Synthesis of γ-Fe2O3 by Thermal Decomposition of Ferrous Gluconate Dihydrate

Ferrous gluconate dihydrate (FeC₁₂H₂₂O₁₄⋅2H₂O), was prepared and its thermal decomposition was studied by means of simultaneous thermal analysis, supplemented with a two probe d.c. electrical conductivity measurements under the atmospheres of static air, dynamic air and dynamic nitrogen. Under all the atmospheres final product was found to be α-Fe₂O₃ with FeO, γ-Fe₂O₃, Fe₃O₄ etc. as probable intermediates. γ-Fe₂O₃ was formed under the atmosphere of dynamic air containing water vapour. γ-Fe₂O₃ thus synthesised was characterised for its structure, morphology, thermal and magnetic behaviour. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of iron oxide support preparation method on the properties of Ru/Fe2O3 catalysts for water-gas shift reaction

Studies were undertaken of phase transitions of iron oxide obtained from iron oxide-hydroxides of type α-, β-, γ- and δ-FeOOH, and used as a support of ruthenium catalysts Ru/Fe₂O₃, employed in the water-gas shift reaction. In asprepared pure supports and ruthenium catalysts the main phase was α-Fe₂O₃. After use in the water-gas shift reaction, the support showed the presence of different phases of iron oxide. The most active Ru/Fe₂O₃ catalysts prepared on the basis of α- and δ-FeOOH, after use in the water-gas shift reaction, revealed the presence of Fe₃O₄ or a mixture of phases Fe₃O₄ and γ-Fe₂O₃. The least active catalysts, prepared on the basis of β- and γ-FeOOH, contained a solid solution of Fe₃O₄-γ-Fe₂O₃ with traces of α-Fe₂O₃.     

Thermal stability of amino acid-(tyrosine and tryptophan) coated magnetites

The thermal stability of two amino acid-(tyrosine and tryptophan) coated magnetite and their corresponding precursors, [Fe₂^IIIFe^II(Tyr)₈]·9H₂O and [Fe₂^IIIFe^II(Trp)₂(OH)₄](NO₃)₂·8H2O (where tyrosine=Tyr and tryptophan=Trp), was analyzed in comparison with free amino acids. The complexes present a lower thermal stability relative to the free ligand, due to the catalytic effect introduced by the iron cation and the presence of NO₃⁻ groups. The presence of NO₃⁻ group determines also a different degradation’s stoichiometry of the amino acid anion comparative with the one expressed by the free ligand molecule. The amino acid bonded to magnetite decomposes in two steps, its presence inducing an increasing of γ-Fe₂O₃→Fe₂O₃ conversion temperature.     

Oxygen stoichiometry,unit cell volume,and thermodynamic quantities of perovskite-type oxides

Perovskite-type oxides with A, A′=La, Ba, Sr; B, B′=Mn, Fe, Co were investigated by means of thermal analysis, solid electrolyte cells, and X-ray diffraction. Partial molar thermodynamic quantities are determined and their relations with O/M stoichiometry, unit cell volume, and phase stability were studied. The absolute values of partial molar enthalpies of perovskite-type oxides increase with increasing O/M stoichiometries and with decreasing unit cell volumes of the cubic perovskite-type structure, corresponding to higher chemical stabilities. The substitution of Ba for La, Ba for Sr, Co for Fe, and Fe for Mn lead to increase in unit cell volumes and decrease in absolute values of ΔH ⁰. The ΔH ⁰ values of the cobaltites/ferrites range from −33.5 kJ/mol for SrCo_0.8Fe_0.2O_3−x to −72.5 kJ/mol for La_0.2Sr_0.8Co_0.6Fe_0.4O_3−x, and of the manganates up to −132 kJ/mol for Ca_0.5Sr_0.5Mn_0.8Fe_0.2O_3−x .     

Thermal decomposition of some metal-organic precursors

In this paper we present a study on the synthesis of Fe(III) oxide, by thermal decomposition of some complex combinations of Fe(III) with carboxylate type ligands, obtained in the redox reaction between some polyols (ethylene glycol (EG), 1,2-propane diol (1,2PG), 1,3-propane diol (1,3PG) and glycerol (GL)) and NO₃ ^– ions (from ferric nitrate). Fe₂O₃ was obtained by thermal decomposition of the synthesized metal-organic precursors at low temperatures. γ-Fe₂O₃ was obtained as nanoparticles at 300°C, while at higher temperatures α-Fe₂O₃ starts to crystallize and becomes single phase at ~500°C. The formation of the metal-organic precursors and their thermal decomposition were studied by thermal analysis and FTIR spectroscopy.     

Solar-driven electrochemically assisted semiconductor-catalyzed iodide ion oxidation. Enhanced efficiency by oxide mixtures

Oxidation of iodide ion from an air-saturated solution under natural sunlight (900±50 W m⁻²) on the surfaces of TiO₂, ZnO, Fe₂O₃, MoO₃ and CeO₂ enhances by 6 to 12-fold on application of a cathodic bias of −0.2 to −0.3 V (vs NHE) to the semiconductors; light, the semiconductor and dissolved oxygen are essential for iodine generation. The semiconductors under an anodic bias of +0.2 to +0.3 V (vs NHE) fail to oxidize iodide ion from air-saturated solution under sunlight. Under cathodic bias, semiconductor mixtures like TiO₂-ZnO, TiO₂-Fe₂O₃ and ZnO-Fe₂O₃ show enhanced photocatalytic activity, indicating improved charge separation in oxide mixtures. The mechanism of photocatalysis under cathodic bias is discussed.      

Electrochromism in Materials Prepared by the Sol-Gel Process

Electrochromism is defined as the persistent but reversible optical change (usually transmission) produced electrochemically. The preparation by the sol-gel process of thin films made of amorphous or crystalline nanoparticles of WO₃, V₂O₅, Nb₂O₅, TiO₂, CeO₂, Fe₂O₃ and mixed compounds such as WO₃−TiO₂, CeO₂−TiO₂, CeO₂−SnO₂, have opened remarkable new opportunities for obtaining electrochromic layers exhibiting large optical transmission variation in the UV, visible or infrared range and acceptable kinetics under H⁺ or Li⁺ insertion. In this paper we give an overview of what has been recently achieved in this field, with emphasis for cathodic electrochromic coatings of Nb₂O₅ and TiO₂ composition. Finally we stress the future developments in this fast growing field.     

Preparation and characterization of Co0.5Zn0.5Fe2(C4H2O4)3·6N2H4 A precursor to prepare Co0.5Zn0.5Fe2O4 nanoparticles

A good precursor is foremost in the preparation of nanosized metal or mixed metal oxides. In the present study a novel precursor, cobalt zinc fumarato-hydrazinate Co_0.5Zn_0.5Fe₂(C₄H₂O₄)₃·6N₂H₄ has been prepared which decompose at a much lower temperature to give nanosized mixed-metal oxides. X-ray investigations, confirms the formation of single spinel phase. The FTIR spectra show N-N stretching vibration at 965 cm⁻¹ which confirms the bidentate bridging hydrazine. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential scanning calorimetric analysis. The precursor shows two-step dehydrazination followed by decarboxylation to form Co_0.5Zn_0.5Fe₂O₄, the chemical analysis of the sample is corroborative of this.     

Combustion Derived Ultrafine γ-Fe2O3 Structure,morphology and thermal studies

A novel combustion method of employing poly(ethylene glycol) with the precursor in a fixed ratio for the synthesis of ultrafine γ-Fe₂O₃ through a self-propagating combustion synthesis is reported. Four different precursors viz. ferrous hydroxide, ferrous oxalate dihydrate, ferric 8-hydroxyquinoline and ferric acetylacetonate are employed in this study for the conversion of these precursors to ultrafine g-Fe₂O₃ particles. The as synthesized γ-Fe₂O₃ samples are characterized by XRD, SEM and thermal techniques. A case study for the synthesis of γ-Fe₂O₃ employing ferric acetyl acetonate as precursor is reported. The importance of employing thermal analysis techniques in understanding the combustion synthesis is envisaged. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sol–gel synthesis, characterization, and catalytic activity of Fe(III) titanates

Nanostructured iron–titanium mixed oxides with different Fe/Ti ratios were prepared by sol–gel methods under different preparative conditions. When equal molar amounts of Fe and Ti ions were employed, the product calcined at 500 °C showed an X-ray diffraction pattern that resembles Fe₂Ti₃O₉. On the other hand, lower Fe/Ti ratios favored the formation of Fe₂TiO₅ while higher ratios resulted in free α-Fe₂O₃ and TiO₂. Besides the effect of the Fe/Ti ratio, the composition of the final product was dependent on the preparative conditions and the calcination temperature. Enhancing the gelation process by heating or by employing an acid catalyst favored the formation of Fe₂TiO₅ at relatively low temperatures. Compared with the corresponding pure oxides, the prepared iron–titanium mixed oxides showed modified textural characteristics which were also dependent on the composition and the calcination temperature. The mixed oxides showed higher catalytic activity in the oxidation of methanol than their corresponding pure oxides with a noticeable enhanced oxidation potential forming methyl formate and carbon dioxide.     

Beiträge zur Kenntnis von Oxyden

Zusammenfassung Es werden tensieudiometrische und r?ntgenographische Untersuchungen amγ-Fe₂O₃ mitgeteilt, die zeigen, da?γ-Fe₂O₃ bei 300° im Hochvakuum thermisch nicht merkbar zu zerlegen ist. Der von Girard und Chaudron und anderen beobachtete Zerfall desγ-Fe₂O₃ in Fe₃O₄ wird auf die Gegenwart von reduzierenden Stoffen (aus Schlauch, Fett usw.) zurückgeführt und das Auftreten von CO₂ spektroskopisch bewiesen. Mit der Reduktion geht eine Umlagerung desγ-Fe₂O₃ inα-Fe₂O₃ parallel, ein Befund, der auch durch magnetische Untersuchungen erh?rtet wird. Platin-Mohr ist als Katalysator derγ-Fe₂O₃-Zersetzung bei 300° unwirksam. Der Jahrhundertstiftung unserer Hochschule sind wir für Bereitstellung von Mitteln zur Durchführung dieser Untersuchungen zu gro?em Dank verpflichtet. Die Literatur über diese Arbeitsreihe ist zusammengestellt bei Simon und Fehér, Z. Elektrochem.38, 137 (1932).     

Structure and magnetic properties of the nanocomposites γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>

The structural features and magnetic properties of composite materials Fe₂O₃-SiO₂ consisting of γ-Fe₂O₃ nanoparticles in an amorphous porous matrix of SiO₂ were considered. The studied samples were synthesized by the sol-gel method. The structure of γ-Fe₂O₃-SiO₂ depending on the heating temperature was studied by electron microscopy, X-ray diffraction analysis, ESR and IR spectroscopy. Magnetic measurements were performed on a SQUID magnetometer in the range 2–350 K.     

Femtosecond relaxation of photoexcited states in nanosized semiconductor particles of iron oxides

Relaxation of photoexcited states in nanosized semiconductor particles of iron oxides was studied by femtosecond laser photolysis techniques: (1) in an aqueous colloidal solution of -Fe₂O₃; (2) in Fe₂O₃ particles in the Nafion^® cation-exchange polymeric membrane; (3) in an aqueous colloid of -Fe₂O₃; and (4) in nanocrystals of ferrihydrite 5Fe₂O₃·9H₂O, which are contained in the protein shell of ferritine. The photoinduced excited states relax at the femtosecond and picosecond time scale. The spectra of photoinduced absorption of photoexcited states and the relaxation dynamics in the studied iron oxides weakly depend on the structure and surface environment of a nanoparticle.     

Highly transparent UV absorption TiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> films without oxidation catalytic activity prepared by a room temperature sol–gel route

TiO₂-SiO₂-Fe₂O₃ films as new UV absorption material were prepared through an epoxide derived sol–gel route. The films were formed at room temperature by doping of a little amount of γ-Fe₂O₃ nanoparticles in TiO₂-SiO₂. The obtained films show advantages such as high stability, efficient absorption in the UV region, high transparency in the visible range, and low oxidation catalytic activity to organic materials. It was found that 2.3 nm γ-Fe₂O₃ nanoparticles doped films exhibit stronger UV absorption than the films doped with 5.1 nm particles because of the increased grain strain of the nanoparticles with smaller size. These advantages of the films guarantee the broad application of this inorganic UV absorption film in the protection of heat sensitive organic materials such as artworks.     

Infrared studies of the diatomic molecules O2, N2, NO and H2 adsorbed on Fe2O3

An infrared spectroscopic study of the diatomic molecules O₂, N₂, NO and H₂ adsorbed under different conditions on Fe₂O₃ has been performed.Complex patterns of absorption on both α-Fe₂O₃ and γ-Fe₂O₃ activated in O₂ at high temperature are assigned to vibrations of two different chemisorbed O₂ species.N₂ molecules do not interact with “oxygen rich” α-Fe₂O₃ surfaces, but give N₂O^? and N₂O₂^2? species when chemisorbed on evacuated surfaces.NO molecules give complex patterns of absorption, depending on the gas pressure. Three different types of nitrate structures can be identified, as well as NO, NO^? and cis-N₂O₂ chemisorbed species. Chemisorbed water molecules are formed by contact of H₂ with Fe₂O₃ surfaces even at room temperature.     

纳米TiO2光催化萘转化为α-萘酚

研究了共溶剂、电子受体和表面改性等因素对TiO2光催化萘直接合成α-萘酚反应的影响.纳米TiO2催化剂在紫外光照射下产生·OH,使得萘羟基化得到α-萘酚.在TiO2体系中加入Fe3+,Fe2+,Fe3++H2O2和Fe2++H2O2时,均可有效提高萘转化率和α-萘酚收率,其中以体系中加入Fe3++H2O2时,α-萘酚收...     

Synthesis on an ultra large scale of nearly monodispersed γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles with La(III) doping through a sol–gel route assisted by propylene oxide

Nearly monodispersed La³⁺ doped γ-Fe₂O₃ nanoparticles were synthesized on an ultra-large scale of about 60 g in a single reaction by a low temperature sol–gel route. The nanoparticles were obtained by the reaction of FeCl₂ and La(NO₃)₃ in ethanol solution with propylene oxide to form the sol, followed by the boiling of the sol solution. The La³⁺ doping promotes the phase transformation temperature of γ-Fe₂O₃ nanoparticles from 350 to 650 °C by the La³⁺ doping induced enhancement of phase transformation activation energy. This large scale synthesis strategy offers important advantages over other conventional routes for the preparation of undoped and doped γ-Fe₂O₃ nanoparticles. These guarantee the promising application of this route in the industrial production.     

A general ultra large scale strategy for low temperature sol–gel synthesis of nearly monodispersed metal ions doped γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

A general sol–gel strategy was established for the synthesis of metal ions doped γ-Fe₂O₃ nanoparticles with narrow particle size distribution. The unique chemistry of the route guarantees the simple preparation procedure for the preparation of doped γ-Fe₂O₃ nanoparticles, which includes the boiling of the ethanolic solution of precursor salts after the addition of gelation agent, and the following drying of the obtained sol solution. On the other hand, it guarantees the production of the nanoparticles with nearly monodispersed state and median size of about 5 nm on an ultra large scale of about 60 g in a single reaction. The doping of metal ions in γ-Fe₂O₃ allows the great promotion of phase transformation temperature from γ-Fe₂O₃ to α-Fe₂O₃. Due to the advantages of this strategy over other routes, it is very promising to be applied in the industrial production of undoped and doped γ-Fe₂O₃ nanoparticles as a general route.     

Effect of various oxidants in a photocatalysis/filtration system for the treatment of contaminants

This study was conducted to investigate the effect of a photocatalysis/oxidant system for the treatment of humic acid and hazardous heavy metals in aqueous solutions. Hydrogen peroxide, ozone, and potassium peroxodisulfate were tested as oxidants. The effect of oxidant concentration was conducted with a pH of 7, a UV intensity of 64 W, and a TiO₂ dosage of 0.3 g L⁻¹. The oxidant addition in the UV/TiO₂ system enhanced the degradation efficiency of humic acid and hazardous heavy metals compared to no addition of an oxidant. The addition of oxidants over the amounts of H₂O₂ 50 mg L⁻¹, O₃ 20 g m⁻³, and K₂S₂O₈ 50 mg L⁻¹ inhibits the system efficiency. The negative effect of higher oxidant concentrations likely results from OH radical quenching caused by the excess oxidant. Therefore, the optimal dosages of oxidants such as a hydrogen peroxide, ozone, and potassium peroxodisulfate were found to be 50 mg L⁻¹, 20 g m⁻³, and 50 mg L⁻¹, respectively. The degradation efficiency of UV/TiO₂/oxidant systems for the removal of humic acid and hazardous heavy metals was much greater in the UV/TiO₂/H₂O₂ system using H₂O₂ as an oxidant.     

The magnetocaloric effect of superfine magnets

The magnetocaloric effect (MCE) of aqua suspensions based on superfine magnetite (Fe₃O₄), hematite (α-Fe₂O₃), maghemite (γ-Fe₂O₃), samarium ferrite (SmFe₂O₄) and gadolinium ferrite (GdFe₂O₄) as well as of magnetite-based ferrofluids was calorimetrically determined in the range of the temperatures from 283 to 253 K. MCE has a positive magnitude for all investigated systems except a hematite-based system. For the suspensions on the basis of MCE temperature dependence it was determined that superfine magnetite transformed into α-Fe₂O₃ at the temperature above 328 K in contrast to monocrystal magnetite. For aqua suspensions of samarium ferrite and gadolinium ferrite and magnetite-based ferrofluids MCE temperature dependence has an extreme behavior which is connected with a second-order phase transition. For the first time it is established that the magnetocaloric effect (MCE) is greatly increased when the magnet is a nanosized material.