Thermal analysis of iron(II) sulphate heptahydrate in air

Iron(II) sulphate hydrates (hexa- through mono-) have been prepared and their thermal decomposition behaviours have been studied in air by isothermal and dynamic thermal analysis methods. The results show that their behaviours are similar to that of the heptahydrate. The stepwise loss of water molecules is accompanied by oxidation. Under a restricted supply of oxygen, the anhydrous sulphate is oxidized directly to Fe₂O(SO₄)₂ without the formation of Fe(OH)SO₄. When free exchange with oxygen is allowed, Fe(OH)SO₄ is formed, which in turn decomposes to Fe₂O(SO₄)₂. The decomposition of Fe₂(SO₄)₂ to iron(III) oxide and sulphur oxides appears to occur via two independent paths — one direct and other through iron(III) sulphate.     

Reaction pathway and kinetics of the thermal decomposition of synthetic brochantite

The reaction pathway of the thermal decomposition of synthetic brochantite, Cu₄(OH)₆SO₄, to copper(II) oxide was investigated through the detailed kinetic characterization of the thermal dehydration and desulferation processes. The dehydration process was characterized by dividing into two overlapped kinetic processes with a possible formation of an intermediate compound, Cu₄O(OH)₄SO₄. The dehydrated sample, Cu₄O₃SO₄, was found first to be amorphous by means of XRD, followed by the crystallization to a mixture of CuO and CuO-CuSO₄ at around 776 K. The specific surface area and the crystallization behaviour of the amorphous dehydrated compound depend largely on the dehydration conditions. The thermal desulferation process is influenced by the gross diffusion of the gaseous product SO₃, which is governed by the advancement of the overall reaction interface from the top surface of the sample particle assemblage to the bottom.     

Ferric hydrous oxide sols I. Monodispersed basic iron(III) sulfate particles

The methods of preparation of basic ferric sulfate sols consisting of particles uniform in shape of extremely narrow size distribution are described in detail. To produce such sols, acidic solutions containing ferric ions and sulfate ions were aged at elevated temperatures for a few hours. Solids formed from solutions containing a mixture of a ferric salt with a metal sulfate consisted of Fe₃(SO₄)₂(OH)₅· 2H₂O, which is the basic formulation for the alunite mineral group, whereas particles formed from ferric sulfate solutions also included Fe₄(SO₄)-(OH)₁₀ in varying proportions. The morphology of the particles was strongly dependent on the [Fe³⁺]: [SO₄²⁻] ratio in solution. Changes in the cation (K⁺, NH₄⁺, Na⁺) of the sulfate salt used in the mixture with ferric nitrate solutions greatly affected the particle size and also exhibited some effect on the lattice parameters. Certain cations (Mg²⁺, Ni²⁺, Cu²⁺) completely inhibited particle formation. During the first few hours of growth of the Fe₃(SO₄)₂-(OH)₅· 2H₂0 particles their diameters increased essentially linearly with time, indicating that the rate determining step was the surface reaction. The relevance of these systems to the study of corrosion of iron and steel is discussed.     

Sorption of chromate ions on oxyhydroxides prepared from iron(III) and aluminum sulfates

Sorption properties with respect to the chromate ions of ferro- and alumogels prepared from Fe(III) and aluminum sulfates, and the composition of oxyhydroxides (OH), are studied. It is determined that the sorption values of chromate ions on ferrogels and alumogels (with NaCl) are notably higher than those on OH prepared from other precursors. It is shown that the sorption of CrO ₄ ^2? on alumogels with Na₂SO₄ is almost completely inhibited. It is found that gels retain substantial amounts of sulfate ions during precipitation from precursor solutions, while alumogels retain substantially more than ferrogels. The sorption of SO₄-gels is explained from the viewpoint of their composition and interaction with Na₂SO₄ solution. The competitive sorption of chromate and phosphate ions is studied and it is demonstrated that phosphate ions completely inhibit the sorption of chromate ions at comparable concentrations.     

Formation de la rouille verte II sulfatée Fe2(OH)12SO4 par oxydation du sulfate ferreux par l'eau

Sulphated green rust can result from the partial oxidation of FeSO₄ by water itself in the presence of sodium hydroxide (Fe(II)/OH⁻ = 0.600). The equilibrium constant of the reaction is higher than 3·10⁴, the standard potential of Fe₆(OH)₁₂SO₄/Fe(OH)₂ system being −0.56 V vs. NHE. An equipment under vacuum allows to detect the hydrogen release and to evidence the typical blue-green colour of the GR otherwise identified by its Raman spectrum. Consequently this compound can be formed in anoxic media; it is stable in the presence of hydrogen.     

Redox Equilibria in the System Fe(OH)3(H2SO4)-Na2SO3-H2O Involving Precipitation of Iron(II) Sulfite as a Fe2O3 Precursor

Experimental data on the equilibria Fe²⁺/Fe³⁺ and SO₃ ²⁻/SO₄ ²⁻ in the system Fe(OH)₃(H₂SO₄)-Na₂SO₃-H₂O are presented. The quantitative relations between the reduction of Fe(III) and the precipitation of FeSO₃·2.5H₂O as a Fe₂O₃ precursor have considered graphically.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 1, 2005, pp. 41–44.Original Russian Text Copyright © 2005 by Vasekha, Motov.     

On Structural Features Necessary for Near‐IR‐Light Photocatalysts

In the search for photocatalysts that can directly utilize near‐IR (NIR) light, we investigated three oxides Cu₃(OH)₄SO₄ (antlerite), Cu₄(OH)₆SO₄, and Cu₂(OH)₃Cl by photodecomposing 2,4‐dichlorophenol over them under NIR irradiation and by comparing their electronic structures with that of the known NIR photocatalyst Cu₂(OH)PO₄. Both Cu₃(OH)₄SO₄ and Cu₄(OH)₆SO₄ are NIR photocatalysts, but Cu₂(OH)₃Cl is not. Thus, in addition to the presence of two different CuO_m and Cu′O_n polyhedra linked with Cu?O?Cu′ bridges, the presence of acceptor groups (e.g., SO₄, PO₄) linked to the metal oxygen polyhedra is necessary for NIR photocatalysts.     

Synthesis and characterization of sulfate and dodecylbenzenesulfonate intercalated zinc-iron layered double hydroxides by one-step coprecipitation route

Inorganic sulfate- and organic dodecylbenzenesulfonate (DBS)-intercalated zinc-iron layered double hydroxides (LDHs) materials were prepared by one-step coprecipitation method from a mixed salt solutions containing Zn(II), Fe(II) and Fe(III) salts. The as-prepared samples have been characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), low-temperature nitrogen adsorption, scanning electron microscopy (SEM), inductively coupled plasma emission spectroscopy (ICP), and Mössbauer spectroscopy (MS). The XRD analyses demonstrate the typical LDH-like layered structural characteristics of both products. The room temperature MS results reveal the characteristics of both the Fe(II) and Fe(III) species for SO₄²⁻-containing product, while only the Fe(III) characteristic for DBS-containing one. The combination characterization results and Rietveld analysis illustrate that the SO₄²⁻-containing product possesses the Green Rust two (GR2)-like crystal structure with an approximate chemical composition of [Zn_0.435·Fe^II_0.094·Fe^III_0.470·(OH)₂]·(SO₄²⁻)_0.235·1.0H₂O, while the DBS-containing one exhibits the common LDH compound-like structure. The contact angle measurement indicates the evident hydrophobic properties of DBS-containing nanocomposite, compared with SO₄²⁻-containing product, due to the modification of the internal and external surface of LDHs by the organic hydrophobic chain of DBS.     

Kaliumhydrogensulfat-Dihydrogensulfat,K(HSO4)(H2SO4) – Synthese und Kristallstruktur

Potassium Hydrogensulfate Dihydrogensulfate, K(HSO₄)(H₂SO₄) – Synthesis and Crystal Structure Single crystals with the composition KH₃(SO₄)₂ have been synthesized from the system Potassium sulfate/sulfuric acid. The hitherto crystallographically not investigated compound crystallizes in the monoclinic space group P2₁/c (14) with the unit cell parameters a = 7.654(3), b = 11.473(5) and c = 8.643(3) Å, β = 112.43(3)°, V = 701.6 ų, Z = 4 and D_x = 2.22 g · cm^?3. The structure contains two types of tetrahedra, SO₃(OH) and SO₂(OH)₂. These tetrahedra form tetramers via hydrogen bonds consisting of both, two SO₃(OH) and two SO₂(OH)₂ tetrahedra. The tetramers are linked to each other via hydrogen bonds. Potassium is coordinated by 9 oxygen atoms which belong to both kinds of tetrahedra. These potassium oxygen polyhedra are connected by common faces forming chains running parallel z.     

Synthesis and characterization of secondary‐amine‐functional microparticles

Secondary‐amine‐functional microparticles were prepared in the range of 50–250 μm through the suspension polymerization of styrene, divinylbenzene (DVB), and 2‐(tert‐butylamino)ethyl methacrylate (tBAEMA). This study focused on the effects of the DVB, tBAEMA, initiator, and stabilizer concentrations and shaking rate on the experimental amine content, swelling ratio, average particle size, and particle size distribution. The suspension polymerization experiments were carried out in two different systems. In the first system, an organic phase, including the monomers and initiator, was dispersed in an aqueous medium in the presence of Al₂(SO₄)₃. Al₂(SO₄)₃, in the presence of an amine monomer (pH ～ 10), formed colloidal Al(OH)₃, which built a nonsticky layer on the surface of the polymerizing droplets that prevented them from coalescing and aggregating. Individual and spherical particles within the range of 50–200 μm were obtained by this polymerization method. The second method was similar to the first polymerization protocol, except that a certain amount of sodium dodecyl sulfate was added as a costabilizer in the presence of Al₂(SO₄)₃. In these experiments, individual and spherical particles were obtained within the range of 130–250 μm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem: 3708–3719, 2004     

Effect of the nature of the salt precursor of an oxide-hydroxide sorbent on the sorption of oxalate ions

Generalizations are made on the effect of the nature of a precursor (the original salt of a metal) on the sorption activity of hydrogels of oxidehydroxides (OHes) towards oxalate ions using the example of an OH obtained by the alkaline hydrolysis of chloride, perchlorate, and sulfate of Fe(III); chloride, sulfate, and nitrate of Al; and nitrate of Zr(IV). It is established that the sorption of C₂O ₄ ^2? on the studied OHes is described by the Langmuir equation. We find that the sorption activity depends on the nature of the precursor: Al₂(SO₄)₃ > Al(NO₃)₃ > AlCl₃ > ZrO(NO₃)₂ > Fe₂(SO₄)₃ > FeCl₃ > Fe(ClO₄)₃.     

A Review on the Degradation of Pollutants by Fenton-Like Systems Based on Zero-Valent Iron and Persulfate: Effects of Reduction Potentials,pH, and Anions Occurring in Waste Waters

Among the advanced oxidation processes (AOPs), the Fenton reaction has attracted much attention in recent years for the treatment of water and wastewater. This review provides insight into a particular variant of the process, where soluble Fe(II) salts are replaced by zero-valent iron (ZVI), and hydrogen peroxide (H₂O₂) is replaced by persulfate (S₂O₈²⁻). Heterogeneous Fenton with ZVI has the advantage of minimizing a major problem found with homogeneous Fenton. Indeed, the precipitation of Fe(III) at pH > 4 interferes with the recycling of Fe species and inhibits oxidation in homogeneous Fenton; in contrast, suspended ZVI as iron source is less sensitive to the increase of pH. Moreover, persulfate favors the production of sulfate radicals (SO₄^•−) that are more selective towards pollutant degradation, compared to the hydroxyl radicals (^•OH) produced in classic, H₂O₂-based Fenton. Higher selectivity means that degradation of SO₄^•−-reactive contaminants is less affected by interfering agents typically found in wastewater; however, the ability of SO₄^•− to oxidize H₂O/OH⁻ to ^•OH makes it difficult to obtain conditions where SO₄^•− is the only reactive species. Research results have shown that ZVI-Fenton with persulfate works best at acidic pH, but it is often possible to get reasonable degradation at pH values that are not too far from neutrality. Moreover, inorganic ions that are very common in water and wastewater (Cl⁻, HCO₃⁻, CO₃²⁻, NO₃⁻, NO₂⁻) can sometimes inhibit degradation by scavenging SO₄^•− and/or ^•OH, but in other cases they even enhance the process. Therefore, ZVI-Fenton with persulfate might perform unexpectedly well in some saline waters, although the possible formation of harmful by-products upon oxidation of the anions cannot be ruled out.     

Effects of structural properties of silicon carbide-derived carbons on their electrochemical double-layer capacitance in aqueous and organic electrolytes

High surface area silicon carbide-derived carbons (Si-CDCs) synthesized by chlorination of beta silicon carbide (βSiC) with two different particle sizes (6 μm and 50 nm) show different porosities with graphitic structure. Transmission electron microscopy, Raman spectroscopy and argon (Ar) and carbon dioxide (CO₂) sorption analyses are used to examine the textural properties of the Si-CDCs. The results show that the particle size of the precursor affects the surface area and porosity of carbons. Furthermore, an additional heat treatment of the Si-CDC with 50-nm particle size for 24 h at 1,000 °C results in a collapse of the pore structure and reduces the surface area. The capacitive behaviours are investigated in H₂SO₄ and in tetraethyl ammonium tetrafluoroborate (TEABF₄)/acetonitrile (AN). The electrochemical performance of the Si-CDCs is influenced by the particle size, surface area, pore volume and pore size distribution. The Si-CDCs exhibit capacitances in 1 M H₂SO₄ of up to 179 F g^?1 and very stable charge–discharge performance over 5,000 cycles. This study shows the crucial importance of ultramicropores less than 1 nm combined with nanosized particles for achieving high capacitance in aqueous electrolyte. Moreover, the graphitic degree at the surface of the Si-CDCs enhances considerably the rate capability and stability in both electrolytes.     

Determination of 237 Np in marine sediment and seawater

Procedures for determination of neptunium in marine sediment and seawatersamples are described. Iron hydroxide Fe(OH)₂ –Fe(OH)₃ is used for preliminary pre-concentration of neptunium. Secondly,neptunium Np⁴⁺ and Pu³⁺ are separated by tri-isooctylamine-(TIOA)extraction in 8–10M HCl by redox with SO₃ ^2–-Fe³⁺ Neptunium Np⁴⁺ and uranium U⁶⁺ areseparated by back extraction the Np⁴⁺ with 2M HCl. Finally, theneptunium is purified from the uranium and thorium by anion exchange in 8MHNO₃ and 12M HCl. The stripping of 6M HCl + NH₂ OH HClfurther separates the neptunium Np³⁺ and uranium. Reduction bySO 3_2– –Fe³⁺ appeared to be an efficientway to obtain Np⁴⁺ The decontamination factors of the procedureare 4.0. 10⁴ for ²³² Th, 5.6 . 10⁴ for uraniumand 1.6 . 10⁴ for plutonium.     

Solid complexes of iron(II) and iron(III) with rutin

Solid complex compounds of Fe(II) and Fe(III) ions with rutin were obtained. On the basis of the elementary analysis and thermogravimetric investigation, the following composition of the compounds was determined: (1) FeOH(C₂₇H₂₉O₁₆)·5H₂O, (2) Fe₂OH(C₂₇H₂₇O₁₆)·9H₂O, (3) Fe(OH)₂(C₂₇H₂₉O₁₆)·8H₂O, (4) [Fe₆(OH)₂(4H₂O)(C₁₅H₇O₁₂)SO₄]·10H₂O. The coordination site in a rutin molecule was established on the basis of spectroscopic data (UV–Vis and IR). It was supposed that rutin was bound to the iron ions via 4C=O and 5C—oxygen in the case of (1) and (3). Groups 5C–OH and 4C=O as well as 3′C–OH and 4′C–OH of the ligand participate in binding metals ions in the case of (2). At an excess of iron(III) ions with regard to rutin under the synthesis conditions of (4), a side reaction of ligand oxidation occurs. In this compound, the ligands’ role plays a quinone which arose after rutin oxidation and the substitution of Fe(II) and Fe(III) ions takes place in 4C=O, 5C–OH as well as 4′C–OH, 3′C–OH ligands groups. The magnetic measurements indicated that (1) and (3) are high-spin complexes.     

Hydrothermal synthesis and thermodynamic analysis of dawsonite-type compounds

Dawsonite-type compounds of formula MAl(OH)₂CO₃ (M=Na,K,NH₄) were hydrothermally synthesized. The influences of the composition of starting materials, reaction temperature, acidity of the reaction medium on the formation, morphology and particle size of MAl(OH)₂CO₃ powders were systematically investigated. The experiment results show that increase in the amount of MHCO₃ favors the formation of MAl(OH)₂CO₃ phase with more slender particle morphology. The higher the reaction temperature, the grosser the particle is. It was also demonstrated that the particle size of the MAl(OH)₂CO₃ phase are most uniform when the pH value of reaction system is 10.3 for sodium dawsonite and potassium dawsonite, but it is 9.79 for that of ammonium dawsonite. The thermodynamics of the formation of dawsonite-type compounds have also been analyzed in details.     

Ein neues Lithiumhydrogensulfat,Li2(HSO4)2(H2SO4) – Synthese und Kristallstruktur

A New Lithium Hydrogen Sulfate, Li₂(HSO₄)₂(H₂SO₄) – Synthesis and Crystal Structure The title compound crystallizes in good shaped single crystals from the system lithium sulfate/sulfuric acid in the orthorhombic space group Pccn, unit cell parameters a = 17.645(4), b = 5.378(1), c = 10.667(3) Å. V = 1 012.2 ų, Z = 4, D_x = 2.009 g cm^?3. There are two types of SO₄ tetrahedra, SO₃(OH) and SO₂(OH)₂, connected via hydrogen bonds forming layers parallel to the xy-plane. The layers are linked by Li atoms, which are tetrahedral coordinated by O atoms coming two by two from neighboured layers.     

Formation of extractable species from metal sulfate and amine chlorides

The extraction of Fe, Zn and In by La₂HCl from H₂SO₄ solutions has been studied. The formation of the aqueous complexes H₂Fe(SO₄)₂HSO₄, HZn(SO₄)HSO₄ and HInSO₄(HSO₄)₂ is discussed. The formation of mixed ligand species H₂Fe(SO₄)₂Cl, HZnSO₄Cl and HInSO₄Cl₂ from the interaction of Cl⁺ in aqueous solution or in LA₂HCl before extraction is explained. The reactions in the system to produce the extractable species are discussed. The possible separations are given.     

Interaction of SO2 with unsaturated Schiff-base complexes; thermal,magnetic, and spectroscopic studies

A series of Schiff-base complexes are prepared and characterized by elemental and thermal analyses, IR and electronic spectra, and magnetic measurements. SO₂ interacted with solutions of the complexes forming complexes [M(SB)(SO₂)₂] where M = Mg(II), Cu(II), Mn(II), and [M(SB)(SO₂)₂]OH where M = Fe(III). These complexes are subjected to elemental and thermal analyses, conductance measurements and IR, electronic, and ESR spectra to indicate changes from interaction of SO₂ with the Schiff-base complexes.     

Investigation of copper oxide impregnants prepared from various precursors for respirator carbons

Copper oxide impregnated activated carbon was prepared by three methods and studied as a respirator carbon. Using techniques such as dynamic flow testing, X-ray diffraction (XRD), thermal analysis, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), copper oxide impregnants, derived from different sources such as basic copper carbonate (Cu₂CO₃(OH)₂), copper nitrate (Cu(NO₃)₂) and copper chloride (CuCl₂) reacted with sodium hydroxide (NaOH), have been studied. Dynamic flow tests performed using sulfur dioxide (SO₂), ammonia (NH₃) and hydrogen cyanide (HCN) challenge gases allow the determination of the stoichiometric ratio of reaction (SRR) between challenge gas and impregnant. Thermal gravimetric analysis experiments showed that an inert heating environment was required when thermally decomposing the Cu(NO₃)₂ impregnant to CuO to avoid damaging the activated carbon substrate. SEM has been used to investigate dispersal and particle size of the impregnant on the activated carbon. XRD permits the identification of crystalline and amorphous phases as well as the grain size of the impregnant. XRD analysis of samples before and after exposure to SO₂ has allowed the active impregnant in SO₂ adsorption to be identified. The relationship between SRR, impregnant loading and grain size is discussed. Methods to improve impregnant distribution are presented and their impact discussed.