Kinetics of sulfur transfer from H2S to digenite (Cu2−xS) at 500°C

The kinetics of sulfur transfer from H₂S to cuprous sulfide (digenite) at 500°C has been established by the resistance relaxation technique. The resistance measurements have been carried out by the van der Pauw method, which uses a four probe configuration. The rate of the forward reaction decreases with the increase in the activity of sulfur in the sulfide (rate a _s ^–0.55 ) while the rate of the backward reaction is found to be nearly independent of the sulfur activity. Based on these results, the rate limiting step for sulfur transfer reaction to digenite is shown to be: H₂S (g) + 2e^– = S^2–(ad) + H₂(g).     

One-pot-solid preparation of novel three-dimensional FexS1-x/g-C3N4 heterostructures for efficient photocatalytic mixed-pollutants removal

In order to overcome the problem of low photocatalytic rate of g-C₃N₄, the 3D Fe_xS_1-x/g-C₃N₄ heterojunction was prepared via a simple one-pot solid method. The X-Ray Diffraction (XRD) and scanning electron microscope (SEM) results demonstrated that the Fe_xS_1-x/g-C₃N₄ heterojunction was established and a g-C₃N₄ nanosheet was tightly bound to Fe_xS_1-x. Compared with g-C₃N₄ samples, Fe_xS_1-x coupling resulted in substantial enhancement of visible light absorption, moreover, the bandwidth of heterojunction was also expanded. In addition to effectively degrading RhB and reducing Cr(VI), the redox performance of Fe_xS_1-x/g-C₃N₄ was also increased in the Cr(VI)/RhB mixed system. Based on a variety of experimental results, the enhanced synergistic photocatalytic activity of the 3D Fe_xS_1-x/g-C₃N₄ heterojunction was attributed to enhancement of the separation of e^- and h⁺ in FeS_2, which resulted from the effective conversion of FeS into FeS₂ under UV-light irradiation. The type II heterojunction structure that was produced via one-pot solid fabrication also inhibited the recombination of electron/hole pairs. Fe_xS_1-x doping and heterojunction building improve the photocatalysis capacity of g-C₃N₄ and broaden the visible-light response of pure g-C₃N₄.     

Improving room temperature negative thermal expansion performance of Fe2-xScx(MoO4)3

Negative thermal expansion (NTE) performance of Fe₂(MoO₄)₃ is only found in a high-temperature range due to its monoclinic-to-orthorhombic (M-O) phase transformation temperature (PTT) at 503.5°C. To stabilize the orthorhombic phase of Fe₂(MoO₄)₃ at room temperature, a series of Fe_2-xSc_x(MoO₄)₃ (0≤x≤1.5) (abbreviated as F_2-xS_xM) were fabricated via solid-state reaction. Results indicate that the M-O PTT of Fe₂(MoO₄)₃ is successfully reduced from 503.5°C to 34.5°C by A-site cation substitution of Sc³⁺. The regulation mechanism is considered to be the decrease in electronegativity of (Fe_2-xSc_x)⁶⁺ in F_2-xS_xM. Both variable temperature X-ray diffraction (XRD) and thermal mechanical analysis (TMA) analysis results indicate that F_0.5S_1.5 M exhibits anisotropic NTE in 100–700°C. The results indicate that it can effectively improve the densification of Sc-substituted F_0.5S_1.5 M ceramics by two-step calcination process. Furthermore, higher second-step calcination temperature is beneficial for the formation of single-phased orthorhombic F_0.5S_1.5 M. The NTE response temperature range of F_0.5S_1.5 M ceramics second-step sintered at 1000°C is broadened to 30–600°C, and the corresponding coefficient of thermal expansion is -5.74 × 10⁻⁶°C⁻¹. The ease in the proposed design and preparation method makes NTE F_0.5S_1.5 M potential for a wide range of applications in precision mechanical, electronic, optical, and communication instruments.     

Synthesis and characterization of yttrium iron garnet nanoparticles doped with cobalt

In this work, we have synthesized and characterized yttrium iron garnet nanoparticles doped with cobalt. The X-ray diffraction data showed a single phase, belonging to the cubic structure of Y₃Fe₅O₁₂. Rietveld refinement revealed variation of the angles and interionic distances (Fe³⁺(a)-O^2-Y³⁺(c) and Fe³⁺(d)-O^2--Y³⁺(c) when Fe³⁺ ions are replaced by Co³⁺ ions in the tetrahedral (d) and octahedral (a) sites of YIG. In addition, the lattice parameter a, decreases from 12.3846?Å to 12.3830?Å with the increasing of cobalt concentration. The analysis by Infrared and Raman spectroscopies has shown a slight stretching at lower wave numbers as the dopant concentration increased. The magnetic measurements confirm the substitution of Fe³⁺ by Co³⁺ in the a-sites and d-sites with the reduction of the saturation magnetization from 26.63?emu/g to 24.92?emu/g, for 0.000?≤?y?≤?0.030. Changes in the coercive field varying the dopant concentration were related to the particle size and pinning centers existence.     

Synthesis and X-ray characterization of the quindecanuclear nickel/sulfur paramagnetic cluster [Ni15(μ3-S)6(μ4-S)9(PEt3)6]+

The quindecanuclear nickel/sulfur cluster [Ni₁₅(μ₃-S)₆(μ₄-S)₉(PEt₃)₆]⁺ has been isolated by reaction of Ni(ClO₄)₂·6H₂O with H₂S and PEt₃ in ethanol\dichloromethane solution and has been characterized by X-ray diffraction studies.     

Low-temperature catalytic decomposition of hydrogen sulfide on metal catalysts under layer of solvent

When hydrogen sulfide decomposition {2 H₂S ? 2 H₂?+?S₂^(gas)} is carried out in the flow regime at room temperature on metal catalysts placed in a liquid capable of dissolving H₂S and sulfur, the reaction equilibrium can be significantly (up to 100%) shifted to the right yielding the desired product – hydrogen. The process efficiency was demonstrated using aqueous solutions of monoethanolamine (MEA), sodium carbonate, which is widely used in industry for H₂S absorption from tail gases, and aqueous hydrazine as examples. IR and Raman spectroscopy data demonstrated that sulfur obtained in the solutions is in the form of diatomic molecules. DFT calculations showed that diatomic sulfur forms weakly bound coordinative complexes with solvent molecules. Some problems related to sulfur accumulation and recovery from the solvents are discussed.     

The first anion template cubic cyanometallate cage and its 3,5-dimethyltris(pyrazolyl)methane iron(II, III) tricyanide building blocks

Several 3,5-dimethyltris(pyrazolyl)methane iron(II, III) tricyanide building units have been prepared and characterized. Treatment of K[(HC(3,5-Me₂Pz)₃)Fe^II(CN)₂](K⁺1^-) with Fe^II(H²O)⁶(BF⁴)² affords a new anion template cubic cyanometallate cage [(BF₄) ⊂ {Fe^II(H₂O)}₄{(HC(3,5-Me₂Pz)₃)Fe^II (CN)₃}₄](BF₄)³ 3.     

Desulfurization performance of iron-manganese-based sorbent for hot coal gas

A series of iron-manganese-based sorbents were prepared by co-precipitation and physical mixing method, and used for H₂S removal from hot coal gas. The sulfidation tests were carried out in a fixed-bed reactor with space velocity of 2000 h⁻¹(STP). The results show that the suitable addition of manganese oxide in iron-based sorbent can decrease H₂S and COS concentration in exit before breakthrough due to its simultaneous reaction capability with H₂S and COS. Fe₃O₄ and MnO are the initial active components in iron-manganese-based sorbent, and FeO and Fe are active components formed by reduction during sulfidation. The crystal phases of iron affect obviously their desulfurization capacity. The reducibility of sorbent changes with the content of MnO in sorbent. S7F3M and S3F7M have bigger sulfur capacities (32.68 and 32.30 gS/100 g total active component), while S5F5M has smaller sulfur capacity (21.92 gS/100 g total active component). S7F3M sorbent has stable sulfidation performance in three sulfidation-regeneration cycles and no apparent structure degradation. The sulfidation performance of iron-manganese-based sorbent is also related with its specific surface area and pore volume.     

Carbonate and sulphate green rusts—Mechanisms of oxidation and reduction

The oxidation and reduction of carbonate, GR(CO₃), and sulphate, GR(SO₄), green rusts (GR) have been studied through electrochemical techniques, electrochemical quartz crystal microbalance (EQCM), FTIR, XRD and SEM. The used samples were made of thin films electrodeposited on gold substrate. The results from the present work, from our previous studies and from literature were compiled in order to establish a general scheme for the formation and transformation pathways involving carbonate or sulphate green rusts. Depending on experimental conditions, two routes of redox transformations occur. The first one corresponds to reaction via solution and leads to the formation of ferric products such as goethite or lepidocrocite (oxidation) or to the release of Fe^II ions into the solution (reduction) with soluble Fe^II-Fe^III complexes acting as intermediate species. The second way is solid-state reaction that involve conversion of lattice Fe²⁺ into Fe³⁺ and deprotonation of OH groups in octahedra sheets (solid-state oxidation) or conversion of lattice Fe³⁺ into Fe²⁺ and protonation of OH groups (solid-state reduction). The solid-state oxidation implies the complete transformation of GR(CO₃) or GR(SO₄) to ferric oxyhydroxycarbonate exGRc-Fe(III) or ferric oxyhydroxysulphate exGRs-Fe(III), for which the following formulas can be proposed, Fe^III₆(OH)_(12−2y)(O)_(2+y)(H₂O)_(y)(CO₃) or Fe^III₆(OH)_(12−2z)(O)_(2+z)(H₂O)_(6+z)(SO₄) with 0 ≤ y or z ≤ 2. The solid-state reduction gives ferrous hydroxycarbonate exGRc-Fe(II) or ferrous hydroxysulphate exGRs-Fe(II), which may have the following chemical formulas, [Fe^II₆(OH)₁₀(H₂O)₂]·[CO₃, 2H₂O] or [Fe^II₆(OH)₁₀(H₂O)₂]·[SO₄, 8H₂O].     

Electrochemical pitting behaviour of type 321 stainless steel in sulfide-containing chloride solutions

The pitting behaviour of type 321 stainless steel in sulfide-containing chloride aqueous environments was studied using cyclic potentiodynamic polarization. A well-established correlation between H₂S and Na₂S₂O₃ in the study of corrosion was applied, that is, H₂S was simulated by Na₂S₂O₃. The major factors affecting the pitting corrosion of type 321 stainless steel are the Cl^- concentration, solution pH and temperature. The results clearly indicate that both E_pit and E _pp decrease with increasing Cl^- concentration and temperature, while I _pass is more sensitive to temperature variation. E _pit decreased with decreasing pH in the range 2 < pH < 7.5. The surface morphology and chemistry of the corroded type 321 stainless steel resulting from anodic polarization in 0.01 M S₂O ₃ ^2- -containing Cl^- solution were analysed by XRD, SEM and EPMA. A higher concentration of sulfur was found in the pits, and the dark surface film was mainly composed of FeS and -Fe₂O₃. The results describe the pitting behaviour of type 321 stainless steel in sulfide-containing Cl^- aqueous environments.     

Reduction of n-C5H11N3 Catalyzed by [Mo2Fe6S8(OMe)3(SC6H4-p-n-C8H17)6]3– in an Aqueous Micellar Solution

Reduction of n-C₅H₁₁N₃ by Na₂S₂O₄ was performed in the presence of (n-Bu₄N)₃ [Mo₂Fe₆S₈(OMe)₃(SC₆H4-p-n-C₈H₁₇)₆] ((n-Bu₄N)₃ [Mo-Fe]) as a catalyst in aqueous Triton X-100 micellar solutions. The rate of the reduction is enhanced efficiently by the addition of methyl viologen (MV²⁺). The methyl viologen radical cation (MV⁺) produced by the reaction of MV²⁺ with Na₂S₂O₄ undergoes a disproportionation reaction to afford MV²⁺ and MV° in the micellar solution. The resultant MV° formed in the micelle transfers two electrons to [Mo-Fe]³⁻ effectively to give [Mo-Fe]⁵⁻, which reduces n-C₅H₁₁N₃ with two electrons to produce n-C₅H₁₁NH₂ and N₂.     

Iron—molybdenum—oxide catalysts for selective oxidation of hydrogen sulfide to sulfur

The selective oxidation of hydrogen sulfide to sulfur was studied over iron-molybdenum oxides with various Fe-Mo ratios. Strong synergistic phenomenon in catalytic activity was observed for the Fe-Mo-O binary oxides. Under identical reaction conditions, the areal rates of the binary oxides were superior to those of the corresponding single oxide catalysts, which suggest that the new compound Fe₂(MO₄)₃ formed in the binary oxide is more active than Fe₂O₃ and MoO₃. The oxidation rates of H₂S were found to exhibit first-order dependence on the hydrogen sulfide concentration, which implies that the activation of H₂S is the rate-limiting step.     

Anion doped bimetallic selenide as efficient electrocatalysts for oxygen evolution reaction

The development of highly efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) is of great importance in advancing the practical applications of green and sustainable hydrogen energy. Doping with either cations or non-metallic anions is a typical strategy used to improve the electrocatalytic activity for OER catalysts. In this study, an anion doped bimetallic selenide Co_0.75Fe_0.25(S_0.2Se_0.8)₂ solid solution is prepared via the simultaneous sulfuration and selenylation of a scalably produced CoFe-layered double hydroxide (CoFe-LDH) precursor, using commercially available sulfur and selenium powders as S and Se sources, respectively. Electrocatalytic test shows that the anion doped bimetallic selenide Co_0.75Fe_0.25(S_0.2Se_0.8)₂ electrode requires an overpotential of 293 mV and a low Tafel slope of 77 mV dec⁻¹ at a current density of 10 mA cm⁻² in an alkaline media, and it exhibits the significantly enhanced electrocatalytic performance for the OER compared with its counterparts of Co_0.75Fe_0.25S₂ and Co_0.75Fe_0.25Se₂. The enhanced electrocatalytic performance is supported experimentally by the results of charge-transfer resistance and electrochemically active surface area. Our LDH precursor-based protocol can provide a strategy to prepare non-metallic anion doped bimetallic selenides as efficient electrocatalysts for water splitting.     

A 31P-NMR study of peroxo species formed during oxidation of cyclohexene with hydrogen peroxide in tri-n-butylphosphate catalyzed by heteropolyacids

In the oxidation of cyclohexene with H₂O₂in monophasic tri-n-butylphosphate (TBP) solution catalyzed by Keggin-type 12-heteropolyacids, i.e., H₃PMo_12-xW _x O₄₀(x=0–12), several peroxo species were observed by ³¹P-NMR spectroscopy in lower field than the original heteropolyacids. Their composition varied regularly with that of the starting catalyst. The P-containing peroxo species formed was deduced as [PM₄O₈(O₂)₈]^3-(M = Mo, W). The peroxo species formed more easily with a decrease in the W content, x of H₃PMo_12-xW_xO₄₀. It was further indicated from the reactivity with cyclohexene and the comparison with catalytic performance that W-rich peroxo species were catalytically more active than Mo-rich peroxo species for the oxidation of cyclohexene in this reaction system.     

Kinetics of absorption of hydrogen sulfide into aqueous Fe(III) solutions

In our recent studies, absorption of H₂S into the aqueous Fe₂(SO₄)₃ and FeCl₃ solutions with various values of ionic strength and pH was investigated in an agitated vessel with a flat interface. The experimental results for both systems revealed that the species which reacts with H₂S is FeOH²⁺. The absorption rates were explained by the theory of gas absorption with an irreversible (l,l)-th order reaction between H₂S and FeOH₂₊. The reaction rate constants were independent of the ionic strength of the solution and correlated as a function of temperature. In this paper, kinetics and mechanism of these absorption reactions are reviewed and the identity for both systems is emphasized.     

Synthesis and analysis of structural,compositional, morphological,magnetic, electrical and surface charge properties of Zn-doped nickel ferrite nanoparticles

Zn-doped nickel ferrite nanoparticles (Zn_xNi_(1-x)Fe₂O₄) were synthesized using the co-precipitation technique. The structural and compositional studies of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles revealed their face-centred cubic spinel structure and an appropriate amount of Zn doping in nickel ferrite nanoparticles, respectively. The morphological analysis had been carried out to obtain the particle size of the synthesized nanoparticles. The magnetic studies revealed the superparamagnetic nature of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles, and the maximum magnetization of 30 emu/g for the Zn_0.2N_0.8Fe₂O₄ sample. The M ? H curves were fitted with the Langevin function to obtain the magnetic particle diameter of Zn_xNi_(1-x)Fe₂O₄ nanoparticles. The electrical conduction in Zn_xNi_(1-x)Fe₂O₄ nanoparticles was explained through the Verway hopping mechanism. The Zn_0.2N_0.8Fe₂O₄ nanoparticle exhibited a higher electrical conductivity of 42 μS/cm and surface charge of ?29/7 mV due to the enhanced hopping of Fe³⁺ ions in the octahedral sites. Owing to this nature, they were identified as the suitable candidates in the applications such as thermoelectrics, hyperthermia, magnetic coating and for the preparation of conducting ferrofluids.     

Simulation studies on a rotating ring disk electrode: Effects of ionic migration with kinetic complication-disk results

In continuation to my previous work (Guha S. AIChE J. 2013;59(4):1390-1399), in this work, effects of ionic migration are evaluated for disk region of a rotating ring disk electrode system by numerically solving complex differential equations, developed for mass transfer along with kinetic complication in presence of ionic migration under limiting current condition. The system for simulation is 0.01 M Fe₂(SO₄)₃ solution with H₂SO₄ as supporting electrolyte. Simulation cases are presence and absence of ionic migration with kinetic complication (oxidation of Fe²⁺ to Fe³⁺ under O₂ pressure). Results show that concentration boundary layer thickness of reactant Fe³⁺ reduces appreciably and steady-state disk current reduces substantially in presence of migration. Simulated steady-state disk current in absence of migration case agrees well with published data. Results indicate higher Fe²⁺ concentration in presence of migration and thereby higher rate of oxidation of Fe²⁺ to Fe³⁺ at all rate constant values.     

Selective oxidation of hydrogen sulfide containing excess water and ammonia over Bi-V-Sb-O catalysts

We investigated the selective oxidation of hydrogen sulfide to elemental sulfur and ammonium thiosulfate by using Bi₄V_2-xSb_xO_11-y catalysts. The catalysts were prepared by the calcination of a homogeneous mixture of Bi₂O₃, V₂O₅, and Sb₂O₃ obtained by ball-milling adequate amounts of the three oxides. The main phases detected by XRD analysis were Bi₄V₂O₁₁, Bi_1.33V₂O₆, BiSbO₄ and BiVO₄. They showed good H₂S conversion with less than 2% of SO₂ selectivity with a feed composition of H₂S/O₂/NH₃/H₂O/He=5/2.5/5/60/27.5 and GHSV=12,000 h^-1 in the temperature ranges of 220–260 ‡C. The highest H₂S conversion was obtained for x=0.2 in Bi₄V_2-xSb_xO_11-y catalyst. TPR/TPO results showed that this catalyst had the highest amount of oxygen consumption. XPS analysis before and after reaction confirmed the least reduction of vanadium oxide phase for this catalyst during the reaction. It means that the catalyst with x=0.2 had the highest reoxidation capacity among the Bi₄V_2-xSb_xO_11-y catalysts.     

Binuclear cyano-bridged complex derived from [MnIII(salpn)] and [FeIII(CN)6]: Synthesis,structure and magnetic properties

The reaction of the neutral [Mn(salpn)C(CN)₃(H₂O)] (salpn^2 − = N,N^′-1,3-propylenebis(salicylideneiminato) dianion) with [Fe^III(CN)₆]^3 − in the presence of strong oxidizer (NH₄)₂S₂O₈ yields a binuclear anion complex [NH₃CH₂CH₂CH₂NH₃]^2 +{[Mn^III(salpn)(H₂O)][Fe^III(CN)₆]}^2 − (1). Its structure, DC and AC susceptibility have been studied. Frequency dependence of the AC susceptibility characteristic for single-molecule magnets has been found.     

Mechanism study of iron-based catalysts in co-liquefaction of coal with waste plastics

The state and active site of iron-based catalysts in co-liquefaction of coal with low-density polyethylene (LDPE) have been discussed. The catalysts used were sulfur-promoted iron oxides (Fe₂O₃+S), ferrous sulfide (FeS), ferrous sulfate (FeSO₄·7H₂O) and the mineral pyrite (FeS₂). It was found by X-ray photoelectron spectrometry that the active site in the working state of Fe₂O₃+S catalyst was not Fe_1−XS and the main form of sulfur existing in the spent Fe₂O₃+S catalyst was sulfate, followed by sulfite (SO₃²⁻). A finding from autoclave tests was that the ferrous sulfate before and after oxidation treatments showed sufficiently high activity for the co-liquefaction of coal with LDPE. It was concluded that an active site of the iron-based catalysts was sulfate species formed on the catalyst surface during the hydroliquefaction process of coal.