Sulfur-containing Anions Research Articles

Ionic Liquids as Extreme Pressure Additives for Bearing Steel Applications

The protection of steel surfaces from wear under extreme pressure conditions is of major importance in several industries as it provides better performance and longer life of machinery. The motivation for this work was to study the lubrication of steel by ionic liquids (ILs), which have recently emerged as greener alternatives to commercial lubricants and additives. Three ILs based on sulfur-containing anions, used as 2-wt% additives in polyethylene glycol base oil (MW 200; PEG 200), were tested in the lubrication of ASTM 52100 bearing steel contacts in extreme pressure conditions (under mixed lubrication with a Hertzian pressure of 1.12 GPa) using a mini traction machine (MTM). Due to the poor resistance to corrosion of bearing steel, a semi-ester of succinic acid derivative corrosion inhibitor (Lanxess RC 4801) was added to the mixtures at a 1 wt% concentration. The ILs 1-hexyl-methylimidazolium trifluoromethanesulfonate ([C6mim][TfO]) and 1-hexyl-4-picolinium trifluoromethanesulfonate ([C6-4-pic][TfO]) revealed promising results in terms of surface protection of bearing steel. In contrast, 4-picolinium hydrogen sulfate ([4-picH][HSO4]) as 2-wt% additive to PEG 200 + 1% RC 4801 did not show any improvement in wear performance compared to neat PEG 200 + 1% RC 4801. PEG 200 + 2% [C6mim][TfO] + 1%RC 4801 allowed for a decrease in wear up to ~ 76% and PEG 200 + 2% [C6-4-pic][TfO] + 1%RC 4801 up to ~ 46% when compared with neat PEG 200 + 1% RC 4801. Optical microscopy images suggest the formation of an adsorbed layer, which was further supported by chemical analysis via x-ray photoelectron spectroscopy (XPS) data for [C6mim][TfO].Graphical abstract

Multi-chamber membrane capacitive deionization coupled with peroxymonosulfate to achieve simultaneous removal of tetracycline and peroxymonosulfate reaction byproducts

Advanced oxidation technologies based on peroxymonosulfate (PMS) have been extensively applied for the degradation of antibiotics. However, the degradation process inevitably introduces SO42- and other sulfur-containing anions, these pollutants pose a huge threat to the water and soil environment. Addressing these concerns, this study introduced PMS oxidation into a multi-chamber membrane capacitive deionization (MC-MCDI) device to achieve simultaneous tetracycline (TC) degradation and removal of PMS reaction byproduct ions. The experimental results demonstrated that when the TC solution (40 mg L−1) was pre-adsorbed for 10 min, the voltage was 1.2 V and the concentration of PMS solution added was 4 mg mL−1, the removal efficiency of TC and ion can reach 77.4 % and 46.5 % respectively. Furthermore, the activation process of PMS in MC-MCDI/PMS system and the reactive oxygen (ROS) that mainly produce degradation were deeply investigated. Finally, liquid chromatography-mass spectrometry (LC-MS) was employed to identify intermediates of TC degradation, propose potential degradation pathways, and analyze the toxicities of the intermediates. In addition, in five cycles, the MC-MCDI/PMS system demonstrated excellent stability. This study provides an effective strategy for treating TC wastewater and a novel approach for simultaneous TC degradation and desalination.

Metal-cation-induced shifts in thiolate redox and reduced sulfur speciation.

Sulfur-containing anions (e.g. thiolates, polysulfides) readily exchange in solution, making control over their solution speciation and distribution challenging. Here, we demonstrate that different redox-inactive alkali, alkaline earth, and transition metals (Li+, Na+, K+, Mg2+, Ca2+, Zn2+, and Cd2+) shift the equilibria of sulfur catenation or sulfur reduction/oxidation between thiolate, polysulfanide, and polysulfide anions in acetonitrile solution. The thermodynamic factors that govern these equilibria are examined by identification of intermediate metal thiolate and metal polysulfide species using a combination of NMR spectroscopy, electronic absorption spectroscopy, and mass spectrometry. Electrochemical measurements demonstrate that the metal cation of the electrolyte modulates both sulfur reduction and thiolate oxidation potentials. DFT calculations suggest that the changes in equilibria are driven by stronger covalent interactions between polysulfide anions and more highly charged cations.

Sulfur-Containing Radical Anions Formed by Photolysis of Thiosulfate: Quantum-Chemical Analysis.

The photochemistry of sodium thiosulfate (S2O32-) in aqueous solutions is rather complicated. Several sulfur-containing radical anions are formed upon photoexcitation. Any of them are rather common (SO3•-, SO2•-, and SO5•-); others are rare (S2O3•-, •S4O63-, and S•-) or never documented (S2O5•-). In order to support the identification of intermediate radical anions, quantum-chemical (QM─quantum mechanical) calculations of the geometric and electronic structures of S2O3•-, S2O5•-, and •S4O63- were performed. Two different approaches, time-dependent density functional theory and complete active space self-consistent field, were applied to identify the method optimal for the reproduction of the experimental electronic absorption spectra. Several of the most commonly used functionals were considered. The best agreement with the experimentally observed spectra of reference compounds (common sulfur-containing anions and radical anions) was achieved for the WB97X-D3 functional. Using this approach, satisfactory agreement between experimental and calculated spectra of S2O3•-, S2O5•-, and •S4O63- was achieved. It was shown that S2O5•- and •S4O63- can exist in two isomeric forms with different spectral properties. These isomers are S2O3O2•-; SO3SO2•- for the case of S2O5•- and (S2O3)2•3-; (S3O32-...SO3•-) for the case of •S4O63-.

Characteristics of Anode Materials for Nickel Electroforming

This study comprised an investigation of the characteristics of commercial nickel anode materials routinely employed in sulfamate-based electroforming processes. These included examples of sulfur depolarised anodes containing a relatively high sulfur content and those with much lower levels. Electrochemical studies indicate that the sulfur depolarised anodes underwent dissolution in the active region and were capable of sustaining large current densities at low potentials without passivating, and with current efficiencies approaching 100%. In contrast, low-sulfur containing anodes could only sustain low current densities in the active region, and were prone to passivation. These materials could only undergo high rate dissolution in the transpassive region, but this required relatively high anode potentials and was accompanied by various side reactions which lowered the current efficiency. Additional studies were performed to characterise the sulfamate oxidation products which generates a distinct UV absorption band at 245 nm. These species were produced only when low-sulfur content or inert (platinum) anodes were used, and were absent when sulfur depolarised anodes were employed. The principal anode product was azodisulfonate, but trace amounts of other sulfonate species and sulfur-containing anions may also be present.

Imidazolium-Modified Bispyrene-Based Fluorescent Aggregates for Discrimination of Multiple Anions in Aqueous Solution.

A great number of anions exist in biological systems and natural environment, and are highly relevant to human health and environment quality. It is necessary to develop simple and effective sensors to differentiate and identify those similar or different anions. Here, an imidazolium-modified bispyrene-based fluorescent amphiphilic probe DPyDIM was synthesized and its aggregates were applied to detect and discriminate various anions. The fluorescent aggregates exhibit ratiometric responses to different types of anions. Moreover, the ratiometric responses to different types of anions are featured with multiple-wavelength cross-reactivity. The collection of fluorescence variation at four typical wavelengths can generate distinct recognition patterns to specific anions. The heat map and principal component analysis results verify that this single fluorescent sensor system can effectively and sensitively identify 16 kinds of anions that belong to phosphorus-containing, sulfur-containing anions, and anionic surfactants. The cross-reactive sensing of the amphiphilic fluorescent aggregates was attributed to the different influences on the aggregation behaviors of the probes by different anions. The present work provides a promising strategy for effective detection and discrimination of multiple anions by employing dynamic fluorescent aggregates as a sensing platform.

A review of gold extraction using noncyanide lixiviants: Fundamentals, advancements, and challenges toward alkaline sulfur-containing leaching agents

Alkaline sulfur-containing lixiviants, including thiosulfate, polysulfides, and alkaline sulfide solutions, stand out as a promising class of alternatives to cyanide because of their low toxicity, high efficiency, and strong adaptability. In this paper, we summarized the research progress and remaining challenges in gold extraction using these noncyanide reagents. After a brief introduction to the preparation method, the transformation process of various sulfur-containing species in alkaline solutions was discussed. Thereafter, some insights into the mechanism of gold leaching in alkaline sulfur-containing solutions were presented from different aspects, including thermodynamics analysis, electrochemical dissolution, and leaching kinetics. Moreover, recent progress in in-situ generation of sulfur-containing anions from gold-bearing sulfide minerals was outlined as well. Gold passivation caused by sulfur species was discussed in particular because it is considered the greatest challenge facing sulfur-containing leaching systems. Alkaline sulfur-containing lixiviants are expected to serve as alternatives in industrial applications of gold extraction, particularly for refractory gold ores containing copper and carbonaceous matter.

Deep eutectic solvents (DES) based on sulfur as alternative lubricants for silicon surfaces

Deep eutectic mixtures composed of hydrogen-bond donors (HBDs) and hydrogen-bond acceptors (HBAs), the so-called DESs, have recently being proposed as possible “green” alternatives to mineral oils and ionic liquids (ILs) in the lubrication of steel surfaces. DESs have similar physical properties to ILs but have the advantage of being cheaper and easier to prepare. In this work, new DESs containing sulfur units in their composition were prepared and tested in the lubrication of silicon surfaces which are relevant for nano/microelectromechanical systems (NEMS/MEMS). The following new DESs were prepared: ethyldibutyl sulfonium ethylsulfate: polyethylene glycol ([S4,4,2][EtSO4]:PEG), 1-ethyl-tetrahydrothiophenium ethylsulfate: polyethylene glycol ([C2-THT][EtSO4]:PEG), 1-ethyl-3-methylimidazolium (S)-camphorsulfonate: polyethylene glycol ([C2MIM][(S)CSA]:PEG), and 1-methyl-3-picolinium methyl sulfate: polyethylene glycol ([C1-3-pic][MeSO4]:PEG). Other DES, already reported, were tested for comparison purposes: tetrabutylammonium bromide: sulfolane ([N4,4,4,4][Br]:Sulf), choline chloride: polyethylene glycol (ChCl:PEG), and tetrabutylammonium bromide: polyethylene glycol ([N4,4,4,4][Br]:PEG). All DESs were characterized in terms of their water content, viscosity, wettability, and tribological properties. The friction coefficients were measured in a nanotribometer using steel spheres against Si surfaces. The new DES prepared from salts based on the sulfur-containing anions showed good tribological performance, but the best results were obtained with [C2MIM][(S)-CSA]:PEG and [C1-3-pic][MeSO4]:PEG which reduced the friction coefficients to values <0.1, typical of excellent lubrication conditions.

Determination of sulfur-containing anions in alkaline solutions using arrays of DP-sensors based on hybrid perfluorinated membranes with proton-donor dopants

The influence of proton-donor properties and concentration of dopant nanoparticles introduced into Nafion and MF-4SС perfluorosulfonic cation-exchange membranes on the characteristics of cross-sensitive DP-sensors (sensors whose analytical signal is the Donnan potential) in alkaline solutions of sulfur-containing organic compounds were studied. The dopants were acid salts of heteropoly acids (HPAs) and hydrated silica SiO2 and zirconia ZrO2 surface-modified with sulfur-containing groups and an acid HPA salt. A correlation was revealed between the DP-sensor sensitivity to anions (and zwitter-ions) in alkaline solutions, size and proton-donor ability of the added particles, and diffusion permeability of hybrid membranes. Optimum compositions of membranes for arrays of cross-sensitive DP-sensors ensuring the simultaneous determination of cations and anions (and zwitter-ions) in the test solutions with an error of less than 18% were selected.

Reactions of Sulfur- and Oxygen-Containing Anions with Hydrogen Atoms: A Comparative Study.

Reactions of hydrogen atoms with small sulfur-containing anions, SCN-, CH3COS-, C6H5COS-, -SCH2COOH, C6H5S-, 2-HOOCC6H4S-, and related oxygen-containing anions, OCN-, CH3COO-, C6H5COO-, HOCH2COO-, C6H5O-, 2-HOOCC6H4O-, have been studied both experimentally and computationally. The experimental results show that associative electron detachment (AED) is the only channel for the reactions. The rate constants for reactions between sulfur-containing anions and H atoms are generally higher than for the related oxygen-containing anions with the exception of the reaction of SCN-. The generally higher reactivity of the sulfur anions contrasts with previous results where AED reactivity was found to correlate with reaction exothermicity. Density functional theory calculations indicate that the reaction enthalpies, the characteristics of the reaction potential energy surfaces, and other structural and electronic factors can influence the reaction rate constants. This study indicates that organic sulfur anions can be more reactive than related oxygen anions in the interstellar medium where hydrogen atoms are abundant.

Spectroscopic study of Se(IV) removal from water by reductive precipitation using sulfide

This study investigates the removal of selenium (IV) from water by reductive precipitation using sodium sulfide at neutral pH. Also, it examines the application of UV light as an activating method to enhance reductive precipitation. Furthermore, this work evaluates the effects of sulfide dose and solution pH on behavior of Se(IV) reduction. Selenium was effectively removed in sulfide solution at both neutral and acidic pH. UV irradiation did not enhance removal efficiency of Se(IV) at conditions tested, but it affected solids morphology and composition. SEM/EDS and XPS results showed that selenite was reduced to elemental Se or Se-S precipitates (e.g. SenS8-n) in sulfide solution. High resolution S 2p XPS spectra suggested the presence of sulfur-containing anions (e.g. S2O32−, HSO3−, etc.) or elemental S (S0), monosulfide (S2−), and polysulfides (Sn2−), which could be produced from sulfide photolysis or reaction with Se. In addition, large aggregates of irregular shape, which suggest Se-S precipitates or elemental sulfur, were found more prominently at pH 4 than at pH 7, and they were more noticeable in the presence of UV with longer reaction times. In addition, XRD patterns showed that gray elemental Se solids were dominant in experiments without UV, whereas Se-S precipitates (Se3S5) with an orange color were found in those with UV.

Sensors based on zirconia-modified perfluorinated sulfonic acid membranes sensitive to organic anions in multiionic aqueous solutions

The effect of modification of perfluorinated sulfonic acid membranes with zirconia on their conducting properties and electrode-active properties for potentiometric sensors whose analytical signal is the Donnan potential (DP) has been studied. It has been found that the incorporation of ZrO2 particles into the membrane matrix results in an increase in the ionic conductivity, as compared with unmodified membranes, and the proton diffusion coefficient changes nonmonotonically. Membranes with a gradient dopant distribution along the sample length provide for a partial decrease in the cation-exchange function of DP sensors because of a decrease in the concentration of fixed cation-exchange groups and due to the sorption of coions. This results in an increase in the sensor sensitivity to organic and sulfur-containing anions in multiionic aqueous solutions. Multivariate calibration methods with a nonorthogonal experimental design were used to evaluate the effects of the concentrations and nature of counterions and coions and pH in the test solutions on the characteristics of DP sensors.

Perfluorinated sulfocation-exchange membranes modified with zirconia for sensors susceptible to organic anions in multiionic aqueous solutions

Potentiometric sensors whose analytical signal is the Donnan potential can be developed for the determination of organic and sulfurcontaining anions in multiionic aqueous solutions based on perfluorinated sulfonated cation-exchange membranes modified with zirconia.

Estimated Dietary Intake of Thiocyanate from Brassicaceae Family in Korean Diet

Glucosinolate, sulfur-containing organic anions bonded to glucose, is found in plants including the family of Brassicaceae. Glucosinolate is hydrolyzed by myrosinase and produces various by-products that possess biological activities. Among the decomposed products, thiocyanate is known for its adverse effects on thyroid metabolism due to competition with iodine. This is of concern in that Korean dietary habits consist of consumption of large amounts of Brassicaceae vegetables such as cabbage and radishes, which may be correlated with high incidence of thyroid dysfunction. Thus, quantification of thiocyanate in Brassicaceae vegetables was performed by hydrolysis and spectrophotometrical detection. Average daily intake of Brassicaceae vegetables was obtained from the Third Korea National Health and Nutrition Examination Survey (KNHANES III), 2005—Nutrition Survey and from The Vegetable Production Statistics, 2007. Average daily intake of thiocyanate through Brassicaceae vegetables in Korea was estimated to be 16.3 μmol SCN−/d/person. When this was compared to published animal studies, average thiocyanate intake per person was lower than doses required to produce adverse effects. However, further studies may be warranted to ensure safety with sufficient margins of safety.

Novel 3D, 2D, and 0D First-Row Coordination Compounds with 4,4‘-Bipyridine-N,N‘-dioxide Incorporating Sulfur-Containing Anions

The reaction of M(S2O6) (M = Cu(II), Ni(II), and Co(II)) with 4,4'-bipyridine-N,N'-dioxide (bpdo) results in the formation of novel 3D, 2D, and mononuclear complexes. Complex 1, {[Cu(H2O)(bpdo)2](S2O6)(H2O)}n, is a 2-D wavelike polymer with the Cu(II) ion located on a 2-fold axis and having a distorted square-pyramidal coordination sphere. With Co(II) and Ni(II), 3-D complexes, {[M(bpdo)3](S2O6)(C2H5OH)7}n [M = Co(II) (2), Ni(II) (3)], were obtained. The metal atoms are situated on centers of symmetry and have octahedral environments coordinated to six bpdo molecules. The same reaction in aqueous solution with a metal/ligand ratio of 1:1 results in the formation of mononuclear complexes, {[M(bpdo)(H2O)5](SO4)(H2O)2} [M = Co(II) (4), Ni(II) (5)], accompanied by the decomposition of the dithionate anions S2O6(2-) to sulfate anions SO4(2-).

Speciation of sulfur-containing anions by use of capillary electrophoresis

Optimization of a CE method with indirect UV detection for speciation of sulfur-containing anions is described. Sensitivity, selectivity, and separation using a chromate background electrolyte (the electrolyte most often used for inorganic anions) and a pyromellitate electrolyte are compared. The pyromellitate electrolyte is recommended because its use results in better sensitivity for the ions analyzed. The composition of the electrolyte was 2.25 mM pyromellitic acid, 6.5 mM NaOH, 0.75 mM hexamethonium hydroxide, and 1.6mM triethanolamine, pH 10. Separation of seven sulfur-containing anions with indirect detection at 254 nm was achieved in one run in less than 7 min.

Method development and validation for the determination of various sulfur-containing anions and other anions in the corrosion process by capillary ion electrophoresis with indirect detection.

A method of capillary ion electrophoresis with indirect detection is developed for the simultaneous determination of the sulfur-containing anions S2O4(2-), S2O3(2-), SO4(2-), SO3(2-), and S2- and other anions (Cl-, Br-, NO2-, NO3-, (COO)2(2-), F-, and PO4(3-)) in the corrosion process. The effects of pH, tetradecyltrimethylammonium hydroxide, chromate, 2-[n-cyclohexylamino]-ethane sulfonate, calcium gluconate, and acetonitrile on the migration and resolution of the anions and the stability of sulfur-containing anions are systematically investigated. The detection limits, repeatability, and linearity for the anions are comparatively studied at 374, 274, and 254 nm, and the results show that 374 nm is the optimal length. The simultaneous multiwavelength detection at 374, 254, 214, and 195 nm can assist in confirming the identification of UV-absorbing anions.

Quantitative determination of sulfur-containing anions in complex matrices with capillary electrophoresis and conductivity detection

The analysis of sulfur species in complex matrices, like environmentally related samples, requires selective and sensitive as well as robust determination methods. As many as possible different anions need to be quantified in a reasonable analysis time. Besides ion chromatography, capillary electrophoresis has proven to be a very efficient technique for the separation and determination of ionic compounds. With the advantages of less sample and solvent consumption compared to conventional LC, short separation time, inexpensive and robust capillaries, CE was used to separate the anions sulfate, sulfite, thiosulfate, thiocyanate and sulfide. Detection and injection modes and the composition of the separation buffers have been varied to find the most suitable conditions. Conductivity detection after electrokinetic sample injection and improvement of calibration linearity allowed the determination of sulfur containing anions with low limits of detection (8 to 50 μg/l). The developed CE method was applied to the analysis of water from an open-pit mining lake.

Ion chromatographic separation of sulfur-containing inorganic anions with an ICP–MS as element-specific detector

An inductively coupled plasma mass spectrometer (ICP–MS) was used as element-specific detector for sulfide, sulfite, sulfate, and thiosulfate after their chromatographic separation on a Dionex IonPac ® AS12A analytical column. The sulfur-containing anions were detected as 32S 16O + at m/z=48 with the ICP–MS operated with cool and normal plasma conditions, both tuned for the production of high oxide ratios. Three different mobile phases [(NH 4) 2CO 3, Na 2CO 3, and NaOH] were tested. The ICP–MS signal at m/z=48 for the sulfur-containing anions was obtained only with NaOH based eluents and application of a membrane suppressor for removal of sodium. The detection limits ( S/N=3, calculated on elemental basis) at optimal chromatographic conditions for sulfide, sulfite, sulfate, and thiosulfate were 35 μg l −1, 200 μg l −1, 130 μg l −1, and 270 μg l −1, respectively. A lower detection limit for sulfide was found to be a result of a higher absolute sulfur amount input into the plasma due to the release of the dissolved H 2S from the aerosol droplets into the gas phase. Severe signal suppression for sulfide with cool plasma and shortening of the sulfide retention with normal plasma were observed in the case of highly saline samples. Both effects were confirmed to be caused by chloride anions.

Reverse osmosis for separation of reaction solutions in homogeneous catalysis

The potentials of reverse osmosis (RO) in separation of soluble homogeneous catalysts from reaction products were studied. Two environmentally important liquid phase processes were considered: (A) detoxication of NO and H 2S catalyzed by iron-containing phosphotungstenate heteropoly anion PW 11Fe II (H 2O)O 5− 39: 2 NO + 2 O 2 + H 2S → 2 HNO 3 + S and (B) detoxication of the water soluble sulfides catalyzed by the sodium salt of tetra (sulfophthalocyanine) cobalt (II): S 2− + O 2 → (S, SO 2− 3, SO 2− 4, S 2O 2− 3) For reaction (A), the RO retention of the NO − 3 product was found to decrease with the concentration of the heteropoly anion catalyst, reaching negative values, whereas the retention of the catalyst amounted to 99%. Due to the negative retention of the nitrate ions and high positive retention of the catalyst, their efficient separation was achieved. For reaction (B), RO allowed to retain the catalyst almost completely (retention exceeded 99.9%), while the products (sulfur-containing anions) exhibited markedly lower retentions. For both reactions, the structure and activity of the catalysts remained unchanged after the RO separation, thus enabling their multifold re-use.