Formation of a N/O/F-Rich and Rooflike Cluster-Based Highly Stable Cu(I/II)-MOF for Promising Pipeline Natural Gas Upgrading by the Recovery of Individual C3H8 and C2H6 Gases

Due to the ultralow amounts of C₃H₈ and C₂H₆ gases, to design and synthesize water-stable MOFs that are promising for real-world efficient pipeline natural gas (NG) upgrading by the recovery of individual C₃H₈ and C₂H₆ gases is still a great challenge. Here, a N/O/F heteroatom-rich and rooflike [Cu(II)₄Cu(I)₂(COO)₄(tetrazolyl)₆] cluster-based ultra-microporous tsi-MOF (SNNU-Bai68) was afforded as a multiple heteroatom-rich and curved-surface-shaped cluster-based ultra-microporous MOF and the first porous MOF based upon such rooflike [Cu(II)_xCu(I)_y(tetrazolyl)_z]^(2x+y-z)+ cluster. In SNNU-Bai68, the rooflike cluster was further assembled into a 1D chain secondary building block (SBB), which led to a high density of accessible potential adsorptive sites. Very interestingly, it exhibited the most promising balance of high gas adsorption uptakes at 0.01, 0.03, and 0.05 bar, high C₃H₈/CH₄, C₃H₈/C₂H₆, and C₂H₆/CH₄ adsorption selectivities, moderate adsorption enthalpies, and high water and chemical stability for pipeline natural gas upgrading by the recovery of individual C₃H₈ and C₂H₆ gases, which was further confirmed by the breakthrough experiments of the gas mixtures with/without 74% RH. Furthermore, the SC-XRD and GCMC studies revealed that the successful separation of C₃H₈, C₂H₆, and CH₄ gases in SNNU-Bai68 is due to different synergistic effects of H-bonds between the frameworks at three adsorptive sites around each rooflike cluster and those different gas molecules, which were initially described systematically by the number of H atoms from the gas molecules, the total number of H-bonds within the synergistic H-bonds, and the binding energy of the framework at an adsorption site toward the gas molecules. In addition, this work may provide a method for the construction of a multiple heteroatom-rich and curved-surface-shaped cluster-based ultra-microporous MOF as a novel approach to build MOFs with polar pore surfaces, suitable pore sizes, and unique pore shapes to maximize the synergistic H-bonds between the framework and guests.

Structure, Luminescent Sensing and Proton Conduction of a Boiling-Water-Stable Zn(II) Metal-Organic Framework

A novel Zn(II) metal-organic framework [Zn₄O(C₃₀H₁₂F₄O₄S₈)₃]_n, namely ZnBPD-4F4TS, has been constructed from a fluoro- and thiophenethio-functionalized ligand 2,2',5,5'-tetrafluoro-3,3',6,6'-tetrakis(2-thiophenethio)-4,4'-biphenyl dicarboxylic acid (H₂BPD-4F4TS). ZnBPD-4F4TS shows a broad green emission around 520 nm in solid state luminescence, with a Commission International De L'Eclairage (CIE) coordinate at x = 0.264, y = 0.403. Since d¹⁰-configured Zn(II) is electrochemically inert, its photoluminescence is likely ascribed to ligand-based luminescence which originates from the well-conjugated system of phenyl and thiophenethio moieties. Its luminescent intensities diminish to different extents when exposed to various metal ions, indicating its potential as an optical sensor for detecting metal ion species. Furthermore, ZnBPD-4F4TS and its NH₄Br-loaded composite, NH₄Br@ZnBPD-4F4TS, were used for proton conduction measurements in different relative humidity (RH) levels and temperatures. Original ZnBPD-4F4TS shows a low proton conductivity of 9.47 × 10^-10 S cm^-1 while NH₄Br@ZnBPD-4F4TS shows a more than 25,000-fold enhanced value of 2.38 × 10^-5 S cm^-1 at 40 °C and 90% RH. Both of the proton transport processes in ZnBPD-4F4TS and NH₄Br@ZnBPD-4F4TS belong to the Grotthuss mechanism with E_a = 0.40 and 0.32 eV, respectively.

Green synthesis of white light emitting carbon quantum dots: Fabrication of white fluorescent film and optical sensor applications

In this work, we have reported on the facile synthesis of white light-emitting carbon quantum dots (CQD) from corncob by hydrothermal method. This CQD has a broad emission from 380 nm to 650 nm with high photoluminescence intensity even after three months of shelf-life and stable at variable pH conditions. The presence of Si and N impurities in the biomass gives a greater advantage in producing white light emission with high quantum yield (54%) and enhanced lifetime at ambient conditions. The CQD is highly sensitive towards DNA, paracetamol, Pb²⁺, Cu²⁺, Fe³⁺, and Cr³⁺ fluorescence sensing and signifies its application as a multi-modal fluorescence sensor. The results of optical sensitivity calculated from the linear range of 1-10 ng/mL, 0.10-0.30 mg/mL, 2.5446 ng/mL, 0.0694 mg/mL, 0.3103-1.5515 μM/mL, 0.4299-4.7293 μM/mL, 1.3010 μM/mL and 0.05-2.5 μM/mL. The limit of detection is 2.5446 ng/mL, 0.0694 mg/mL, 0.8641 μM/mL, 1.2454 μM/mL, 1.3010 μM/m, 0.8550 μM/mL and 2.8562 μM/mL, respectively. And also, the relative standard deviation values of 2.30%, 4.46%, 1.79%, 1.84%, 0.26%, 1.23% and 0.35% are evidences its possibility of development towards potential optical sensor applications. Flexible white light-emitting sheets were fabricated from the CQD, illuminates uniform brightness, and has good color reproducibility and higher stability under various UV light excitation.

Chemically Stable Metal-Organic Frameworks: Rational Construction and Application Expansion

Metal-organic frameworks (MOFs) have been attracting tremendous attention owing to their great structural diversity and functional tunability. Despite numerous inherent merits and big progress in the fundamental research (synthesizing new compounds, discovering new structures, testing associated properties, etc.), poor chemical stability of most MOFs severely hinders their involvement in practical applications, which is the final goal for developing new materials. Therefore, constructing new stable MOFs or stabilizing extant labile MOFs is quite important. As with them, some "potential" applications would come true and a lot of new applications under harsh conditions can be explored. Efficient strategies are being pursued to solve the stability problem of MOFs and thereby achieve and expand their applications.In this Account, we summarize the research advance in the design and synthesis of chemically stable MOFs, particularly those stable in acidic, basic, and aqueous systems, as well as in the exploration of their applications in several expanding fields of environment, energy, and food safety, which have been dedicated in our lab over the past decade. The strategies for accessing stable MOFs can be classified into: (a) assembling high-valent metals (hard acid, such as Zr⁴⁺, Al³⁺) with carboxylate ligands (hard base) for acid-stable MOFs; (b) combining low-valent metals (soft acid, such as Co²⁺, Ni²⁺) and azolate ligands (soft base, such as pyrazolate) for alkali-resistant MOFs; (c) enhancing the connectivity of the building unit; (d) contracting or rigidifying the ligand; (e) increasing the hydrophobicity of the framework; and (f) substituting liable building units with stable ones (such as metal metathesis) to obtain robust MOFs. In addition, other factors, including the geometry and symmetry of building units, framework-framework interaction, and so forth, have also been taken into account in the design and synthesis of stable MOFs. On the basis of these approaches, the stability of resulting MOFs under corresponding conditions has been remarkably enhanced.With high chemical stability achieved, the MOFs have found many new and significant applications, aiming at addressing global challenges related to environmental pollution, energy shortage, and food safety.A series of stable MOFs have been constructed for detecting and eliminating contaminations. Various fluorescent MOFs were rationally customized to be powerful platforms for sensing hazardous targets in food and water, such as dioxins, antibiotics, veterinary drugs, and heavy metal ions. Some hydrophobic MOFs even showed effective and specific capture of low-concentration volatile organic compounds.Novel MOFs with record-breaking acid/base/nucleophilic regent resistance have expanded their application scope under harsh conditions. BUT-8(Cr)A, as the most acid-stable MOF yet, showed reserved structural integrity in concentrated H₂SO₄ and recorded high proton conductivity; the most alkali-resistant MOF, PCN-601, retained crystallinity even in boiling saturated NaOH aqueous solution, and such base-stable MOFs composed of non-noble metal clusters and poly pyrazolate ligands also demonstrated great potential in heterogeneous catalysis in alkaline/nucleophilic systems for the first time.It is believed that this Account will provide valuable references on stable MOFs' construction as well as application expansion toward harsh conditions, thereby being helpful to promote MOF materials to step from fundamental research to practical applications.

Stable Crystalline Organic-Inorganic Hybrid Indium Phosphate with Dye Removal and Ractopamine Detection Applications

A highly stable framework of an organic-inorganic hybrid indium phosphate (NTOU-7) was synthesized under hydro(solvo)thermal conditions and structurally characterized by single-crystal X-ray diffraction and solid-state NMR spectroscopy. This is the first example of a post-transition-metal phosphate incorporating tetradentate organic molecules. The In atoms in the inorganic layers are coordinated by imidazole rings of the 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene linkers to generate a new solid-state material. NTOU-7 showed high chemical stability and displayed excellent performance for both dye removal and ractopamine (RAC) detection, which are interesting environmental and biosensing applications. The sensitivity and ultralow limit of detection were 607.9 μA·μM·cm^-2 and 2.74 × 10^-10 mol·L^-1 (0.08 ppb), which meet the requirements stated by the Codex Alimentarius Commission (10 ppb RAC residue in beef and pork). The detection performance was confirmed by sensing spiked-in RAC in real pork samples. We also reported the synthesis, characterization, structural stability, dye removal, and sensing properties of NTOU-7.

Sonocrystallisation of ZIF-8 in water with high excess of ligand: Effects of frequency, power and sonication time

A systematic study on the sonocrystallisation of ZIF-8 (zeolitic imidazolate framework-8) in a water-based system was investigated under different mixing speeds, ultrasound frequencies, calorimetric powers and sonication time. Regardless of the synthesis technique, pure crystals of ZIF-8 with high BET (Brunauer, Emmett and Teller) specific surface area (SSA) can be obtained in water after only 5 s. Furthermore, 5 s sonication produced even smaller crystals (~0.08 µm). The type of technique applied for producing the ZIF-8 crystals did not have any significant impact on crystallinity, purity and yield. Crystal morphology and size were affected by the use of ultrasound and mixing, obtaining nanoparticles with a more spherical shape than in silent condition (no ultrasound and mixing). However, no specific trends were observed with varying frequency, calorimetric power and mixing speed. Ultrasound and mixing may have an effect on the nucleation step, causing the fast production of nucleation centres. Furthermore, the BET SSA increased with increasing mixing speed. With ultrasound, the BET SSA is between the values obtained under silent condition and with mixing. A competition between micromixing and shockwaves has been proposed when sonication is used for ZIF-8 production. The former increases the BET SSA, while the latter could be responsible for porosity damage, causing a decrease of the surface area.

Chitin/Metal-Organic Framework Composites as Wide-Range Adsorbent

Composites based on chitin (CH) biopolymer and metal-organic framework (MOF) microporous nanoparticles have been developed as broad-scope pollutant absorbent. Detailed characterization of the CH/MOF composites revealed that the MOF nanoparticles interacted through electrostatic forces with the CH matrix, inducing compartmentalization of the CH macropores that led to an overall surface area increase in the composites. This created a micro-, meso-, and macroporous structure that efficiently retained pollutants with a broad spectrum of different chemical natures, charges, and sizes. The unique prospect of this approach is the combination of the chemical diversity of MOFs with the simple processability and biocompatibility of CH that opens application fields beyond water remediation.

High and Tunable Proton Conduction in Six 3D-Substituted Imidazole Dicarboxylate-Based Lanthanide-Organic Frameworks

Six isostructural three-dimensional (3D) Ln(III)-organic frameworks, {[Ln₂(HMIDC)₂(μ₄-C₂O₄)(H₂O)₃]·4H₂O}_n [Ln^III = Gd^III (1), Eu^III (2), Sm^III (3), Nd^III (4), Pr^III (5), and Ce^III (6)], have been fabricated by using a multifunctional ligand of 2-methyl-1H-imidazole-4,5-dicarboxylic acid (H₃MIDC). Ln-metal-organic frameworks (MOFs) 1-6 present 3D structures and possess abundant H-bonded networks between imidazole-N atoms and coordinated and free water molecules. All the six Ln-MOFs demonstrate humidity- and temperature-dependent proton conductivity (σ) having the optimal values of 2.01 × 10^-3, 1.40 × 10^-3, 0.93 × 10^-3, 2.25 × 10^-4, 1.11 × 10^-4, and 0.96 × 10^-4 S·cm^-1 for 1-6, respectively, at 100 °C/98% relative humidity, in the order of Ce^III (6) < Pr^III (5) < Nd^III (4) < Sm^III (3) < Eu^III (2) < Gd^III (1). In particular, the σ for 1 is 1 order of magnitude higher than that for 6, and it enhances systematically according to the decreasing order of the ionic radius, indicating that the lanthanide-contraction tactics can effectively regulate the proton conductivity while retaining the proton conduction routes. This will offer valuable guidance for the acquisition of new proton-conducting materials. In addition, the outstanding water stability and electrochemical stability of such Ln-MOFs will afford a solid material basis for future applications.

Modeling of Water Generation from Air Using Anhydrous Salts

The atmosphere contains 3400 trillion gallons of water vapor, which would be enough to cover the entire Earth with a one-inch layer of water. As air humidity is available everywhere, it acts as an abundant renewable water reservoir, known as atmospheric water. The efficiency of an atmospheric water harvesting system depends on the sorption capacities of water-based absorption materials. Using anhydrous salts is an efficient process in capturing and delivering water from ambient air, especially under a condition of low relative humidity, as low as 15%. Many water-scarce countries, like Saudi Arabia, receive high annual solar radiation and have relatively high humidity levels. This study is focused on the simulation and modeling of the water absorption capacities of three anhydrous salts under different relative humidity environments: copper chloride (CuCl2), copper sulfate (CuSO4), and magnesium sulfate (MgSO4), to produce atmospheric drinking water in water-scarce regions. By using a mathematical model to simulate water absorption, this study attempts to compare and model the results of the current computed model with the laboratory experimental results under static and dynamic relative humidities. This paper also proposes a prototype of a system to produce atmospheric water using these anhydrous salts. A sensitivity analysis was also undertaken on these three selected salts to determine how the uniformity of their stratified structures, thicknesses, and porosities as applied in the mathematical model influence the results.

Optimization of plasmonic metal structures for improving the hydrogen production efficiency of metal-organic frameworks

The introduction of plasmonic metals of gold (Au) nanoparticles onto metal-organic frameworks (MOFs) has been testified as an efficient approach to boost the H2 evolution ability because the excited Au particles can generate hot electrons that can then be injected into MOFs to inhibit the recombination of charges. Generally, Au particles possess two modes of polarization, which are transverse and longitudinal polarizations. However, which of the two modes is more efficient remains unclear and is yet to be disclosed. Herein, we report a strategy of finely controlling the transverse and longitudinal polarizations by gradually reducing the length, without changing the width of Au rods, and then combining with MOF Pt@MIL-125 to construct Pt@MIL-125/Au Schottky junctions, for investigating the polarization mode effects. The results indicate that with the reduction in the length of Au rods from 67 nm to 38 nm, the transverse polarization will be increased, which can lead to a significant enhancement in the electron-hole separation efficiency and H2 generation activity. When Au is in spherical shape, the transverse polarization effect reaches the highest level, thereby achieving the highest H2 production rate of 265.1 μmol g-1 h, which is 1.6 times more than that of 67 nm Au rods. The enhancement can be attributed to the significant accelerated electron transfer rate induced by transverse polarization and evidenced by ESR analysis. The results indicate that the transverse polarization is more efficient for hot electron injection and highlight that the Au sphere is a more appropriate candidate for producing the maximum SPR effect during photocatalysis.

Defect Engineering of Nanoscale Hf-Based Metal-Organic Frameworks for Highly Efficient Iodine Capture

With the rapid development of the nuclear industry, how to deal with radioactive iodine waste in a timely and effective manner has become an important issue to be solved urgently. Herein, the defect-engineering strategy has been applied to develop a metal-organic framework (MOF)-based solid adsorbent by using the classical UiO-type Hf-UiO-66 as an example. After simple acid treatment, the produced defect-containing Hf-UiO-66 (DHUN) not only retains its topological structure, high crystallization, and regular shape but also shows a great increase in the Brunauer-Emmett-Teller value and pore size in comparison with the original Hf-UiO (HUN). These formed defects within DHUN have been demonstrated to be important for the great enhancement of the iodine capture and following application in computed tomography imaging in vitro. This present work gives a new insight into the control and formation of defect sites, and this simple and efficient defect-engineering strategy also shows great promise for the development of novel solid adsorbents and other functional MOF materials.

2D Metal-Organic Framework-Based Thin-Film Nanocomposite Membranes for Reverse Osmosis and Organic Solvent Nanofiltration

Metal-organic frameworks (MOFs) are promising candidates for membrane-based liquid separations due to their intrinsic microporosity, but many are limited by their insufficient stability. In this work, a copper-benzoquinoid (Cu-THQ) MOF was synthesized and demonstrated structural stability in water and organic solvents. After incorporation into the polyamide layer, the hydrophilicity of the membranes was enhanced. The resultant thin-film nanocomposite (TFN) membranes broke the permeability-selectivity tradeoff by showing 242 % increase in water permeance and slightly enhanced salt rejection at MOF loading of 0.0192 mg cm^-2 . The underlying mechanism was probed by different chemical and morphological characterizations. The membranes also showed improved tolerance to chlorine oxidation. With their excellent stability, the Cu-THQ MOF-based membranes further demonstrated impressive performance in organic solvent nanofiltration involving dimethylformamide.

Highly-Efficient Sulfonated UiO-66(Zr) Optical Fiber for Rapid Detection of Trace Levels of Pb2

Lead detection for biological environments, aqueous resources, and medicinal compounds, rely mainly on either utilizing bulky lab equipment such as ICP-OES or ready-made sensors, which are based on colorimetry with some limitations including selectivity and low interference. Remote, rapid and efficient detection of heavy metals in aqueous solutions at ppm and sub-ppm levels have faced significant challenges that requires novel compounds with such ability. Here, a UiO-66(Zr) metal-organic framework (MOF) functionalized with SO3H group (SO3H-UiO-66(Zr)) is deposited on the end-face of an optical fiber to detect lead cations (Pb2+) in water at 25.2, 43.5 and 64.0 ppm levels. The SO3H-UiO-66(Zr) system provides a Fabry–Perot sensor by which the lead ions are detected rapidly (milliseconds) at 25.2 ppm aqueous solution reflecting in the wavelength shifts in interference spectrum. The proposed removal mechanism is based on the adsorption of [Pb(OH2)6]2+ in water on SO3H-UiO-66(Zr) due to a strong affinity between functionalized MOF and lead. This is the first work that advances a multi-purpose optical fiber-coated functional MOF as an on-site remote chemical sensor for rapid detection of lead cations at extremely low concentrations in an aqueous system.

In Situ Porphyrin Substitution in a Zr(IV)-MOF for Stability Enhancement and Photocatalytic CO2 Reduction

Despite numerous inherent merits of metal-organic frameworks (MOFs), structural fragility has imposed great restrictions on their wider involvement in many applications, such as in catalysis. Herein, a strategy for enhancing stability and enabling functionality in a labile Zr(IV)-MOF has been proposed by in situ porphyrin substitution. A size- and geometry-matched robust linear porphyrin ligand 4,4'-(porphyrin-5,15-diyl)dibenzolate (DCPP^2- ) is selected to replace the 4,4'-(1,3,6,8-tetraoxobenzo[lmn][3,8]phenanthroline-2,7(1H,3H,6H,8H)-diyl)dibenzoate (NDIDB^2- ) ligand in the synthesis of BUT-109(Zr), affording BUT-110 with varied porphyrin contents. Compared to BUT-109(Zr), the chemical stability of BUT-110 series is greatly improved. Metalloporphyrin incorporation endows BUT-110 MOFs with high catalytic activity in the photoreduction of CO₂ , in the absence of photosensitizers. By tuning the metal species and porphyrin contents in BUT-110, the resulting BUT-110-50%-Co is demonstrated to be a good photocatalyst for selective CO₂ -to-CO reduction, via balancing the chemical stability, photocatalytic efficiency, and synthetic cost. This work highlights the advantages of in situ ligand substitution for MOF modification, by which uniform distribution and high content of the incoming ligand are accessible in the resulting MOFs. More importantly, it provides a promising approach to convert unstable MOFs, which mainly constitute the vast MOF database but have always been neglected, into robust functional materials.

Removal of low Sb(V) concentrations from mining wastewater using zeolitic imidazolate framework-8

Wastewater generated during mining remains a significant source of antimony pollution, because techniques to quickly and efficiently remove antimony from wastewater do not exist. In this study, zeolitic imidazolate framework-8 (ZIF-8), a specific type of Metal Organic Frameworks (MOFs), was successfully used to remove trace levels (1 mg L^-1) of Sb(V) with a high removal efficiency when the ZIF-8 dose was 0.5 g L^-1. Scanning electron microscopy-X-ray energy dispersive spectrometry (SEM-EDS) indicated that Sb(V) was adsorbed onto the ZIF-8surface. The powder X-ray diffraction (XRD) pattern of ZIF-8 before and after adsorption of Sb(V) indicated that ZIF-8 was successfully synthesized, and remained structurally stable after Sb(V) was adsorbed. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) both suggested complexation of zinc on ZIF-8 with Sb(V), where removal of Sb(V) by ZIF-8 followed the Langmuir adsorption isotherm with pseudo second-order kinetics. Thus, a possible removal mechanism was proposed which involved Sb(V) complexing with the zinc hydroxyl groups on ZIF-8 (Zn-OH-Sb). Practically, ZIF-8, could remove 78.6% of Sb(V) from a mining wastewater containing 20 μg L^-1 Sb(V). Furthermore, ZIF-8 could be remain active after repeated uses and could still remove and 42.3% of Sb(V) from wastewater containing 1 mg L^-1) Sb(V) even when the ZIF-8 was reused five time. This indicated that ZIF-8 had potential for practical removal of Sb(V) from mining wastewaters.

An amino-functionalized three-dimensional cadmium metal–organic framework: Synthesis, characterization and excellent fluorescence sensing of Fe3+

An amino-functionalized three-dimensional cadmium metal–organic framework, [Cd1.5(L)(DMF)]·2H2O (complex 1) L = H3TTCA-NH2 = 2′-amino-[1,1′:3′,1″-terphenyl]-4,4″,5′-tricarboxylic acid), is successfully synthesized under solvothermal conditions and structurally characterized. Interestingly, as a transition metal organic framework, the cadmium metal–organic framework exhibits favorable luminescence properties. In addition, the cadmium metal–organic framework reveals excellent selective and sensitive fluorescence sensing for the recognition of Fe3+ with high quenching efficiency ( Ksv = 3.340 × 103 M−1), demonstrating that the cadmium metal–organic framework can be used as a potential sensor for Fe3+.

Extending photocatalysis to the visible and NIR: the molecular strategy

Photocatalysis exploits light to perform important processes as solar fuel production by water splitting, and CO2 reduction or water and air decontamination. Therefore, photocatalysis contributes to the satisfaction of the increasing needs for clean energy, environmental remediation and, most recently, sanification. Most of the efficient semiconductor nanoparticles (NP), developed as photocatalysts, work in the ultraviolet (UV) spectral region and they are not able to exploit either visible (Vis) or near infrared (NIR) radiation. This limitation makes them unable to fully exploit the broad band solar radiaton or to be applied in indoor conditions. Recently, different approaches have been developed to extend the spectral activity of semiconductor NP, like for example band-gap engineering, integration with upconversion NP and plasmonic enhancement involving also hot-electron injection. Nevertheless, the use of organic molecules and metal complexes, for enhancing the photoactivity in the Vis and NIR, was one of the first strategies proposed for sensitization and it is still one of the most efficient. In this minireview we highlight and critically discuss the most recent and relevant achievements in the field of photocatalysis obtained by exploiting dye sensitization either via dynamic or static quenching.

Understanding the Effect of Water on CO2 Adsorption

Carbon capture from large sources and ambient air is one of the most promising strategies to curb the deleterious effect of greenhouse gases. Among different technologies, CO₂ adsorption has drawn widespread attention mostly because of its low energy requirements. Considering that water vapor is a ubiquitous component in air and almost all CO₂-rich industrial gas streams, understanding its impact on CO₂ adsorption is of critical importance. Owing to the large diversity of adsorbents, water plays many different roles from a severe inhibitor of CO₂ adsorption to an excellent promoter. Water may also increase the rate of CO₂ capture or have the opposite effect. In the presence of amine-containing adsorbents, water is even necessary for their long-term stability. The current contribution is a comprehensive review of the effects of water whether in the gas feed or as adsorbent moisture on CO₂ adsorption. For convenience, we discuss the effect of water vapor on CO₂ adsorption over four broadly defined groups of materials separately, namely (i) physical adsorbents, including carbons, zeolites and MOFs, (ii) amine-functionalized adsorbents, and (iii) reactive adsorbents, including metal carbonates and oxides. For each category, the effects of humidity level on CO₂ uptake, selectivity, and adsorption kinetics under different operational conditions are discussed. Whenever possible, findings from different sources are compared, paying particular attention to both similarities and inconsistencies. For completeness, the effect of water on membrane CO₂ separation is also discussed, albeit briefly.

Porous walnut-like La2O2CO3 derived from metal-organic frameworks for arsenate removal: A study of kinetics, isotherms, and mechanism

Exploration of renewable materials for efficient elimination of arsenic from water is highly imperative. Herein, one kind of novel porous walnut-like La₂O₂CO₃ composite is reported for the first time, fabricated via direct pyrolysis of La-MOFs at 550 °C under the air atmosphere. The as-synthesized material predominantly consists of La₂O₂CO₃, featuring micrometer-scale walnut-like morphology and an abundant mesoporous structure. Adsorption experiments demonstrated that a pseudo-second-order model with a high correlation coefficient (0.9976-0.9988) can depict this adsorption process in a good manner and indicates chemical adsorption. Analysis of the isotherms further revealed that this adsorption is a monolayer and homogeneous process, with an excellent adsorption capacity (210.1 As mg/g), as calculated from the Langmuir model. Thermodynamic parameters indicated this adsorption process to be a spontaneous and endothermic, with a positive change in entropy. By characterization results, it can be deduced that the anion-exchange interaction (i.e. carbonate is prone to being replaced by arsenate) and inner-sphere complexation were both responsible for arsenate removal. A broad working pH range (3.0-9.0) and a good cyclic performance (removal rate is above 90% for the fourth cycle) as well as an excellent adsorption capacity make this adsorbent a promising arsenic scavenger.

Tailoring Electronic Structure and Size of Ultrastable Metalated Metal-Organic Frameworks with Enhanced Electroconductivity for High-Performance Supercapacitors

Utilization of metal-organic frameworks (MOFs) as electrodes for energy storage/conversion is challenging because of the low chemical stability and poor electrical conductivity of MOFs in electrolytes. A nanoscale MOF, Co_0.24 Ni_0.76 -bpa-200, possessing ultrahigh stability with uncommon semiconductor behavior (σ=4.2×10^-3  S m^-1 ) was fabricated. The MOF comprises a robust hydrophobic paddlewheel and an optimized Co/Ni ratio, with consequent control over MOF size and the degree of conjugation of the coligand. A DFT study revealed that appropriate Ni²⁺ doping reduces the activation energy of the system, thus providing a higher carrier concentration, and the strongly delocalized N-donor ligand notably increases the metal-ligand orbital overlap to achieve efficient charge migration, leading to continuous through-bond (-CoNi-N-CoNi-)_∞ conduction paths. These structural features endow the MOF with a good cycling stability of 86.5 % (10 000 cycles) and a high specific capacitance of 1927.14 F g^-1 among pristine MOF-based electrodes.

Hydrophobic Metal-Organic Frameworks and Derived Composites for Microelectronics Applications

The extraordinary characteristic features of metal-organic frameworks (MOFs) make them applicable for use in a variety of fields but their conductivity in microelectronics over a wide relative humidity (RH) range has not been extensively explored. To achieve good performance, MOFs must be stable in water, i. e., under humid conditions. However, the design of ultrastable hydrophobic MOFs with high conductivity for use in microelectronics as conducting and dielectric materials remains a challenge. In this Review, we discuss applications of an emerging class of hydrophobic MOFs with respect to their use as active sensor coatings, tunable low-κ dielectrics and conductivity, which provide high-level roadmap for stimulating the next steps toward the development and implementation of hydrophobic MOFs for use in microelectronic devices. Several methodologies including the incorporation of long alkyl chain and fluorinated linkers, doping of redox-active 7,7,8,8-tetracyanoquinodimethane (TCNQ), the use of guest molecules, and conducting polymers or carbon materials in the pores or surface of MOFs have been utilized to produce hydrophobic MOFs. The contact angle of a water droplet and a coating can be used to evaluate the degree of hydrophobicity of the surface of a MOF. These unique advantages enable hydrophobic MOFs to be used as a highly versatile platform for exploring multifunctional porous materials. Classic representative examples of each category are discussed in terms of coordination structures, types of hydrophobic design, and potential microelectronic applications. Lastly, a summary and outlook as concluding remarks in this field are presented. We envision that future research in the area of hydrophobic MOFs promise to provide important breakthroughs in microelectronics applications.

Aluminum-based metal-organic frameworks (CAU-1) highly efficient UO22+ and TcO4- ions immobilization from aqueous solution

In this research, an Al-based metal-organic framework (MOFs), CAU-1 was prepared through complexation between 2-aminoterephthalic acid and Al (III) by solvothermal approach, and simple operation and cost-effective synthetic route. The objective was to immobilize the typical positive/negative radionuclide ions (UO₂²⁺/TcO₄^-) in aqueous solution. The synthesized CAU-1 was characterized by XRD, FT-IR, TGA, FESEM, TEM-SAED, pH_pzc, XPS and N₂ physisorption analysis. The structure of CAU-1 possessed excellent thermostability, rich functional groups (‒NH₂ and ‒OH groups), as well as large surface area (1636.3 m²/g) and the micropore volume (0.51 m³/g). Furthermore, batch experiments demonstrated that CAU-1 with superior adsorption capacity was 648.37 (UO₂²⁺) mg/g and 692.33 (ReO₄^-) mg/g calculating from Langmuir isotherm model, respectively. Thermodynamic investigation showed the adsorption process was endothermic and spontaneous. In addition, the adsorption mechanism of ReO₄^- ion onto CAU-1 could be electrostatic attraction and chelation effect, while for UO₂²⁺ ion, was mainly chelation effect induced by nitrogen-containing and oxygen-containing functional groups. Hence, the inexpensive and high-capacity CAU-1 could be considered as a practical material for sequestrations of radioactive pollutants from water environment.

Metal-Organic-Framework-Based Materials for Antimicrobial Applications

To address the serious threat of bacterial infection to public health, great efforts have been devoted to the development of antimicrobial agents for inhibiting bacterial growth, preventing biofilm formation, and sterilization. Very recently, metal-organic frameworks (MOFs) have emerged as promising materials for various antimicrobial applications owing to their different functions including the controlled/stimulated decomposition of components with bactericidal activity, strong interactions with bacterial membranes, and formation of photogenerated reactive oxygen species (ROS) as well as high loading and sustained releasing capacities for other antimicrobial materials. This review focuses on recent advances in the design, synthesis, and antimicrobial applications of MOF-based materials, which are classified by their roles as component-releasing (metal ions, ligands, or both), photocatalytic, and chelation antimicrobial agents as well as carriers or/and synergistic antimicrobial agents of other functional materials (antibiotics, enzymes, metals/metal oxides, carbon materials, etc.). The constituents, fundamental antimicrobial mechanisms, and evaluation of antimicrobial activities of these materials are highlighted to present the design principles of efficient MOF-based antimicrobial materials. The prospects and challenges in this research field are proposed.

A water-stable multi-responsive luminescent Zn-MOF sensor for detecting TNP, NZF and Cr2O72- in aqueous media

The wide prevalence of organic and inorganic pollutants in water from various industries is responsible for serious environmental problems and endangers human beings. Therefore, the search for effective methods to detect these pollutants has gained great importance. In this work, a new luminescent MOF, {[Zn(L)(bpe)_0.5]·DMF}_n (1) [H₂L = 4,4'-((naphthalene-1,4-dicarbonyl)bis(azanediyl))dibenzoic acid, bpe = 1,2-bis(4-pyridyl)ethene], was solvothermally synthesized and structurally characterized. In this MOF, Zn-SBUs (SBUs = secondary building units) were connected by acylamide-containing dicarboxylate L^2- and nitrogen-containing bpe molecules to yield a 3D porous framework with isolated DMF molecules in the pores. The activated solvent-free MOF sample (denoted as 1a) with good water-stability was obtained by the solvent-exchange and vacuum heat treatment techniques. The luminescence sensing experiments showed that 1a could sensitively, selectively and reversibly detect 2,4,6-trinitrophenol (TNP), nitrofurazone (NZF) and Cr₂O₇^2- in aqueous media, and the corresponding luminescence quenching mechanism has also been discussed. In addition, MOF 1a could quantitatively detect TNP, NZF and Cr₂O₇^2- in tap water samples, indicating that MOF 1a has the potential to detect the aforesaid pollutants in various environmental water matrices.

Polyvinylpyrrolidone (PVP) assisted in-situ construction of vertical metal-organic frameworks nanoplate arrays with enhanced electrochemical performance for hybrid supercapacitors

Construction of two-dimensional (2D) metal-organic frameworks (MOFs) for energy storage and conversion has attracted great attention due to the synergistic advantages of 2D nanostructures and MOFs. Herein, a Co-MOF material with different 2D morphologies of vertical nanoplate arrays and faveolate nanosheets are in-situ fabricated on Ni foam with and without using polyvinylpyrrolidone (PVP) as a regulator. Toward the application in energy storage, both of two morphologies of the Co-MOF exhibit good electrochemical properties. In particular, the vertical Co-MOF nanoplate arrays deliver a high areal capacity of 8.56 C/cm² at the current density of 5 mA/cm², which is much higher than that of faveolate Co-MOF nanosheets (2.39 C/cm² at 5 mA/cm²). Moreover, a hybrid supercapacitor (HSC) device using the Co-MOF nanoplate arrays positive electrode and activated carbon (AC) negative electrode is assembled, which delivers a volumetric capacitance of 17.9 F/cm³ at 10 mA/cm², a high energy density of 7.2 mW h cm^-3 and a good cyclic stability (retaining over 88.0% of initial capacitance after 3000 cycles). These findings demonstrate that the as-fabricated 2D Co-MOFs possess a huge potential in energy storage.