Cobalt chromium-layered double hydroxide, α- and β- Co(OH)2 and amorphous Cr(OH)3: synthesis, modification and characterization (original) (raw)
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Formation of Cr(III) Hydroxides from Chrome Alum Solutions
Journal of Colloid and Interface Science, 1996
linized and subsequently aged. The rapid alkalinization leads The formation of active chromium hydroxide, Cr(OH) 3 r3H 2 O, to the immediate precipitation of a crystalline solid having was studied through potentiometric titrations and turbidimetric the empirical formula Cr(OH) 3 r3H 2 O (10). It consists in measurements. UV-Vis and IR spectroscopies were also employed Cr(OH) (H 2 O) 3 units linked through Cr(H)O-HrrrO to characterize the synthesized solid. The rapid addition of NaOH (H) -Cr hydrogen bonds and was named ''active chromium solution to aqueous chrome alum (KCr(SO 4 ) 2 r12H 2 O) solutions hydroxide'' (11) or ''active monomer hydroxide'' (12). The caused the immediate precipitation of the active material. Only aging of this material, on the other hand, results in a polymonomeric Cr(III) species seemed to be participating in the premeric and amorphous solid (13). Its new chemical and struccipitation process; neither chromium polymers nor complexes with anions (SO 20 4 , Cl 0 , NO 0 3 , ClO 0 4 ) influenced the fast formation of tural properties are almost equal to those of solids studied Cr(OH) 3 r3H 2 O. Titration studies allowed the determination of by Matijević . The unique appreciable difference several hydrolysis and precipitation constants for Cr(III). Neverbetween these two particulates is that precipitation of active theless, they cannot be used for the estimate of Cr(OH) 0 3 formation chromium hydroxide and its subsequent aging lead to a polyconstant. ᭧ 1996 Academic Press, Inc.
Synthesis, Modification and Optical Characterization of Co-Cr Layered Double Hydroxide
2018
Cobalt and chromium based layered double hydroxides (LDHs) have been successfully synthesized by the co-precipitation method at a constant pH of 10. The intercalation of stearic acid (C18H36O2) into CoCr-LDH and preparation of their polymer nanocomposites using two different methods were studied in the paper. The obtained samples were characterized before and after modification by X-ray diffractometry (XRD) and Ultraviolet visible (UV-Vis) spectroscopy. It has been shown that different reaction temperature profoundly affects the band-gaps of inorganic and composite structures.Three optical band gap values (Eg1, Eg2 and Eg3) for the samples obtained before and after modification. Two optical band gap values were estimated in polymer/LDH nanocomposites. The high-value band gaps for CoCr-LDH(100°C)- NBR and CoCr-LDH(100°C)-SA- NBR were determined to be 5.9 eV and 5.7 eV, respectively. The low-value band gaps for CoCr-LDH(100°C)-NBR and CoCr-LDH(100°C)-SA- NBR were determined to be 4.1 ...
Journal of Cluster Science, 2005
Thermal treatment in air of the organometallic polymerf NPðO 2 C 12 H 8 Þ ½ 0:8 NPðOC 6 H 4 CH 2 CN ½CrðCOÞ 5 0:13 Þ 2 Â Ã 0:18 g n (1) results in the formation of nanometer-size metal oxide particles. Cr particles in the 35-85 nm range, mostly 54 nm, immersed in an phosphorus oxides matrix were found. ATG studies in air suggest that the formation of the nanostructures occurs in four steps, the first involving loss of the carbonyl groups of the Cr(CO) 5 fragment. The following steps involve the oxidation of the organic matter and finally the oxidation of the chromium to give the pyrolytic product. The use of these kinds of organometallic polymers as precursors for a general and potential new route to materials having metal/metal oxide nanostructures is discussed.
Journal of Materials Science, 2017
This study reports the preparation and characterization of the spinel CoCr 2 O 4. In order to obtain 20% CoCr 2 O 4 /80% SiO 2 and 50% CoCr 2 O 4 /50% SiO 2 (mol%) nanocomposites, we have used a versatile pathway based on the thermal decomposition of some particular precursors, Co(II) and Co(III) carboxylatetype complex combinations, inside the SiO 2 matrix. The ligands of these coordination compounds result in the redox reaction between Co(II) and Cr(III) nitrates and 1,3-propylene glycol by heating at 150°C of the gels (tetraethylorthosilicate-metal nitrates-1,3-propylene glycol). The as-obtained precursors, embedded in silica gels, were characterized by FT-IR spectrometry and thermal analysis. Both precursors decompose up to 350°C, leading to the corresponding metal oxides inside the silica matrix. X-ray diffraction of the powders annealed at different temperatures has evidenced the formation of CoCr 2 O 4 starting with 400°C for 20% CoCr 2 O 4 /SiO 2 and 300°C for 50% CoCr 2 O 4 /SiO 2. This behaviour can be explained by the fact that, by thermal decomposition of the chromium carboxylates, a nonstoichiometric chromium oxide Cr 2 O 3?x is formed. At * 400°C, Cr 2 O 3?x turns to a-Cr 2 O 3 , which interacts with CoO leading to cobalt chromite nuclei inside the pores of the silica matrix. CoCr 2 O 4 has been obtained as nanocrystallites homogenously dispersed within the silica matrix as resulted from XRD, TEM and EDX mapping, with mean particle size in the range 5-20 nm.
Synthesis, characterization, and growth mechanism of α-Cr< sub> 2 O< sub> 3 monodispersed particles
Journal of Physics and …, 2011
Monodispersed spherical particles of chromium (III) oxide, a-Cr 2 O 3 , were successfully synthesized from a diluted solution of KCr(SO 4 ) 2 Á 12H 2 O using the Aqueous Chemical Growth (ACG) technique. The spherical a-Cr 2 O 3 particles obtained were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Raman spectroscopy for structural, surface morphological, chemical, and physical properties, as a function of deposition time. The XRD and Raman spectroscopy showed that aging had no apparent effect on the structure of the obtained uniform fine (in the range of micronnano-level)-spherical particles of a-Cr 2 O 3 . The use of SEM demonstrated that aging had a clear influence on the size and the particles size distribution. Accordingly, the time dependence of the average diameter of a-Cr 2 O 3 spherical particles follows the d 3 law as required for diffusion-limited Ostwald ripening.
Authors personal copy Saleh Mani et al Cr2O3 nanoparticles 2011
Monodispersed spherical particles of chromium (III) oxide, a-Cr 2 O 3 , were successfully synthesized from a diluted solution of KCr(SO 4 ) 2 Á 12H 2 O using the Aqueous Chemical Growth (ACG) technique. The spherical a-Cr 2 O 3 particles obtained were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Raman spectroscopy for structural, surface morphological, chemical, and physical properties, as a function of deposition time. The XRD and Raman spectroscopy showed that aging had no apparent effect on the structure of the obtained uniform fine (in the range of micronnano-level)-spherical particles of a-Cr 2 O 3 . The use of SEM demonstrated that aging had a clear influence on the size and the particles size distribution. Accordingly, the time dependence of the average diameter of a-Cr 2 O 3 spherical particles follows the d 3 law as required for diffusion-limited Ostwald ripening.
Synthesis and structure screening of nanostructured chromium oxide powders
Journal of Alloys and Compounds, 2009
The evolution with calcinations of chromium oxide (Cr 2 O 3 ) nanocrystals of catalytic interest, prepared from reduction of K 2 Cr 2 O 7 with maleic acid has been studied. The characterization of the materials was confirmed by X-ray diffraction (XRD), Fourier transformation infrared (FT-IR), transmission electron microscope (TEM), N 2 adsorption-desorption isotherms, and thermo-analytical methods. The influence of the operating variables such as molar ratio, pH, gelation time and specific surface area was investigated and discussed. The results showed that the K 2 Cr 2 O 7 /maleic acid of 1:1.7 molar ratio at pH 7 and 15 days gelation time were considered to be the best conditions for producing Cr 2 O 3 of the pore diameter distribution in the range of 2-6 nm and specific surface area of 123 m 2 /g. The particle size and phases of chromium oxide were affected by the ratio of K 2 Cr 2 O 7 to maleic acid, temperature, and time of calcination. The amorphous phase appeared at room temperature, whereas it turned to crystalline phase when the calcination temperature increased to about 400 • C.
Interconversion of CrO2 formed by decomposition of chromium(III) nitrate nonahydrate
Journal of Solid State Chemistry, 1995
The products of the decomposition of chromium(II1) nitrate nonahydrate (CNN) and interconversions occurring in the system CrO,-CrOOH have been investigated using thermal analysis, mass spectrometry, X-ray powder diffraction, and magnetic resonance. The studies indicate that changes in the conditions of CNN calcination, especially in the temperature, greatly influence the ratio of Cr(IV) to Cr(II1) oxides in the products. CrO, formed during slow heating to ca. 350°C is very stable and its complete transformation into Cr,Oj requires a temperature higher than 600°C. The rapid crystallization of the amorphous products of CNN calcination, occurring at ca. 38O"C, leads to the decomposition of all intermediates during this strongly exothermal reaction, finally resulting in Cr,O,. The interconvertability of the components of the redox cycle CrO,-CrOOH was proven experimentally. Due to its unique characteristics, this redox cycle is suggested for the difficult identification of CrO, in amorphous chromium-oxygen systems. o 1~s Academic Press, Inc.
High-temperature reactions in the Co3Cr4(PO4)6–Cr(PO3)3 system
Journal of Thermal Analysis and Calorimetry
A new dichromium(III) cobalt(II) diphosphate(V) of the formula CoCr 2 (P 2 O 7) 2 was detected in the Co 3 Cr 4 (PO 4) 6-Cr(PO 3) 3 system. The new compound was obtained as a result of high-temperature solid-state reactions between CoCO 3 , Cr 2 O 3 and (NH 4) 2 HPO 4 as well as between Cr(PO 3) 3 and Co 3 Cr 4 (PO 4) 6. CoCr 2 (P 2 O 7) 2 was characterized using XRD, DTA and IR methods. Results demonstrated that CoCr 2 (P 2 O 7) 2 crystallizes in the triclinic system and its unit cell parameters were calculated. Its infrared spectrum was presented. CoCr 2 (P 2 O 7) 2 melts incongruently at 1270±10°C with a formation of solid a-CrPO 4. The compound Co 3 Cr 4 (PO 4) 6 , component of the system under study, was obtained for the first time as a pure phase. Its thermal stability was also investigated. Co 3 Cr 4 (PO 4) 6 is stable in air up to 1410 ± 20°C.
Nanocrystalline Cr2O3 and amorphous CrO3 produced by solution combustion synthesis
Journal of the European Ceramic Society, 2006
The synthesis of chromium oxides by solution combustion synthesis was investigated. Ammonium dichromate, glycine, urea and ammonium nitrate dissolved in aqueous solution were used as the precursors of the oxides. The effect of different reaction parameters, such as fuel richness, stoichiometry and fuel leanness was evaluated; such parameters were modified by changing the reagents and the fuel/oxidant ratio. Amorphous CrO 3 and crystalline Cr 2 O 3 were synthesized. The results suggest that glycine is a better complexing/combustible agent for ammonium dichromate than urea. Addition of extra ammonium nitrate to stoichiometric compositions improved the specific surface area and reduced the crystallite size. The smallest crystallite size (≈20 nm) of Cr 2 O 3 was obtained with glycine as fuel/complexant agent in fuel-lean mixtures. The highest specific surface area (63 m 2 /g) was observed with urea in fuel-rich mixtures, forming amorphous CrO 3 .