Comparative study of the synthesis of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> in silica through the polymerized complex route of the sol–gel method

In this work the synthesis of CoFe₂O₄-SiO₂ and NiFe₂O₄-SiO₂ nanocomposites was studied via the sol–gel method, using the polymerized complex route. The polymerized precursors obtained by the reaction of citric acid, ethylene glycol, tetraethylorthosilicate, ferric nitrate, and cobalt nitrate or nickel chloride were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. NMR and IR spectra of the precursors, without and with metallic ions, show the formation of polymeric chains with ester and ether groups and complexes of metal-polymeric precursor. The nanocomposites were obtained by the thermal decomposition of the organic fraction and characterized by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). XRD patterns show the formation of CoFe₂O₄ and NiFe₂O₄ in an amorphous silica matrix above 400 °C in both cases. When the calcination temperature was 800 °C the particle size of the crystalline phases, calculated using the Scherrer equation, reached ∼35 nm for the two oxides. VSM plots show the ferrimagnetic behavior that is expected for this type of magnetic material; the magnetization at 12.5 KOe of the CoFe₂O₄-SiO₂ and NiFe₂O₄-SiO₂ compounds was 29.5 and 17.4 emu/g, respectively, for samples treated at 800 °C.     

Explosive degradation of woody biomass under the presence of metal nitrates

The influence of various metal nitrates (Fe, Ni, Cu, Zn, etc.) has been studied in the pyrolysis of woody biomass under inert atmosphere. Pyrolysis samples have been prepared by impregnation of wood with aqueous solution of the salts as well as by mechanical mixing of powders of wood and nitrates. Thermogravimetric analysis showed that the addition of nickel, copper and zinc nitrates reduced significantly the decomposition temperature of wood below 150 °C. The decomposition of wood completes explosively at the temperature. The pyrolysis products have been analysed by GC–MS and XRD methods. Preliminary result of the quantitative analysis of emitted NO_x gas in the pyrolysis treatment is also presented.     

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.     

The thermal behavior of some polymeric precursors used in CaAl12O19 synthesis

CaAl₁₂O₁₉ was synthesised using three different precursors: (a) a polyesteric type precursor resulted from the traditional Pechini method; (b) a polyesteric type precursor resulted from the reaction between citric acid and calcium and aluminum nitrates; and (c) a polymeric type precursor resulted from the reaction between acrylic acid and calcium an aluminum nitrates. The thermal behavior of the three precursors used in the CaAl₁₂O₁₉ synthesis was monitored to underline the thermal effects associated to the CaAl₁₂O₁₉ formation. Thermal analyses performed on precursors do not reveal clear differences regarding the thermal effects assigned to calcium aluminates formation, at temperatures over 800?°C. In contrast, thermal analysis of samples pre-fired at 200?°C, and especially at 600?°C, show clear differences between samples obtained in different ways. It is noted that in samples obtained from acrylic acid and nitrates, and citric acid and nitrates, CA₆ is practically single phase after calcination at 1,200?°C. However, in the sample obtained from citric acid, ethylene glycol, and nitrates, calcined at 1,200?°C, CA₆ is present along with CA₂ and ??-Al₂O₃.     

Preparation of CuFe2O4/SiO2 nanocomposite starting from Cu(II)–Fe(III) carboxylates embedded in hybrid silica gels

Nanocomposites of the type 30 % CuFe₂O₄/70 % SiO₂ were synthesized using the modified sol–gel method starting from tetraethylorthosilicate, metal nitrates (Fe(NO₃)₃·9H₂O, Cu(NO₃)₂·3H₂O) and the diol: 1,3-propane diol. The obtained hybrid gel, which contains within the pores, the metal nitrates and diol, was thermally treated at 140 °C, when the redox reaction between metal nitrates and 1,3-propane diol takes place forming Cu(II)–Fe(III) carboxylate compounds of malonate type. The thermal decomposition of the carboxylates within the gels pores, at ~300 °C, leads to simple or mixed metal oxides, uniformly distributed within the amorphous silica matrix. The spinel system CuFe₂O₄/SiO₂ was obtained starting with 700 °C. The evolution of the spinel phase with the annealing temperature was investigated and resulted that at 1,000 °C, the matrix crystallizes into cristobalite and quartz. The formation of bulk CuFe₂O₄, starting from the same type of Cu(II)–Fe(III) carboxylate compounds was also investigated. A comparison between the thermal evolution of bulk CuFe₂O₄ and CuFe₂O₄/SiO₂ starting from Cu(II)–Fe(III) carboxylate compounds was made. The magnetic behavior of the ferrite nanocrystallites depending on the annealing temperature was also investigated.     

Effect of gamma-irradiation on surface and catalytic properties of Co3O4 and NiO catalysts

The effects of g-irradiation (0.2-1.6 MGy) on the particle size, specific surface area and catalytic activity of Co₃O₄ and NiO solids were investigated. The investigated solids were prepared by heat treatment of cobalt carbonate at 500 and 700 °C and basic nickel carbonate at 400 °C. The techniques employed were XRD, nitrogen adsorption at -196 °C and decomposition of H₂O₂ at 30-50 °C. The results showed that g-irradiation resulted in a small decrease in the particle size of the investigated solids and effected a progressive increase in their specific surface areas. On the other hand, the exposure of Co₃O₄ and NiO catalysts to a dose of 0.2 MGy resulted in a significant decrease in their catalytic activities, which suffered further progressive decrease upon increasing the doses up to 1.6 MGy. Gamma-irradiation did not modify the activation energy of the catalyzed reaction but decreased the concentration of catalytically active sites without changing their energetic nature. These results were discussed in terms of splitting of the particles of the treated solids and removal of chemisorbed species present in nonstoichiometric cobalt and nickel oxides.     

Thermal studies of hypervalent iodine reagents

The use of unconventional synthesis methods in the formation of CaO·2Al₂O₃ (CA₂) is justified because it reduces the formation temperature of the compound. CA₂ is formed by classical method at temperatures above 1,400 °C. The polymeric precursor method allows a significant temperature decrease in CA₂ synthesis reaching temperatures of 1,000 °C. This paper deals with CA₂ synthesis by “citrate” method which is often presented as Pechini method, starting from a mixture of citric acid, ethylene glycol and calcium, and aluminum nitrates. A method based on the formation of a polymeric precursor was also used, starting from a mixture of acrylic acid and nitrates of calcium and aluminum. The results showed a net difference in favor of samples obtained from acrylic acid, which by annealing at 800 °C for 1 h, contain pure CA₂. The samples obtained from citric acid, after annealing at 800 °C are amorphous. After annealing at 900 °C in all samples CA₂ is single phase.     

Redox reactions between metal nitrates and polyols with the formation of nanopowders

The reduction of metal nitrates (Cu(NO₃)₂ · 6H₂O, AgNO₃, and Ni(NO₃)₂ · 6H₂O) by polyols under hydrothermal conditions at temperatures of 150–250°C was studied. The possibility of synthesizing copper, silver, and nickel powders with average particle sizes of 10 to 150 nm depending on the concentration of initial reagents, the temperature, and the nature of a reducer was established using X-ray diffraction analysis and atomic force microscopy. Lanthanide and alkali-earth nitrates were shown to form highly dispersed powders of metal carbonates with an average particle size of ～23 nm under similar conditions.     

Co(III), Ni(II), and Cu(II) complexes of bidentate N,O-donor Schiff base ligand derived from 4-methoxy-2-nitroaniline and salicylaldehyde

Asymmetric bidentate Schiff base ligand (HL) and its cobalt(III), nickel(II), and copper(II) complexes have been synthesized (where L = 2-[(4-methoxy-2-nitrophenyl)iminomethyl]phenol). The ligand and its metal complexes have been characterized by elemental analyses (CHN) and FTIR spectroscopy. Thermogravimetric analyses of the compounds reveal their thermal stabilities along with their thermal decomposition pattern. In addition, the complexes have been used for the preparation of corresponding metal oxide nanoparticles by controlled aerobic thermal decomposed at 500 °C. The FTIR pattern of the obtained solids receals the formation of the metal oxides nanoparticles.     

Thermal decomposition of nickel aluminium mixed hydroxides and formation of nickel aluminate spinel

Various nickel aluminium mixed hydroxide samples of different compositions were prepared by co-precipitation from their nitrate solutions using dilute NH₄OH. Additional samples were prepared by impregnation of hydrated Al₂O₃, preheated at 600 and 900°C, with nickel nitrate solution in an equimolar ratio. The thermal decomposition of different mixed solids was studied using DTA. The X-ray investigation of thermal products of the mixed solids was also studied.The results obtained revealed that the presence of NiO up to 33.3 mole % with aluminium oxide much enhanced the degree of crystallinity of the γ-Al₂O₃ phase. In contrast, the presence of Al₂O₃ much retarded the crystallization process of the NiO phase. With the exception of samples containing 20 mole% NiO, all the mixed hydroxide samples, when heated in air at 900°C, led to the formation of well-crystalline Ni Al₂O₄ spinel, alone, or together with either NiO or γ-Al₂O₃, depending on the composition of the mixed oxide samples. The solid containing 20% NiO and heated at 900°C was constituted of amorphous NiO dispersed in γ-Al₂O₃. Heating the nickel nitrate-impregnated Al₂O₃ in air at 800–1000°C led to the formation of Ni Al₂O₄ together with non-reacted NiO and γ-Al₂O₃. The degree of crystallinity of the spinel was found to increase by increasing the calcination temperature of the impregnated solids from 800 to 1000°C and by increasing the preheating temperature of the hydrated Al₂O₃ employed from 600 to 900°C.     

Effects of gamma-irradiation on physicochemical state of surface and catalytic properties of CuO/MgO and NiO/MgO systems

Copper and nickel oxide samples supported on MgO were prepared by wet impregnation method. The obtained solids were heated at 350 °C and 450 °C. The extent of copper and nickel oxides was fixed at 16.7 mol%. The effect of g-irradiation (0.2-1.6 MGy) on the surface and catalytic properties of the solids were investigated. The techniques employed were XRD, nitrogen adsorption at -196 °C and H₂O₂ decomposition. The results revealed that the g-irradiation up to 0.8 MGy of CuO/MgO-450 °C effected a measurable decrease in the crystallite size of CuO phase with subsequent increase in its degree of ordering. Irradiation at a dose of 1.6 MGy brought about a complete conversion of MgO into Mg(OH)₂ during its cooling from 450 °C to room temperature via interacting with atmospheric water vapor. The S _BET and total pore volume of CuO/MgO precalcined at 350 °C and 450 °C increased progressively as a function of g-ray dose reached a maximum limit at 0.8 MGy. Gamma-irradiation of NiO/MgO-450 °C solids up to 0.8 MGy increased the degree of ordering of MgO and NiO phases without changing their crystallite size. The exposure of these solids to 1.6 MGy led to an effective transformation of some of NiO (not dissolved in MgO lattice) into Ni(OH)₂ via interacting with atmospheric water vapor during cooling from 450 °C to room temperature. Gamma-irradiation led to a measurable increase in the S _BET and V _p of NiO/MgO system. Gamma-irradiation of the two investigated systems resulted in both increase and decrease in their catalytic activities in H₂O₂ decomposition depending mainly on the irradiation dose and calcination temperature. This treatment, however, did not modify the mechanism of the catalytic reaction, but changed the catalytic active sites without changing their energetic nature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rapid calcination of ferrite Ni0.75Zn0.25Fe2O4 by microwave energy

Ferrites Ni_0.75Zn_0.25Fe₂O₄ were obtained by polymeric precursor method and calcined in a short time with microwave energy to assess the morphological and microstructural characteristics. Samples were calcined at 500, 650, 800, and 950 °C for 30 min in a microwave oven. The resulting powders were characterized by thermal analysis (TG/DSC), X-ray diffraction (XRD), Fourier transform infrared spectrometer, field-emission gun scanning electron microscope (FEG-SEM), and energy-dispersive X-ray spectroscopy. The XRD results showed the formation of single ferrite phase at temperature of 500 °C for 30 min. The FEG-SEM analysis showed agglomerated particles with formation of non-dense longitudinal plates, with interparticle porosity and agglomerated fine particles. The rapid calcination by microwave energy demonstrated satisfactory results in relatively low temperature of 500 °C for 30 min and appeared to be a promising technique for obtaining nickel–zinc ferrite powders.     

Preparation of CoxFe3?xO4 nanoparticles by thermal decomposition of some organo-metallic precursors

This paper presents a study for the preparation of Co_xFe_3−xO₄ (x = 0.02, 0.2, 0.5, 0.8, 1.0, 1.1, 1.5) nanoparticles, starting from metal nitrates: Co(NO₃)₂·6H₂O, Fe(NO₃)₃·9H₂O and ethylene glycol (C₂H₆O₂). By heating the solutions metal nitrates-ethylene glycol, the redox reaction took place between the anion NO₃ ⁻ and OH–(CH₂)₂–OH with formation of carboxylate anions. The resulted carboxylate anions reacted with Co(II) and Fe(III) cations to form coordinative compounds which are precursors for cobalt ferrite. XRD and magnetic measurements have evidenced the formation of cobalt ferrite for all studied molar ratios. The average diameter of the cobalt ferrite crystallites was estimated from XRD data and showed values in the range 10–20 nm. The crystallites size depends on the annealing temperature. The magnetization of the synthesized samples depends on the molar ratio Co/Fe and on the annealing temperature.     

Thermodynamics of ion association XXV. Transition metal complexes of proline and hydroxyproline

Calorimetric and potentiometric measurements have been made at 25°C of the formation of the mono- and bis-hydroxyproline complexes of cobalt(II), nickel(II), copper(II) and zinc(II) and the proline complexes of copper(II) and nickel(II). The data have been used to calculate ΔG, ΔH and ΔS values for both protonation and metal complexation and these are discussed in terms of the nature of the metal—ligand binding.     

Liquid–liquid extraction of Cu(II), Co(II) and Ni(II) with salicylidèneaniline from sulphate media

For a fundamental study on the development of novel extraction divalent metal, the extraction behaviour of copper(II), cobalt(II) and nickel(II) is studied with salicylidèneaniline (SAN). The phenol group in the Schiff base moiety leads to a large increase in the percentage of transition metal ions. SAN has both good reactivity towards metal ions and solubility in organic solvents. The solvent extraction of copper(II), cobalt(II) and nickel(II) with salicylidèneaniline from sulphate media is studied with the following parameters: pH, concentration of the extractant and the nature of diluent. The stoichiometry coefficients of the extracted species are determined by the slope analysis method. The extraction reaction proceeds by cation exchange mechanism and the extracted species are: CuL₂HL, CoL₂HL and NiL₂. The extaction constants are evaluated for the different diluents. Under suitable conditions of pH, the solvent extraction of cobalt(II) and nickel(II) in different diluents leads to third phase formation. This tendency is confirmed from numerical extraction constants for both metal cations (log?K _ex?=??15.10?±?0.03 for nickel(II) in CHCl₃) and (log?K _ex?=??12.56?±?0.04 for cobalt(II) in CHCl₃). The extraction efficiency is found to follow the order Cu(II)?>?Co(II)?>?Ni(II).     

In situ XRD study of nanocrystalline cobalt oxide reduction

The reduction of nanocrystalline cobalt oxide samples (single-phase and supported on γ-Al₂O₃) was studied using in situ X-ray diffraction (XRD) analysis. The atomic structures of single-phase and supported Co₃O₄ samples were refined, and the occurrence of cationic vacancies was demonstrated. A set of methods (XRD, temperature-programmed reduction, and differential dissolution) was used to find that the reduction of supported and unsupported model cobalt oxide was considerably different. The single-phase sample was reduced in undiluted hydrogen to cobalt metal with a hexagonal closely packed structure. The reduction of the supported sample (unlike the single-phase sample) occurred through the formation of a crystalline CoO phase to the formation of cobalt metal with a face-centered cubic structure. Interaction of cobalt oxide with the γ-Al₂O₃ support, which hinders the reduction to cobalt metal, was detected.     

Thermal and structural studies of the chloro complexes of cobalt,nickel and copper with 3-phenylpyridine

The chloro complexes of cobalt, nickel and copper with 3-phenylpyridine were prepared in ethanolic solution from which solid compounds were isolated. The cobalt and copper complexes have stoichiometry M₂LCl₄ while the nickel complex has stoichiometry NiLCl₂. The suggested structure for the cobalt and copper complexes is tetrahedral, while for the nickel complex it is octahedral. Thermal analysis studies show that the cobalt and copper complexes form intermediate complexes before their metal oxides are produced. The nickel complex also forms an intermediate complex and then nickel chloride before the nickel oxide is obtained.     

Synthesis and properties of transition and lanthanide complexes with benzyl monohydrazone-3-hydrazine- 4-benzyl-6-phenyl pyridazine ligand (BHP)

Synthesis and characterization of benzyl-monohydrazone-3-hydrazino-4-benzyl-6-phenyl pyridazine (BHP) and its complexes with copper(II), nickel(II), cobalt(II), zinc(II), manganese(II), cadmium(II), thorium(IV), dioxyuranium(VI), samarium(III) and erbium(III) are presented. The protonation equilibrium of BHP ion and complex formation equilibrium with the metal ions have been studied by potentiometry in 75% (v/v) dioxane-water and 0.10M KNO₃ at different temperatures (10, 20, 30 and 40°C). A series of mononuclear complexes [ML _n ]^{(1? z )+} (L^? =?BHP and n =?1 ??z) were found in solution and their formation constants, enthalpies and entropies were determined.

The solid metal complexes and corresponding thermal products were elucidated by elemental analysis, conductance, IR and electronic spectra, magnetic moments, ¹H NMR and TG-DSC measurements as well as by mass spectroscopy. The use of BHP as analytical reagents for the determination of copper(II), nickel(II) and cobalt(II) as well as extracting agents for these metal ions are discussed.     

Correlation between the basicity of Cu–M<Subscript>x</Subscript>O<Subscript>y</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> (M = Ba,Mg, K or La) oxide and the catalytic performance in the glycerol conversion from adsorption microcalorimetry characterization

The synthesis of CuO species highly dispersed in M_xO_y–Al₂O₃ (M = Ba, Mg, K or La) basic supports was studied, and the catalytic proprieties of the solids in glycerol conversion to bioproducts were subsequently evaluated. A correlation between the copper oxide/catalytic support structure, specific surface area/porosity and the basicity (strength and amount of basic sites) of M_xO_y–Al₂O₃ (M = Ba, Mg, K or La) supports were observed through the following characterization techniques: XRD (structure), N₂ adsorption/desorption isotherms (surface area/porosity) and microcalorimetry of CO₂ adsorption (basicity). The XRD results of the different supports indicated that the basic species (BaO, MgO, K₂O or La₂O₃) are highly dispersed in the Al₂O₃ matrix. The XRD patterns of the Ba and K-containing solids combined with copper present a CuO and Al₂O₃ formation; however, an isolated CuO phase for the Mg and La-based catalysts is not observed, demonstrating that Cu species are highly dispersed in basic support. N₂ physisorption isotherms ascribed that most of the samples are mesoporous with a surface area between 26 and 178 m² g^?1, depending on the solid composition. Microcalorimetry of CO₂ adsorption presented the following basic strength using the first points of the adsorption heat: 10MgAl > 10LaAl > 10KAl > 10BaAl for the sample without copper and 5CuMgAl > 5CuKAl > 5CuLaAl > 5CuBaAl for the materials with Cu. The amount of basic site varies greatly depending on the type of basic metal used. The different materials without copper are practically inactive at the end of the reaction. However, the Cu-based solids are active and selective for the conversion of glycerol to acetol. The initial glycerol conversion and the catalyst stability are related to basic strength and amount of basic sites, respectively.     

Non-Stoichiometric CoFe2O4 Nanoparticles Supported on an Amorphous Silica Matrix

Non-Stoichiometric CoFe₂O₄ nanoparticles dispersed in an silica matrix with a silica content of 87 wt% and Co/Fe molar ratio of 1:1, were prepared by the sol-gel method using an ethanolic solution of tetraethoxysilane and either iron(III) and cobalt(II) nitrates or iron(II) and cobalt(II) acetates. The influence of different metal precursors on the xerogels were examined by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and N₂ physisorption measurements at 77 K. Magnetic properties of the samples were investigated by field cooled FC and zero field cooled ZFC measurements.Depending on the metal precursor, different spinel oxides of a few nanometers were observed in the samples treated at 350°C. After heating at 900°C non-stoichiometric CoFe₂O₄ was formed in both samples, whose average particle size was only slightly larger than in samples treated at 350°C.