Preparation and characterization of novel polyoxometalate/CoFe2O4/metal–organic framework magnetic core–shell nanocomposites for the rapid removal of organic dyes from water

In this study, the MIL-101(Cr) metal–organic framework was functionalized with a Dowson-type polyoxometalate (P₂W₁₈O₆₂⁶⁻; POM) and magnetic spinel cobalt ferrite (CoFe₂O₄; CFO) through a hydrothermal route and was characterized by means of FT-IR, XRD, FE-SEM, EDX, BET, and VSM measurements. All analyses confirmed the successful encapsulation of POM (∼32.2 wt%) into the magnetic MIL-101(Cr) framework. Compared to the pristine MIL-101(Cr) MOF, the as-prepared magnetic ternary nanocomposite (abbreviated as POM/CFO/MIL-101(Cr)) demonstrated a notable decrease in both the surface area and pore volume because of the incorporation of CoFe₂O₄ nanoparticles and huge P₂W₁₈O₆₂⁶⁻ polyanions into the cages of the MIL-101(Cr) framework. The POM/CFO/MIL-101(Cr) was then applied as a magnetically separable adsorbent for the rapid elimination of rhodamine B (RhB), methyl orange (MO), and methylene blue (MB) dye pollutants from aqueous solutions. For achieving the optimized conditions, the effects of initial pH, initial dye concentration, temperature, salt effect, and adsorbent dose on MB and RhB elimination were investigated. The dye adsorption isotherms followed the Langmuir model and pseudo-second-order kinetic model. The POM/CFO/MIL-101(Cr) composite material not only exhibited a fast adsorption rate towards dye molecules, but also demonstrated the selective adsorption of the cationic dyes in wastewater. The recycling experiments also demonstrated that the POM/CFO/MIL-101(Cr) adsorbent was highly stable and could be quickly recovered under a magnetic field without any alteration in the structure. The high adsorption capacity, simple fabrication method, rapid separation by a magnet and supreme reusability of the POM/CFO/MIL-101(Cr) nanocomposite make it an attractive adsorbent for the elimination of cationic dyes from wastewater.

The magnetic CoFe₂O₄/MIL-101 (Cr) metal–organic framework nanocomposite containing P₂W₁₈O₆₂⁶⁻ polyoxometalate was fabricated and applied as an ultrafast adsorbent to remove organic dyes from water.     

K6P2W18O62 encapsulated into magnetic Fe3O4/MIL-101 (Cr) metal–organic framework: a novel magnetically recoverable nanoporous adsorbent for ultrafast treatment of aqueous organic pollutants solutions

In this study, a Wells–Dawson type K₆P₂W₁₈O₆₂ polyoxometalate was encapsulated into the magnetic Fe₃O₄/MIL-101 (Cr) metal–organic framework and applied as a new magnetically recoverable ternary adsorbent to remove organic dyes from aqueous solutions. The as-prepared ternary magnetically recyclable hybrid (denoted as P₂W₁₈O₆₂@Fe₃O₄/MIL-101 (Cr)) was characterized by FT-IR spectroscopy, powder X-ray diffraction (XRD), Raman spectroscopy, EDX, SEM, BET surface area, and magnetic measurements. The results showed the successful encapsulation of K₆P₂W₁₈O₆₂ (∼26.5 wt%) into the magnetic Fe₃O₄/MIL-101 (Cr) framework. The magnetic hybrid had a high specific surface area of 934.89 m² g⁻¹. The adsorption efficiency of this nanohybrid for the removal of methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) from aqueous solutions was evaluated. The magnetic nanohybrid demonstrated the fast and selective adsorption of cationic dyes from mixed dye solutions. The adsorption rate and capacity of P₂W₁₈O₆₂@Fe₃O₄/MIL-101 (Cr) were increased as compared with MIL-101 (Cr), P₂W₁₈O₆₂, and Fe₃O₄/MIL-101 samples due to the increased electrostatic attraction. The effects of parameters such as the adsorbent dosage, temperature, dye concentration, and pH were investigated on the adsorption process. The adsorption kinetics was analyzed by the Freundlich, Langmuir, and Temkin isotherm models and pseudo-second-order and pseudo-first-order kinetics models, with the Langmuir isotherm and pseudo-second-order kinetic model found to be suitable to describe the equilibrium data. Also, the thermodynamic results of the nanohybrid indicated that the adsorption was an endothermic and spontaneous process. After the adsorption reaction, the magnetic nanohybrid could be easily separated and reused without any change in structure. Based on the results of this study, the nanohybrid was an efficient adsorbent for eliminating cationic dyes.

A Wells–Dawson-type K₆P₂W₁₈O₆₂ polyoxometalate was encapsulated into the magnetic Fe₃O₄/MIL-101 (Cr) metal–organic framework and applied as a new magnetically recoverable ternary adsorbent to remove organic dyes from aqueous solutions.     

Novel crystalline organic–inorganic hybrid silicate material composed of the alternate stacking of semi-layered zeolite and microporous organic layers

A novel type of crystalline organic–inorganic hybrid microporous silicate material, KCS-5, was synthesized supposedly from a lamellar precursor composed of amphiphilic organosilicic acids. This well-ordered material has a crystalline structure, is thermally stable up to 500 °C and has lipophilic 1-dimensional micropores.

A novel crystalline organic–inorganic hybrid microporous silicate material was successfully synthesized from a lamellar precursor composed of amphiphilic organosilicic acids.

Organic–inorganic hybridization of silicate materials has been diligently studied because it can control surface properties to improve their adsorption capacities and catalytic activities. In these studies, bridged organosilanes, where an organic group connects two trialkoxysilyl species, are frequently employed as a silicon source. For example, Shea et al. prepared microporous amorphous materials named bridged polysilsesquioxanes¹ by sol–gel synthesis from various organosilanes with bulky bridging organic groups, such as bis(triethoxysilyl)benzene (BTEB), and Inagaki et al. obtained surfactant-templated hexagonally-ordered mesoporous silicates from organosilanes bridged with aliphatic or aromatic organic groups.² Tatsumi et al. discovered an improvement in catalytic activities and surface hydrophobicity through the syntheses of a mesoporous titanosilicate³ and zeolites⁴ from bridged organosilanes. In particular, Bellussi et al. crystallized microporous aluminosilicates called ECS,⁵ composed of layered aluminosilicate and bridging organic groups. Such bridged organosilanes were used as a single silicon source, presumably because they can theoretically build a three-dimensional silicate framework without introducing structural defects.In contrast to bridged organosilanes, terminal organosilanes, where a terminal organic group like a methyl or phenyl group functionalizes trialkoxysilyl species, were not employed as a single silicon source but were subsidiarily added as part of a silicon source because terminal organic groups inevitably cause structural defects which cause a deterioration in the 3-dimensional structure of tectosilicates. However, we conceived an idea to obtain well-ordered materials only from terminal organosilanes inspired by our material KCS-2.⁶ KCS-2, also synthesized using a bridged organosilane BTEB, is a crystalline organic–inorganic hybrid material with a large 12-ring micropore and unique amphiphilic inner surface properties. Considering that the finely-designed layered structure of KCS-2 is similar to that of a Langmuir–Blodgett membrane, it is deduced that KCS-2 is crystallized via a well-ordered lamellar precursor composed of hydrolysed bridged organosilane (Fig. 1 middle). Because a lamellar structure is formed from amphiphilic surfactant molecules (Fig. 1 top), a well-ordered lamellar precursor should also be formed from amphiphilic organosilicic acid molecules made from terminal organosilanes (Fig. 1 bottom). For example, phenyltriethoxysilane (PTES) was hydrolysed into an amphiphilic molecule with a hydrophilic trihydroxysilyl head group and a hydrophobic phenyl group, which would be self-organized into a lamellar phase. Therefore, through the condensation of silicic acid (with aluminum, if necessary), it would be possible to synthesize a crystalline layered (alumino)silicate.Open in a separate windowFig. 1The induced formation scheme of lamellar precursors from bridged and terminal organosilanes.Actually, we have succeeded in synthesizing a novel crystalline silicate material, KCS-5, from PTES as a single silicon source. In a typical synthesis (please refer to ESI^†), a mixture with the molar composition of 1.0 PTES : 1.0 NaOH : 5.0H₂O was stirred at r.t. for 2–4 days to promote the hydrolysis of PTES to amphiphilic organosilicic acid, which could be arranged into a lamellar-structured precursor. After the addition of fumed alumina powder (Al₂O₃/Si = 0.2), this mixture was hydrothermally treated at 100 °C for 7 days under static conditions. Generally, KCS-5 was obtained preferentially from mixtures with low H₂O/PTES ratios, where the concentration of amphiphilic organosilicic acid was high. In addition, no crystalline products were obtained from this organosilane without the addition of an aluminum source. Fig. 2 exhibits the powder X-ray diffraction (PXRD) pattern of KCS-5. A low and wide background ranging from 15° to 40° would be derived from a concomitant amorphous by-product and a borosilicate glass capillary tube. By an indexing analysis, the lattice constant belonging to an orthorhombic system was uniquely found. A crystal structure model of KCS-5 was tentatively built from local structural units, such as SiO₄, AlO₄ and C₆H₅–SiO₃, elucidated from the solid-state NMR. (The ²⁹Si, ²⁷Al, and ¹³C solid-state MAS NMR spectra are shown in ESI.^†) The packing structure of these units was solved by the direct-space method with the parallel tempering algorithm using the program FOX.⁷8 using the program RIETAN-FP.⁹ Reliability factors obtained in this analysis were small enough. The calculated and difference plots obtained by the Rietveld analyses are also exhibited in Fig. 2.Open in a separate windowFig. 2Observed (red) and calculated (light blue), background (black), and difference (blue) intensity curves of KCS-5 obtained by Rietveld refinement. The green tick marks denote the peak positions of possible Bragg reflections.Conditions for the PXRD experiments and crystallographic information obtained therein for KCS-5

Synthesis,structure, and fluorescence properties of a calcium-based metal–organic framework

The solvothermal reaction of a mixture of calcium acetylacetonate and 1,4-naphthalenedicarboxylic acid (H₂NDC) in a solution containing ethanol and distilled water gave rise to a metal–organic framework (MOF), {(H₃O⁺)₂[Ca(NDC)(C₂H₅O)(OH)]}₄·1.1H₂O. This MOF possesses a new structure composed of calcium clusters and H₂NDC linker anions and shows a unique fluorescence property; it exhibits a fluorescence peak at 395 nm (λ_ex = 350 nm) at room temperature, which is blue-shifted compared with that exhibited by the free H₂NDC ligand. One of the possible mechanisms for this fluorescence is likely attributable to a ligand-to-metal charge transfer (LMCT) transition and is the first example of a calcium-based MOF exhibiting blue-shifted fluorescence due to LMCT.

The solvothermal reaction of a mixture of calcium acetylacetonate and 1,4-naphthalenedicarboxylic acid (H₂NDC) in a solution containing ethanol and distilled water gave rise to a metal–organic framework (MOF), {(H₃O⁺)₂[Ca(NDC)(C₂H₅O)(OH)]}₄·1.1H₂O.     

One-pot synthesis of Ag–Cu–Cu2O/C nanocomposites derived from a metal–organic framework as a photocatalyst for borylation of aryl halide

Mixed metal–metal oxide/C (Ag–Cu–Cu₂O/C) nanocomposites were synthesized by the heat treatment of a metal–organic framework under a N₂ flow using the one-pot synthesis method. The as-prepared nanocomposites were characterized using a range of techniques, such as TEM, elemental mapping, XRD, N₂ sorption, UV-Vis DRS, and XPS. The nanoparticles were successfully formed with high dispersion in porous carbon materials and high crystallinity based on the analysis results. The Ag–Cu–Cu₂O/C nanocomposites (35 nm) showed high photocatalytic activity and good recyclability toward the borylation of aryl halides under a xenon arc lamp. This result can enhance the interest in photocatalysis for various applications, particularly in organic reactions, using a simple and efficient synthesis method.

Ag–Cu–Cu₂O/C nanocomposites derived from metal–organic framework through one-pot thermal reduction method were synthesized. The material exhibits high catalytic activity in the borylation of aryl halide under xenon lamp condition across 7 cycles, with no yield decrease.     

A photosensitive metal–organic framework having a flower-like structure for effective visible light-driven photodegradation of rhodamine B

Porphyrin-based metal–organic frameworks (MOFs) have great photocatalytic potential due to their good photosensitivity. Their photocatalytic performance is not only determined by molecular structure but also by morphology. Flower-like MOFs are considered to be good materials for catalysis due to their larger specific surface area, more exposed active sites, and good stability. Here, we first proposed a method to synthesize flower-like porphyrin-based MOFs using trifluoroacetic acid as a morphology control agent. These MOFs had a large BET surface area (605.04 m² g⁻¹), a stable structure and a complete morphology. Meanwhile, we discussed their self-assembly process and mechanism in detail. In addition, we studied the photocatalytic performance of flower-like porphyrin-based MOFs and found that the flower-like Cu-TCPP (TCPP = tetrakis(4-carboxyphenyl)porphyrin) has excellent photocatalytic activity. Its photodegradation efficiency toward the cationic dye rhodamine B reached 88% within 100 min and the sample still maintained its stable catalytic activity and complete flower-like morphological structure after five repeated uses. Furthermore, this synthetic strategy can be extended to control the morphology of other MOFs.

Using the method of adding morphological control agent-trifluoroacetic acid (TFA), a flower-like porphyrin-based metal organic framework can be prepared, which shows a good effect on the photocatalytic degradation of rhodamine B.     

Three-dimensional Ni4O4-cubane metal–organic framework as a high-performance electrocatalyst for urea oxidation

The urea oxidation reaction (UOR) is considered to be a replacement of the sluggish anodic oxygen evolution reaction (OER) in overall water-splitting. A three-dimensional (3D) nickel-containing metal–organic framework {[Ni^II₂(pdaa)(OH)₂(H₂O)]_n (MOF 1) (where, H₂pdaa = 1,4-phenylene diacetic acid) was investigated as a robust and highly efficient electrocatalyst for the UOR. MOF 1 comprised 1D nickel(ii) chains crosslinked through Ni₄O₄ cubane units to form a 3D extended network. Dangling Ni⋯OH⁻ groups were exposed in the MOF 1 structure, and could act as active catalytic centers for the UOR. MOF 1 required a very small onset potential of 1.18 V for urea oxidation in KOH (1 M) and urea (0.33 M) and had a low Tafel slope of 38.8 mV dec⁻¹ (in contrast to 1.84 V for the oxygen evolution reaction). The overpotential required to attain a catalytic current density of 10 mA cm⁻² was 1.24 V, which is much lower than that for many materials. Controlled potential electrolysis, powder X-ray diffraction, and X-ray photoelectron spectroscopy affirmed the physicochemical integrity of the catalyst over a 17 h test reaction. This work not only addresses the problem of urea contamination, it also helps to utilize it in an energy-conversion process.

The phenomenally low potential required by MOF 1 for the UOR can be an efficient replacement for the sluggish OER.     

Earth-abundant and environment friendly organic–inorganic hybrid tetrachloroferrate salt CH3NH3FeCl4: structure,adsorption properties and photoelectric behavior

Organic–inorganic hybrid-based lead perovskites show inherent and unavoidable problems such as structural instability and toxicity. Therefore, developing low-cost and environment-friendly organic–inorganic hybrid materials is extremely urgent. In this study, we prepared earth-abundant and environment-friendly organic–inorganic hybrid tetrachloroferrate salt CH₃NH₃FeCl₄ (MAFeCl₄) for optoelectronic applications. The single crystal diffraction data are assigned to the orthorhombic MAFeCl₄ (Pnma space group), with parameters a = 11.453 (5) Å, b = 7.332 (3) Å, c = 10.107 (5) Å, α = 90.000, β = 90.000, and γ = 90.000. The band gap of MAFeCl₄ is approximately 2.15 eV. Moreover, three-emission luminescence (398, 432 and 664 nm) was observed. To the best of our knowledge, this is the first study involving the investigation of the structure, adsorption properties and photoelectric behavior of MAFeCl₄. A low cost photodetector based on the MAFeCl₄ thin film is efficient under different monochromatic light from 330 nm to 410 nm with different chopping frequencies (1.33 Hz to 40 Hz). The photoelectric conversion efficiency based on FTO/TiO₂/MAFeCl₄/carbon electrode device reaches 0.054% (V_oc = 319 mV, J_sc = 0.375 mA cm⁻², and fill factor = 0.45) under AM1.5, 100 mW cm⁻² simulated illumination. Our findings will attract attention from the magnetic, piezoelectric and photoelectronic research fields.

We prepare earth-abundant and environmentally friendly organic–inorganic hybrid tetrachloroferrate salt CH₃NH₃FeCl₄ (MAFeCl₄) for optoelectronic applications.     

Thermal and structural properties,and molecular dynamics in organic–inorganic hybrid perovskite (C2H5NH3)2ZnCl4

The thermal and structural properties and molecular dynamics of layered perovskite-type (C₂H₅NH₃)₂ZnCl₄ are investigated by differential scanning calorimetry, thermogravimetric analysis, and magic angle spinning nuclear magnetic resonance spectroscopy. The thermal properties and phase transitions are studied. Additionally, the Bloembergen–Purcell–Pound (BPP) curves for the ¹H spin–lattice relaxation time T_1ρ in the C₂H₅NH₃ cation and for the ¹³C T_1ρ in C₂H₅ are shown to have minima as a function of inverse temperature. This observation implies that these curves represent the rotational motions of ¹H and ¹³C in the C₂H₅NH₃ cation. The activation energies for ¹H and ¹³C in the C₂H₅NH₃ cation are obtained; the molecular motion of ¹H is enhanced at the C-end and N-end of the organic cation, and that at the carbons of the main chain is not as free as that for protons at the C-end and N-end.

The thermal and structural properties and molecular dynamics of layered perovskite-type (C₂H₅NH₃)₂ZnCl₄ are investigated by DSC, TGA, and MAS NMR spectroscopy.     

Crystal structures,phase transitions,and nuclear magnetic resonance of organic–inorganic hybrid [NH2(CH3)2]2ZnBr4 crystals

Organic–inorganic hybrid [NH₂(CH₃)₂]₂ZnBr₄ crystals were grown via slow evaporation, and their monoclinic structure was determined using single-crystal X-ray diffraction (XRD). The two phase transition temperatures at 401 K (T_C1) and 436 K (T_C2) were defined using differential scanning calorimetry and powder XRD. In the nuclear magnetic resonance spectra, a small change was observed in the ¹H chemical shifts for NH₂, ¹³C chemical shifts for CH₃, and ¹⁴N resonance frequency for NH₂ near T_C1. ¹H spin-lattice relaxation times T_1ρ and ¹³C T_1ρ for NH₂ and CH₃, respectively, rapidly decreased near T_C1, suggesting that energy was easily transferred. NH₂ in the [NH₂(CH₃)₂]⁺ cation was significantly influenced by the surrounding environments of ¹H and ¹⁴N, indicating a change in the N–H⋯Br hydrogen bond with the coordination geometry of the ZnBr₄ anion. These fundamental properties open efficient avenues for the development of organic–inorganic hybrids, thus qualifying them for practical applications.

Thermal ellipsoid plot (50% probability) for the [NH₂(CH₃)₂]₂ ZnBr₄ structure at 300 K.     

Sulfonic acid functionalized metal–organic framework (S-IRMOF-3): a novel catalyst for sustainable approach towards the synthesis of acrylonitriles

A sulfonic acid functionalized metal–organic framework (S-IRMOF-3) has been synthesized by dropwise addition of chlorosulfonic acid (0.5 mL) in IRMOF-3 (1 g) containing 20 mL of CHCl₃ at 0 °C under simple stirring. The catalyst was applied in Knoevenagel condensation of various aromatic and hetero-aromatic aldehydes forming acrylonitrile derivatives. The catalyst was characterized thoroughly by using FT-IR, XRD, ¹³C MAS NMR, SEM, EDX, elemental mapping, TEM, BET, NH₃-TPD and TGA/DTA techniques. The presence of characteristic bands at 1694 cm⁻¹, 1254–769 cm⁻¹ and 1033 cm⁻¹ in the FT-IR spectrum, 2θ ≃ 6.7° and 9.8° in the XRD pattern and δ = 31.79, 39.55, 129.61, 131.46 (4C, CH), 133.54, 140.07 (2C), 167.71, 171.47 ppm (2C, 2C O) in the solid state ¹³C MAS NMR spectrum confirmed the successful formation of catalyst. This new eco-friendly approach resulted in a significant improvement in the synthetic efficiency (90–96% yield), high product purity, and minimizing the production of chemical wastes without using highly toxic reagents for the synthesis of acrylonitriles with selectivity for (Z)-isomer. Steric interactions seem to have an influence on the control of the Z-configurational isomers. By performing DFT calculations, it was found that the (Z)-isomer 3a is stabilized by 1.64 kcal mol⁻¹ more than the (E)-isomer. The catalyst could be reused for five consecutive cycles without substantial loss in catalytic activity.

Sulfonic acid functionalized metal–organic framework (S-IRMOF-3) as an efficient heterogeneous catalyst has been synthesized and employed for sustainable approach towards the synthesis of acrylonitriles in high yield and shorter reaction time period.     

Facile solvothermal synthesis of a MIL-47(V) metal–organic framework for a high-performance Epoxy/MOF coating with improved anticorrosion properties

The vanadium-based metal–organic framework MIL-47 distinguishes itself among other MOFs for its distinctive structure and unique properties (e.g., flexible structure, high thermal stability, and high surface area). The synthesis of MIL-47 has been reported from various metal precursors, including vanadium(iii) chloride (VCl₃) as a rich source of metal ions. Attempts have been made to include other starting materials, a step forward towards large-scale production. Synthesis from various solid materials is encouraged, seeking an economic and greener approach. In this study, vanadium pentoxide (V₂O₅), a readily abundant low-cost and thermodynamically stable metal source, was used to synthesize the MIL-47(V) framework via a facile solvothermal route. This precursor provides a controllable rate of metal ion production depending on the applied reaction conditions. In our method, the synthesis took place at a low temperature and reaction time (180 °C for 20 h, instead of 220 °C for 72 h), yielding MIL-47 microrods. Moreover, among its unique properties, the metal centers of MIL-47 oxidize under the influence of thermal or chemical treatments, preserving the framework structure. This unusual character is not commonly witnessed in comparable MOF structures. This property can be leveraged in anti-corrosion applications, whereby a redox reaction would sacrifice the framework components, protecting the metal in contact. However, the chemical stability of MIL-47 is doubted against a corrosive medium. Thus, an epoxy coating with 10 wt% MOF loading was incorporated in our investigation to extend the aluminum alloy (AA2024) surface protection for prolonged exposure duration. The uniformity of distribution of the prepared MOF within the epoxy matrix was confirmed using SEM/EDX. Electrochemical impedance spectroscopy (EIS) was used to evaluate the corrosion performance of the coated samples. The results showed that the inclusion of V-MOF offers extended corrosion prevention, over 60 days, for the AA2024 alloy against artificial seawater. The neat epoxy coating could not prevent the corrosion of AA2024 over two weeks of immersion, whereby pitting corrosion was clearly observed. The V-MOF could induce a series of redox reactions leading to the precipitation of vanadium on the cathodic sites of metal surfaces.

The well-known MIL-47(V) metal–organic framework was synthesized solvothermally with high quality using V₂O₅ as a precursor. Applying the MOF particles in an epoxy coating resulted in an improved anticorrosion protective barrier for the AA2024 substrate against a chloride-rich environment.     

From metal–organic framework to morphology- and size-controlled 3D mesoporous Cr2O3 toward a high surface area and enhanced volatile organic compound oxidation catalyst

Morphology- and size-controlled 3D mesoporous Cr₂O₃ have always been a research hotspot due to their wide applications. Herein, we for the first time report that the carbonized Cr-MOFs can ignite spontaneously at room temperature and form the corresponding 3D mesoporous Cr₂O₃ with high specific surface areas (219.25 to 303.44 cm² g⁻¹). More importantly, the shape and size of 3D mesoporous Cr₂O₃ can be well controlled by a facile adjustment of the Cr-MOF synthesis conditions. Furthermore, these materials showed an exceptionally high catalytic performance in formaldehyde oxidation. These results are predicted to offer a novel method in the design and synthesis of 3D porous Cr₂O₃.

Morphology- and size-controlled 3D mesoporous Cr₂O₃ have always been a research hotspot due to their wide applications.     

Organic–inorganic hybrid [NH3(CH2)6NH3]ZnBr4 crystal: structural characterization,phase transitions,thermal properties,and structural dynamics

Organic–inorganic hybrid [NH₃(CH₂)₆NH₃]ZnBr₄ crystals were prepared by slow evaporation; the crystals had a monoclinic structure with space group P2₁/c and lattice constants a = 7.7833 Å, b = 14.5312 Å, c = 13.2396 Å, β = 90.8650°, and Z = 4. They underwent two phase transitions, at 370 K (T_C1) and 430 K (T_C2), as confirmed by powder X-ray diffraction patterns at various temperatures; the crystals were stable up to 600 K. The nuclear magnetic resonance spectra, obtained using the magic-angle spinning method, demonstrated changes in the ¹H and ¹³C chemical shifts were observed near T_C1, indicating changing structural environments around ¹H and ¹³C. The spin–lattice relaxation time, T_1ρ, increased rapidly near T_C1 suggesting very large energy transfer, as indicated by a large thermal displacement around the ¹³C atoms of the cation. However, the environments of ¹H, ¹⁴N, and C1 located close to NH₃ in the [NH₃(CH₂)₆NH₃] cation did not influence it significantly, indicating a minor change in the N–H⋯Br hydrogen bond with the coordination geometry of the ZnBr₄ anion. We believe that the information on the physiochemical properties and thermal stability of [NH₃(CH₂)₆NH₃]ZnBr₄, as discussed in this study, would be key to exploring its application in stable, environment friendly solar cells.

Organic–inorganic hybrid [NH₃(CH₂)₆NH₃]ZnBr₄ crystals were prepared by slow evaporation; the crystals had a monoclinic structure with space group P2₁/c and lattice constants a = 7.7833 Å, b = 14.5312 Å, c = 13.2396 Å, β = 90.8650°, and Z = 4.     

Unique and efficient adsorbents for highly selective and reverse adsorption and separation of dyes via the introduction of SO3H functional groups into a metal–organic framework

In this study, an unsaturated Cu-based MOF, HKUST (Cu₃(BTC)₂), was fabricated and modified with sulfonate groups in two steps, leading to the construction of a novel sulfo-functionalized MOF. The prepared framework was utilized in the adsorption and separation of various organic dyes (MB, Er, FS, and MV). The adsorption process represented intriguing features due to the introduction of the SO₃H functional groups into the framework. Such an attractive feature has rarely been depicted in previous works. In addition to the substantially increased adsorption capacity of the modified framework compared with that of pristine MOF, a reverse and selective phenomenon was perceived in the cases of FS and MV. The sulfo-functionalized MOF could adsorb MV with high adsorption capacity but barely adsorbed FS, and the opposite condition was observed for pristine MOF. In addition, the prepared framework showed high selectivity in a mixed solution of dyes. On the other hand, the modified framework had no role in the first step of the adsorption and separation process and showed the same behavior as pristine MOF. Furthermore, the sulfonate functional groups could not be directly incorporated into HKUST. The experimental data followed the pseudo-second-order kinetics and the Langmuir isotherm model. Thermodynamic studies demonstrated an exothermic spontaneous mechanism for the dye adsorption process. The prepared adsorbents were capable of being recycled for four sequential cycles. Hereupon, this study presents a notably efficacious approach for the reverse performance of frameworks for the dye adsorption and separation process.

A novel sulfo-functionalized MOF was utilized as an efficient adsorbent for a reversal in the removal and selective separation of dyes from contaminated water.     

Investigation of structural,electronic and magnetic properties of breathing metal–organic framework MIL-47(Mn): a first principles approach

The structural, electronic and magnetic properties of the MIL-47(Mn) metal–organic framework are investigated using first principles calculations. We find that the large-pore structure is the ground state of this material. We show that upon transition from the large-pore to the narrow-pore structure, the magnetic ground-state configuration changes from antiferromagnetic to ferromagnetic, consistent with the computed values of the intra-chain coupling constant. Furthermore, the antiferromagnetic and ferromagnetic configuration phases have intrinsically different electronic behavior: the former is semiconducting, the latter is a metal or half-metal. The change of electronic properties during breathing posits MIL-47(Mn) as a good candidate for sensing and other applications. Our calculated electronic band structure for MIL-47(Mn) presents a combination of flat dispersionless and strongly dispersive regions in the valence and conduction bands, indicative of quasi-1D electronic behavior. The spin coupling constants are obtained by mapping the total energies onto a spin Hamiltonian. The inter-chain coupling is found to be at least one order of magnitude smaller than the intra-chain coupling for both large and narrow pores. Interestingly, the intra-chain coupling changes sign and becomes five times stronger going from the large pore to the narrow pore structure. As such MIL-47(Mn) could provide unique opportunities for tunable low-dimensional magnetism in transition metal oxide systems.

The structural, electronic and magnetic properties of the MIL-47(Mn) metal–organic framework are investigated using first principles calculations.     

A pillared-layered copper(i) halide-based metal–organic framework exhibiting dual emission,and piezochromic and thermochromic properties with a large temperature-dependent emission red-shift

We report a new copper halide-based compound [Cu₆I₆Br₂C₁₆H₃₂N₄] (1) with a 3D 2-fold interpenetrated framework structure. Upon excitation at 290 nm and 350 nm, compound 1 shows dual emission at ca. 500 nm and ca. 530 nm. As the temperature decreased from 300 K down to 6 K, the luminescent properties of compound 1 show large red shifts of 120 nm and 72 nm, respectively.

A pillared-layered copper(i) halide-based metal–organic framework [Cu₆I₆Br₂C₁₆H₃₂N₄] exhibiting dual emission, and piezochromic and thermochromic properties with a large temperature-dependent emission red-shift is reported.     

Highly efficient and rapid removal of arsenic(iii) from aqueous solutions by nanoscale zero-valent iron supported on a zirconium 1,4-dicarboxybenzene metal–organic framework (UiO-66 MOF)

A zirconium 1,4-dicarboxybenzene metal–organic framework (UiO-66 MOF) was successfully used as a template to enhance the distribution and activity of nanoscale zero-valent iron (NZVI). MOF-NZVI showed good anti-interference ability to co-existing ions (Ca²⁺, Mn²⁺, Cu²⁺, H₂PO₄⁻ and SO₄²⁻) and organic acids (oxalic acid and citric acid). SEM and TEM analyses indicated that the MOF as a support efficiently prevent NZVI from aggregation for quick and effective removal of As(iii). Through the non-linear least-squares (NLLS) adjustment, As(iii) removal by MOF-NZVI could be well fitted by pseudo first and second order reaction kinetics, as well as the Freundlich isotherm. FTIR, XRD and XPS results verified that NZVI and iron oxyhydroxides (Fe₃O₄, γ-Fe₂O₃, γ-FeOOH and α-FeOOH) might be responsible for the effective removal of As(iii) and its oxidized product As(v) with an adsorption capacity of 360.6 mg As per g NZVI through chemical oxidation and physical adsorption. This work indicates that MOF-NZVI with good reusability and high efficiency is promising for application in As(iii)-polluted wastewater treatment.

A zirconium 1,4-dicarboxybenzene metal–organic framework (UiO-66 MOF) was successfully used as a template to enhance the distribution and activity of nanoscale zero-valent iron (NZVI).     

The fabrication of a novel polyacrylonitrile/reduced graphene oxide-amino-halloysite/bimetallic metal–organic framework electrospun nanofiber adsorbent for the ultrasonic-assisted thin-film microextraction of fatty acid methyl esters in dairy products with gas chromatography-flame ionization detection

In this work, electrospun polyacrylonitrile/reduced graphene oxide-amino-halloysite/bimetallic metal–organic framework (PAN/rGO-amino-HNT/Co_0.5Zn_0.5(MeIm)₂) nanofiber film was synthesized and investigated as a novel adsorbent for the ultrasonic-assisted thin-film microextraction (UA-TFME) of fatty acid methyl esters (FAMEs), including palmitic methyl ester (PAME), oleic methyl ester (OAME), stearic methyl ester (SAME), and linoleic methyl ester (LAME), from dairy products. The hybrid nanocomposite was obtained via bonding halloysite nanotubes to reduced graphene oxide, followed by loading with bimetallic metal–organic frameworks. The determination of FAMEs with nanofiber film was performed in two stages of desorption and absorption where, initially, the analytes were adsorbed onto the nanofiber film and then desorbed with organic solvent. In this study, ultrasound was used for both the adsorption and desorption stages. The advantages of ultrasonication are extensive, overcoming the shortcomings of conventional techniques in terms of energy consumption and solvent use, allowing a shorter treatment time with a low cost of implementation. Based on PAN/rGO-amino-HNT/Co_0.5Zn_0.5(MeIm)₂ thin film, a microextraction-gas chromatography-flame ionization detection (TFME-GC-FID) method was developed. Experimental parameters affecting the extraction and desorption steps were optimized. The desorption parameters, including desorption time and the properties of the desorption solvent, were investigated one factor at a time. Then, effective parameters in the adsorption step were optimized using a Box–Behnken design and Design-Expert 7 software. Under the optimal conditions, the method detection limits (S/N = 3) were in the range of 0.03–0.06 μg L⁻¹ and the limits of quantification (S/N = 10) were within 0.11–0.23 μg L⁻¹. The relative standard deviations for intra-day and inter-day precision were 2.4–4.7% and 2.6–3.4%, respectively. In the present work, the UA-TFME method was successfully applied for the quantification of fatty acid methyl esters in dairy products (milk, yogurt, cheese, yogurt soda and butter samples) for the first time. The fatty acids were transesterified using standard procedures and were subjected to UA-TFME treatment prior to GC-FID determination. The developed method possesses the advantages of simplicity, rapidity, cost-effectiveness, sensitivity, and non-invasiveness.

Electrospun polyacrylonitrile/reduced graphene oxide-amino-halloysite/bimetallic metal–organic framework nanofiber film was synthesized and successfully applied to the ultrasonic-assisted thin-film microextraction (UA-TFME) of fatty acid methyl esters from dairy products.     

Polyoxometalate supported on a magnetic Fe3O4/MIL-88A rod-like nanocomposite as an adsorbent for the removal of ciprofloxacin,tetracycline and cationic organic dyes from aqueous solutions

In this work, a magnetic H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) rod-like nanocomposite as a stable and effective ternary adsorbent was fabricated by the hydrothermal method and utilized for the removal of ciprofloxacin (CIP), tetracycline (TC) and organic dyes from aqueous solution. Characterization of the magnetic nanocomposite was accomplished by FT-IR, XRD, Raman spectroscopy, SEM, EDX, TEM, VSM, BET specific surface area and zeta potential analyses. The influencing factors on the adsorption potency of the H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) rod-like nanocomposite including initial dye concentration, temperature and adsorbent dose were studied. The maximum adsorption capacities of H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) for TC and CIP were 370.37 mg g⁻¹ and 333.33 mg g⁻¹ at 25 °C, respectively. In addition, the H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) adsorbent had high regeneration and reusability capacity after four cycles. In addition, the adsorbent was recovered through magnetic decantation and reused for three consecutive cycles without a considerable reduction in its performance. The adsorption mechanism was mainly ascribed to electrostatic and π–π interactions. According to these results, H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) can act as a reusable effective adsorbent for the fast elimination of tetracycline (TC), ciprofloxacin (CIP) and cationic dyes from aqueous solutions.

A magnetic Fe₃O₄/MIL-88A Fe rod-like nanocomposite containing H₃PW₁₂O₄₀ was fabricated and applied as a new magnetically recoverable ternary adsorbent to remove antibiotics and dyes from aqueous solutions.