Cobalt Aluminate Research Articles

Effect of metal ions on structural, morphological and optical properties of nano-crystallite spinel cobalt-aluminate (CoAl2O4)

The bright blue nano crystallite cobalt aluminate (CoAl2O4) was synthesized by sol–gel method using a mixture of chelating agent of glycerol and citric acid. The effects of changing (0.05, 0.075, 0.10, 0.25, 0.50, and 0.75 mol/L) metal ion concentration on the structural, morphological and color properties of synthesized CoAl2O4 were characterized by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Nanoparticle size analyzer, Simultaneous Thermal Analyzer (STA), UV–vis absorption spectroscopy, and CIE-LAB colorimetric analysis. From the X-ray peak profile analysis, the crystallite size was measured by Debye-Scherrer (D-S) equation, and three different models presenting average crystallite sizes between 88.3 and 125.4 nm.The average lattice strain, dislocation density, lattice constant, cell volume, and zeta potential were between 0.00021 and 0.0058, (1.73 to 12.8) × 1014 (lines/m2), 8.10658 to 8.11181 Å, 533.60 to 533.81 Å3, −56.4 to − 63.5 mV, respectively. Using UV–vis absorption spectroscopy, the band gap was calculated from Kubelka-Munk method, and the values of band gap increasing from 1.82 to 1.84 eV, respectively. The reflectance spectra and the CIE-L*a*b* values of cobalt aluminate is also measured which confirmed the formation of blue nano crystallite cobalt aluminate.

Cleaner preparation of high blueness cobalt blue composite pigments using dolomite and kaolin tailing sand

Cleaner and value-added resourceful utilization of the tailings or natural mineral resources has gained increasingly attention under the advanced concept of green and sustainable development. To develop an environmental-friendly preparation process for cobalt blue pigments with high chroma and low cobalt consumption, a dolomite-induced mechanochemical technology was developed for fabrication of cobalt blue composite pigments with controllable high blue intensity in the presence of kaolin tailing sand without using and discharging waste liquids. It revealed that the excellent color performance (L* = 37.63, a* = 10.68, b* = −54.87, C* = 55.91) benefitted from the Ca/Mg species and the lamellar morphology of dolomite by the mechanical force, which could facilely adjust the color performance and in-situ load pigment nanoparticles, respectively. The composite pigments presented a flaky morphology decorated with about 10 nm of nanoparticles, and consisted of calcium aluminate, anorthite, quartz and spinel magnesium cobalt aluminates. It is worth mentioning that the as-prepared composite pigments exhibited excellent environmental stability and good application performance as painting ink on rice paper. Therefore, this novel and cleaner technology is expected to produce high-performance cobalt blue pigments with lower cobalt consumption, as well as simultaneously realize the resource utilization of kaolin tailing sand and dolomite.

Deciphering the role of water and a zinc-doping process in a polyol-based approach for obtaining Zn/Co/Al-based spinels: toward "green" mesoporous inorganic pigments.

Two new families of zinc/cobalt/aluminum-based pigments, with a unique composition, were obtained through the polyol method. The hydrolysis process of a mixture of Co(CH3COO)2, Zn(acac)2 and Al(acac)3 (acac- = acetylacetonate ion) in 1,4-butanediol afforded dark blue gels (wPZnxCo1-xAl), in the presence of a supplementary amount of water, and light green powders (PZnxCo1-xAl), respectively, for the water-free procedure (x = 0, 0.2, 0.4). The calcination of the precursors yielded dark green (wZnxCo1-xAl) and blue (ZnxCo1-xAl) products. XRD measurements and Rietveld refinement indicate the co-existence of three spinel phases, in different proportions: ZnxCo1-xAl2O4, Co3O4 and the defect spinel, γ-Al2.67O4. The Raman scattering and XPS spectra are in agreement with the compositions of the samples. The morphology of wZnxCo1-xAl consists of large and irregular spherical particle aggregates (ca. 5-100 mm). Smaller agglomerates (ca. 1-5 mm) with a unique silkworm cocoon-like hierarchical morphology composed of cobalt aluminate cores covered with flake-like alumina shells are formed for ZnxCo1-xAl. TEM and HR-TEM analyses revealed the formation of crystalline, polyhedral particles of 7-43 nm sizes for wZnxCo1-xAl, while for ZnxCo1-xAl, a duplex-type morphology, with small (7-13 nm) and larger (30-40 nm) particles, was found. BET assessment showed that both series of oxides are mesoporous materials, with different pore structures, with the water-free samples exhibiting the largest surface areas due, most likely, to the high percent of aluminum oxide. A chemical mechanism is proposed to highlight the role of the water amount and the nature of the starting compounds in the hydrolysis reaction products and, further, in the morpho-structural features and composition of the resulting spinel oxides. The CIE L*a*b* and C* colorimetric parameters indicate that the pigments are bright, with a moderate degree of luminosity, presenting an outstanding high blueness.

Structural Morphology and Optical Properties of Strontium-Doped Cobalt Aluminate Nanoparticles Synthesized by the Combustion Method.

The study of structural morphology and the optical properties of nanoparticles produced by combustion methods are gaining significance due to their multifold applications. In this regard, in the present work, the strontium-doped cobalt aluminate nanoparticles were synthesized by utilizing Co1-xSrxAl2O4 (0 ≤ x ≤ 0.5) L-Alanine as a fuel in an ignition cycle. Subsequently, several characterization studies viz., X-ray diffraction (XRD), energy-dispersive X-ray (EDX) analysis, high-resolution scanning electron microscopy (HRSEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet (UV) spectroscopy and vibrating sample magnetometry (VSM) were accomplished to study the properties of the materials. The XRD analysis confirmed the cubic spinel structure, and the average crystallite size was found to be in the range of 14 to 20 nm using the Debye-Scherrer equation. High-resolution scanning electron microscopy was utilized to inspect the morphology of the Co1-xSrxAl2O4 (0 ≤ x ≤ 0.5) nanoparticles. Further, EDS studies were accomplished to determine the chemical composition. Kubelka-Munk's approach was used to determine the band gap, and the values were found to be in the range of 3.18-3.32 eV. The energy spectra for the nanoparticles were in the range of 560-1100 cm-1, which is due to the spinel structure of Sr-doped CoAl2O4 nanoparticles. The behavior plots of magnetic induction (M) against the magnetic (H) loops depict the ferromagnetic behavior of the nanomaterials synthesized.

Hydrothermal synthesis of CoAl2O4 spinel: effect of reaction conditions on the characteristic and morphological features

Abstract The spinel form of cobalt aluminate (CoAl2O4) was synthesized by a hydrothermal method in moderate conditions. The synthesized phases were qualitatively and quantitively identified by means of different characterization techniques. The effects of reaction conditions of Co/Al ratio, pH, stirring time, reaction temperature, reaction time and capping agent addition on the color performance and morphology were studied. The capping agents of n-cetyl-n, n, n trimethylammonium bromide (CTAB), 2-pyrrolidinone (PVP), triethylamine (TEA) and oleic acid (OA) were used. The probable reaction mechanism can be explained with the steps of (i) formation of Co–Al–O complexes and (ii) conversion to Co-spinel. In the reaction mechanism, the addition of capping agents improved the conversion of complexes to Co-spinel. The characteristic band values were observed at 550, 595 and 650 nm in the ultraviolet–visible wavelength range, in UV analyses. The lowest b* and the highest BET surface area were determined in the TEA added sample with values of – 37.4 and 16.02, respectively. Layer shaped particles were obtained in CTAB added samples whereas the angled cubic particles were seen in the TEA and OA added samples. The smallest particles were observed in the use of PVP addition to spinel, and the particle size was around 100 nm. The experimental results proved that characteristic properties of prepared samples can be enhanced by the selection of a suitable capping agent.

Oxygen deficient Ce doped CO supported on alumina catalyst for low-temperature CO oxidation in presence of H2O and SO2

The carbon monoxide (CO) oxidation has been carried out using Ce doped Co/Al2O3 prepared by coprecipitation followed by deposition precipitation. The 0.1 mol Ce doped Co supported on alumina showed maximum CO oxidation activity compared to the undoped catalyst at a low temperature. The physicochemical characteristics of synthesized catalysts were investigated by FTIR, XRD, Raman, XPS, 27Al solid-state NMR, H2-TPR, HR-TEM, etc. Ce doping promoted a distortion in the cobalt lattice structure. The distortion leads to an increase in reactive oxygen and the number of oxygen vacancies. In addition, Ce modification prevents the generation of the cobalt aluminate phase and stimulates the production of the Co3O4 active phase for CO oxidation. The presence of hexa and penta-coordinated alumina increases the defect and oxygen vacancy formation, which was responsible for a higher CO oxidation rate. The Ce doped Co/Al2O3 catalyst showed maximum water and SO2 tolerance due to the Ce doping. The mechanistic and kinetic details for CO oxidation have been explained by correlating with characterization.

Synthesis, characterization and magnetic properties of Mg2+ doped green pigment Cobalt aluminate nanoparticles

Synthesis, characterization and magnetic properties of Mg2+ doped green pigment Cobalt aluminate nanoparticles

A surface modification layer with cobalt aluminate inhibits 4.6 V high-voltage phase transition of LiCoO2

Inhibiting the high-voltage phase transition of lithium cobaltate has been a major challenge. Here, we utilize a simple and feasible strategy by using the surface modification layer with cobalt aluminate to achieve ultra-long cyclicity of LiCoO2 at high voltage. This strategy can protect the electrode from electrolyte attack without hindering the migration of lithium ions, and reduce the loss of active cobalt. Simultaneously, Co (II) of the modified layer is oxidized Co (III) in the redox reaction, which provides extra electrons to induce the deintercalation/intercalation of lithium ions for the half-cell in process of the initial charge/discharge. Electrochemical in-situ characterization reveals that the compound material presents excellent high-voltage structural stability due to reversible phase transition induced by the surface modification layer. As a result, CoAl2O4 coated LiCoO2 achieves excellent ultra-long cycling with high-capacity retention of 86.3% after 500 cycles at 1 C (1C = 274 mA g−1, 3.0–4.6 V).

Shepherd Color's new blue pigment claims maximum chromaticity

Shepherd Color has announced the launch of their new specialty Cobalt Aluminate Blue 20G599.

Nickel doped CoAl2O4@CNT nanocomposite: Synthesis, characterization, and evaluation of sunlight driven catalytic studies

The breakdown of the coloured and colourless organic dyes under natural sunlight was investigated by the prepared photocatalysts. Cobalt aluminate (CoAl2O4, CA) and nickel doped cobalt aluminate (Ni–CoAl2O4, NCA) were well synthesized by an easy pechini route. Ultra-sonication route was followed to prepare composite with carbon nanotubes (CoAl2O4@CNT, NCA@CNT). The prepared catalysts were comprehensively characterized by various techniques. Spinel structure and functional groups of synthesized photocatalysts was confirmed by XRD and FT-IR techniques. The surface morphology of the synthesized materials was analyzed via SEM. The optical properties of fabricated photocatalysts were investigated via UV–Visible spectroscopy. NCA@CNT nanocomposite exhibited greater photocatalytic activity than doped and undoped photocatalysts. NCA@CNT exhibited 92.7%, 88.77%, and 63.34% photodegradation of crystal violet, methylene blue, and benzoic acid respectively. A scavenger experiment was carried out to figure out efficient photoactive species taking part in the photodegradation of organic pollutants.

A comparative study of ultrasonic-assisted methods to synthesise spinel (CoAl2O4) nanoparticles

In this study, a spinel form of cobalt aluminate (CoAl2O4) was successfully synthesized using different experimental procedures assisted by ultrasonics. The effects of ultrasonic treatment with co-precipitation and hydrothermal experimental methods were compared with traditional techniques. The results indicated that enhanced chromatic features resulted from the experimental procedures modified by ultrasonic treatment. In chromatic analyses, the lowest b* value of −47.19 was observed in the sample synthesized by the ultrasonic-assisted co-precipitation method. This synthesized phase was identified as “Spinel” with the chemical formula of CoAl2O4 according to Powder Diffraction File number (PDF no.) 01-0820-2251 from XRD analyses. The optimum samples were determined to be UC-8 and UH-9 for the modified methods. For these samples the particle sizes were measured between 62 and 83 nm, whereas crystallite sizes were estimated to be in the range from 33 to 43 nm. The thermal analyses results proved the stability of the sample structure up to 1000 °C.

Ce-doped cobalt aluminate catalysts for the glycerol hydrodeoxygenation (HDO) with in-situ produced hydrogen

In this study, the hydrodeoxygenation (HDO) of glycerol with in-situ produced H2, via aqueous-phase reforming, was investigated over Ce-doped CoAl2O4 catalysts synthesized by coprecipitation. The catalytic runs were performed at 50 bar/260 ºC for 3 h TOS in a fixed bed reactor. The synthesized catalysts were extensively characterized to better understand the effect of physicochemical and surface characteristics on the catalytic performance. The results revealed that doping with Ce increases the population and strength of acid centers, which results in a higher selectivity towards deoxygenated liquid products. Ce-doped catalysts exhibited higher yield to hydroxyacetone and 1,2-propanediol. Post-reaction characterization revealed a decrease of the metallic surface area, mainly due to alumina coating, and to a lesser extent, due to the oxidation and leaching of the cobalt.

Structural investigation and optical properties of cobalt aluminate pigments derived from thermal decomposition of mixed-metal nitrate co-crystals

In this study, the coloration mechanism of cobalt aluminate spinel materials derived by thermal decomposition of the co-crystallized mixed-metal precursors has been reported. The structural alteration of cobalt aluminates, along with the origins of chroma values at the different calcination temperatures from 600 °C to 1200 °C were thoroughly investigated by combining XRF, XRD, XAS, UV-VIS DRS, FT-IR, and FT-Raman techniques. In-depth analyses of structural information and corresponding optical properties suggested that the coloration can be modified by controlling Co2+/Co3+ contents and their site occupancies in the spinel structure by adjusting calcination temperatures and selecting the counter ions with appropriate oxidizing power. The interplays among (1) the oxidation process at low temperatures, (2) the deoxidation process at high temperatures, (3) the reduction in the degree of spinel inversion (toward the emerging of normal-spinel CoAl2O4 structure), and (4) the existence of the minor Al2O3 domains are found to be key imperatives for tailoring the color appearances of cobalt aluminate powders in the broad range from black, dark-green, green, greenish-blue, dark-blue, towards bright-blue. Herein, we reveal the correlation between the synthetic parameters and the structural features of the obtained spinel-based materials, which could further exhibit the crucial procedure to control the coloration of inorganic pigments systematically.

Investigating the Colour Difference of Old and New Blue Japanese Glass Pigments for Artistic Use

Colour consistency is an important consideration when selecting pigments used on works of art. In this study, we analyse the colour difference between two sets of synthetic blue glass pigments acquired at least 8 years apart from the same manufacturer in Japan. The old pigment set (unused, dry powder with four different grain sizes) appears faded compared to the new set. These pigments are made available for artistic use, commonly in Nihonga or Japanese paintings. Raman spectroscopy and SEM-EDS results characterize these pigments as cobalt aluminate spinels dissolved in leaded glaze, a special class of complex coloured inorganic pigments that is not well-understood in the field of conservation. Colour difference between the old and new pigments with four different grain sizes were quantified by analysing photomicrographs with image analysis software. Blue pigments with coarse and extremely fine grains showed significant colour change compared to pigments with medium and fine grain sizes. The high occurrence of crystallites in the finer grains give a final colour that is bluer and lighter. Possible causes for the colour difference including manufacturing methods and storage environment are discussed.

Long-acting CoAl2O4 spinel catalyst developed on activated alumina pellets by facile synthesis to activate peroxymonosulfate: Controllable cobalt leaching and environmental adaptability

A novel composite catalyst prepared by fixing cobalt aluminate (CoAl2O4) spinel on formed alumina carrier by impregnation-calcination route is reported, which can be used to efficiently activate peroxymonosulfate (PMS) to degrade p-nitrophenol (PNP). The internal laws of phase composition and preparation conditions are explored in detail, and the results show that the introduction of additional aluminum ions in the preparation process changes the coordination environment and the electronic state of cobalt ions, which leads to the transformation of spinel/inverted spinel in the composition, and further affects the activity and stability of the catalyst. The selected CoAl-Aaps-600 catalyst has high CoAl2O4 content, showing good cycle performance and low cobalt leaching, and has great catalytic degradation performance at different temperatures and a wide pH range. Most notably, a fixed bed reactor packed with 20 g of CoAl-Aaps-600 exhibits excellent capacity to continuously treat 60 L of PNP solution with acceptable PNP removal ratio and low cobalt leaching content. Sulfate radical and singlet oxygen are identified as the main reactive oxygen species produced in CoAl-Aaps-600/PMS system, and the reaction mechanism is reasonably inferred. This work provides a potential application material and process for the treatment of continuous organic wastewater.

Facile microwave synthesis, structural, optical, and magnetic properties of Zn2+ doped CoAl2O4 spinel nanoparticles

CoAl2O4 and Zn:CoAl2O4 nanoparticles (NPs) were synthesized via microwave combustion process (MCP) and L-alanine used as fuel. The average crystallite size is found in the range of 10–18 nm. Spherical aggregated particle morphology is obtained for synthesized sample and the same confirmed by HR-SEM images and nonexistence of impurities in the prepared samples were confirmed by EDX spectra. The band gap values of the prepared samples were found to be in the range of 3.35–2.32 eV. Further in FTIR spectra a couple of strong absorption bands observed which lie in the range of 500–1100 cm−1, ensuring the formation of cubic spinel structure. Thermal studies confirmed the weight loss and exothermic transitions in pure and Zn2+ ion doped cobalt aluminate samples. The prepared Zn ion modified cobalt aluminate samples exhibited diamagnetic magnetic characteristics at room temperature and the same have been confirmed.

Structural, magnetic and adsorptive properties of nano spinel of cobalt aluminate doped with nickel for Cr(VI) removal

Nanocrystallines of cobalt aluminate spinel doped with Nickel (MAl2O4; M = Co+2, Ni+2) were synthesized by sol-gel method. The MAl2O4 samples were prepared by using aluminum nitrate; cobalt nitrate, nickel nitrate, citric acid and diethylene glycol mono ethyl ether as precursor materials. The nanocrystallines spinel were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction(XRD), Thermal gravimetric (TGA), Scanning electron microcopy (SEM) with the energy dispersive X-ray spectroscopy (EDX) methods. The Specific surface area of the synthesized powders was measured with a Brunauer-Emmet-Teller (BET) apparatus using N2 adsorption. According to obtained XRD patterns the formation of single phase MAl2O4 completed up 800 °C. The average crystallite's sizes spinel and specific surface area at 800 °C were estimated about 11.07 nm and 154 m2 g−1, respectively. The results of SEM analysis show that the nanoparticles shape are as spherical shape, uniform and a little agglomerated. The magnetic behavior of spinels showed the magnetization decreased with increasing nickel ions. Adsorption of Cr(VI) by as prepared spinels were considered. The highest percent of Cr(VI) adsorption was occurred at contact time of 45 min, pH 7.0, and adsorbent dose of 2 g L−1. The order of adsorption capacity of sorbent samples for Cr(VI) removal was as follow: Ni0.5Cu0.5Al2O4 >Ni0.7Cu0.3Al2O4 >Ni0.3Cu0.7Al2O4>NiAl2O4> CoAl2O4. Kinetic studies indicated that the adsorption process follows by pseudo second-order model. Thermodynamic results revealed that the adsorption of Cr(VI) is endothermic, spontaneously process and feasible in the range of 298–338 K.

Raman identification of the different glazing technologies of Blue-and-White Ming porcelains

Shards of Blue-and-White Ming porcelain from shipwrecks of Portuguese ships found on the coasts of South Africa plus a shard from Mombasa (Kenya) were analyzed by optical microscopy, SEM-EDS and Raman microspectroscopy (458 nm). Whereas the Raman signature of porcelain body paste compositions which are based on mullite, quartz and an amorphous phase with the minor presence of anatase and feldspar are very comparable whatever the variable alumina content, at least two types of glazes are observed: a high-temperature soda-potassium glaze, and glazes richer in calcium and similar to a celadon glaze (with the possibility of wollastonite formation). The blue decoration is obtained with a material rich in manganese typical of the Ming productions. Some shards exhibit a two-layer glaze and the blue decoration is either placed under-glaze, or in-glaze as found in the Vietnamese productions of the same period. Previous assignments of the Raman signature of feldspar to cobalt aluminate are now not favoured (blue colour is obtained with Co2+ ions dissolved in the glassy silicate) and several black spots exhibit the characteristic spectrum of an epsilon Fe2O3 phase being present.

Photocatalytic degradation of rhodamine B in the visible region using nanostructured CoAl2−xLaxO4 (x = 0, 0.01, 0.03, 0.07, and 0.09) series: Photocatalytic activity and DFT calculations

In the present research, we focused on the study of the photocatalytic activity of nanostructured CoAl2−xLaxO4 (x = 0, 0.01, 0.03, 0.07, and 0.09) as photocatalysts synthesized by the citric sol–gel method which were used for the photocatalytic degradation of rhodamine B (RhB) under visible light. Doping of lanthanum ion, La3+ in the cobalt aluminate matrices were characterized by XRD, XPS, FT-IR, Raman, Dif-UV, TEM, and N2 adsorption/desorption isotherms using Brunauer-Emmett-Teller (BET). Also, The first principle DFT calculations were performed to study the band structure and charge distribution of the spinel compounds, and the results showed the presence of a direct bandgap at the G symmetry point. The Optoelectronic properties revealed that the energy bandgap values of CoAl2−xLaxO4 decreased from 3.7 to 2.8 eV upon increasing the La ratio. The photocatalytic activities were evaluated in the removal of the textile dye (RhB) from aqueous solutions. Several conditions such as initial dye concentrations and contact times were investigated. The mechanism of photocatalytic activity of CoAl2−xLaxO4 (x = 0.00 and 0.07) substitution on the RhB above the liquid surface make clear that both hydroxyl and superoxide anions radicals are the main active species that play the main role in removing RhB from solutions. The PL spectra were measured to suggest the impact of La dopant on the photoactivity of the CoAl2O4. The blue shift in the visible emission peak was caused by the quantum size effect in cobalt aluminate nanostructures due to the substitution of Al3+ with La3+ ions. Also, PL intensity decreased dramatically when the La3+ substitution with the Al3+ ions.

Acrolein production by oxidative coupling of alcohols over zinc and cobalt aluminate spinels enlightened by adsorption calorimetry study

This work reports on the production of acrolein by oxidative coupling of biosourced alcohols (methanol and ethanol). This reaction is performed in a two-step process using iron molybdate catalyst to produce formaldehyde and acetaldehyde and zinc and cobalt aluminate spinels, with or without vacancies, to perform the cross-aldolization of aldehydes. In this study, adsorption microcalorimetry of NH3 and SO2 was used to determine the acid-base properties of the catalysts. The catalytic activity was monitored and correlated to catalysts acid-base properties. Moreover, to enlighten the behavior of reactants over the surface and the mechanism of the reaction, an extensive adsorption microcalorimetric study using acetaldehyde and formaldehyde as probe molecules was performed to determine molar enthalpies, molar entropies, thermokinetic parameters but also energy spectra. This broad calorimetric study provided a better understanding of the reaction and allowed to confirm the preferential adsorption of formaldehyde compared to acetaldehyde thus justifying the absence of crotonaldehyde in the products of the catalytic reaction.