

Significant research efforts are being devoted to achieve metal-organic framework (MOF) thin films with tailored film thickness and high stability on solid substrates. We demonstrate the successful synthesis of uniform Cu-BTC films directly on a copper metal substrate, using rapid and efficient heat treatment assisted by a nanosecond laser. An oxidized copper substrate with an organic ligand is irradiated by the second harmonic of Nd3+:Y3Al5O12 laser (532 nm), thereby forming Cu-BTC thin films through the photothermal process. The temperature of the laser-irradiated surface was estimated using COMSOL Multiphysics, aiding the optimization of the laser energy density for Cu-BTC crystal growth. The prepared Cu-BTC films exhibit a high surface area (985 m2/g) at 30 mJ/cm2, with a peak surface temperature of ∼364 K. Notably, 3000 laser shots generate Cu-BTC films with a thickness of 10 µm. Thus, the study offers a novel fabrication method for a design strategy, involving the rapid growth (∼ 2 min) of MOF thin films on metal substrates.

CO2 coordination-driven top-down synthesis of a 2D non-layered metal–organic framework

Combining the physical advantages of two-dimensional (2D) inorganic nanosheets and the modular design and programmed structure of metal-organic frameworks (MOFs), 2D MOFs remain at the forefront of functional material research. Despite tremendous efforts, precise control in the synthesis of 2D nonlayered MOFs with predesigned topology for desired applications remains challenging. Success in the bottom-up synthesis of 2D nonlayered MOFs via ligand exchange motivated us to incorporate partial BTC (BTC = 1,3,5-benzenetricarboxylate) ligand dissociation and CO2 capped coordination into the top-down treatment of bulk Cu-BTC MOF, leading to successful conversion of a 3D nonlayered network to a 2D Cu-based topological structure. Notably, a supercritical CO2-containing solvent mixture is employed to provide the desired defect and coordination engineering. Thus, our work introduces a new top-down concept based on modulated synthesis to fabricate high-quality 2D nonlayered MOFs for the first time.

Enhanced Antimicrobial Activity and Low Phytotoxicity of Acoustically Synthesized Large Aspect Ratio Cu-BTC Metal-Organic Frameworks with Exposed Metal Sites.

Metal-organic frameworks (MOFs) have recently been shown to be effective antimicrobial agents, particularly if they comprise pathogenicidal metal ions. Nevertheless, the accessibility of these active metal sites to the pathogen, and hence the MOFs' antimicrobial activity itself, is often poor since the metal nodes are usually embedded deep within its three-dimensional (3D) structure. We show that a unique copper-based (copper(II)-benzene-1,3,5-tricarboxylate) MOF, whose quasi-two-dimensional (quasi-2D) swordlike structure facilitates exposure of the metal ions along its surface, exhibits enhanced antimicrobial properties against three representative plant pathogens: a bacterium (Pseudomonas syringae), a fungus (Fusarium solani), and a virus (Odontoglossum ringspot virus (ORSV)). Such superior antimicrobial activity results in low minimum inhibitory concentrations (MICs)─half that of a commercial pesticide and an eighth of its conventional 3D cubic MOF counterpart (HKUST-1)─and hence low phytotoxicity, which can be attributed to the accessibility of the surface copper sites to the pathogen, thereby facilitating their adhesion and physical contact with the MOF. Additionally, we observed that orchids treated with the quasi-2D MOF showed negligible phytotoxicity and 80% decreased viral load. This work constitutes the first study to demonstrate the antimicrobial properties of this novel MOF against bacterial, fungal, and viral plant pathogens, and the first chemical control of ORSV.

Cu-BTC metal-organic framework as a biocompatible nanoporous carrier for chlorhexidine antibacterial agent.

Antibacterial materials are an essential part of modern life and many efforts have been made to find a new and effective type of them. In this study, chlorhexidine (CHX) was loaded on Cu-BTC metal-organic framework (MOF), that both of them are known to have antibacterial properties. The antibacterial properties of Cu-BTC, CHX and CHX@Cu-BTC were investigated against Gram-positive and Gram-negative bacteria. Agar well-diffusion method and MIC test showed that CHX@Cu-BTC has high antibacterial activity. Characterization methods, such as FT-IR, XRD, N2 adsorption-desorption isotherm, TGA, SEM, EDX, TEM and zeta potential, were employed to characterize their structures. Cu-BTC MOF nanoparticles were synthesized and used as nanoporous carriers for chlorhexidine. The loading was about 10%, which was absorbed into the pores. Antibacterial activity was investigated against Gram-negative and Gram-positive bacteria by Agar well diffusion method and MIC (minimal inhibitory concentration) assay. The CHX@Cu-BTC had synergistic antibacterial activity of Cu-BTC and chlorhexidine.

Salt-free synthesis of Cu-BTC metal-organic framework exhibiting mesoporosity and enhanced carbon dioxide adsorption

Cu-BTC (HKUST-1) metal-organic framework (MOF) in crystalline powder form was prepared by using a copper mesh as the metal source without involving any additional metal precursor, and its performance was evaluated for CO 2 capture. The crystalline structure, morphology, textural characteristics and surface chemical properties of the synthesized HKUST-1 samples were examined by XRD, SEM, N 2 physisorption, and FTIR. The MOF synthesized using the salt-free method exhibited high crystallinity, small size (~2 μm) and uniform crystal morphology, and mesoporosity. The CO 2 adsorption on the MOF was assessed at various temperatures and evaluated with respect to capacity, selectivity, kinetics, and heat of adsorption. Compared to HKUST-1 synthesized by the conventional method, the mesh-derived MOF exhibited a higher CO 2 adsorption capacity (48% higher at 1 bar and 25 °C), increase in CO 2 /N 2 adsorptive selectivity (~11%), as well as faster adsorption kinetics (by 73%). The heat of adsorption was found to increase as well particularly at higher coverages. The obtained CO 2 uptake (~5.2 mmol/g at 1 bar and 25 °C) is among the highest reported for this MOF. The synthesis procedure presented here encompasses high yield (up to 85%), while it requires fewer chemicals and generates less waste compared to the solvothermal approach. As such, it holds the potential to facilitate scaled-up production in a cost-effective and greener way, as the demand for highly efficient porous materials for gas adsorption applications, including CO 2 capture and H 2 storage, is anticipated to significantly increase in the near future. • A novel method for producing MOF powder crystals without using metal salts is reported. • Cu-BTC (HKUST-1) MOF was produced using copper mesh as the Cu source. • Crystal film is grown on the mesh and then dispatched into solution. • The salt-free derived HKUST-1 exhibited enhanced Cu active sites and bimodal porosity in the mesoporous range. • The mesh-derived MOF exhibited significantly enhanced CO 2 adsorption performance.

Cu-BTC Metal-Organic Frameworks as Catalytic Modifier for Ultrasensitive Electrochemical Determination of Methocarbamol in the Presence of Methadone

In this study, an electrochemical sensor based on copper benzene-1, 3, 5-tricarboxylate (Cu-BTC) metal-organic frameworks (MOF) (Cu-MOF/CPE), in an attempt to modify the carbon paste electrode as a highly sensitive sensor, are synthesized and designed for the simultaneous determination of methocarbamol (METO) in the presence of methadone (META). These drugs have been evaluated because of their impacts on the central nervous system (CNS) and the potential damage which they can cause with overuse or concomitant. The observed responses were recorded by electrochemical techniques such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Excellent sensing performance of the suggested electrode was confirmed according to two linear ranges from 0.09 to 100 μM and from 100 to 900 μM with low limit of detection (LOD) of 0.02 μM were achieved for METO analysis, also two linear ranges from 0.08 to 80 μM and from 80 to 800 μM, with low detection limit of 0.05 μM were obtained for META analysis. Several techniques such as scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) and Brunauer–Emmett–Teller (BET) are employed to investigate of copper BTC metal-organic framework structure. The results revealed close packing of hierarchically porous and crystal structure of Cu-BTC MOF. According to results, Cu-BTC MOF was improved the surface area of the modified sensor with significant increase in the oxidation signals owing to their high porosity with remarkable electrochemical properties for measuring these drugs in real samples, including human blood, human urine and tablet.

Hierarchically mesoporous mixed copper oxide/calcined layered double hydroxides composites for iodide high-efficiency elimination

The leakage of iodide (I−)-containing wastewater into environment could cause water pollution owing to the toxicity and radioactivity of iodine isotopes. Therefore, multifunctional adsorbents with high-efficiency removal toward iodide are in high demanded. In the present research, the hierarchically mesoporous mixed copper oxide anchored on calcined layered double hydroxide (Cu2O/CuO@CLDH) materials were synthesized by direct pyrolysis of Cu-BTC metal-organic framework @ layered double hydroxide (HKUST-1@LDH) under N2. Subsequently, the resultant materials were characterized and applied to remove iodide from simulated wastewater. The batch adsorption experiments showed a high I− adsorption amount of 120.9 ​mg/g with relatively fast kinetic removal process as well as good selectivity, and wide working pH range. The adsorption behavior, with spontaneity and exothermic, matched well with the Langmuir isotherm and pseudo-second-order kinetic models, which suggests a homogenous monolayer adsorption and chemisorption characteristics of the as-fabricated materials toward iodide. The outstanding adsorption performance of Cu2O/CuO@CLDH could be attributed to the reconstruction of the layered structures of CLDH and the strong chemical interaction between Cu2O and I−. This study proposes a promising material for iodide elimination.

Simulation and Experimental Studies of Size Effects on Plasmonic Gas Sensing with Nanohole Arrays

Simulation and Experimental Studies of Size Effects on Plasmonic Gas Sensing with Nanohole Arrays

Room temperature and ambient pressure deposition of Cu-BTC MOF on SBA-15 functionalized silica supports by simple spray layer-by-layer method

Metal-organic frameworks (MOFs) have received intense interest over the past decade due to its wide application such as catalysis, membrane-based gas separation, gas adsorption, sensing, and biomedical devices. Growth of MOFs on different solid surfaces allows improving their mechanical properties. Silica is a potential candidate. Due to the difficulty of rising Cu-BTC MOF on silica substrate our group was motivated to achieve a successful coating. This work outlines the functionalization of the gold surface through the MHDA self-assembled monolayer (SAM) and the construction of a MOF film (SURMOF) of Cu-BTC upward. The same MOF was also grown onto a modified mesoporous SBA-15 silica substrate. The first obtained silica particles were previously conformed and activated to receive the MOF. The layer-by-layer method was used to deposit MOF onto the substrates. The deposited MOFs films were characterized by X- ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed SBA-15 as a potential MOF support.

Cu-BTC metal organic framework (MOF) derived Cu-doped TiO2 nanoparticles and their use as visible light active photocatalyst for the decomposition of ofloxacin (OFX) antibiotic and antibacterial activity

Herein, we report the ultrasonic-assisted precipitation technique for the fabrication of Cu-doped TiO2 nanoparticles. The prepared sample showed high crystallinity, purity and nanoparticles like structure with the diameter in the range of 10–22 nm. The bandgap for Cu-doped TiO2 nanoparticles was estimated to be 2.91 eV using Tauc plot, which is considerable for improving the light-harvesting capacity. Further, the prepared Cu-doped TiO2 was used as photocatalyst for the eradication of ofloxacin (OFX), an antibiotic from an aqueous phase under visible illuminations. About 72% degradation of OFX (10 mg/L, pH 7) was achieved with Cu-doped TiO2 nanoparticles after 180 min of visible illumination. The probable photocatalytic mechanism for the decomposition of OFX has been proposed based on reactive species trapping study. Moreover, the antibiotic efficiency of OFX was investigated against Escherichia coli and it was observed that its antimicrobial activity was significantly diminished after the photocatalytic decomposition of the OFX solution with synthesized nanoparticles.

Enhancing effect of UV activation of graphene oxide on carbon capture performance of metal-organic framework / graphene oxide hybrid adsorbents

• Novel CO 2 adsorbents by in-situ growth of Cu-BTC MOF on UV-irradiated GO developed. • UV treatment altered porosity characteristic and distribution of active sites. • The UV-GO/HKUST-1 adsorbents exhibited enhanced performance compared to pure MOF. • UV treatment is facile and can be easily scalable to produce highly-efficient hybrid adsorbents at industrial scale. Ability to capture carbon dioxide from diverse sources and conditions is vital in mitigating the impact of continuously increasing CO 2 levels into the atmosphere. Here, we developed a novel adsorbent based on Cu-BTC metal–organic framework (HKUST-1) and UV-irradiated graphene oxide (UV-GO) by in-situ growth, and assessed its CO 2 capture performance. The effect of the pre-growth UV activation of the GO counterpart on the chemical characteristics, microstructure, morphology, thermal behavior, and textural properties of the resulting hybrid adsorbent was evaluated. Equilibrium CO 2 adsorption isotherms and capture capacity were determined, while selectivity, regenerability, kinetics, and enthalpy of adsorption were evaluated as well. Water adsorption studies and stability, as well as CO 2 adsorption under the effect of humidity were also examined as to assess the capability of the hybrid adsorbents to capture CO 2 from humid mixtures. Formation of additional micro- and mesopores compared to pure HKUST-1 crystals was realized, which was enhanced upon 10-h UV treatment of the GO counterpart (HKUST-1@10UV-GO). Indicatively, the HKUST-1@10UV-GO hybrid adsorbent exhibited a CO 2 adsorption capacity of 5.14 mmol g −1 at 25 °C and 1 bar corresponding to a 45% increase compared to pure HKUST-1, accompanied with significantly enhanced CO 2 adsorption kinetics at higher temperatures. Comparing the adsorption performance at different temperatures (0, 25, 40, and 60 °C), a high CO 2 uptake of 9.5 mmol/g was evidenced for the HKUST-1@10UV-GO at 0 °C and 1 bar. Furthermore, the UV-treated hybrid adsorbents exhibited higher CO 2 /N 2 selectivity at 100 mbar rendering them promising for capture from low CO 2 concentration sources. Interestingly, the CO 2 uptake of HKUST-1@10UV-GO was not compromised in the presence of low amount of water (10% RH), rather it was slightly increased (by up to 3.2%), while hydrophilicity was suppressed compared to pure MOF, which brings an additional advantage for capture from humid mixtures.

Photo-Electrochemical Water Splitting Behavior of Directionally Aligned CdSe Quantum Dots on Copper(II) Benzene-1,3,5-Tricarboxylate Metal-Organic Frameworks (MOFs).

Herein, a facile synthesis protocol for the development of directional alignment of CdSe quantum dots (QDs) on the surface of Copper benzene-1, 3, 5-tricarboxylate (CuBTC) metal-organic frameworks (MOFs) was proposed. The sensitization of CdSe QDs with MOFs offered enhancement of light-harvesting properties in the visible region of the solar spectrum due to the broad absorption band of CdSe QDs. As a photo-anode, it has generated current density of ˜20 mA/cm² at 1.70 V (vs. Reversible hydrogen electrode (RHE)) during the photo-electrochemical water splitting in 1 M Na₂S electrolyte. The present investigation demonstrates the directional attachment of CdSe QDs on CuBTC is beneficial in facilitating light-harvesting and photo-electrochemical properties of CuBTC MOFs.

Mixed Matrix CO2 Separation Membranes based on Polysulfone with Cu-BTC Metal-Organic Framework and Poly(ethylene glycol)-grafted-Carbon Nanotubes

Mixed matrix membranes (MMMs) are heterogeneous membranes comprised of inorganic fillers distributed in a polymer matrix, and have been receiving considerable attention in gas separation. The objective is to take advantage of the benefits provided by each phase that can include high selectivity and permeability due to the inorganic fillers, economical processability of the polymers, and enhanced mechanical properties. Yet, the advancement of MMMs is mostly challenged by the fabrication of defect-free membranes, the proper filler dispersion, and the selectivity/permeability trade-off. In this work, we have developed polysulfone (PSF) MMMs by exploring two different fillers, namely, Cu-BTC (HKUST-1) metal-organic framework and polyethylene glycol-grafted-carbon nanotubes (PEG-g-CNTs) via solvent casting. Following morphological and structural characterization of the developed PSF/HKUST-1 and PSF/PEG-g-CNTs membranes, their CO2 separation performance was evaluated in a gas permeation rig in terms of permeance and selectivity for three different gases, namely, CO2, CH4 and N2 at 2.5 bar and room temperature. Indicatively, an increase in CO2 permeance by 23% was obtained for the MMM containing 10 wt% of HKUST-1, while for the one loaded with 10 wt% of PEG-g-CNT, an increase in CO2 permeance by 35% was observed.

UV-Activated Graphene Oxide for Carbon Capture: Application as Self-Supported Foam Adsorbent and Counterpart in Metal-Organic Framework/Graphene Oxide Hybrid Adsorbents

To follow the low-carbon environmental directives, it is imperative to develop sustainable carbon capture technologies. From an industrial viewpoint, carbon capture by adsorption shows increasing potential by virtue of energy and cost benefits. In this work, graphene oxide (GO)-based adsorbents, namely self-supported GO foam (GOF) and Cu-BTC metal-organic framework (MOF)/GO hybrids, were explored after applying UV activation on the GO. Gas adsorption evaluation indicated that UV activation of GO increased the CO2 uptake in both GOF and MOF/UV-GO, while selective adsorption of CO2 from N2 was also increased upon UV irradiation.

Peculiarities of high-pressure hydrogen adsorption on Pt catalyzed Cu-BTC metal-organic framework.

Hydrogen adsorption ability is a key parameter characterizing advanced porous materials. Herein, the influence of platinum catalyst on the interaction of Cu-BTC with hydrogen is thoroughly investigated using volumetric measurements, calorimetric titration, XRD, and IR- and EPR spectroscopy. The first hydrogen adsorption by the Cu-BTC + Pt/C composite leads to an irreversible chemical reaction related to the formation of structural defects during synthesis. This process results in a partial reduction of Cu2+ to Cu0 and is accompanied by a decrease in the specific surface area and the appearance of additional mesopores. The following hydrogen adsorption-desorption cycles are completely reversible and reproducible. Besides, the Pt-containing material maintains a positive trend in excess adsorption up to ultra-high pressures in contrast with pristine Cu-BTC. Above 300-400 bars, it demonstrates a significant superiority in hydrogen capacity over the catalyst-free MOF. The possible nature of such a peculiar phenomenon is suggested.

The effect of Cu-BTC metal–organic framework (MOF) in mixed matrix membranes on permeability and separation of carbon dioxide and methane

This research was conducted aimed to investigate the performance of mixed matrix membranes including polysulfone (PSF) and poly (ether sulfone) (PES) as polymers and cooper (II)-benzene-1, 3, 5-tricarboxylate (Cu-BTC) as filler with different blend ratios. The response surface methodology (RSM) was employed to design the experiments. The permeation of CO2 and CH4 gases was measured at a feed pressure of 3–9 bar. Morphology, thermal stability, spectral properties and mechanical properties of the membranes were evaluated by SEM, TGA, FTIR, XRD and tensile tests, respectively. According to the results, an increase in the pressure led to a gradual fall in the permeability of CO2 and CH4. Thermal and mechanical stability of the membranes increased by the addition of nanoparticles and polymers to the pure PSF and PES membranes, molecular interaction between the two polymers and MOF was observed by FTIR analysis. The morphology of the membranes was homogenous and good disperse of MOF in matrix polymer. Gas permeability studies indicated that the permeation and ideal selectivity were improved by 100% and 34% with the addition of the Cu-BTC (20%) and PES (73%) in the PSF matrix. It was concluded that synthesized PSF/PES/CUBTC mixed matrix membranes provided an optimized performance with a good combination of permeability, selectivity.

Mixed-Metal Cu-BTC Metal-Organic Frameworks as a Strong Adsorbent for Molecular Hydrogen at Low Temperatures.

The advancement of hydrogen and fuel cell technologies hinges on the development of hydrogen storage methods. Metal–organic frameworks (MOFs) are one of the most favorable materials for hydrogen storage. In this study, we synthesized a series of isostructural mixed-metal metal–organic frameworks (MM-MOFs) of 1,3,5-benzenetricarboxylate (BTC), M-Cu-BTC, where M = Zn2+, Ni2+, Co2+, and Fe2+ using the post-synthetic exchange (PSE) method with metal ions. The powder X-ray diffraction patterns of MM-MOFs were similar with those of single-metal Cu-BTC. Scanning electron microscopy indicates the absence of amorphous phases. Inductively coupled plasma mass spectroscopy of the MM-MOFs shows successful metal exchanges using the PSE method. The N2 adsorption measurements confirmed the successful synthesis of porous MM-MOFs. The metal exchanged materials Ni-Cu-BTC, Zn-Cu-BTC, Fe-Cu-BTC, and Co-Cu-BTC were studied for hydrogen storage and showed a gravimetric uptake of 1.6, 1.63, 1.63, and 1.12 wt %; respectively. The increase in hydrogen adsorption capacity for the three metal exchanged materials is about 60% relative to that of the parent MOF (Cu-BTC). The improvement of gravimetric uptake in M-Cu-BTC (where M = Ni2+, Zn2+, and Fe2+) is probably due to the increase in binding enthalpy of H2 with the unsaturated metal sites after the partial exchange from Cu2+ to other metal ions. The higher charge density of metal ions strongly polarizes hydrogen and provides the primary binding sites inside the pores of Cu-BTC and subsequently enhances the gravimetric uptake of hydrogen.