A Multi‐responsive Regenerable Europium–Organic Framework Luminescent Sensor for Fe3+, CrVI Anions,and Picric Acid

A novel luminescent microporous lanthanide metal–organic framework (Ln‐MOF) based on a urea‐containing ligand has been successfully assembled. Structural analysis revealed that the framework features two types of 1D channels, with urea N?H bonds projecting into the pores. Luminescence studies have revealed that the Ln‐MOF exhibits high sensitivity, good selectivity, and a fast luminescence quenching response towards Fe³⁺, Cr^VI anions, and picric acid. In particular, in the detection of Cr₂O₇^2? and picric acid, the Ln‐MOF can be simply and quickly regenerated, thus exhibiting excellent recyclability. To the best of our knowledge, this is the first example of a multi‐responsive luminescent Ln‐MOF sensor for Fe³⁺, Cr^VI anions, and picric acid based on a urea derivative. This Ln‐MOF may potentially be used as a multi‐responsive regenerable luminescent sensor for the quantitative detection of toxic and harmful substances.     

Magnetic Nitrogen-Doped Porous Carbon Nanocomposite for Pb(II) Adsorption from Aqueous Solution

We report in the present study the in situ formation of magnetic nanoparticles (Fe₃O₄ or Fe) within porous N-doped carbon (Fe₃O₄/N@C) via simple impregnation, polymerization, and calcination sequentially. The synthesized nanocomposite structural properties were investigated using different techniques showing its good construction. The formed nanocomposite showed a saturation magnetization (M_s) of 23.0 emu g⁻¹ due to the implanted magnetic nanoparticles and high surface area from the porous N-doped carbon. The nanocomposite was formed as graphite-type layers. The well-synthesized nanocomposite showed a high adsorption affinity toward Pb²⁺ toxic ions. The nanosorbent showed a maximum adsorption capacity of 250.0 mg/g toward the Pb²⁺ metallic ions at pH of 5.5, initial Pb²⁺ concentration of 180.0 mg/L, and room temperature. Due to its superparamagnetic characteristics, an external magnet was used for the fast separation of the nanocomposite. This enabled the study of the nanocomposite reusability toward Pb²⁺ ions, showing good chemical stability even after six cycles. Subsequently, Fe₃O₄/N@C nanocomposite was shown to have excellent efficiency for the removal of toxic Pb²⁺ ions from water.     

Novel Fe3O4/hydroxyapatite/β‐cyclodextrin nanocomposite adsorbent: Synthesis and application in heavy metal removal from aqueous solution

The increased global concern on environmental protection has made researchers focus their attention on new and more efficient methods of pollutant removal. In this research, novel nanocomposite adsorbents,i.e., magnetic hydroxyapatite (Fe₃O₄@HA) and magnetic hydroxyapatite β‐cyclodextrin (Fe₃O₄@HA‐CD) were synthesized and used for heavy metal removal. The adsorbents were characterized by FTIR, XRD, TGA, VSM, and SEM. In order to investigate the effect of β‐cyclodextrin (β‐CD) removal efficiency, adsorption results of nine metal ions were compared for both adsorbents. β‐CD showed the most increasing effect for Cd²⁺ and Cu²⁺ removal, so these two ions were selected for further studies. The effect of diverse parameters including pH, contact time, initial metal ion concentration and adsorbent dosage on the adsorption process was discussed. The optimum pH was 6 and adsorption equilibrium was achieved after 1 hr. Adsorption kinetic data were well fitted by pseudo‐second‐order model proposing that metal ions were adsorbed via chemical reaction. Adsorption isotherm was best described by the Langmuir model, and maximum adsorption capacity for Cd²⁺ and Cu²⁺ was 100.00 and 66.66 (mg/g), respectively. Desorption experiment was also done, and the most efficient eluent used for desorption of metal ions was EDTA (0.001 M) with 91% and 88% of Cd²⁺ and Cu²⁺ release, respectively. Recyclability studies also showed a 19% decrease in the adsorption capacity of the adsorbent after five cycles of regeneration. Therefore, the synthesized adsorbents were recognized as potential candidates for heavy metal adsorption applications.     

Simultaneous removal of Cu2+ and Cr3+ ions from aqueous solution based on Complexation with Eriochrome cyanine‐R and derivative spectrophotometric method

TiO₂ nanoparticles deposited on activated carbon (TiO₂–NP–AC) was prepared and characterized by XRD and SEM analysis. Subsequently, simultaneous ultrasound‐assisted adsorption of Cu²⁺ and Cr³⁺ ions onto TiO₂‐NPs‐AC after complexation via eriochrome cyanine R (ECR) has been investigated with UV–Vis and FAA spectrophotometer. Spectra overlapping of the ECR‐Cu and ECR‐Cr complex was resolve by derivative spectrophotometric technique. The effects of various parameters such as initial Cu²⁺ (A) and Cr³⁺ (B) ions concentrations, TiO₂‐NPs‐AC mass (C), sonication time (D) and pH (E) on the removal percentage were investigated and optimized by central composite design (CCD). The optimize conditions were set as: 4.21 min, 0.019 mg, 20.02 and 13.22 mg L^?1 and 6.63 for sonication time, TiO₂–NP–AC mass, initial Cr³⁺ and Cu²⁺ ions concentration and pH, respectively. The experimental equilibrium data fitting to Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models show that the Langmuir model is a good and suitable model for evaluation and the actual behavior of adsorption process and maximum adsorption capacity of 105.26 and 93.46 mg g^?1 were obtained for Cu²⁺ and Cr³⁺ ions, respectively. Kinetic evaluation of experimental data showed that the adsorption processes followed well pseudo second order and intraparticle diffusion models.     

Combining field‐amplified sample stacking with moving reaction boundary electrophoresis on a paper chip for the preconcentration and separation of metal ions

A common drawback of paper‐based separation devices is their poor detection limit. In this study, we combined field‐amplified sample stacking with moving reaction boundary electrophoresis on a paper chip with six array channels for the parallel separation and concentration of multiple samples. With a new hyphenated technique, the brown I₂ from the Fe³⁺/I⁻ oxidation–reduction reaction emerged near the boundary between the dilute ethylene diamine tetraacetic acid and potassium iodide and highly concentrated KCl solutions. For the separation and concentration of three components, Cr³⁺, Cu²⁺, and Fe³⁺, the Fe³⁺ detection limit was improved at least 266‐fold by comparing the hyphenated technique with moving reaction boundary electrophoresis. The detection limit of Fe³⁺ was found to be as low as 0.34 ng (20 μM) on the paper chip. We also demonstrated the analysis of a real sample of four metal ions, with detection limits as follows: 0.16 μg Cr³⁺, 1.5 μg Ni²⁺, 0.64 μg Cu²⁺, and 1.5 μg Co²⁺. The synergy of field‐amplified sample stacking and moving reaction boundary electrophoresis in the micron paper‐based array channels dramatically improved the detection limit and throughput of paper‐based electrophoresis.     

Laser-induced luminescence of model Fe/Al2O3 and Cr/Al2O3 catalysts

The laser-induced luminescence of Cr³⁺ impurity ions in model Fe/Al₂O₃ and Cr/Al₂O₃ catalysts with different calcination temperatures was studied. It was found that an additional luminescence band at 770 nm appeared in the luminescence spectra of low-temperature samples as a result of the interaction of octahedrally coordinated Cr³⁺ ions with Fe³⁺ impurity ions. In the θ-Al₂O₃ phase with a concentration of Cr³⁺ ions higher than 0.1 wt %, the interaction of the Cr³⁺-Cr³⁺ ion pairs in the immediate surroundings resulted in the appearance of N _θ lines due to the splitting of R _θ lines. The differences of these lines from the N _α lines of α-Al₂O₃ were related to the individuality of the crystal lattice of the θ phase and the coordination of Cr³⁺ impurity ions in the immediate surroundings, which is different from that in the α phase. Based on the laser-induced luminescence spectroscopic data, it was found that regions with a local Cr³⁺ concentration higher than the average Cr³⁺ concentration in the bulk of a catalyst by one order of magnitude were formed in the α-Al₂O₃-Fe₂O₃ system with the bulk Fe and Cr concentrations of 2.5 and 0.04 wt %, respectively, which was calcined at 1220°C, as a result of the diffusion of chromium and iron ions.     

A serial of 2D Co-Zn isomorphous metal–organic frameworks for photodegradation and luminescent detection properties

A series of 2D isomorphous MOFs [M (HBTC)(BMIOPE)·DMF·H₂O]_n (M = Zn ( 1 ), Zn_0.7Co_0.3 ( 2 ), Zn_0.5Co_0.5 ( 3 ), Zn_0.3Co_0.7 ( 4 ), Co ( 5 ), H₃BTC = 1,3,5-benzenetricarboxylic acid, BMIOPE = 4,4′-bis(2-methylimidazol-1-yl)diphenyl ether) were synthesized to investigate the correction between the center metal ions and the photocatalytic behaviors. The photocatalytic results show that with the increase of Co²⁺ content, the photodegradation properties are continuously improved from 1 to 5 , which fully indicate that only changing metal ions could regulate the photodegradation properties. In detail, 1 is an inactive photocatalyst to degrade methylene blue (MB), while 5 exhibits preeminent photocatalytic properties under visible light irradiation. Moreover, 1 shows good selective sensing toward Fe³⁺, Cr³⁺, UO₂²⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions in aqueous solution. To the best of our knowledge, 1 is the first MOF example for the optical detection of Fe³⁺, Cr³⁺, UO₂²⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions in aqueous solution.     

Bulgarian natural diatomites: modification and characterization

Natural Bulgarian diatomite modified by oxidation with sulfuric acid and H₂O₂ or by coating with manganese oxide was characterized considering its chemical composition, surface area, pore volume, and structure. Modified diatomites displayed larger surface area and pore volumes in comparison with untreated natural diatomite, which favored their sorption behavior. Sorption properties of diatomites towards Fe³⁺, Pb²⁺, Cu²⁺, Cd²⁺, Mn²⁺, Ni²⁺, Co²⁺, Cr³⁺, Pd²⁺, Ca²⁺, and Mg²⁺ were investigated and their sorption capacities were determined. Sorption properties of manganese oxide-modified diatomite were superior to those of diatomite modified by oxidation. Owing to its high sorption capacity towards Co²⁺, Ni²⁺, Pb²⁺, Cr³⁺, Fe²⁺, Cu²⁺, and Cd²⁺, the manganese oxide-modified diatomite is a promising low-cost sorbent for selective removal of milligram amounts of these toxic metal ions from contaminated water.     

The MOF+ Technique: A Significant Synergic Effect Enables High Performance Chromate Removal

A significant synergic effect between a metal–organic framework (MOF) and Fe₂SO₄, the so‐called MOF⁺ technique, is exploited for the first time to remove toxic chromate from aqueous solutions. The results show that relative to the pristine MOF samples (no detectable chromate removal), the MOF⁺ method enables super performance, giving a 796 Cr mg g⁻¹ adsorption capacity. The value is almost eight‐fold higher than the best value of established MOF adsorbents, and the highest value of all reported porous adsorbents for such use. The adsorption mechanism, unlike the anion‐exchange process that dominates chromate removal in all other MOF adsorbents, as unveiled by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), is due to the surface formation of Fe_0.75Cr_0.25(OH)₃ nanospheres on the MOF samples.     

Heavy Metal Removal from Synthetic Solutions with Magnetic Beads Under Magnetic Field

The aim of this study is to prepare magnetic beads which can be used for the removal of heavy metal ions from synthetic solutions. Magnetic poly(ethylene glycol dimethacrylate‐vinyl imidazole) [m‐poly(EGDMA‐VIM)] beads were produced by suspension polymerization in the presence of magnetite Fe₃O₄ nano‐powder. The specific surface area of the m‐poly(EGDMA‐VIM) beads was found to be 63.1 m²/g with a size range of 150–200 µm in diameter and the swelling ratio was 85%. The average Fe₃O₄ content of the resulting m‐poly(EGDMA‐VIM) beads was 12.4%. The maximum binding capacities of the m‐poly(EGDMA‐VIM) beads were 32.4 mg/g for Cu²⁺, 45.8 mg/g for Zn²⁺, 84.2 mg/g for Cd²⁺and 134.5 mg/g for Pb²⁺. The affinity order on mass basis is Pb²⁺>Cd²⁺>Zn²⁺>Cu²⁺. Equilibrium data agreed well with the Langmuir model. pH significantly affected the binding capacity of the magnetic beads. Binding of heavy metal ions from synthetic wastewater was also studied. The binding capacities were 26.2 mg/g for Cu²⁺, 33.7 mg/g for Zn²⁺, 54.7 mg/g for Cd²⁺ and 108.4 mg/g for Pb²⁺. The magnetic beads could be regenerated up to about 97% by treating with 0.1 M HNO₃. These features make m‐poly(EGDMA‐VIM) beads a potential candidate for support of heavy metal removal under magnetic field.     

Zn‐ and Cd‐based Coordination Polymers Offering H‐Bonding Cavities: Highly Selective Sensing of S2O72− and Fe3+ Ions

We present two Zn^II‐ and Cd^II‐based coordination polymers (CPs), L ‐Zn and L ‐Cd , offering H‐bonding‐based cavities of varying dimensions. Both CPs were used for the highly selective detection of S₂O₇^2? and Fe³⁺ ions where H‐bonding based cavities played an important role. Fluorescence quenching, competitive binding studies and binding parameters substantiated significant recognition of S₂O₇^2? and Fe³⁺ ions by both CPs.     

Extension of the “1201” Family to Strontium-Rich Chromite and Ferrite, Bi0.4Sr2.5Cr1.1O4.9 and Bi0.4Sr2.5Fe1.1O5

Two new Sr-rich “1201”-type oxides, Bi_0.4Sr_2.5Cr_1.1O_4.9 and Bi_0.4Sr_2.5Fe_1.1O₅ have been synthesized. These compounds, intergrowths of double rock-salt layers with single perovskite layers, show a 1:1 ordering between (Bi,M) and Sr species within the intermediate rock-salt layer [Bi_0.4M_0.1Sr_0.5O]. The XANES study shows that bismuth is mainly trivalent, whereas iron is mixed valent containing 50% Fe³⁺ and 50% Fe⁴⁺ (also confirmed by Mössbauer), and chromium could be a mixture of Cr³⁺ and Cr⁶⁺ sitting in the perovskite and rock-salt-type sites, respectively. Both compounds exhibit antiferromagnetic interactions. The Cr-phase is a strong insulator, whereas the Fe-phase exhibits a semi-conductor-like resistivity whose value at room temperature is close to that of isotypic cobaltite.     

Cr3+:SrGa12O19: A Broadband Near‐Infrared Long‐Persistent Phosphor

Cr³⁺‐doped SrGa₁₂O₁₉ is demonstrated to be a broadband near‐infrared (650–950 nm) long‐persistent phosphor whose luminescence can last for more than 2 h after ultraviolet irradiation is stopped. Detailed analysis of the photoluminescence and thermoluminescence spectra and of the persistent decay behavior of the Cr³⁺‐doped SrGa₁₂O₁₉ samples indicate that the persistent energy transfer from the SrGa₁₂O₁₉ host to the Cr³⁺ ions and the filling and release of electrons into and from the shallow and deep traps through the conduction band is responsible for the long‐persistent phosphorescence.     

Preparation and properties of the systems Fe2−xCrxWO6, Fe2−xRhxWO6, and Cr2−xRhxWO6

Solid solutions of the end members Fe₂WO₆, Cr₂WO₆, and Rh₂WO₆ have been prepared and their crystallographic and magnetic properties studied. All solid solutions crystallize with the trirutile structure, and their magnetic behavior is characterized by the existence of antiferromagnetic interactions and effective molar Curie constants corresponding to those expected from contributions of the spinonly moments of high-spin Fe³⁺, Cr³⁺, and diamagnetic low-spin Rh³⁺ ions. Fe₂WO₆ crystallizes with the tri-α-PbO₂ structure and is antiferromagnetic and conducting. The random rutile Rh₂WO₆ is conducting, and the difference between its magnetic and electric properties and those of the inverse trirutile Cr₂WO₆ are discussed in terms of possible interactions between Cr³⁺(3d) or Rh³⁺(4d) orbitals and W⁶⁺(5d) orbitals.     

Application of nano-scale zero-valent iron adsorbed on magnetite nanoparticles for removal of carbon tetrachloride: Products and degradation pathway

Nano-scale zero-valent iron (nZVI) attached to Fe₃O₄ nanoparticles (Fe⁰@Fe₃O₄), which has better dispersibility and a larger specific surface area than the nanoparticles alone, were prepared and applied to the reductive dechlorination of carbon tetrachloride (CT). CT removal efficiencies by Fe⁰@Fe₃O₄ composites with different ratios of the two components were compared. Under optimum conditions, when the Fe⁰/Fe₃O₄ ratio was 1:2, almost no CT was detected after 50 min and it took only about 30 min to reach a removal efficiency of 90%, compared with 120 min for an Fe⁰/Fe₃O₄ ratio of 1:4. An increase in the amount of nZVI in the catalyst effectively improved the removal of CT and accelerated the reaction rate. Chloroform was the main product. Compared with Fe₃O₄ alone, a significant increase in the solution concentrations of ferrous and ferric ions occurred in the Fe⁰@Fe₃O₄ system: both Fe²⁺ and Fe³⁺ reached their maximum concentrations at 60 min and then tended to decline over the next 60 min. The increase in Fe²⁺ concentration was attributed to the reaction between nZVI and CT, which produces ferrous ions when electrons transfer from Fe⁰ to organic chlorides. Synergistic effects between the composite constituents promoted the relative rates of mass transfer to reactive sites and Fe²⁺ generated in solution facilitated the reduction of chlorinated organic pollutants by magnetite. Thus, Fe⁰@Fe₃O₄ nanoparticles effectively achieved reductive dechlorination of CT and provide an improved nZVI catalyst for the remediation of chlorinated organic compounds.     

Magnetocaloric Properties of Heterometallic 3d–Gd Complexes Based on the [Gd(oda)3]3− Metalloligand

A series of heterometallic 3d–Gd³⁺ complexes based on a lanthanide metalloligand, [M(H₂O)₆][Gd(oda)₃] ? 3 H₂O [M=Cr³⁺ ( 1‐Cr )] (H₂oda=2,2′‐oxydiacetic acid), [M(H₂O)₆][MGd(oda)₃]₂ ? 3 H₂O [M=Mn²⁺ ( 2‐Mn ), Fe²⁺ ( 2‐Fe ) and Co²⁺ ( 2‐Co )], and [M₃Gd₂(oda)₆(H₂O)₆] ? 12 H₂O [M=Ni²⁺ ( 3‐Ni ), Cu²⁺ ( 3‐Cu ), and Zn²⁺ ( 3‐Zn )], are reported. Magnetic and heat‐capacity studies revealed a significant impact on the magnetocaloric effect depending on the anisotropy of the 3d transition metal ions, as confirmed by comparison of the observed maximum values of ?ΔS_m between complexes 2‐Co and 1‐Cr . In these two complexes, the 3d metal ions have the same spin (S=3/2 for Co²⁺ and Cr³⁺ ions), and the theoretical calculation suggested a larger ?ΔS_m value for 2‐Co (47.8 J K^?1 kg^?1) than 1‐Cr (37.5 J K^?1 kg^?1); however, the significant anisotropy of Co²⁺ ions in 2‐Co , which can result in smaller effective spins, gives a smaller value of ?ΔS_m for 2‐Co (32.2 J K^?1 kg^?1) than for 1‐Cr (35.4 J K^?1 kg^?1) at ΔH=9 T.     

Silver,iron, and nickel immobilized on hydroxyapatite‐core‐shell γ‐Fe2O3 MNPs catalyzed one‐pot five‐component reactions for the synthesis of tetrahydropyridines by tandem condensation of amines,aldehydes, and methyl acetoacetate

In this study, Ag, Ni²⁺, and Fe²⁺ immobilized on hydroxyapatite‐core‐shell γ‐Fe₂O₃ nanoparticles (γ‐Fe₂O₃@HAp‐Ag, γ‐Fe₂O₃@HAp‐Ni²⁺, and γ‐Fe₂O₃@HAp‐Fe²⁺) as a new and reusable Lewis acid magnetic nanocatalyst was successfully synthesized and reported for an atom economic, extremely facile, and environmentally benign procedure for the synthesis of highly functionalized tetrahydropyridines derivatives 4a‐t is described by one‐pot five‐component reaction of 2 equiv of aldehydes 1 , 2 equiv of amines 2 , and 1 equiv of methyl acetoacetate 3 in EtOH at room temperature in good to high yields and short reaction time. The presented methodology offers several advantages such as easy work‐up procedure, reusability of the magnetic nanocatalyst, operational simplicity, green synthesis avoiding toxic reagents and solvent, mild reaction conditions, and no tedious column chromatographic separation.     

A novel spinel coating on cobalt‐based Superalloy GH605 via an in‐situ oxidation approach

Cr‐Mn‐O spinel coating was prepared on the surface of cobalt‐based superalloy GH605 via an in‐situ oxidation method in H₂O‐H₂ environment. The composition, morphology, and chemical value state of the oxide spinel coatings were investigated by SEM, EDS, XRD, Raman spectra, and XPS. It indicated that the morphology of coating varied with oxidation temperature, and granular surface appeared when oxidation temperature increased to 1100°C. The formed Cr‐Mn‐O spinel coating was composed of Cr₂O₃ and MnCr₂O₄, and the thickness increased significantly with oxidation temperature. In the coating, Cr element existed in the state of Cr³⁺ ions and Cr⁶⁺ ions, while Mn element only existed in the form of Mn²⁺ ions.     

Mössbauer Spectroscopy of Spinels

Soon after the discovery of the Mössbauer effect, studies were performed on spinels containing various transition metal ions (mostly Fe²⁺). This method proved very useful for investigating the local symmetry at transition metal ions. In spite of the numerous results, the correct interpretation of the complex quadrupole split spectra is still not given for numerous spinel structures. Since spectra of different shapes were measured for FeAl₂O₄ and FeCr₂O₄ by different authors, we performed new measurements on these spinels. The results on FeAl₂O₄ showed that the statistical distribution of another kind of ions in the positions A may influence the electric field gradient at the Fe²⁺ ions in the tetrahedral interstices. In FeCr₂O₄ and in the mixed Fe_0.5Mg_0.5Cr₂O₄, the electric field gradient exists at the Fe²⁺ ions at room temperature indicating that the degeneracy of the orbital doublet of the Fe²⁺ is removed.     

Magnetic Silica‐Coated Sub‐Microspheres with Immobilized Metal Ions for the Selective Removal of Bovine Hemoglobin from Bovine Blood

Magnetic silica‐coated magnetite (Fe₃O₄) sub‐microspheres with immobilized metal‐affinity ligands are prepared for protein adsorption. First, magnetite sub‐microspheres were synthesized by a hydrothermal method. Then silica was coated on the surface of Fe₃O₄ particles using a sol–gel method to obtain magnetic silica sub‐microspheres with core‐shell morphology. Next, the trichloro(4‐chloromethylphenyl) silane was immobilized on them, reacted with iminodiacetic acid (IDA), and charged with Cu²⁺. The obtained magnetic silica sub‐microspheres with immobilized Cu²⁺ were applied for the absorption of bovine hemoglobin (BHb) and the removal of BHb from bovine blood. The size, morphology, and magnetic properties of the resulting magnetic micro(nano) spheres were investigated by using scanning microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), and a vibrating sample magnetometer (VSM). The measurements showed that the magnetic sub‐microspheres are spherical in shape, very uniform in size with a core‐shell, and are almost superparamagnetic. The saturation magnetization of silica‐coated magnetite (Fe₃O₄) sub‐microspheres reached about 33 emu g^?1. Protein adsorption results showed that the sub‐microspheres had a high adsorption capacity for BHb (418.6 mg g^?1), low nonspecific adsorption, and good removal of BHb from bovine blood. This opens a novel route for future applications in removing abundant proteins in proteomic analysis.