Missing Linker Defects Research Articles

The Impact of Missing Linker Defects in UiO-66 on Adsorption and Diffusion of Isopropyl Alcohol

The Impact of Missing Linker Defects in UiO-66 on Adsorption and Diffusion of Isopropyl Alcohol

Construction of 2D MOF nanosheets with missing-linker defects for enhanced supercapacitor performance

Metal-Organic Frameworks (MOFs) are highly promising as electrode materials for supercapacitor development due to their large specific surface areas and tunable pore structures. Nevertheless, the intrinsic poor conductivity and suboptimal electrochemical performance of MOFs present substantial challenges. Traditional pyrolysis methods often compromise the inherent characteristics of MOFs. Consequently, a reasonable design of the original MOFs is a promising approach to enhancing its performance. This study commenced with pristine two-dimensional (2D) Ni-BTC (BTC = Trimesic acid) and improved their electrical conductivity and active site accessibility by embedding isophthalic acid (IPA) as missing linkers, resulting in defective Ni-BTC/IPA-x. The physicochemical properties of Ni-BTC/IPA were systematically characterized. The results indicate that defects effectively modulate the electronic structure of the metal center, pore structures, and specific surface areas of MOFs, which is conducive to improving supercapacitor performance. Electrochemical measurements reveal that Ni-BTC/IPA-3 exhibits an exceptional specific capacity of 1209 F g−1 at 0.5 A g−1, demonstrating a rate performance of 70.8 %. Furthermore, hybrid supercapacitor (HSC) devices, incorporating the Ni-BTC/IPA-3, possess an energy density of 30 Wh kg−1 at a power density of 1775.8 W kg−1. These HSC devices successfully power multi-colored light-emitting diodes (LEDs), highlighting their significant potential for practical energy storage applications.

Implications of Defect Density and Polymer Interactions for CO2 Capture on Amine-Functionalized MIL-101(Cr).

Rising anthropogenic carbon emissions have dire environmental consequences, necessitating remediative approaches, which includes use of solid sorbents. Here, aminopolymers (poly(ethylene imine) (PEI) and poly(propylene imine) (PPI)) are supported within solid mesoporous MIL-101(Cr) to examine effects of support defect density on aminopolymer-MOF interactions for CO2 uptake and stability during uptake-regeneration cycles. Using simulated flue gas (10 % CO2 in He), MIL-101(Cr)-ρhigh (higher defect density) shows 33 % higher uptake capacity per gram adsorbent than MIL-101(Cr)-ρlow (lower defect density) at 308 K, consistent with increased availability of undercoordinated Cr adsorption sites at missing linker defects. Increasing aminopolymer weight loadings (10-50 wt.%) within MIL-101(Cr)-ρlow and MIL-101(Cr)-ρhigh increases amine efficiencies and CO2 uptake capacities relative to bare MOFs, though both incur CO2 diffusion limitations through confined, viscous polymer phases at higher (40-50 wt.%) loadings. Benchmarked against SBA-15, lower polymer packing densities (PPI>PEI), weaker and less abundant van der Waals interactions between aminopolymers and pore walls, and open framework topology increase amine efficiencies. Interactions between amines and Cr defect sites incur amine efficiency losses but grant higher thermal and oxidative stability during uptake-regeneration cycling. Finally, >25 % higher CO2 uptake capacities are achieved for aminopolymer/MIL-101(Cr)-ρhigh under humid conditions, demonstrating promise for realistic applications.

Tuning oxygen vacancy and missing linkers of defective MOF-808 for advanced adsorption of Yb(III) from aqueous solution

To improve the adsorption performance of rare earth elements by metal organic frameworks (MOFs) based adsorbents from aqueous solution, two kinds of defective MOF-808 with abundant oxygen vacancies are fabricated via the different strategies, and named as MOF-808-DLX and MOF-808-DSX, respectively. The as-prepared defective MOF-808 were characterized by X-ray diffraction (XRD), infrared spectrometer (IR), thermogravimetric analyzer (TGA), electron paramagnetic resonances (EPR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), confirming the crystal structures, the morphologies, the presences of oxygen vacancies and missing-linker defects. In addition, the adsorption kinetics, adsorption isotherms, and the effects of pH, different rare earth ions on adsorption performance, as well as the cyclic stability of two typical defective MOF-808 were carefully investigated. The results showed that MOF-808-DL1 and MOF-808-DS2 exhibited much higher adsorption capacities than the corresponding pristine MOF-808 at 30 °C and pH = 6. Furthermore, the adsorption mechanisms were clarified through energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Zeta potential, and density functional theory (DFT) calculations, verifying the complexation interaction between Yb(III) and oxygen vacancies originated from Zr6 clusters both for MOF-808-DLX and MOF-808-DSX. Meanwhile, the electrostatics attraction also contributed to the adsorption of Yb(III) for MOF-808-DSX. In summary, this work provides two feasible strategies for manufacturing MOF-808 with missing-linkers defects to promote their potential applications in adsorbing Yb(III) from aqueous solutions.

Missing-linker defects in a covalent organic framework photocatalyst for highly efficient synthesis of tetrahydroquinoline

A unique imine-based covalent organic framework heterogeneous catalyst with missing-linker defects was designed and synthesized, and the catalyst exhibited excellent photocatalytic activity for efficient synthesis of tetrahydroquinolines.

Boosting the activity of UiO-66(Zr) by defect engineering: efficient aldol condensation of furfural and MIBK for the production of bio jet-fuel precursors

The combination of missing-linker and missing-cluster defects within the UiO-66(Zr) MOF structure dramatically boosts the catalytic performance of the material.

Reduction on specific lattice planes for metal–organic frameworks/poly-pyrrole composites with dilated porosity

A novel orientation–modification strategy is proposed for the fabrication of MOFs/poly-pyrrole composites with dilated porosity, which is realized according to missing linker defects induced by reduction on the specific lattice plane of MOFs.

Sub-Tg promoted solid-state interfacial linker exchange in ZIF-based hybrid membranes towards enhanced gas-sieving performance

Minimizing non-selective defects in mixed matrix membranes (MMMs) is a highly desirable, yet challenging task. A generalizable strategy of sub-glass transition temperature (Tg) promoted solid-state linker exchange is presented here, which effectively seals non-selective voids and transforms insignificant defective MMMs into highly selective ones. The progression of solid-state linker exchange is initiated by the methyl groups in a thermal-oxidative environment at sub-Tg temperatures, creating the missing linker defects in the embedded ZIF-8 fillers. The essential ligand groups of benzimidazole of the polymer matrix gain the chain mobility at sub-Tg and concurrently bind to defective ZIF-8 crystals to accomplish the linker exchange, which is accompanied with the methyl group-involved covalent crosslinking in the polymer and ZIF-8, eventually yielding an ultra-selective MMM. The ideal selectivities of H2/CH4 and CO2/CH4 can be tuned up to 584 and 145, respectively, which are two to ten times greater than conventional MMMs. The linker exchange process is validated to be the most impactful factor for gas selectivity enhancement. A representative membrane modified by this strategy has an extremely high mixed-gas CO2/CH4 selectivity of 219 at −25 °C and CO2 permeability of 61 Barrer, exceeding the 2019 Robeson upper bound. The solvent-free sub-Tg promoted linker exchange strategy is employed on benzimidazole containing polyimides/ZIF-7 to demonstrate its versatility and could be extended to a wide range of polymer/MOF hybrids to manipulate interfacial structure.

Supported Cu catalysts on UiO-66 toward enhanced methanol selectivity by CO2 hydrogenation: Effect of Cu loading

The xCu/MOF catalysts were synthesized by incipient-wetness impregnation of copper precursor on UiO-66 support, in which the Cu loadings were 5, 10, and 20% (wt.%). To gain insight into the properties of the materials, a range of techniques, including XRD, TEM, TGA, N2 physisorption, CO2-TPD, EDS, N2O chemisorption, XPS, IR, and NMR, were employed. The effectiveness of catalysts was evaluated for synthesizing methanol through CO2 hydrogenation under various Gas Hourly Space Velocities (GHSVs) and reaction conditions, including pressures of 10 and 30 bar, CO2/H2 ratios of 1:3, and CO2/H2/N2 ratios of 1:3:0.14 M, all conducted at a temperature of 250 °C. The active site in the Cu/UiO-66 catalyst is the interface between Cu+ nanoparticles (NPs) with Zr oxide SBU [Zr6O4(OH)4(−CO2) and the defects related to unsaturated Zr sites of the Zr-Oxo cluster due to the increase of Cu NPs occupying missing linker defects of the MOF structure. 20Cu/MOF catalyst, with the highest copper loading, showed the best methanol formation rate and CO2 conversion due to the strong metal-support interaction and the highest amount of the missing linker defects of the MOF structure.

Imperfect perfection: Selective induction of CO2 during diffusion in mixed matrix membranes

Metal-organic frameworks (MOFs) are one of the optimal choice to be endowed for designing high-performance CO2 separation membranes as the fillers, ascribing their unprecedented tunability and chemical functionalities. However, while pursuing more types of MOFs, researchers have slightly explored their inherent properties. Thus, we incorporated missing-linker defects into Zirconium Metal−Organic Framework for tailoring the superior CO2 transport channel through tune their microporosity. And a series of defect-engineered UiO-66 (UiO-AcOH) fillers were synthesized and mingled into PIM-based matrix with large free volume. Resistance model simulations and gas permeation tests confirmed that the defective UiO-66 can greatly improved the competitive adsorption of the dispersed phase in Mixed Matrix Membranes (MMMs), offering more degree of freedom for the transportation of CO2. At the optimal ratio, the CO2 permeability of the UiO-AcOH-1.4/PIM-15 wt% MMMs increased nearly 3.5 times (CO2 =11261 Barrer, and the CO2/N2 selectivity is 26, almost increasing 23% contrasted pure film. Moreover, MMMs possess excellent long-term working stability and anti-aging properties, showing excellent gas separation performance.

Accelerated Multi-step Sulfur Redox Reactions in Lithium-Sulfur Batteries Enabled by Dual Defects in Metal-Organic Framework-based Catalysts.

The sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs) are recognized as the main obstacles to the practical applications of the lithium-sulfur (Li-S) batteries. Accelerated conversion by catalysis can mitigate these issues, leading to enhanced Li-S performance. However, a catalyst with single active site cannot simultaneously accelerate multiple LiPSs conversion. Herein, we developed a novel dual-defect (missing linker and missing cluster defects) metal-organic framework (MOF) as a new type of catalyst to achieve synergistic catalysis for the multi-step conversion reaction of LiPSs. Electrochemical tests and first-principle density functional theory (DFT) calculations revealed that different defects can realize targeted acceleration of stepwise reaction kinetics for LiPSs. Specifically, the missing linker defects can selectively accelerate the conversion of S8 →Li2 S4 , while the missing cluster defects can catalyze the reaction of Li2 S4 →Li2 S, so as to effectively inhibit the shuttle effect. Hence, the Li-S battery with an electrolyte to sulfur (E/S) ratio of 8.9 mL g-1 delivers a capacity of 1087 mAh g-1 at 0.2 C after 100 cycles. Even at high sulfur loading of 12.9 mg cm-2 and E/S=3.9 mL g-1 , an areal capacity of 10.4 mAh cm-2 for 45 cycles can still be obtained.

Accelerated Multi‐step Sulfur Redox Reactions in Lithium‐Sulfur Batteries Enabled by Dual Defects in Metal‐Organic Framework‐based Catalysts

AbstractThe sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs) are recognized as the main obstacles to the practical applications of the lithium‐sulfur (Li−S) batteries. Accelerated conversion by catalysis can mitigate these issues, leading to enhanced Li−S performance. However, a catalyst with single active site cannot simultaneously accelerate multiple LiPSs conversion. Herein, we developed a novel dual‐defect (missing linker and missing cluster defects) metal–organic framework (MOF) as a new type of catalyst to achieve synergistic catalysis for the multi‐step conversion reaction of LiPSs. Electrochemical tests and first‐principle density functional theory (DFT) calculations revealed that different defects can realize targeted acceleration of stepwise reaction kinetics for LiPSs. Specifically, the missing linker defects can selectively accelerate the conversion of S8→Li2S4, while the missing cluster defects can catalyze the reaction of Li2S4→Li2S, so as to effectively inhibit the shuttle effect. Hence, the Li−S battery with an electrolyte to sulfur (E/S) ratio of 8.9 mL g−1 delivers a capacity of 1087 mAh g−1 at 0.2 C after 100 cycles. Even at high sulfur loading of 12.9 mg cm−2 and E/S=3.9 mL g−1, an areal capacity of 10.4 mAh cm−2 for 45 cycles can still be obtained.

Efficient Generation of Large Collections of Metal-Organic Framework Structures Containing Well-Defined Point Defects.

High-throughput molecular simulations of metal-organic frameworks (MOFs) are a useful complement to experiments to identify candidates for chemical separation and storage. All previous efforts of this kind have used simulations in which MOFs are approximated as defect-free. We introduce a tool to readily generate missing-linker defects in MOFs and demonstrate this tool with a collection of 507 defective MOFs. We introduce the concept of the maximum possible defect concentration; at higher defect concentrations, deviations from the defect-free crystal structure would be readily evident experimentally. We studied the impact of defects on molecular adsorption as a function of defect concentrations. Defects have a slightly negative or negligible influence on adsorption at low pressures for ethene, ethane, and CO2 but a strong positive influence for methanol due to hydrogen bonding with defects. Defective structures tend to have loadings slightly higher than those of defect-free structures for all adsorbates at elevated pressures.

Titanium metal organic framework based electrocatalytic membrane for fast antibiotics removal: Synergy of defects and hierarchical pore

The spread of antibiotics became a serious risk to human health during wastewater reclamation. Herein, a novel electrocatalytic membrane (ECM) was constructed by facile incorporation of titanium metal organic frameworks (Ti-MOFs) with tunable defect and pore structure into polyvinylidene fluoride (PVDF) membrane for antibiotics removal under electro-assistance. The results showed Ti-MOFs with moderate missing-linker defects and hierarchical pores (Ti-MOFs-1) imparted the membrane with much higher water flux (618.6 L·m−2·h−1·bar−1), oxygen evolution potential (2.16 V), electrochemically active surface area (0.0306 cm2), and lower charge-transfer resistance compared to defect-free Ti-MOFs, thereby rendering higher electrocatalytic activity, increasing tetracycline (TC) removal by more than 40% and reducing the toxicities of intermediates. Interestingly, ECM presented a volcano-type trend in TC removal with the gradual increase of defects and pore size in Ti-MOFs due to the synergistic effect of moderately exposed active sites for generation of •OH and •O2– and hierarchical pore feature for accelerated mass transfer of antibiotics toward the catalytic sites. In addition, the application of ECM in reclamation of simulated municipal wastewater was evaluated. The efficient antibiotics removal efficiency (100%), electrically-driven self-cleaning ability (flux recovery = 100%) and electrochemical stability with low residence time (50.2 s) and energy consumption (0.533 W•h/m3) verify its potential in antibiotics removal.

In-situ preparation of sulfonated carbonaceous copper oxide-zirconia nanocomposite as a novel and recyclable solid acid catalyst for reduction of 4-nitrophenol

The missing-linker defects of UiO-66 were exploited to covalently anchor Cu nanoclusters (Cu/UiO-66). The molecular interactions between the metals and oxides as copper-zirconia interfaces in Cu/UiO-66 are essential for heterogeneous catalysis, leading to remarkable synergistic impacts on activity and selectivity. Homogeneously distributed carbonaceous mixed metal oxides (CuO/ZrO2@C) nanocomposite was prepared via carbonization of the Cu/UiO-66 at 600 °C for 3 h in air. To enhance the acidity properties of the CuO/ZrO2@C nanocomposite, a small amount of sulfuric acid was added and heated at 150 °C under an N2 atmosphere (CuO/ZrO2-SO3H@C). The synthesised Cu/UiO-66 and CuO/ZrO2-SO3H@C catalysts were used as novel catalysts in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The Cu/UiO-66 and CuO/ZrO2-SO3H@C catalysts displayed complete conversion of the 4-NP solution during (4 and 2 min) stirring at room temperature, respectively. These two catalysts exhibited a high reduction rate of 8.61 × 10–3 s−1, and 18.3 × 10–3 s−1, respectively. The X-ray photoelectron spectroscopic (XPS) analysis showed the charge of copper atoms in the Cu/UiO-66 catalyst was Cu0/CuII and in the CuO/ZrO2-SO3H@C catalyst was CuI/CuII with nearly the same ratio (65/35). The particle size and the elemental composition of the CuO/ZrO2-SO3H@C catalyst were analysed by using high resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy (EDS), and elemental mapping, respectively. The key point beyond the high catalytic activity and selectivity of the CuO/ZrO2-SO3H@C catalyst is both the carbon–metal oxides heterojunction structure that leads to good dispersion of the CuO and ZrO2 over the carbon sheets, and the high acidity properties that come from the combination between the Brønsted acid sites from sulfuric acid and Lewis acid sites from the UiO-66. The catalysts exhibited good recyclability efficiency without significant loss in activity, indicating their good potential for industrial applications.

Effect of Missing-Linker Defects and Ion Exchange on Stability and Proton Conduction of a Sulfonated Layered Zr-MOF.

Intentionally introduced defects into solid materials create opportunities to control and tune their diverse physicochemical properties. Despite the growing interest in defect-engineered metal-organic frameworks (MOFs), there are still only a handful of studies on defective proton-conducting MOFs, including no reports on two-dimensional ones. Ion-conducting materials are fundamentally of great importance to the development of energy storage and conversion devices, including fuel cells and batteries. In this work, we demonstrate the introduction of missing-linker defects into a sulfonated proton conductive 2D zirconium-based MOF (JUK-14), using a facile post-synthetic approach and compare the stability and performance of the resulting materials, including proton conductivity, as well as adsorption of N2, CO2, and H2O molecules. We also discuss the associated presence of interlayer counterions and their effect on the properties and stability. Our approach to defect engineering can be extended to other layered MOFs and used for tuning their activity.

Advancements in wastewater Treatment: A computational analysis of adsorption characteristics of cationic dyes pollutants on amide Functionalized-MOF nanostructure MIL-53 (Al) surfaces

Recently, research has become increasingly concerned with removing cationic synthetic dyes from the environment because of their aromatic rings and ecological stability, which causes serious health risks for humans and other living organisms. A dye-adsorption system is widely acknowledged as one of the most reliable and practical approaches to wastewater treatment, which is verified for its high effectiveness, low cost, simplicity, and adsorbent reusability. Interestingly, metal–organic frameworks (MOFs) have gained immense attention for their applications in removing dye pollutants from water. This study investigates the adsorption characteristics of well-known cationic dye pollutants, comprising Malachite green (MG), Rhodamine B (RHB), Methylene blue (MB), Toluidine Blue (TB), Gentian violet (GV), Neutral red (NR) on MOF nanostructures functionalized with amide groups using amide/MIL-53 (Al) in two acidic and basic environments via a multiscale computational approach, including Monte Carlo (MC), molecular dynamics (MD) simulations, quantum mechanics tools. The adsorption behaviour of amide/MIL-53 (Al) adsorbent was discussed regarding dye hydration, the role of the nature of the central metal, missing linker defects (MLDs) and missing cluster defects (MCDs) in its structure. The results showed that the amide/MIL 53 had a high adsorption capacity for the cationic dyes because of its robust interaction with positive charges on the dye molecules. The high adsorption potential was assigned to various interactions between the dyes and the adsorbent, including π-π stacking, van der Waals and electrostatic interactions, hydrogen bonding and other weak interactions. According to our findings, the benzene rings of RHB dyes interact more strongly with amide/MIL-53 (Al) surfaces owing to their higher π–π stack bonding energies and hydrogen bonding. The computational study also played a crucial role in predicting the cationic dye adsorption behaviour on the amide/MIL-53 (Al) nanostructure surfaces. The findings of this study have significant implications for the design and development of advanced adsorbent materials for removing cationic dye pollutants from contaminated water.

Removal of norfloxacin from high salinity wastewater by Hf-porphyrin MOF with missing linker defects: Insights into anion trapping and photoinduced charge transfer effects

Treatment of saline wastewater with advanced oxidation technologies has been an urgent challenge due to the inhibitory effect of coexisting ions on reactive oxygen species in real wastewater. Herein, monocarboxylic acids with varying acidity coefficient were employed to modulate the number of missing-linker defects in Hf-porphyrin MOFs (Hf-TCPP-X) to regulate their performance in removing norfloxacin (NFX) from complex aqueous matrices. The missing-linker defect density in Hf-MOFs promoted the removal efficiency of NFX from 8.5 % to 93.6 %. In various anion surroundings, the adsorption and photocatalysis performance of Hf-TCPP-FA with missing-linker defects was enhanced significantly. Quenching tests and the electron paramagnetic resonance (EPR) exhibited that O2∙−, 1O2, and ∙OH dominated NFX removal and their content rising in Hf-TCPP-FA/NaCl/visible-light (Hf-TCPP-FA/NaCl/vis) system. Density functional theory (DFT) calculations displayed that the adsorption energy of Hf-TCPP-FA for NFX decreased from −12.128 eV to −19.157 eV after adding Cl−. The missing-linker defects of catalysts facilitated the photoinduced charge transfer (PICT) under the visible-light irradiation and increased the number of active sites (Hf) in high salinity water. Additionally, favorable NFX removal efficiency could be sustained in Hf-TCPP-FA/visible-light (Hf-TCPP-FA/VIS) system from a wide pH range of aqueous solutions, high coexisting ion concentrations, and in the actual water matrices, and be performed well in cycling tests. This work suggests a promising route to tailor MOF-based photocatalysts by defect engineering and thus improve the removal performance of contaminants in highly saline water.

Acoustomicrofluidic Defect Engineering and Ligand Exchange in ZIF-8 Metal-Organic Frameworks.

A way through which the properties of metal-organic frameworks (MOFs) can be tuned is by engineering defects into the crystal structure. Given its intrinsic stability and rigidity, however, it is difficult to introduce defects into zeolitic imidazolate frameworks (ZIFs)-and ZIF-8, in particular-without compromising crystal integrity. In this work, it is shown that the acoustic radiation pressure as well as the hydrodynamic stresses arising from the oscillatory flow generated by coupling high frequency (MHz-order) hybrid surface and bulk acoustic waves into a suspension of ZIF-8 crystals in a liquid pressure transmitting medium is capable of driving permanent structural changes in their crystal lattice structure. Over time, the enhancement in the diffusive transport of guest molecules into the material's pores as a consequence is shown to lead to expansion of the pore framework, and subsequently, the creation of dangling-linker and missing-linker defects, therefore offering the possibility of tuning the type and extent of defects engineered into the MOF through the acoustic exposure time. Additionally, the practical utility of the technology is demonstrated forone-pot, simultaneous solvent-assisted ligand exchange under ambient conditions, for sub-micron-dimension ZIF-8 crystals and relatively large ligands-more specifically 2-aminobenzimidazole-without compromising the framework porosity or overall crystalstructure.

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.