Adsorption of fatty acids on iron (hydr)oxides from aqueous solutions

The interaction of iron (hydr)oxides with fatty acids is related to many industrial and natural processes. To resolve current controversies about the adsorption configurations of fatty acids and the conditions of the maximum hydrophobicity of the minerals, we perform a detailed study of the adsorption of sodium laurate (dodecanoate) on 150 nm hematite (α-Fe(2)O(3)) particles as a model system. The methods used include in situ FTIR spectroscopy, ex situ X-ray photoelectron spectroscopy (XPS), measurements of the adsorption isotherm and contact angle, as well as the density functional theory (DFT) calculations. We found that the laurate adlayer is present as a mixture of inner-sphere monodentate mononuclear (ISMM) and outer-sphere (OS) hydration shared complexes independent of the solution pH. Protonation of the OS complexes does not influence the conformational order of the surfactant tails. One monolayer, which is filled through the growth of domains and is reached at the micellization/precipitation edge of laurate, makes the particles superhydrophobic. These results contradict previous models of the fatty acid adsorption and suggest new interpretation of literature data. Finally, we discovered that the fractions of both the OS laurate and its molecular form increase in D(2)O, which can be used for interpreting complex spectra. We discuss shortcomings of vibrational spectroscopy in determining the interfacial coordination of carboxylate groups. This work advances the current understanding of the oxide-carboxylate interactions and the research toward improving performance of fatty acids as surfactants, dispersants, lubricants, and anticorrosion reagents.     

Reductimetric determination of peroxydisulphate, hydrogen peroxide, sodium perborate, nitrate and nitrite in concentrated phosphoric acid medium with iron(II)

A direct reductimetric method for the determination of peroxydisulphate, hydrogen peroxide, sodium perborate, nitrate and nitrite in fairly concentrated phosphoric acid medium with iron(II) has been developed, with both potentiometric and visual end-point detection. Cacotheline, Methylene Blue, thionine, Azure A, Azure B, Azure C, Toluidine Blue, new Methylene Blue, ferroin, N-phenylanthranilic acid, p-ethoxychrysoidine and barium diphenylaminesulphonate are used as indicators. The method is useful in the analysis of binary mixtures of peroxydisulphate and peroxide or perborate and in the estimation of the nitrate content of fertilizers.     

Colloidal catalysts based on iron(III) oxides. 1. Decomposition of hydrogen peroxide

The catalytic activity of a colloidal catalyst based on iron(III) oxides in decomposition of H₂O₂ is studied. The catalyst is obtained by hydrolysis followed by peptization of FeCl₃ · 6H₂O salt in water in the presence of 1% ethanol. The structure, composition, and size of colloidal particles of the catalyst are studied by the methods of Mössbauer spectroscopy, X-ray fluorescence, X-ray diffraction, and transmission electron microscopy. The obtained catalyst is based on α-Fe₂O₃ crystals with an admixture of other crystalline structures of iron oxides and carbon-containing compounds. The activity of the catalyst with respect to H₂O₂ decomposition undergoes nonlinear and nonmonotonic variations and its particle size enlarges beginning from 1 to 3 nm with increasing initial concentration of FeCl₃ · 6H₂O. The catalyst obtained under optimal conditions exhibits high activity corresponding to the most efficient agents of H₂O₂ decomposition.     

Wavelength-sensitive photocatalytic degradation of methyl orange in aqueous suspension over iron(III)-doped TiO2 nanopowders under UV and visible light irradiation

Well-crystallized iron(III)-doped TiO2 nanopowders with controlled Fe3+ doping concentration and uniform dopant distribution, have been synthesized with plasma oxidative pyrolysis. The photocatalytic reactivity of the synthesized TiO2 nanopowders with a mean particle size of 50-70 nm was quantified in terms of the degradation rates of methyl orange (MO) in aqueous TiO2 suspension under UV (mainly 365 and 316 nm) and visible light irradiation (mainly 405 and 436 nm). The photodecomposition of MO over TiO2 nanopowders followed a distinct two-stage pseudo first order kinetics. Interestingly, the photocatalytic reactivity depends not only on the iron doping concentration but also on the wavelength of the irradiating light. Under UV irradiation, nominally undoped TiO2 had much higher reactivity than Fe3+ -doped TiO2, suggesting that Fe3+ doping (> 0.05 at. %) in TiO2 with a mean particle size of approximately 60 nm was detrimental to the photocatalytic decomposition of methyl orange. Whereas, under visible light irradiation, the Fe3+ -doped TiO2 with an intermediate iron doping concentration of approximately 1 at. % had the highest photocatalytic reactivity due to the narrowing of band gap so that it could effectively absorb the light with longer wavelength. A strategy for improving the photocatalytic reactivity of Fe3+ -doped TiO2 used in the visible light region is also proposed.     

Determination of hydrogen peroxide by thallium(III) in the presence of iron(II)

A method for estimating hydrogen peroxide by oxidation with excess of thallium(III) in the presence of iron(II) and iodometric determination of excess of thallium(III) is described. Nitrate, sulphate, manganese(II) and copper(II) have no effect. Chloride interferes.     

Adsorption of zinc(II) on hydrous iron oxides

The adsorption of Zn²⁺ ions on amorphous Fe(OH)₃ and -Fe₂O₃, as a function of pH, has been investigated. In the pH region corresponding to the formation of positively charged Zn-hydroxy complexes, an abrupt increase in adsorption was observed. The influence of EDTA and glycine on the adsorption of Zn²⁺ by -Fe₂O₃ has also been investigated. Strong suppression of the adsorption of Zn²⁺ was observed for high [EDTA or Gly]/[Zn²⁺] concentration ratios. The results of the adsorption of Zn²⁺ in the presence of an organic ligand were explained by the formation of Zn-EDTA or Zn-glycine complexes and also by the occupation of adsorption sites by the free organic ligand.     

Photoinduced degradation by iron(III): removal of triphenyltin chloride from water

The photoredox process taking place in iron(III) aquacomplexes was used to cause the complete degradation of triphenyltin (TPT). TPT elimination was proved to come only from attack by hydroxyl radicals generated upon irradiation at 365 nm of Fe(H₂O)₅OH²⁺, the iron(III) species present under the experimental conditions ([Fe(III)] in the range (3–6) × 10^?4 mol l^?1). The first step is the formation of an adduct between hydroxyl radicals and the benzene ring. The main process is a stepwise dephenylation of the starting TPT. Hydroxylated phenyltin derivatives were also formed, but only as minor photoproducts. The process was shown to be efficient with artificial light as well as with solar light. Copyright © 2001 John Wiley & Sons, Ltd.     

Electro-surface properties of nickel(II) and iron(III) oxides in aqueous solutions of 1,2,4-triazole

It was studied in systems constituted by aqueous solutions of 1,2,4-triazole, and NiO and Fe₂O₃ adsorbents how the electrokinetic potential of the surface of the oxides, amount of adsorbed triazole, and its concentration in solution vary during a long time.     

Periodate oxidation of dicyano-bis-(1, 10-phenanthroline) iron(II) dihydrate in aqueous sodium dodecyl sulphate (SDS)

Periodate oxidation of bis-(1,10-phenanthroline)-dicyano iron(II) ([Fe(C₁₂H₈N₂)(CN)₂]), known also as ferrocyphen, in SDS surfactant was studied in aqueous and acidic medium. The redox reaction is catalysed 124-fold in 1.220 × 10⁻⁴ mol dm⁻³ H₂SO₄ acid. The catalytic factor is much lower in absence of acid. The higher rates in acid-micelle solution are the reverse to what is observed in surfactant-free medium where acid inhibits the reaction. The results are interpreted in terms of electrostatic attraction between the protonated species and the anionic surfactant aggregates.     

Catalytic efficiency of iron(III) oxides in decomposition of hydrogen peroxide: competition between the surface area and crystallinity of nanoparticles

Various iron(III) oxide catalysts were prepared by controlled decomposition of a narrow layer (ca. 1 mm) of iron(II) oxalate dihydrate, FeC(2)O(4).2H(2)O, in air at the minimum conversion temperature of 175 degrees C. This thermally induced solid-state process allows for simple synthesis of amorphous Fe(2)O(3) nanoparticles and their controlled one-step crystallization to hematite (alpha-Fe(2)O(3)). Thus, nanopowders differing in surface area and particle crystallinity can be produced depending on the reaction time. The phase composition of iron(III) oxides was monitored by XRD and (57)Fe M?ssbauer spectroscopy including in-field measurements, providing information on the relative contents of amorphous and crystalline phases. The gradual changes in particle size and surface area accompanying crystallization were evaluated by HRTEM and BET analysis, respectively. The catalytic efficiency of the synthesized nanoparticles was tested by tracking the decomposition of hydrogen peroxide. The obtained kinetic data gave an unconventional nonmonotone dependence of the rate constant on the surface area of the samples. The amorphous nanopowder with the largest surface area of 401 m(2) g(-1) revealed the lowest catalytic efficiency, while the highest efficiency was achieved with the sample having a significantly lower surface area, 337 m(2) g(-1), exhibiting a prevailing content of crystalline alpha-Fe(2)O(3) phase. The obtained rate constant, 26.4 x 10(-3) min(-1) (g/L)(-1), is currently the highest value published. The observed rare catalytic phenomenon, where the particle crystallinity prevails over the surface area effects, is discussed with respect to other processes of heterogeneous catalysis.     

Efficient epoxidation reaction of terminal olefins with hydrogen peroxide catalyzed by an iron (II) complex

A highly active iron (II) complex that catalyzed epoxidation of terminal olefins with hydrogen peroxide was described. The catalytic system displayed excellent catalytic ability for the selective oxidation of terminal olefins to epoxides with high selectivity (up to 97.8%) in CH₃CN at 25?°C. The catalytic activity of three similarly structural iron (II) complexes was comparatively studied. The effect of various auxiliary ligands on epoxidation was investigated in detail.     

Fluoranthene removal in aqueous phase by Fe(II) activated sodium percarbonate: mechanisms and degradation pathways

Research on Chemical Intermediates - In this study, the removal performance and degradation mechanisms of fluoranthene (FLT) in sodium percarbonate (SPC) activated by Fe(II) system were...     

Reaction of hydrogen peroxide with tetraazamacrocyclic complex of iron(II) in the presence of nitrogeneous bases

The kinetics of hydrogen peroxide oxidation of Fe(II) to Fe(III) complexed with tetraazamacrocyclic ligand was studied, and a decrease in the reaction rate was observed in the presence of nitrogeneous bases, capable of forming hexacoordinated complexes with tetraazamacrocyclic compound of iron(II). The rate of reaction is proprotional to the concentration of the iron complex and hydrogen peroxide and inversely proportional to the concentration of the nitrogeneous base. A mechanism for the course of the reaction has been proposed, and the rate constants of the oxidation of the pentacoordinated iron(II) complexes have been calculated. It was shown that the addition of the fifth donor particle (in particular imidazole) activates the iron(II) atom with respect to the oxidation reaction. It was found that a tetraazamacrocyclic complex of iron(II) is capable of displaying a peroxidase type activity.Translated from Teoreticheskaya Eksperimental'naya Khimiya, Vol. 22, No. 3, pp. 309–316, May–June, 1986.     

Specific adsorption of simple organic acids on metal(hydr)oxides: a radiotracer approach

The pH dependence of adsorption of (14)C-labeled benzoic and oxalic acids on gamma-Al(2)O(3) and hematite was studied in acid medium in the presence of 0.5 mol dm(-3) NaClO(4) supporting electrolyte. It was found that the adsorption of the organic species starts at pH values where the protonation of the oxide surface takes place. In the case of benzoic acid the extent of adsorption with decreasing pH goes through a sharp maximum at a pH value not far from the pK (4.2) of the acid, while in the case of oxalic acid only a small decrease can be observed at very low pH values (pH<1). In indirect radiotracer studies using (35)S-labeled sulfate ions it was shown that the competitive adsorption of formic, malonic, maleic, and oxalic acids with sulfate ions depends on pH and the effect of the organic acid on the anion adsorption becomes pronounced at pH values about and above the pK of the acid. On the basis of these observations and considerations concerning the dissociation of the organic acids studied it is assumed that the specific adsorption of the anionic form of the acids takes place. It is, however, emphasized that the negative charge of the anions, consequently the electrostatic forces, do not play significant role in the adsorption.     

Reactions of triphenylarsine oxide with aqueous hydrogen fluoride: Crystal structure of bis(triphenylarsine oxide)hydrogen(I) tetrafluoroborate

Fluorination of triphenylarsine oxide by aqueous hydrogen fluoride (1–40%) in the absence of glass readily gives triphenylarsine difluoride. When the reaction with dilute (1%) aqueous hydrogen fluoride is carried out in borosilicate glass apparatus, the glass participates in the reaction resulting in the formation of the crystalline 2:1 adduct 2Ph₃AsO·HBF₄. Crystals of this compound are monoclinic, $\text{P}$2₁/$\text{c}$, $\text{a}$ = 12.926(4), $\text{b}$ = 17.819(6), $\text{c}$ = 14.994(4) Å, β = 98.97(3)°, Z = 4. The structure contains cations [(Ph₃AsO)₂H]⁺ in which $\text{O}\text{?}$O is 2.44(2)Å, and anions BF₄^?.     

How metal (hydr)oxides are protonated in aqueous media: the (n+1) rule and the role of the interfacial potential

The mechanism of the protonation of solid metal (hydr)oxides in aqueous media, which is closely interrelated to many processes of great technological and environmental importance, has been elucidated using simulation and experimental work. The electrical potential, smeared out at the interfacial region, changes the concentration of the H+ ions on the surface of the (hydr)oxide, thus promoting or hindering protonation. This is manifested by the shifts of the protonation peaks of the various kinds of surface sites and the appearance of an extra peak in the differential potentiometric titration curve.     

The thermal decomposition of calcium,sodium, silver and copper(II) acetates

The thermal decomposition of the acetates of calcium, sodium, silver and copper(II) have been investigated using thermogravimetry and differential thermal analysis, together with analysis of the gaseous products formed during the decomposition process. The results indicate that the major organic product formed is either acetone or acetic acid, depending on whether the final solid product is the oxide or the metal.     

12-Tungstocobaltate(II) catalyzed selective oxidation of sulfides to sulfoxides using aqueous hydrogen peroxide under solvent free conditions

12-Tungstocobaltate(II) is found to be a selective, recyclable catalyst for the oxidation of sulfides into sulfoxides. The reaction was carried out under solvent free conditions using 30% H₂O₂.