Metal Chromite Research Articles

Advanced composite material for high-performance supercapacitors: integrating graphene oxide and barium chromate

Graphene oxide-based Barium chromate (BaCr2O4@GO) composites were successfully synthesized through sonication assisted by a hydrothermal process designed for supercapacitor applications. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and morphological analyses were employed to characterize the nanostructured composites. The XRD and FTIR results reveal that the GO nanoparticles are arranged in a honeycomb-like configuration. Moreover, the TEM images reveal the presence of cauliflower-like structures in the morphology of the composites, which is attributed to the effective intercalation of GO during the thermal reduction process. The electrochemical properties of the nanocomposite were compared to those reported in previous studies on metal chromite materials aimed at enhancing supercapacity applications. The analysis of Galvanostatic Charge–Discharge (GCD) data indicates a significant increase in power density values from 292 W kg−1 to 495.5 W kg−1 for the Nanocomposites. The ability to achieve a balance between enhanced power density and efficient ion transport positions the -nanocomposites as a valuable candidate for advancing the performance of supercapacitors.

Fabrication of a novel metal chromite – Carbon nanotube composite for the highly efficient electrocatalytic reduction of hydrogen peroxide

The new electrocatalyst, ZnCr2O4/MWCNTs composite was successfully synthesized by hydrothermal method followed by calcination at 500°C. A potential application of ZnCr2O4/MWCNTs composite modified electrode as enzyme-free sensor to monitor H2O2 has been studied. The sensor exhibited a high sensitivity of 1717.14μAmM−1cm−2 and a low detection limit down to 0.11μM with a linear wide range from 50μM to 34.8mM with a fast response time of 2s. In addition, modified electrode performance was investigated by measuring current responses of the sensor for three weeks to confirm the great stability of the proposed sensor. Along with these considerable analytical advantages, the as-prepared composite showed very high specificity to H2O2 with complete elimination of interference from uric acid, ascorbic acid, dopamine and glucose. The sensor gave satisfactory results in a real sample, when employed for determination of H2O2 in lens cleaning solution.

Liquid phase oxidation of benzyl alcohol with molecular oxygen catalyzed by metal chromites

The spinel type chromites MCr2O4 (M=Co, Ni and Cu) were synthesized by the co-precipitation method and have been characterized by a number of analytical tools. The efficacy of the synthesized system as catalysts for the oxidation of benzyl alcohol by molecular oxygen has been studied wherein it has been observed that benzaldehyde is formed with 100% selectivity. The catalytic activity of the chromites follows the order Co>Ni>Cu. The effect of the reaction parameters like the amount of the catalyst and reaction time was studied and it has been observed that the surface area and chemical hardness of the catalysts play a significant role.

Hydrothermal synthesis and characterization of nanosized transition metal chromite spinels

Homogeneous crystalline transition metal chromite spinels (MCr_2O_4, where M = Co, Mn, and Ni) were prepared by hydrothermal reaction of aqueous solutions containing the respective metal nitrate, chromium(III) nitrate, and sodium hydroxide in stoichiometric amounts at 180-200 °C and pH 10.5-11.5 for 11-13 h. The crystalline structure, microstructure, and thermal stability of the synthesized chromite products were analyzed by X-ray diffraction (XRD), scanning electron microscopy, thermogravimetry, and differential thermal analysis. The analysis results revealed that the CoCr_2O_4 and MnCr_2O_4 crystalline phases were thermally stable in the range of 750-800 °C. UV-visible studies showed that higher characteristic bands corresponded to the region of the visible spectrum of cobalt (CoCr_2O_4, bluish-green) and manganese-doped cobalt chromites (Co_{0.5}Mn_{0.5}Cr_2O_4, dark green). XRD powder diffraction data of specimens revealed the formation of a well-crystallized spinel structure of transition metal chromite (approximately 98%) after calcination at 550-750 °C. The nanocrystallinity of synthesized CoCr_2O_4 was found to be in the range of approximately 100-120 nm.

Structural, Optical, and Magnetic Properties of Highly Ordered Mesoporous MCr2O4 and MCr2–xFexO4 (M = Co, Zn) Spinel Thin Films with Uniform 15 nm Diameter Pores and Tunable Nanocrystalline Domain Sizes

Herein is reported the synthesis and characterization of nanocrystalline cobalt chromite (CoCr2O4) and zinc chromite (ZnCr2O4) thin films with highly ordered cubic networks of open pores averaging 15 nm in diameter. We also show that the synthesis method employed in this work is readily extendable to solid solutions of the type MCr2–xFexO4 (M = Co, Zn), which could pave the way for innovative device design. All of these materials can be prepared by facile coassembly of hydrated nitrate salts with an amphiphilic diblock copolymer, referred to as KLE. The as-made materials are amorphous thin films with face-centered-cubic close-packed pore structures. Electron microscopy, X-ray diffraction, grazing incidence small-angle X-ray scattering, krypton physisorption, UV–vis spectroscopy, time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and Raman spectroscopy studies collectively verify that both the transition metal chromites and the solid solutions are well-defined at the nanoscale and the microscale. In addition, the data show that the different thin film materials are nanocrystalline after annealing in air at 600 °C, adopt the spinel structure in phase-pure form, and that the conversion of the initially amorphous frameworks comes at little cost to the ordering of the cubic pore-solid architectures. Magnetization studies as a function of temperature and field further reveal the high quality of the KLE-templated CoCr2O4 thin films with both long-range ferrimagnetic order and spiral magnetic order at low temperatures, in agreement with previous findings.

Preparation of Nano-sized Calcium, Magnesium, and Zinc Chromite Powder Through Metalo-Organic Precursor Solutions

The metalo-organic complexes in the precursor solution were obtained through complexation of the metal and Cr+3 ions with an organic amine, i.e., triethanolamine (TEA), and an aqueous solution mixture of sucrose and polyvinyl alcohol (PVA) provided the polymeric matrix for the dispersion of the metalo-organic complexes. Rapid evaporation of the precursor solution resulted in mesoporous carbon-rich precursor powders, which on calcination at temperatures less than 500°C generated the respective nano-sized, metal chromite powders. The average particle sizes, as measured by X-ray line broadening and transmission electron microscopy studies, were around ∼150−200 A. That the particles had sizes of the same order as those of crystallite indicated the poor agglomeration of crystallites.

CATALYTIC EFFECT OF SOME CHROMITES ON THE THERMAL DECOMPOSITION OF KClO4 Mechanistic and non-isothermal kinetic studies

The catalytic effect of two different groups of chromites on the non-isothermal decomposition of KClO4was studied. TG and DSC curves of the thermal behaviour obtained for KClO4-alkaline earth chromites (Series 1) mixtures indicate the formation of K2Cr2O7, through a solid-solid interaction, before accelerating the decomposition stage of KClO4. Such an accelerating effect becomes more pronounced in the case of admixing KClO4 with some transition metal chromites (Series 2). The results were discussed taking into consideration the electronic configuration of cations and the electrical properties of the chromite catalysts. The presence of coordinatively active cations, able to form surface complex with the oxygen of the perchlorate anion, was proved to be necessary for obtaining an active catalyst. The kinetic parameters and models describing the catalyzed thermal decomposition process of KClO4 were evaluated by using a computer program that allows the analysis using five different methods. It was found that the adopted kinetic model for pure KClO4 and that mixed with catalysts from Series 1 is one-dimensional movement of phase boundary. On the other hand, random nucleation mechanism was achieved in the presence of catalysts from Series 2. Finally, a tentative reaction mechanism consistent with the obtained results was suggested.

Combustion Synthesis of Metal Chromite Powders

Fine‐particle metal chromites (MCr2O4, where M = Mg, Ca, Mn, Fe, Co, Ni, Cu, and Zn) have been prepared by the combustion of aqueous solutions containing the respective metal nitrate, chromium(III) nitrate, and urea in stoichiometric amounts. The mixtures, when rapidly heated to 350°C, ignite and yield voluminous chromites with surface areas ranging from 5 to 25 m2/g. MgCr2O4, sintered in air at 1500°C for 5 h, has a density of 4.0 g/cm3.

Preparation of fine particle chromites: A combustion approach

Fine particle metal chromites, MCr 2O 4 where M = Mg, Mn, Fe, Co, Ni, Cu and Zn have been obtained by the combustion of a redox mixture containing corresponding divalent metal nitrate, chromium (III) nitrate and tetraformal trisazine (TFTA). An aqueous saturated solution of the redox mixture when rapidly heated at 350°C boils, foams and ignites to yield voluminous, fine particle chromite powder. Formation of chromite was confirmed by X-ray diffraction pattern and IR spectra. Fine particle nature of chromites was studied using particle size analysis, surface area measurements, TEM and SEM. The particle size of chromites is below lum and the surface area ranges from 13 to 30 m 2/g.

Fourier transform-infrared spectroscopic study of the adsorption of hydrogen on chromia and on some metal chromites

Adsorption of hydrogen and deuterium on samples of chromia and on nonstoichiometric zinc, cobalt, and manganese chromites (M/Cr atomic ratio 1:1; M = Zn, Co, Mn), previously activated in hydrogen and vacuum, was studied by means of Fourier transform-infrared spectroscopy. Parallel CO adsorption experiments indicate that all four catalysts are essentially in an oxide form after hydrogen adsorption. Only in the case of the cobalt compound are zerovalent centers observed. Terminal hydrides CrH are formed on chromia, whereas on the three chromites, both terminal and bridged hydride species, thought to be bonded to Zn 2+, Co 2+, and Mn 2+ centers, respectively, are observed. These assignments are based on the H(D) isotopic shift and on a comparison with the spectra of known hydride species of the same metals. The mechanism of formation of these adsorbed forms is briefly discussed.

Mechanism of catalytic activity of metal oxides and chromites on ammonium perchlorate pyrolysis

This study investigates the mechanism of action of transition metal chromites on the decomposition of ammonium perchlorate.