Studies regarding the formation from metal nitrates and diol of NiM 2 III O4 spinels, inside a silica matrix

The present study deals with preparation and characterization of spinel mixed oxide systems NiM ₂ ^III O₄, where M^III?=?Fe^III, Cr^III. In order to obtain 50% NiFe₂O₄/50% SiO₂ and 50% NiCr₂O₄/50% SiO₂ nanocomposite, we have used a versatile route based on the thermal decomposition inside the SiO₂ matrix, of some particular precursors, coordination compounds of the involved M^II and M^III cations with dicarboxylate ligands. The ligands form in the redox reaction between metal nitrates mixture and 1,3-propanediol at the heating around 140?°C of the gels (tetraethylorthosilicate?Cmetal nitrates?C1,3-propanediol?Cwater). The as-obtained precursors, embedded in silica gels, have been characterized by FT-IR spectrometry and thermal analysis. Both precursors thermally decompose up to 350?°C leading to the formation of the corresponding metal oxides inside the silica matrix. X-ray diffraction of the annealed powders have evidenced the formation of NiFe₂O₄ starting with 600?°C, and NiCr₂O₄ starting with 400?°C. This behavior can be explained by the fact that, by thermal decomposition of the Fe(III) carboxylate at 300?°C, the spinelic phase ??-Fe₂O₃ is formed, which interacts with the NiO, forming the ferrite nuclei. By thermal decomposition of chromium carboxylate, a nonstoichiometric chromium oxide (Cr₂O_3+x ) is formed. In the range 380?C400?°C, Cr₂O_3+x turns into Cr₂O₃ which immediately interacts with NiO leading to the formation of nickel chromites nuclei inside the pores of silica matrix. Both spinels have been obtained as nanocrystalites homogenously dispersed as resulted from XRD and TEM data.     

Thermal transformations of Cu–Mg (Zn)–Al(Fe) hydrotalcite-like materials into metal oxide systems and their catalytic activity in selective oxidation of ammonia to dinitrogen

Layered double hydroxides (LDHs) containing Mg²⁺, Cu²⁺ or Zn²⁺ cations in the Me^II positions and Al³⁺ and Fe³⁺ in the Me^III positions were synthesized by co-precipitation method. Detailed studies of thermal transformation of obtained LDHs into metal oxide systems were performed using high temperature X-ray diffraction in oxidising and reducing atmosphere, thermogravimetry coupled with mass spectrometry and temperature-programmed reduction. The LDH samples calcined at 600 and 900 °C were tested in the role of catalysts for selective oxidation of ammonia into nitrogen and water vapour. It was shown that all copper congaing samples presented high catalytic activity and additionally, for the Cu–Mg–Al and Cu–Mg–Fe hydrotalcite samples calcined at 600 °C relatively high stability and selectivity to dinitrogen was obtained. An increase in calcination temperature to 900 °C resulted in a decrease of their catalytic activity, possibly due to formation of well-crystallised metal oxide phases which are less catalytically active in the process of selective oxidation of ammonia.     

High-temperature water gas shift catalyst based on nanodisperse,metastable, partially hydrated iron oxide—two-line ferrihydrite

Two-line ferrihydrite (2L-FH) is a metastable, heavily disordered, partially hydrated Fe(III) oxide. The catalyst prepared by heat treatment of 2L-FH promoted with chromium ions (∼9 at %) and copper ions (4–7 at %) is much more active in the water gas shift (WGS) reaction at low temperatures (<350°C) than the conventional Fe-containing catalysts. According to XAFS spectroscopy data, the copper cations in 2L-FH are in the Cu²⁺ state and are in a tetragonally distorted octahedral environment, while under the WGS conditions at <350°C, copper is in the reduced state, specifically, in the form of ultrafine (<2 nm) Cu⁰ particles. It is due to these particles that the catalyst is very active below 350°C. Above 400°C, the Cu⁰ particles are deactivated under the reaction conditions and the catalytic activity is only due to iron active sites, whose number is proportional to the specific surface area of the catalyst. The specific activity of the catalyst at these temperatures is close to the activity of the conventional (hematite-based) WGS catalysts. The high activity of the 2L-FH-based catalyst at <350°C makes it possible to reduce the starting temperature of the adiabatic high-temperature WGS reactor.     

Mechanistic features of reduction of copper chromite and state of absorbed hydrogen in the structure of reduced copper chromite

The review discusses the experimental data on the unusual mechanism of the reduction of copper cations from the copper chromite, CuCr₂O₄, structure. Treatment of copper chromite in hydrogen at 180–370°C is not accompanied by water formation but leads to absorption of hydrogen by the oxide structure with simultaneous formation of metallic copper as small flat particles which are epitaxially bound to the oxide. This process is due to the redox reaction Cu²⁺ + H₂ → Cu⁰ + 2H⁺; the protons are stabilized in the oxide phase, which is confirmed by neutron diffraction studies. The reduced copper chromite which contains absorbed hydrogen in its oxidized state and the metallic copper particles epitaxially bound to the oxide phase structure exhibit catalytic activity in hydrogenation reactions.     

Kinetics of the amorphous—anatase phase transformation in copper doped titanium oxide

Samples of TiO₂ doped with 2 and 5 mol% of Cu²⁺ were prepared by the sol-gel process. Titanium(IV) isopropoxide and copper(II) nitrate were used as precursors. The samples were prepared as monolithic shapes, dried at 80°C for 72 h and heat treated at various temperatures in the range 200–900°C for 2 h. The structural transformation and texture of the samples were investigated by X-ray powder diffraction (XRD) and nitrogen adsorption. Significant changes were observed during the crystallization process; on the one hand, the crystallization profiles show that crystallization occurs uniformly and is practically insensitive to the dopant concentration, but when the transformation at a given temperature is followed as a function of time, the rate of the amorphous-anatase transformation is larger for the sample containing 2 mol% Cu²⁺. Electron spin resonance (ESR) results show that in this sample there is no segregation of Cu²⁺ ions. The sample containing 2 mol% of Cu²⁺ was selected for the kinetic studies and the temperatures selected were 300, 325, 350, 375 and 400°C, which were taken from the amorphous to anatase crystallization profile. An activation energy of 137 ± 4 kJ/mol for the crystallization process was estimated from the kinetic data. These results showed that the effect of the open structure present in the TiO₂ amorphous phase provides the atomic mobility required for the crystallization. On the other hand, the differences in the crystallization rate due to the amount of Cu²⁺ were explained by the segregation of copper ions to the surface of the samples.     

Zirconium vanadophosphate as an inorganic ion exchanger

Zirconium vanadophosphate was characterized as a stable inorganic ion exchager. The ion-exchange capacity was measured as 1.75 meq. H⁺ g^?1 at room temperature and it is stable up to 300°C. The exchanger is selective for devalent cations and the order of sorption of cations was found to be M²⁺ > M⁺ > M³⁺ M⁴⁺. Separations of Co²⁺?Ni²⁺, Cu²⁺?Hg²⁺ and Cr(VI)?Cr³⁺ were achieved on a column containing the ion exchanger. Copper could be separated from other base metals in geochemical samples. Differential thermal analysis showed an endothermic peak in the range of 65–420°C due to the dehydration of the ion exchanger with a low activation energy of 7.79 kcal mol^?1, which follows first-order kinetics. The ion exchanger did not show any further decomposition up to 1000°C. Infrared studies confirmed the presence of

groups which act as exchange sites for the cations. X-ray diffraction studies revealed that the compound is crystalline, with a crystal structure resembling that of the mineral muscovite.     

Turn‐on fluorogenic and chromogenic detection of cations in complete water media with poly(N‐vinyl pyrrolidone) bearing rhodamine B derivatives as polymeric chemosensor

A hydrophobic organic monomer GRBE with a polymerizable methacrylester moiety had been synthesized by reaction of rhodamine B‐ethanediamine with glycidyl methacrylate. A water‐soluble polymeric chemosensor poly(VP‐GRBE) had been prepared via copolymerization with a hydrophilic comonomer (vinylpyrrolidone) and GRBE, which was able to sense environmentally poisonous cations in completely aqueous media. The chemosensor was a derivative of rhodamine B, which behaved as a fluorescent and chromogenic sensor toward various heavy cations, particularly Cr³⁺, Fe³⁺, and Hg²⁺. Titration curves of Cr³⁺, Fe³⁺, and Hg²⁺ were constructed using rapid, cheap, and widely available technique of fluorescence spectroscopies. The detection limits for Cr³⁺, Fe³⁺, or Hg²⁺ ions were found to be 2.20 × 10^?12, 2.39 × 10^?12, and 1.11 × 10^?12 mol/l in the same medium, respectively. Moreover, a colorimetric response from the polymeric chemosensor permitted the detection of Cr³⁺, Hg²⁺, or Fe³⁺ by “naked eye” because of the development of a pink or brown yellow color when Cr³⁺, Hg²⁺, or Fe³⁺ cations interacted with the copolymer in aqueous media. Copyright © 2015 John Wiley & Sons, Ltd.     

High-yield preparation of rod-like CaSO<Subscript>4</Subscript>/Fe<Superscript>0</Superscript> magnetic composite for effective removal of Cu<Superscript>2+</Superscript> in wastewater

In this study, a simple approach was described for the fabrication of CaSO₄/Fe⁰ composite used as a novel adsorbent for the reductive removal of Cu²⁺ from aqueous solutions. The magnetic CaSO₄/Fe⁰ composite was prepared by a solid state reaction at 550 °C in the H₂ atmosphere using CaSO₄·2H₂O/α-FeOOH as a precursor. The structure and morphology of the as-synthesized magnetic composite were characterized by X-ray diffraction, field emission scanning electron microscopy and a superconducting quantum interference device, respectively. Results showed that the CaSO₄/Fe⁰ composite with a rod-like shape could be easily acquired from the CaSO₄·2H₂O/α-FeOOH precursor with the ratio of 1:0.5 at 550 °C in the H₂ atmosphere for 1 h. The CaSO₄/Fe⁰ composite exhibited enhanced performance relevant to the reductive removal of Cu²⁺. The removal amount of Cu²⁺ increased linearly with increasing of concentration of Cu²⁺ in wastewater. Possible removal mechanisms were proposed as follows: (1) the formation of Cu₂O by fast reduction of Cu²⁺ with Fe⁰ nanoparticles on interface of CaSO₄/Fe⁰ composite, (2) proper adsorption of Cu²⁺ on the surface of CaSO₄/Fe⁰ composite, (3) the hydrous iron oxide (HIO) such as Fe (OH)₃ and FeOOH in situ generated on the rest of CaSO₄/Fe⁰ composite could further adsorb Cu²⁺ from wastewater.     

A thermodynamic study of the Cu-Cr-O system by the EMF method

The equilibrium oxygen pressures of the three-phase regions [Cu, Cr₂O₃, Cu₂Cr₂O₄], [Cu, Cu₂O, Cu₂O₂O₄] and [CuO, Cu₂O, Cu₂Cr₂O₄] were measured as a function of temperature by the solid oxide electrolyte electromotive force method. The measured Gibbs energy of the reaction Cu₂O+ Cr₂O₂ = Cu₂Cr₂O₄ (ΔG°) was found to be −46608 + 7.8328 T J mol⁻¹ (1075–1275 K). The evaluated Gibbs energy of formation of Cu₂Cr₂O₄ (ΔG°(inf,Cu₂Cr₂O₄)) was found to be −1332900 + 332.761 T J mol⁻¹ (900–1350 K).     

Self-Foaming Metal-Organic Gels Based on Phytic Acid and Their Mechanical,Moldable, and Load-Bearing Properties.

A catalogue of metal-organic gels are synthesized from phytic acid (PA) and a diversity of metal ions (Fe³⁺, Cr³⁺, Al³⁺, Ce³⁺, Y³⁺, Co²⁺, Ni²⁺, Mn²⁺, Cu²⁺, Zn²⁺, Mg²⁺) upon heating at 80 °C. PA−M gels have various morphologies, including irregular granular (PA−Fe, PA−Al, PA−Ce, PA−Cr, PA−Ni, PA−Co), spongy (PA−Y), and hollow tremella-like (PA−Cu) morphologies. Interestingly for PA−Fe-1 : 4 (PA:Fe³⁺=1 : 4) a large amount of gas is generated during the gelation process leading to a self-foaming gel. The PA−Fe-1 : 4 self-foaming gel shows reversible gel-sol phase transition. The gel is unusually weakened and transformed into a sol at room temperature, and the sol is reversed to gelation when heated again at 80 °C. PA−Fe-1 : 4 gel also shows shapeable and load-bearing properties, and it can bear up to 200 times of its weight, depending on the gas amount fixed in the foam gel and the aging time. This work provides a catalogue of self-foaming supramolecular gels with tunable properties based on naturally abundant resources.     

Electron spin resonance studies of manganese(II) and copper(II) salts of poly(ethylene-co-methacrylic acid)s

The ionic interaction of poly(ethylene-co-methacrylic acid) ionomer neutralized with Mn²⁺ or Cu²⁺ was studied by ESR spectroscopy to explore the local structure in the ionic aggregate. ESR spectra of the ethylene ionomer were obtained as functions of degree of neutralization and temperature. The existence of both isolated and aggregated cations in the ionomer was confirmed by ESR. In addition, the formation of a Cu²⁺?Cu²⁺ dimer structure similar to the crystal structure of copper acetate monohydrate was found in ethylene ionomer containing the Cu²⁺. Cation-cation interactions changed markedly around 70°C with increasing temperature, representing the onset of the motion of cations in the aggregated ionic structure.     

Charge storage mechanism of copper hexacyanoferrate nanocubes for supercapacitors

The widely accepted theory concerning the electrochemical energy storage mechanism of copper hexacyanoferrate (CuHCF) for supercapacitors is that CuHCF stores charge by the reversible redox processes of Fe³⁺/Fe²⁺ couple and Cu cations are electrochemically inactive. In this work, CuHCF nanocubes (CuHCF-NC) were synthesized in the presence of potassium citrate and its electrochemical properties were tentatively studied in 1 mol/L Na₂SO₄ aqueous electrolyte. Good supercapacitive performance was exhibited. The combined analyses of cyclic voltammogram (CV) and X-ray photoelectron spectroscopy (XPS) disclosed that the CuHCF nanocubes underwent the redox reactions of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ couples to store charges. The Cu²⁺/Cu⁺ redox couple was activated due to the strong coordination interaction between the carboxylate groups of citrate ions and surface Cu cations.     

Synthesis,Crystal Structure,Hydrogen Bonding,and Thermal Behavior of a Three‐Dimensional CuII‐benzene‐1,2,4,5‐tetracarboxylate Templated by 1,9‐Diaminononane

Triclinic single crystals of Cu₄(H₃N–(CH₂)₉–NH₃)(OH)₂[C₆H₂(COO)₄]₂ · 5H₂O were prepared in aqueous solution at 80 °C in the presence of 1,9‐diaminononane. Space group P$\bar{1}$ (no. 2) with a = 1057.5(2), b = 1166.0(2), c = 1576.7(2) pm, α = 106.080(10)°, β = 90.73(2)° and γ = 94.050(10)°. The four crystallographic independent Cu²⁺ ions are surrounded by five oxygen atoms each with Cu–O distances between 191.4(3) and 231.7(4) pm. The connection between the Cu²⁺ coordination polyhedra and the [C₆H₂(COO)₄]^4– anions yields three‐dimensional framework with negative excess charge and wide centrosymmetric channel‐like voids. These voids extend parallel to [001] with the diagonal of the nearly rectangular cross‐section of approximately 900 pm. The channels of the framework accommodate [H₃N–(CH₂)₉–NH₃]²⁺ cations and water molecules, which are not connected to Cu²⁺. The nonane‐1,9‐diammonium cations adopt a partial gauche conformation. Thermoanalytical measurements in air show a loss of water of crystallization starting at 90 °C and finishing at approx. 170 °C. The dehydrated compound is stable up to 260 °C followed by an exothermic decomposition yielding copper oxide.     

Catalytic properties of aluminum/nickel-, copper-containing oxide film compositions

The possibility of the single-step formation of nickel- and copper-containing thin-film oxide systems on aluminum by plasma electrolytic oxidation was demonstrated. The resulting structures were found to be active in the reaction of CO oxidation to CO₂ in the temperature region 300–500°C. However, the resulting structures exhibited stable catalytic activity only in the simultaneous presence of nickel and copper compounds. The films were studied using X-ray diffraction, X-ray spectroscopic analysis, X-ray photoelectron spectroscopy, and electron microscopy. The resulting films exhibited an essentially inhomogeneous composition through the thickness. Electrolyte elements such as nickel, copper, sodium, and phosphorus were concentrated at the surface. Nickel occurred as Ni²⁺, and copper occurred as Cu⁺ and Cu²⁺. The surface contained carbon in detectable amounts.     

Study of the stability of violurate complexes of some d- and f-metals

The stability constants of 1: 1 and 1: 2 acidic copper(II) violurate complexes and the CuL complex, where L is the anion of violuric acid (H₂L), were determined by pH-metry at ionic strength I = 0.1 at 20°C. The stability of the violurate complexes of triply charged cations [ML]⁺ and quadruply charged thorium [ThL]²⁺ increases in the sequence La³⁺, Gd³⁺, Y³⁺, Sc³⁺, Th⁴⁺, Fe³⁺. It was shown that violuric acid behaves as either mono- or dibasic, depending on the conditions, with respect to all of these cations.     

Complexation of metal ions with the novel diazadithia crown ether carrying two anthryl pendants in acetonitrile–tetrahydrofuran

A new crown ether carrying two anthryl groups with nitrogen–sulfur donor atom was designed and synthesized by the reaction of the corresponding macrocyclic compound and 9-chloromethyl anthracene. The influence of metal cations such as Al³⁺, Zn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Mn²⁺, Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ on the spectroscopic properties of the ligand was investigated in acetonitrile–tetrahydofuran solution (1/1) by means of absorption and emission spectrometry. Absorption spectra show isosbestic points in the spectrophotometric titration of Fe²⁺, Fe³⁺, Al³⁺, Cu²⁺ and Hg²⁺. The results of spectrophotometric titration experiments disclosed the complexation stoichiometry and complex stability constant of the novel ligand with Fe²⁺, Fe³⁺, Al³⁺, Cu²⁺and Hg²⁺cations. The presence of excess amounts of Al³⁺, Zn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Mn²⁺, Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ cations caused an enhancement of anthryl fluorescence. The ligand showed good sensitivity for Zn²⁺ with respect to other metal cations with linear range and detection limit of 1.4 × 10^?7 to 4.1 × 10^?6 M and 1.0 × 10^?8 M respectively.     

Synthesis and Characterization of Nanostructured Fe3O4 Micron‐Spheres and Their Application in Removing Toxic Cr Ions from Polluted Water

We present a simple and effective method for the synthesis of nanostructured Fe₃O₄ micron‐spheres (NFMSs) by annealing hydrothermally formed FeCO₃ spheres in argon. The phase structure, particle size, and magnetic properties of the product have been characterized by X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and by means of a superconducting quantum interference device (SQUID). The results have shown that the as‐obtained NFMSs have a diameter of about 5 μm and are composed of nanometer‐sized porous lamellae. The NFMSs have a large specific surface area (135.9 m² g^?1), reductive Fe²⁺ incorporated into their structure, and intense magnetic properties. These properties suggest that NFMSs have potential application in removing toxic Cr⁶⁺ ions from polluted water. At 25 °C, each gram of NFMSs product can remove 43.48 mg of Cr⁶⁺ ions, as compared to just 10.2 mg for nanometer‐sized Fe₃O₄ and 1.89 mg for micron‐sized Fe₃O₄. The enhanced removal performance can be ascribed to the structural features. Moreover, the Cr⁶⁺ ion removal capacity of the NFMSs can reach up to 71.2 mg g^?1 at 50 °C. The influencing parameters in the removal of Cr⁶⁺ ions, such as contact time, pH, and temperature, have been evaluated. The Cr⁶⁺‐removal mechanism has been investigated. We have found that the NFMSs product not only serves as an effective adsorbent to remove toxic Cr⁶⁺ ions from polluted water, but also as an effective reductant in reducing the adsorbed toxic Cr⁶⁺ ions to much less toxic Cr³⁺ through the Fe²⁺ incorporated into its structure.     

A dual chemosensor for Cu2+ and Fe3+ based on π-extend tetrathiafulvalene derivative

A new dual chemosensor (TTF-PBA) for Fe³⁺ and Cu²⁺ in different signal pathways was designed and synthesized. The absorption spectrum, fluorescence spectrum and cyclic voltammograms changed in the presence of Cu²⁺ and Fe³⁺. The optical color changed within 5 s from yellow to orange upon the addition of Cu²⁺, and it changed to dark yellow when Fe³⁺ existed. The cyclic voltammogram of Cu²⁺/TTF-PBA changed from E_ox = 0.50 V, E_red = 0.32 V to E_ox = 0.64 V, E_red = 0.80 V (vs Ag/AgCl) upon the addition of 2.0 equiv. Cu²⁺. As for Fe³⁺/TTF-PBA, its oxidation wave disappeared, and its reduction wave appeared at E_red = ?0.59 V (vs Ag/AgCl) upon the addition of 4.0 equv. Fe³⁺. The sensor displayed high selectivity for Cu²⁺ and Fe³⁺ over other ions including Pb²⁺, Zn²⁺, Ni²⁺, Ag⁺, Cr³⁺, Mn²⁺, Al³⁺, Co²⁺, Pd²⁺, Hg²⁺, Fe^2+, Cd²⁺, Ce³⁺, Bi³⁺ and Au³⁺, the detection limits for Cu²⁺ and Fe³⁺ ion reached as low as 5.33 × 10^?7 mol/L and 5.34 × 10^?7 mol/L, respectively. Furthermore, when Fe³⁺ existed, Cu²⁺ can be detected sequentially by the sensor through the absorption spectrum and the color change observed by naked-eyes.     

Effect of the Nature of the Precursor on the Activity of Copper-Containing Catalysts Based on Erionite in Oxidation of CO

We have studied the catalytic activity of copper-containing zeolite catalysts based on erionite (ERI) in oxidation of CO. We have established that the activity of Cu-ERI systems is due to isolated coordination unsaturated Cu²⁺ cations which are stabilized in the catalyst on sites with strong tetragonal distortion and are reduced to Cu⁺ during catalysis. According to X-ray photoelectron spectroscopy (XPS), diffuse reflection electronic spectra, and temperature programmed reduction by hydrogen (TPR-H₂) spectra, activity differences between 3% Cu-ERI catalysts obtained from different precursors are determined by the different numbers of Cu²⁺ cations capable of being reduced during the reaction at T < 400 °C: the higher the content of such cations in the samples, the higher the activity of the Cu-ERI systems. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 317–322, September–October, 2005.     

Study of formation and thermal stability of the Fe/ZnO(000‐1) interface

Formation and thermal stability of the Fe/ZnO(000‐1) interface have been studied by means of X‐ray photoelectron spectroscopy and low energy electron diffraction. The results indicated a pseudo 2D growth mode for iron on ZnO. In addition, it could be shown that under ultra high vacuum conditions deposited Fe⁰ on a ZnO(000‐1) single crystal was partially oxidized by a small fraction of residual ? OH‐groups and ZnO to FeO. A strong temperature dependence of the interface reactivity was found upon annealing at temperatures up to 600 °C. Starting from 200 °C iron was first oxidized to bivalent iron oxide. After complete oxidation of Fe⁰ to Fe²⁺ at 375 °C, Fe²⁺ reacted to Fe³⁺. Above temperatures of 500 °C the deposited metallic iron was completely oxidized to trivalent iron. Further experiments with FeO on ZnO showed the oxidation state and the oxide film thickness of the deposited iron to be mainly dependent on the annealing temperature. Copyright © 2008 John Wiley & Sons, Ltd.