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1.
In this article, we present a new method for the obtaining of ZnCr2O4 and MgCr2O4 embedded in silica matrix. This method consists in the formation of Cr(III), Zn(II) and Cr(III), Mg(II) hydroxycarboxylate/carboxylate compounds, during the redox reaction between the nitrate ion and diol (1,3-propanediol), uniformly dispersed in the pores of hybrid gels. The thermal decomposition of these precursors leads to a mixture of corresponding metal oxides. The gels were synthesized starting from mixtures of Cr(NO3)3·9H2O, Zn(NO3)2·6H2O and Cr(NO3)3·9H2O, Mg(NO3)2·6H2O with tetraethyl orthosilicate and 1,3-propanediol for final compositions 50% ZnCr2O4/50% SiO2 and 50% MgCr2O4/50% SiO2. The obtained gels have been thermally treated at 140?°C, when the redox reaction nitrates-diol took place with formation of the precursors within the xerogels pores. The thermal decomposition of all precursors took place up to 300?°C, with formation of oxides mixtures (Cr2O3?+?x and ZnO) and (Cr2O3?+?x and MgO), respectively. At 400?°C, Cr2O3?+?x turn to Cr2O3 which reacts with ZnO forming ZnCr2O4/SiO2. Starting with 400?°C, Cr2O3 reacts with MgO to an intermediary phase MgCrO4, which decomposes with the formation of MgCr2O4/SiO2. The formation of the precursors inside the silica matrix and the evolution of the crystalline phases were studied by thermal analysis, FT-IR spectrometry, XRD, and TEM.  相似文献   

2.
The catalytic activity of MIMII 2O3 spinel-type complex oxides (MI = Cu, Ni, Mn, Zn, Mg, Co, MII = Co, Cr, Al) in the oxidation of CO and ethylbenzene has been investigated. The Co-containing catalysts were more active than the Cr- and Al-containing catalysts. The nature of the cation influenced the catalytic activity. Higher activities were observed for the catalysts containing two transition elements. A correlation between the catalytic and adsorption properties was established.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1730–1732, October, 1994.  相似文献   

3.
4.
High-temperature heat capacity measurements were obtained for Cr2O3, FeCr2O4, ZnCr2O4, and CoCr2O4 using a differential scanning calorimeter. These data were combined with previously available, overlapping heat capacity data at temperatures up to 400 K and fitted to 5-parameter Maier–Kelley Cp(T) equations. Expressions for molar entropy were then derived by suitable integration of the Maier–Kelley equations in combination with recent S(298) evaluations. Finally, a database of high-temperature equilibrium measurements on the formation of these oxides was constructed and critically evaluated. Gibbs free energies of Cr2O3, FeCr2O4, and CoCr2O4 were referenced by averaging the most reliable results at reference temperatures of (1100, 1400, and 1373) K, respectively, while Gibbs free energies for ZnCr2O4 were referenced to the results of Jacob [K.T. Jacob, Thermochim. Acta 15 (1976) 79–87] at T = 1100 K. Thermodynamic extrapolations from the high-temperature reference points to T = 298.15 K by application of the heat capacity correlations gave ΔfG(298) = (−1049.96, −1339.40, −1428.35, and −1326.75) kJ · mol−1 for Cr2O3, FeCr2O4, ZnCr2O4, and CoCr2O4, respectively.  相似文献   

5.
This paper assesses the adsorption characteristics of Titan yellow and Congo red on CoFe2O4 magnetic nanoparticles. The adsorption behavior of Titan yellow and Congo red from aqueous solution onto CoFe2O4 magnetic nanoparticles has been determined by investigating the effects of pH, concentration of the dye, amount of adsorbent, contact time, ionic strength and temperature. Experimental results indicated that CoFe2O4 nanoparticles can remove more than 98 % of each dye under optimum operational conditions of a dosage of 15.0 mg CoFe2O4, pH 3.0, initial dye concentration of 22–140 mg L?1, and contact times of 2.0 and 15.0 min for Congo red and Titan yellow, respectively. Langmuir and Freundlich isotherm models have been used to evaluate the ongoing adsorption kinetic equations. Regeneration of the saturated adsorbent was possible by NaCl/acetone solution as eluent. The maximum adsorption capacities were 200.0 and 212.8 mg dye per gram adsorbent for Congo red and Titan yellow, respectively. With the help of adsorption isotherm, thermodynamic parameters such as free energy, enthalpy and entropy have been calculated. On the basis of pseudo-first-order and pseudo-second-order kinetic equations, different kinetic parameters have been obtained.  相似文献   

6.
The ZnO–ZnCr2O4 (Zn–Cr–O) sample obtained by decomposition of Zn-Cr hydrotalcite precursor was subjected to the thermal treatment at different temperatures and the physico-chemical properties of the Zn–Cr–O system were compared with its catalytic behavior in dehydrocyclization of crude glycerol and ethylenediamine (EDA). Upon high temperature treatment of Zn–Cr–O the Cr6+ ions underwent autoreduction to form stable Cr3+ species and the particle size of both ZnO and ZnCr2O4 increased dramatically. Thermal effect did not influence the intermolecular cyclisation of EDA to form pyrazine. By contrast, an inversely proportional dependence was found between the rate of formation of 2-methylpyrazine and the particle size of Zn–Cr–O whereas the rate of 2-pyrazinylmethanol was directly proportional to the particle size.  相似文献   

7.
This research study aims to remove hazardous anionic azo dyes (Congo red (CR)) from aqueous solutions via a simple adsorption method using a poly(3-aminobenzoic acid/graphene oxide/cobalt ferrite) nanocomposite (P3ABA/GO/CoFe2O4) as a novel and low-cost nanoadsorbent, as synthesized by a simple and straightforward polymerization method. Typically, 3-aminobenzoic acid (3ABA), as monomer, was chemically polymerized with graphene oxide (GO) and cobalt ferrite (CoFe2O4) in an aqueous acidic medium containing an ammonium persulfate initiator. The adsorbent P3ABA/GO/CoFe2O4 nanocomposite was characterized using various techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, energy-dispersive analysis by X-ray and Brunauer–Emmett–Teller, vibrating sample magnetometer, and zeta potential techniques. These techniques confirmed the interaction between the poly(3-aminobenzoic acid) with GO and CoFe2O4 due to the presence of π-π interactions, hydrogen bonding, and electrostatic forces. Herein, the removal efficiency of dye from aqueous solution by the adsorbent was studied according to several parameters such as the pH of the solution, dye concentration, dosage of adsorbent, contact time, and temperature. The adsorption of the dye was fitted using a Langmuir model (R2 between 0.9980 and 0.9995) at different temperatures, and a kinetic model that was pseudo-second order (R2 = between 0.9993 and 0.9929) at various initial concentrations of CR dye. In addition, the data revealed that the P3ABA/GO/CoFe2O4 nanocomposite exhibited a high adsorption capacity (153.92 mg/g) and removal for CR dye (98 %) at pH 5. Thermodynamic results showed the adsorption process was an endothermic and spontaneous reaction. It was found that, in terms of reusability, the P3ABA/GO/CoFe2O4 adsorbent can be used for up to six cycles. In this study, P3ABA/GO/CoFe2O4 nanocomposites were found to be low cost, and have an excellent removal capability and fast adsorption rate for CR from wastewater via a simple adsorption method. Moreover, this adsorbent nanocomposite could be simply separated from the resultant solution and recycled.  相似文献   

8.
  • Manganese dioxide/silver (MnO2/Ag) nanoparticles were fabricated by using KMnO4-NaBH4 redox reaction at room temperature. The optical and structural properties of MnO2/Ag were determined using UV–visible and Fourier transform infrared spectroscopies. The morphology was established with scanning and transmission electron microcopies, and X-ray diffraction. MnO2/Ag showed excellent adsorbing activity to the removal of Congo red. The various kinetic models were used to determine the rate of dye removal. Congo red adsorption onto MnO2Ag proceeds through the pseudo-second-order kinetic model. Langmuir adsorption capacity (Q0max = 97.1 mg/g), and sorption intensity (n = 1.6) were estimated with Langmuir and Freundlich adsorption isotherm models for 250 mg/L Congo red. Elovich model suggest the adsorption of Congo red with the MnO2Ag proceeds through the film diffusion. The positive values of enthalpy changes (ΔH0), entropy changes (ΔS0), and negative Gibbs free energy changes (ΔG0) showed that the Congo red adsorption process was endothermic, spontaneous, and chemisorption process followed with physical mechanism. The results showed that the removal efficiency decreases from 98% to 89% after the six consecutive experiments.
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9.
LiCo0.9M0.1PO4 (M = Co2+, Mg2+, Ca2+)/graphitic carbon composites are synthesized by Pechini-assisted sol–gel process and annealed by the 2-steps annealing process (300 °C for 5 min in air, then at 730 °C for 12 h in nitrogen). The structural investigation, performed on powders, reveals the presence of LiCoPO4 as the major crystalline phase and of CoP2O7 (M = Co), of Co2P (M = Mg), of Co2P, Li3PO4, (Ca,Co)3(PO4)2 (M = Ca) as impurities. The morphological investigation of the composites shows the formation of crystalline “islands-like” structures with acicular crystallites with different dimensions (typically 5–50 μm) on the top of them. The voltammetric analysis shows a very good reversibility of the (de)intercalation processes and the presence of two mean peak maxima in the cathodic region at ∼5.01 V and ∼5.05 V respectively. The discharge specific capacities, at a discharge rate of C/10 and room temperature, were 100 mAh g−1 for M = Co, 68 mAh g−1 for M = Mg and 104 mAh g−1 for M = Ca respectively. The electrochemical impedance spectroscopy data reveal a decrease of the electrical resistance and the improvement of the Li-ion conductivity in the Ca and Mg ions containing composites.  相似文献   

10.
Bis-hydrazine complexes of metal glyoxylates and mixed metal glyoxylates of 3d-metal ions of the formula M(OOCCHO)2(N2H4)2, where M = Mg, Mn, Co, Ni, Cu, Zn or Cd and M1/3Co2/3(OOCCHO)2(N2H4)2, where M = Mg, Mn, Ni, Zn or Cd, respectively, have been prepared and studied. The compositions of the complexes have been determined by chemical analyses. The magnetic moments and electronic spectra suggest a high-spin octahedral geometry for the metal complexes. Infrared spectral data indicate the bidentate bridging by hydrazine molecules and monodentate coordination by glyoxylate ions in both the metal and mixed metal compounds. Thermogravimetry and differential thermal analyses in air have been used to study the thermal behaviour of the complexes. The simultaneous TG-DTA traces of all the complexes show multi-step degradation and the final products are found to be the respective metal oxides in the case of metal complexes and metal cobaltites in the case of mixed metal complexes. The final residues were identified by their X-ray powder diffraction patterns. X-ray powder diffraction patterns of the complexes including mixed metal complexes are almost superimposable with in each of the series indicating isomorphism. The metal cobaltites MCo2O4, where M = Mg, Mn, Ni, Zn or Cd were also prepared by decomposing the respective mixed metal complex in a pre-heated silica crucible at about 300 °C, and their identities were confirmed by chemical analyses, infrared spectra and X-ray powder diffraction.  相似文献   

11.
This paper reports an investigation regarding the influence of the cation M(II) (M = Zn, Ni, Mg) on the formation of MCr2O4 by thermal decomposition of the corresponding M(II),Cr(III)-carboxylates (precursors) obtained by redox reaction between the corresponding metal nitrates and 1,3-propanediol. The decomposition products at different temperatures have been characterized by FT-IR spectroscopy and thermal analysis. Thus, we have evidenced that by thermal decomposition of the studied precursors in the range 250–300 °C, different amorphous oxidic phases mixtures form depending on the nature of metalic cation: (Cr2O3+x + ZnO) (Cr2O3+x + Ni/NiO) and (Cr2O3+x+MgO). In case of M = Zn, around 400 °C when the transition Cr2O3+x to Cr2O3 takes place, zinc chromite nuclei form by the interaction ZnO with Cr2O3. In case of M = Ni, due to the partial reduction of Ni(II) at Ni(0) during the thermal decomposition of the precursor the formation of nickel chromite by the reaction NiO + Cr2O3 is shifted toward 500 °C, when Ni is oxidized at NiO. The thermal evolution of the mixture (MgO + CrO3) is different due to the formation as intermediary phase of MgCrO4, which decomposes to MgCr2O4 around 560 °C. In order to investigate the chromites formation mechanism, we have studied the mechanical mixtures of single oxides obtained from the corresponding carboxylates. These mixtures (MO + Cr2O3) have been annealed at 400, 500, and 600 °C to study the evolution of the crystalline phases. It results in the prepared mixture behaving different from the mixtures obtained by thermal decomposition of the binary M(II),Cr(III)-carboxylates, recommending our synthesis method for obtaining binary oxides.  相似文献   

12.
The nano-ZnCr2O4 spinel oxides was synthesized by a ethylene glycol mediated solvothermal method. Catalytic combustion of methane test showed that an excellent activity over nano-ZnCr2O4 with T10% = 300 °C and T90% = 400 °C. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption measurements (BET) indicated that a uniform nano-ZnCr2O4 spinel oxides particles with the high surface area (96.2 m2g−1) was successfully synthesized. Oxygen temperature programmed desorption (O2-TPD) profile revealed there were two obvious desorption of oxygen species from nano-ZnCr2O4 in the range of 300–400 °C and 500–700 °C. It was clear that the desorption temperature range of the first oxygen species coincided with the methane catalytic combustion temperature. X-ray photoelectron spectroscopy (XPS) analysis exhibited that Cr6+ was present in the lattice of ZnCr2O4 apart from Cr3+. High valence cations of chromium in crystal lattice probable caused the presence of interstitial oxygen species in the structure to maintain the electroneutrality. Additionally, Raman spectra proved that there is the interstitial oxygen species in the crystal lattice of ZnCr2O4. Therefore, the excellent catalytic activity for methane combustion was contributed to the flexible interstitial oxygen in the ZnCr2O4.  相似文献   

13.
The chemical compatibility of perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3?δ (BSCF) oxides with Cr2O3 has been examined between room temperature and 1,100 °C. Differential thermal analysis and thermogravimetric analysis were used to analyze the thermal behavior of BSCF–Cr2O3 binary mixtures in all composition ranges (0–100 mass% BSCF). The reaction products were identified by X-ray analysis after heating at 700–1,100 °C. As we expected, it was found that perovskite-type BSCF oxide had a poor chemical compatibility with the Cr2O3 oxide. In particular, the decomposition process of the BSCF–Cr2O3 binary mixture is quite complex and it starts at about 700–750 °C. The mixtures of BSCF and Cr2O3 oxides reacted forming mixed complex oxides based on (Ba/Sr)FeO3, (Co/Fe)CrO4, and (Ba/Sr)CrO4 mixtures.  相似文献   

14.
Luan  Chengyu  Shan  Qiujie  Wang  Peng  Chen  Lin  Chen  Wei  Zhao  Chunyan 《Research on Chemical Intermediates》2021,47(7):3093-3108

In order to achieve the degradation of Congo red dye in wastewater, a new type of three-dimensional porous composite catalyst PW7Mo3Cu2/PANI/MnO2 was prepared by using heteropoly acid [TBA]4H3[PW7Mo3Cu2O38(H2O)2] doped intermediate PANI/MnO2. Using IR, UV, SEM, XPS and other characterization techniques, it was confirmed that the heteropoly acid [TBA]4H3[PW7Mo3Cu2O38(H2O)2] was successfully doped into the intermediate PANI/MnO2 to form a three-dimensional porous structure. The results of N2 adsorption–desorption experiment indicated that the composite catalyst belongs to the type IV (a) mesoporous structure material and has a large pore size and specific surface area. Then, the composite catalyst PW7Mo3Cu2/PANI/MnO2 was used to photocatalyze the degradation of Congo red dye. Under the best photocatalytic conditions, the decolorization rate of Congo red dye reached 93.84%. After recovering and repeating the photocatalysis experiment three times, the decolorization rate of Congo red dye was 73.18%. The experimental results proved that the novel composite catalyst has a strong ability to degrade Congo red dye and reusability, and has potential application value.

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15.
The standard free energies of formation of zinc aluminate and chromite were determined by measuring the oxygen potential over a solid CuZn alloy, containing 10 at.?% Zn, in equilibrium with ZnO, ZnAl2O4+Al2O3(χ) and ZnCr2O4+Cr2O3, in the temperature range 700–900°C. The oxygen potential was monitored by means of a solid oxide galvanic cell in which a Y2O3ThO2 pellet was sandwiched between a CaOZrO2 crucible and tube. The temperature dependence of the free energies of formation of the interoxidic compounds can be represented by the equations,
The heat of formation of the spinels calculated from the measurements by the “Second Law method” is found to be in good agreement with calorimetrically determined values. Using an empirical correlation for the entropy of formation of cubic spinel phases from oxides with rock-salt and corundum structures and the measured high temperature cation distribution in ZnAl2O4, the entropy of transformation of ZnO from wurtzite to rock-salt structure is evaluated.  相似文献   

16.
The catalytic activity of supported chromites MCr2O4/-Al2O3 (M = Cu, Co, Mn, Zn, Mg) in the oxidation of CO, C3H6, and o-xylene and NOx reduction was studied. The catalytic activity depends on the calcination temperature and cation nature. The features of the formation of the catalysts were studied by the UV-Vis diffuse reflectance and IR spectroscopies.  相似文献   

17.
Herein, we highlight redox-inert Zn2+ in spinel-type oxide (ZnXNi1−XCo2O4) to synergistically optimize physical pore structure and increase the formation of active species on the catalyst surface. The presence of Zn2+ segregation has been identified experimentally and theoretically under oxygen-evolving condition, the newly formed VZn−O−Co allows more suitable binding interaction between the active center Co and the oxygenated species, resulting in superior ORR performance. Moreover, a liquid flow Zn–air battery is constituted employing the structurally optimized Zn0.4Ni0.6Co2O4 nanoparticles supported on N-doped carbon nanotube (ZNCO/NCNTs) as an efficient air cathode, which presents remarkable power density (109.1 mW cm−2), high open circuit potential (1.48 V vs. Zn), excellent durability, and high-rate performance. This finding could elucidate the experimentally observed enhancement in the ORR activity of ZnXNi1−XCo2O4 oxides after the OER test.  相似文献   

18.
Catalytic activities of ferrites MFe2O4 (M = Cu, Co, Ni, Mg, and Zn) and M1 0.5M2 0 .5Fe2O4 (M1 = CU; M2 = Co, Zn, and Mg) in oxidation of CO and ethylbenzene were investigated, and their dependences on the cation nature were established. Higher activities were observed for catalysts containing ions with variable valence (Cu, Co, and Ni). A correlation between catalytic and adsorption properties of ferrites was found.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 49–52, January, 1996.  相似文献   

19.
The crystal structure and the cation distribution in a series of InFeMO4 compounds (M=Mg, Co, Ni, Cu and Zn) have been studied by means of X-ray powder diffraction and 57Fe Mössbauer spectroscopy. The M=Mg, Co and Ni samples were confirmed to crystallize with the cubic spinel structure (space group Fd-3m), whereas the M=Cu and Zn samples adopted a hexagonal structure. For all the phases, the cation stoichiometry was found to deviate from the ideal molecular formula, InFeMO4. The paramagnetic Mössbauer spectra of the samples were analyzed using a four-component fitting model suggested by a statistical simulation with point-charge calculation. The Mössbauer data confirmed the trivalent state for iron at both cation sites in all samples. The results from the fitting of the Mössbauer spectra were also employed in Rietveld refinement of the X-ray diffraction data for the determination of exact cation distribution. It was seen that the distribution of Fe at the A and B sites follows very closely the 1:2 ratio of the ideal formula AB2O4 for all samples, whereas trivalent indium was clearly seen to favor the A site and divalent M cation the B site.  相似文献   

20.
In this paper, a novel Zn(II) and Co(II) Schiff base complexes were synthesized by template method via refluxing 2,3-Naphthalenedicarboxaldehyde, Metal(II) chloride (Metal = Zn or Co), and L-phenylalanine. ZnO and Co3O4 nanoparticles were synthesized by thermal decomposition of Zn(II) and Co(II) complexes, respectively. The products were characterized using different instruments such as CHN, Conductivity, FT-IR, XRD, HR-TEM, and UV–Vis spectrophotometer. The experimental results of elemental analysis for Zn(II) and Co(II) complexes, agree with the calculated results, indicating that the Zn(II) and Co(II) complexes have 1:1 ligand/metal ratios. The molar conductance of the Zn(II) and Co(II) complexes, is less than 5 Ω?1cm?1mol?1, confirming the non-electrolytic nature of the synthesized complexes. The average crystallite diameter of the ZnO and Co3O4 samples is 39.64 and 30.38 nm, respectively. The optical energy gap of the ZnO and Co3O4 samples are 2.75 and 3.25 eV, respectively. Methylene blue dye was utilized to examine the photocatalytic properties of the synthesized nanoparticles using UV irradiations in the absence and presence of hydrogen peroxide. The % degradation of the methylene blue dye in the presence of hydrogen peroxide using ZnO and Co3O4 samples after 40 min is 94.55 and 98.98, respectively. Six pathogenic microbes were utilized to examine the antimicrobial properties of the synthesized Schiff base complexes and their nanoparticles: Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Streptococcus species, Aspergillus species, and Candida species. Zn(II) and Co(II) complexes display inhibition towards all the studied microbes. Besides, ZnO and Co3O4 nanoparticles exhibit less inhibition towards Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Streptococcus species. Moreover, ZnO and Co3O4 nanoparticles have no activity towards Aspergillus and Candida species.  相似文献   

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