Modification Of Metal-organic Frameworks Research Articles

Defect-Engineered MOF-801/Sodium Alginate Aerogel Beads for Boosting Adsorption of Pb(II).

Metal-organic frameworks (MOFs) are attractive adsorbents for heavy metal capture due to their superior stability, easy modification, and adjustable pore size. However, their inherent microporous structure poses challenges in achieving a higher adsorption capacity. Defect engineering is considered a simple method to create hierarchical MOFs with larger pores. Here, we employed l-aspartic acid as a mixed linker to bind Zr4+ clusters in competition with fumaric acid of MOF-801 to create defects, and the pore size was increased from 4.66 to 15.65 nm. Mercaptosuccinic acid was subsequently used as a postexchange ligand to graft the resultant MOF-801 by acid-ammonia condensation to further expand the pore size to 22.73 nm. Notably, the -NH2, -COOH, and -SH groups contributed by these two ligands increased the adsorption sites for Pb(II). The obtained defective MOF-801 with larger pores was thereafter loaded onto sodium alginate to form aerogel beads as adsorbents, and an adsorption capacity of 375.48 mg/g for Pb(II) was achieved, which is ∼51 times that of pristine MOF-801. The aerogel beads also exhibited outstanding reusability with a removal efficiency of ∼90.23% after 5 cycles of use. The adsorption mechanism of Pb(II) included ion-exchange interaction, as well as chelation interactions of Pb-O, Pb-NH2, and Pb-S. The versatile combination of defect engineering and composite beads provides novel inspirations for MOF modification for boosting heavy metal adsorption.

Ammonia Storage in Metal-Organic Framework Materials: Recent Developments in Design and Characterization.

Since the advent of the Haber-Bosch process in 1910, the global demand for ammonia (NH3) has surged, driven by its applications in agriculture, pharmaceuticals, and energy. Current methods of NH3 storage, including high-pressure storage and transportation, present significant challenges due to their corrosive and toxic nature. Consequently, research has turned towards metal-organic framework (MOF) materials as potential candidates for NH3 storage due to their potential high adsorption capacities and structural tunability. MOFs are coordination networks composed of metal nodes and organic linkers, offering unprecedented porosity and surface area, and allowing incorporation of various functional groups and metal sites that can enhance NH3 adsorption. However, the stability of MOFs in the presence of NH3 is a significant concern since many degrade upon exposure to NH3, primarily due to ligand displacement and framework collapse. To address this, recent studies have focused on the synthesis and postsynthetic modification of MOFs to enhance both NH3 uptake and stability. In this Account, we summarize recent developments in the design and characterization of MOFs for NH3 storage. The choice of metal centers in MOFs is crucial for stability and performance. High-valence metals such as AlIII and TiIV form strong metal-linker bonds, enhancing the stability of the framework to NH3. The MFM-300 series of materials composed of high-valence 3+ and 4+ metal ions and carboxylic linkers demonstrates high stability and high NH3 uptake capacities. Ligand functionalization is another effective strategy for improving the NH3 adsorption. Polar functional groups such as -NH2, -OH, and -COOH enhance the interaction between the framework and NH3, particularly at low partial pressures, while postsynthetic modification allows fine-tuning of these functionalities to optimize the framework for higher adsorption capacities and stability. For example, MFM-303(Al), incorporating free carboxylic acid groups, exhibits a high NH3 packing density comparable to that of solid NH3. Creating defect sites by removing linkers or adding metal ions increases the number of active sites available for NH3 adsorption and shows promise for enhancing uptake. UiO-66, a stable MOF framework, can be modified to include defect sites, significantly enhancing the level of NH3 uptake. The full characterization of MOFs and especially their interactions with NH3 are vital for understanding and improving their performance. Techniques such as neutron powder diffraction (NPD), inelastic neutron scattering (INS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), electron paramagnetic resonance (EPR) spectroscopy, and solid-state nuclear magnetic resonance (ssNMR) spectroscopy can elucidate host-guest interactions and binding dynamics between NH3 and the framework structure and afford crucial information for the future design and rational development of new sorbents. This Account highlights our current strategies for the synthesis and characterization of MOFs for NH3 capture, providing an overview of this rapidly evolving field.

Effect of Nanoscale Surface Modification on the Interfacial Mechanics of Carbon Fibers

AbstractEnhancing fiber surfaces through in situ growth of nanomaterials is known to improve fiber composite properties by enhancing the interface between the fiber and matrix. In this study, hydrothermal processes are used to achieve two types of interfacial modification for carbon fiber: zinc oxide nanowires (ZnO NWs) and nickel‐based metal–organic frameworks (MOF). The interfacial strengths are evaluated using single fiber push‐in tests via nanoindentation and the interfaces are analyzed through dynamic modulus‐mapping. It is found that ZnO modification increases the interface strength by 9.40%, while MOF modification yields an even higher improvement of 16.34%. The load‐displacement plots exhibit distinctive inflection points, elucidated through microstructural observations. Examining the modulus map of the interface region, a transition in the storage modulus from the fiber to the matrix is identified. A capillary flow‐based model is developed to explain the resin penetration through nanoscale features. The findings reported here indicate that the timescale for resin absorption is significantly shorter than the curing timescales for the surface modifications explored in this study.

Synergistic Construction of Sub-Nanometer Channel Membranes through MOF–Polymer Composites: Strategies and Nanofiltration Applications

The selective separation of small molecules at the sub-nanometer scale has broad application prospects in the field, such as energy, catalysis, and separation. Conventional polymeric membrane materials (e.g., nanofiltration membranes) for sub-nanometer scale separations face challenges, such as inhomogeneous channel sizes and unstable pore structures. Combining polymers with metal–organic frameworks (MOFs), which possess uniform and intrinsic pore structures, may overcome this limitation. This combination has resulted in three distinct types of membranes: MOF polycrystalline membranes, mixed-matrix membranes (MMMs), and thin-film nanocomposite (TFN) membranes. However, their effectiveness is hindered by the limited regulation of the surface properties and growth of MOFs and their poor interfacial compatibility. The main issues in preparing MOF polycrystalline membranes are the uncontrollable growth of MOFs and the poor adhesion between MOFs and the substrate. Here, polymers could serve as a simple and precise tool for regulating the growth and surface functionalities of MOFs while enhancing their adhesion to the substrate. For MOF mixed-matrix membranes, the primary challenge is the poor interfacial compatibility between polymers and MOFs. Strategies for the mutual modification of MOFs and polymers to enhance their interfacial compatibility are introduced. For TFN membranes, the challenges include the difficulty in controlling the growth of the polymer selective layer and the performance limitations caused by the “trade-off” effect. MOFs can modulate the formation process of the polymer selective layer and establish transport channels within the polymer matrix to overcome the “trade-off” effect limitations. This review focuses on the mechanisms of synergistic construction of polymer–MOF membranes and their structure–nanofiltration performance relationships, which have not been sufficiently addressed in the past.

Impact of copper and cobalt-based metal-organic framework materials on the performance and stability of hole-transfer layer (HTL)-free perovskite solar cells and carbon-based

This article investigates the impact of metal-organic frameworks (MOFs) on the performance and stability of perovskite solar cells (PSCs), specifically focusing on the type of metal and the morphology of the MOF. Two types of MOFs, copper-benzene-1,3,5-tricarboxylate (Cu-BTC MOF) with spherical morphology and cobalt-benzene-1,3,5-tricarboxylate (Co-BTC MOF) with rod morphology, are synthesized and spin-coated on TiO2 substrates to form FTO/TiO2/MOF/CH3NH3PbI3/C-paste PSCs. The morphology and size of the MOFs are characterized by scanning electron microscopy (SEM), and the crystallinity and residual PbI2 of the perovskite films are analyzed by X-ray diffraction (XRD). The results show that the Co-BTC MOF PSC exhibits the highest power conversion efficiency (PCE) of 10.4% and the best stability, retaining 82% of its initial PCE after 264 h of storage in ambient air. The improved performance and stability are attributed to the enhanced crystallinity and reduced residual PbI2 of the perovskite film after Co-BTC MOF modification. The paper showcases the immense potential of MOF-based interlayers to revolutionize PSC technology, offering a path toward next-generation solar cells with enhanced performance and longevity.

In-situ surface enhanced Raman spectroscopy revealing the role of metal–organic frameworks on photocatalytic reaction selectivity on highly sensitive and durable Cu-CuBr substrate

Photocatalytic reactions using copper-based nanomaterials have emerged as a new paradigm in green technology. Selective photocatalysis is very important for improving energy utilization efficiency, and in order to directional improve catalytic selectivity, it is necessary to understand the mechanism of interfacial reactions at the molecular level. Therefore, a unique bifunctional Cu-CuBr substrate is first fabricated via an electrochemical method, which overcomes the instability of traditional copper-based materials and endows high surface-enhanced Raman spectroscopy (SERS) sensitivity and photocatalytic performance and can be stored stably for more than a year. Further modification of the surface with Metal-Organic Frameworks (MOFs) containing carboxyl functional groups can significantly tune the surface properties of the substrate. This increases the adsorption of cationic dyes to improve the SERS effect, and 10−10 M methylene blue can easily be detected with this substrate. Surprisingly, in-situ SERS monitoring of the interfacial photocatalytic dehalogenation reaction of aromatic halides through its intrinsic SERS effect reveal two competing selective reaction pathways, self-coupling and hydrogenation. Typically, the SERS spectra reveal that the latter's selectivity was greatly enhanced after MOFs modification, and the yield rate of the hydrogenated product increased from 27.6 % to 46.9 % (selectivity increased from 32.7 % to 51.5 %). This proves that the surface properties of catalysts, especially the affinity for reaction intermediates, can effectively regulate catalytic selectivity.

Highly hydrophilic and surface defect-rich MOF-74-PA15 obtained by phytic acid etching as a robust catalyst for the oxygen evolution reaction.

Water splitting is an energy conversion process of vital importance. The oxygen evolution reaction (OER), as the half-reaction of water splitting, has very slow kinetics due to the complex quaternary electron transfer process involved, which greatly impedes the efficiency of energy conversion. The rational construction and modification of metal-organic frameworks (MOFs) offer a novel alternative for developing efficient OER electrocatalysts. In this study, MOF-74-PA15 with abundant surface defects and high hydrophilicity was successfully in situ constructed by etching MOFs for different reaction times using phytic acid (PA). The etching of PA increases the active area, and improves the hydrophilicity, allowing tighter contact between the material and the electrolyte. As a result, MOF-74-PA15 exhibits the most optimal OER catalytic performance in all the samples. The overpotential is 250 mV in 1 M KOH at 100 mA cm-2, with the lowest Tafel slope (35.59 mV dec-1). Furthermore, MOF-74-PA15 exhibits excellent stability. It maintains stability for 72 hours at a current density of 50 mA cm-2. This study presents a novel and feasible solution for modifying MOFs as electrocatalytic water splitting catalysts.

Performance of ionic liquid functionalized metal organic frameworks in the adsorption process of phenol derivatives.

The growth of industrial activities has produced a significant increase in the release of toxic organic pollutants (OPs) to the environment from industrial wastewater. On this premise, this study reports the use of metal organic frameworks (MOFs) impregnated with various ionic liquids (ILs) in the adsorption of phenol derivatives, i.e., 2,6-dimethylphenol and 4,4'-dihydroxybiphenyl. MOFs were prepared starting from 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) with divalent (Co, Ni, Cu) and trivalent (Ce) metal salts in mild hydrothermal conditions using water as a green solvent. Imidazolium base ionic liquids, namely 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium nitrate, 1-butyl-3-methylimidazolium chloride, and 1-hexyl-3-methyl-imidazolium chloride, were used to modify MOFs, leading to composite materials (IL@MOF), which show the structural characteristics of MOFs, and complement the advantages of ILs. SEM, EDX images, and TG data indicate that the IL is just attached on the surface of the adsorbent material, with no changes in crystal size or morphology, but with slightly altered thermal stabilities of IL@MOF composites compared to the original ILs and MOFs, pointing to some interionic interaction between IL and MOF. This research consists of equilibrium experiments, studying the effect of the initial concentration of OPs on the adsorption efficiency of the as-prepared MOFs and IL@MOF, in order to determine the influence of the nature of the adsorbent on its developed adsorption capacity and to investigate the performance of both ILs and MOFs. To determine the maximum adsorption capacity, several empirical isotherms were used: Langmuir, Freundlich, Redlich-Peterson, and Dubinin-Radushkevich. The characteristic parameters for each isotherm and the correlation coefficient (R2) were identified. The IL modification of MOFs increased the adsorption capacity of IL@MOF for the removal of phenol derivatives from aqueous solution. The adsorption capacity function of the MOF structure follows the trend CeHEDP > CoHEDP > NiHEDP > CuHEDP. The best performance was achieved by adsorbent materials based on Ce.

Synthesis and evaluation of gene delivery vectors based on PEI-modified metal-organic framework (MOF) nanoparticles.

Zirconium-based metal-organic frameworks (MOFs) nanostructures, due to their capability of easy surface modification, are considered interesting structures for delivery. In the present study, the surfaces of UIO-66 and NH2-UIO-66 MOFs were modified by polyethyleneimine (PEI) 10000 Da, and their efficiency for plasmid delivery was evaluated. Two different approaches, were employed to prepare surface-modified nanoparticles. The physicochemical characteristics of the resulting nanoparticles, as well as their transfection efficiency and cytotoxicity, were investigated on the A549 cell line. The sizes of DNA/nanocarriers for PEI-modified UIO-66 (PEI-UIO-66) were between 212-291 nm and 267-321 nm for PEI 6-bromohexanoic acid linked UIO-66 (PEI-HEX-UIO-66). The zeta potential of all was positive with the ranges of +16 to +20 mV and +23 to +26 mV for PEI-UIO-66 and PEI-HEX-UIO-66, respectively. Cellular assay results showed that the PEI linking method had a higher rate of gene transfection efficiency with minimal cytotoxicity than the wet impregnation method. The difference between transfection of modified nanoparticles compared to the PEI 10 kDa was not significant but the PEI-HEX-UIO-66 showed less cytotoxicity. The present study suggested that the post-synthetic modification of MOFs with PEI 10000 Da through EDC/NHS+6-bromohexanoic acid reaction can be considered as an effective approach for modifying MOFs' structure in order to obtain nanoparticles with better biological function in the gene delivery process.

Enhancing photoelectrochemical performance and stability of Ti-doped hematite photoanode via pentanuclear Co-based MOF modification.

Modifying photoanodes with metal-organic frameworks (MOFs) as oxygen evolution reaction (OER) cocatalysts has emerged as a promising approach to enhance the efficiency of photoelectrochemical (PEC) water oxidation. However, designing OER-active MOFs with both high photo- and electrochemical stability remains a challenge, limiting the advancement of this research. Herein, we present a facile method to fabricate a MOF-modified photoanode by directly loading a pentanuclear Co-based MOF (Co-MOF) onto the surface of a Ti-doped hematite photoanode (Ti:Fe2O3). The resulting Co-MOF/Ti:Fe2O3 modified photoanode exhibits an enhanced photocurrent density of 1.80mA∙cm-2 at 1.23V, surpassing those of the Ti:Fe2O3 (1.53mA∙cm-2) and bare Fe2O3 (0.59mA∙cm-2) counterparts. Additionally, significant enhancements in charge injection and separation efficiencies, applied bias photon-to-current efficiency (ABPE), incident photon to current conversion efficiency (IPCE), and donor density (Nd) were observed. Notably, a minimal photocurrent decay of only 5% over 10h demonstrates the extraordinary stability of the Co-MOF/Ti:Fe2O3 photoanode. This work highlights the efficacy of polynuclear Co-based MOFs as OER cocatalysts in designing efficient and stable photoanodes for PEC water splitting applications.

Synthesis and Thio-Functionalization of Metal Organic Frameworks of Isonicotinate Ligands and their Application for Fluorescein Removal from Aqueous Solution

Mechanochemical syntheses of four (4) know metal organic frameworks (MOFs) were obtained by grinding stoichiometric amounts of metal salts [Zn (II) and Cu (II)] and corresponding carboxylate ligands [Fumaric and Isonicotinic acids] in a mortar with a pestle. Also, Solvent-based syntheses of MOFs were carried out with the reaction of metal salts and each carboxylate ligand by mixing in the presence of solvents. The compounds were characterized by the comparison of melting point, elemental analysis, FT-IR spectroscopy and XRPD results with those of the free ligands and literature. The analytical and spectroscopic data of the compounds prepared via the two different methods gave the expected product.
 The presence of coordinatively unsaturated metal centers in the synthesized MOFs provides an accessible way to selectively functionalize them through coordination bonds. In this work, thiol-functionalization of MOFs were described by choosing six well known MOFs in which three (3) are Zn-based while the other three (3) are Cu-based MOF, by a facile coordination based postsynthetic strategy. The obtained thiol-functionalized MOFs were characterized by powder X-ray diffraction, CHN and infrared spectroscopy. The analytical and spectroscopic data of the unmodified and modified compound were different.
 A series of [Cu (Ina)2] samples stoichiometrically decorated with thiol groups has been prepared through coordination bonding of coordinatively unsaturated metal centers with –SH group in thioglycolic acid. [Cu (Ina)2]. H2O and [Cu(Ina)2]-TH were investigated for the adsorptive removal of fluorescein from aqueous solution. The parameters that affect the dye sorption such as contact time, solution pH, initial fluorescein concentration and temperature, have been investigated and optimized conditions determined at PH of 7.8. Dubinin–Radushkevich Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of MOFs and experimental results showed that the removal efficiency decreases in the order of [Cu(Ina)2]-TH > [Cu(Ina)2].H2O both in adsorption rate and adsorption capacity. The Langmuir, Freundlich, Temkin and Dubinin Radushkevich models have been applied and the data correlate well with Dubinin Radushkevich model. The adsorption mechanism may be explained with a simple electrostatic interaction and π- π interaction. Finally, it can be suggested that modification of MOFs can be use to improve their adsorption capacity and rate, making them a better adsorbent to remove emerging dyes contaminants from waste water.

Recent advances in metal-organic framework (MOF)-based agricultural sensors for metal ions: a review.

Metal ions have great significance for agricultural development, food safety, and human health. In turn, there exists an imperative need for the development of novel, sensitive, and reliable sensing techniques for various metal ions. Agricultural sensors for the diagnosis of both agricultural safety and nutritional health can establish quality and safety traceability systems of both agro-products and food to guarantee human health, even life safety. Metal-organic frameworks (MOFs) are utilized widely for the design of diversified sensors due to their distinctive structural characteristics and extraordinary opticalandelectrical properties. To serve agricultural sensors better, this review is dedicated to providing a brief overview of the synthesis of MOFs, the modification of MOFs, the fabrication of MOF-based film electrodes, the applications of MOF-based agricultural sensors for metal ions, which are centered on electrochemical sensors and optical sensors, and current challenges of MOF-based agricultural sensors. In addition, this review also provides potential future opportunities for the development and practical application of agricultural sensors.

Upgrading the oxidative desulfurization performance of metal-organic frameworks with proton stimulation

The modification of metal-organic frameworks (MOFs) to achieve desirable performance is attracting extensive investigation in heterogeneous catalysis, however, exploring the potential peculiarity of pristine MOFs for targeted applications is often overlooked. In this work, we developed an efficient approach for upgrading the oxidative desulfurization (ODS) performance of Zr-MOFs with proton stimulation. The ODS performance of pristine Zr-MOFs prepared under solvothermal conditions was commonly very poor at ambient temperature but could be activated when protons were introduced. Moreover, the upgradation of ODS efficiency by protons exhibited a sharply increasing trend (from 0.05 to 17.5 mmol g−1 h−1) with the increased density of defects in Zr-MOFs. The most defective UiO-66(Zr) showed ultrahigh activity in model oil which removed 1000 ppm sulfur after 25 min at 30 °C or after 4 min at 50 °C upon proton stimulation that is better than the sample pre-treated with 1 M HCl, and in multicomponent model oil which removed 972 ppm sulfur after 20 min at 50 °C in the present of proton. The turnover frequency (TOF) could reach 211.6 h−1 at 50 °C, surpassing the most investigated ODS catalysts. Quenching experiments and EPR tests demonstrated that the reaction pathway of UiO-66(Zr) could be altered by protons from free radical (OH• and O2•-) into non-free-radical (Zr–OOH) that manipulate the sulfur removal efficiency. Experimental results indicated that the terminal Zr–OH/OH2 sites could decompose H2O2 with assistance of H+ to form Zr–OOH, which probably accounts for the enhancement of ODS activity. Our work reveals a facile and efficient strategy for upgrading the ODS performance of pristine MOFs.

Structural modified metal-organic frameworks by hierarchical layer-by-layer method for efficient CO2 capture enhancement

The emission of CO2 has attracted a plenty of concerns owing to its hazardous influence on the climate. In this study, the strategy for structural modification of metal-organic frameworks (MOF) by hierarchical layer-by-layer method is proposed to improve the CO2 capture performance using polyethylenimine-grafted SBA-15 (PEI/SBA) as a substrate. The growth procedure of hierarchical layer-by-layer framework based on HKUST-1 (HLF) was investigated based on the substrate role of PEI/SBA, serving as epitaxial growth sites of the original MOF (HKUST-1) due to the strong coordination interactions between PEI groups and Cu2+ ions. As varying the PEI loading (20, 40, and 60 wt% corresponding to HLF-1, 2, and 3, respectively), the HLFs present superior CO2 adsorption capacity at 25 ℃ and 1 bar, showing the maximum enhancement of 29.2% (4.20 mmol/g at the HLF-2) compared with HKUST-1. The result of CO2 adsorption experiment under post-combustion conditions for the optimal adsorbent (HLF-2) suggests its sufficient feasibility for industrial applications. The structural analysis of HLFs suggests an amelioration in the mass diffusion of CO2 molecules toward the active sites. The isosteric heats of CO2 adsorption for HLFs exhibit an increase compared with that of HKUST-1, indicating the strong interactive affinity toward CO2. The optimal adsorbent confirms stable reusability for 10 cycles under relatively low temperature in the CO2 desorption, suggesting the feasibility of exploiting renewable energy for desorption thermal energy. Abovementioned results can carve out a way to efficiently achieve the carbon neutrality by improving the performance of CO2 adsorbents.

Research progress of MOFs/carbon nanocomposites on promoting ORR in microbial fuel cell cathodes.

With the rapid development of the economy, energy demand is more urgent. Microbial fuel cells (MFCs) have the advantages of non-toxic, safety, and environmental protection, and are considered the ideal choice for the next generation of energy storage equipment. However, the slow kinetics of oxygen reduction reaction (ORR) on MFC air cathodes and the high cost of traditional platinum (Pt) catalysts hinder their practical application, so there is a need to develop efficient, low-cost, and stable electrocatalysts as alternatives. Recently, metal-organic framework (MOFs) has attracted wide attention in electrocatalysis. Electrocatalysts prepared by the nanocomposite of MOFs and carbon nanomaterials have multiple advantages, such as adjustable chemical properties, high specific surface area, and good electrical conductivity, which have been proven to be a promising electrocatalytic material. In this paper, the latest research progress of metal-organic frames (MOFs) and carbon nanocomposites is reviewed, and the preparation methods and modification of MOFs and carbon nanofibers, carbon nanotubes, and graphene composites are introduced, respectively, as well as their applications in MFC cathode. Finally, the main prospects of MOFs/carbon nanocomposite catalysts are put forward.

Book Review Advanced Materials for Wastewater Treatment and Desalination: Fundamentals to Applications

Book Review Advanced Materials for Wastewater Treatment and Desalination: Fundamentals to Applications

Rationally Tailored Mesoporous Hosts for Optimal Protein Encapsulation.

Proteins play important roles in the therapeutic, medical diagnostic, and chemical catalysis industries. However, their potential is often limited by their fragile and dynamic nature outside cellular environments. The encapsulation of proteins in solid materials has been widely pursued as a route to enhance their stability and ease of handling. Nevertheless, the experimental investigation of protein interactions with rationally designed synthetic hosts still represents an area in need of improvement. In this work, we leveraged the tunability and crystallinity of metal-organic frameworks (MOFs) and developed a series of crystallographically defined protein hosts with varying chemical properties. Through systematic studies, we identified the dominating mechanisms for protein encapsulation and developed a host material with well-tailored properties to effectively encapsulate the protein ubiquitin. Specifically, in our mesoporous hosts, we found that ubiquitin encapsulation is thermodynamically favored. A more hydrophilic encapsulation environment with favorable electrostatic interactions induces enthalpically favored ubiquitin-MOF interactions, and a higher pH condition reduces the intraparticle diffusion barrier, both leading to a higher protein loading. Our findings provide a fundamental understanding of host-guest interactions between proteins and solid matrices and offer new insights to guide the design of future protein host materials to achieve optimal protein loading. The MOF modification technique used in this work also demonstrates a facile method to develop materials easily customizable for encapsulating proteins with different surface properties.

Metal-Organic Framework Sub-Nanochannels Formed inside Solid-State Nanopore with Proton Ultra-High Selectivity.

Metal-Organic frameworks (MOFs) have the advantages of high porosity, angstrom-scale pore size, and unique structure. In this work, a kind of MOFs, UiO-66 and its derivatives (including aminated UiO-66-(NH2 )2 and sulfonated UiO-66-(NH-SAG)2 ), were constructed on the inner surface of solid-state nanopores for ultra-selective proton transport. UiO-66 and UiO-66-(NH2 )2 nanocrystal particles were in-situ grown at the orifice of glass nanopores firstly, which were used to investigate the ionic current responses in LiCl and HCl solutions when the monovalent anions (Cl- ) were unchanged. Compared with UiO-66-modifed nanopores, the aminated MOFs modification (UiO-66-(NH2 )2 ) can improve the proton selectivity obviously. However, when the UiO-66-(NH-SAG)2 nanopore is prepared by further post-modification with sulfo-acetic acid, lithium ions can hardly pass through the channel, and the interaction between protons and sulfonic acid groups can promote the transport of protons, thus achieving ultra-high selectivity to protons. This work provides a new way to achieve sub-nanochannels with high selectivity, which can widely be used in ion separation, sensing and energy conversion.

Magnetic Nitrogen-Rich UiO-66 Metal-Organic Framework: An Efficient Adsorbent for Water Treatment.

The postsynthetic modification of metal-organic frameworks (MOFs) has opened up a promising area to widen their water treatment application. However, their polycrystalline powdery state still restricts their widespread industrial-scale applications. Herein, the magnetization of UiO-66-NH2 is reported as a promising approach to facilitate the separation of the used MOFs after water treatment. A two-step postmodification procedure employing 2,4,6-trichloro-1,3,5-triazine (TCT) and 5-phenyl-1H-tetrazole (PTZ) agents was introduced to level up the adsorption performance of the magnetic nanocomposite. Despite a decrement in porosity and specific surface area of the designed MOFs (m-UiO-66-TCT) compared to neat UiO-66-NH2, it outweighs in adsorption capacity. It was observed that m-UiO-66-TCT has an adsorption capacity of ≈298 mg/g for methyl orange (MO) with facile MOF separation using an external magnet. Pseudo-second-order kinetic model and Freundlich isotherm models suitably interpret the experimental data. Thermodynamic studies showed that MO removal using m-UiO-66-TCT is spontaneous and thermodynamically favorable at higher temperatures. The m-UiO-66-TCT composite exhibited easy separation, high adsorption capacity, and good recyclability, rendering it an attractive candidate for the adsorptive removal of MO dye from aqueous environments.

Rare-Earth-Modified Metal-Organic Frameworks and Derivatives for Photo/Electrocatalysis.

Metal-organic frameworks (MOFs) and their derivatives have attracted much attention in the field of photo/electrocatalysis owing to their ultrahigh porosity, tunable properties, and superior coordination ability. Regulating the valence electronic structure and coordination environment of MOFs is an effective way to enhance their intrinsic catalytic performance. Rare earth (RE) elements with 4f orbital occupancy provide an opportunity to evoke electron rearrangement, accelerate charged carrier transport, and synergize the surface adsorption of catalysts. Therefore, the integration of RE with MOFs makes it possible to optimize their electronic structure and coordination environment, resulting in enhanced catalytic performance. In this review, progress in current research on the use of RE-modified MOFs and their derivatives for photo/electrocatalysis is summarized and discussed. First, the theoretical advantages of RE in MOF modification are introduced, with a focus on the roles of 4f orbital occupancy and RE ion organic coordination ligands. Then, the application of RE-modified MOFs and their derivatives in photo/electrocatalysis is systematically discussed. Finally, research challenges, future opportunities, and prospects for RE-MOFs are also discussed.