S2 Molecules Research Articles

High-Entropy Sulfide (FeCoNiCrMn)S2 for Room Temperature NO2 Sensors.

Metal sulfides have been extensively studied in the field of chemical sensors working at room temperature (RT). However, compared to metal oxides, metal sulfides often suffer from incomplete recovery and unsatisfactory selectivity. In this work, we for the first time report the high-entropy sulfide (HES) (FeCoNiCrMn)S2, prepared by the solvothermal method, is a promising candidate for utilization as the sensitive layer in gas sensors. Unlike traditional single-metal sulfides, this HES (FeCoNiCrMn)S2 exhibits reversible recovery for NO2 at RT as well as excellent selectivity. To unveil the sensing mechanism, we simulated the adsorption and charge transfer between (FeCoNiCrMn)S2 and gas molecules by the density functional theory (DFT) calculation, revealing the reason (FeCoNiCrMn)S2 is uniquely selective to NO2. This work explores the application potential of HES (FeCoNiCrMn)S2 as an RT sensor and enriches the material selection for NO2 sensors.

Dual Sources of S2 Observed in Comet 67P: Insights from Comparing ROSINA Measurements and Laboratory Simulations

Hydrogen sulfide (H2S) is the fifth most abundant molecule observed in the coma of comet 67P/Churyumov–Gerasimenko (67P). Prior to its incorporation into cometary materials, H2S likely underwent ultraviolet (UV) radiation exposure, which is thought to initiate a complex sulfur chemistry. We present an investigation into the UV photochemistry of H2S ices using infrared, Raman, and mass spectrometry techniques. Our study reveals the production of complex sulfur allotropes ranging from S2 to S6, alongside polysulfanes (H2S n , n = 2–3). Temperature-programmed desorption measurements postirradiation of H2S exhibit two peaks for S2 molecules: a broad peak between 80 and 140 K and a distinct peak at ∼245 K. Notably, larger allotropes S3–S5 exclusively display the 245 K peak. Furthermore, ROSINA measurements of the S2/H2S ratio during dust impact events and previously reported S2/H2S ratios in the undisturbed coma are compared to our laboratory-determined S2/H2S values. This analysis identifies two distinct sources of S2: a volatile S2 potentially sublimated directly from the comet’s surface and a secondary source likely resulting from fragmentation of larger sulfur chains during dust impacts. We determined the ratio of produced S2 to the initial H2S for both the volatile component and the refractory component at 245 K with both measurements conducted at an irradiation incident fluence of 2.25 × 1017 photons cm−2. These laboratory-derived S2/H2S ratios exhibit concordance with ROSINA measurements. When extrapolated to incident fluences anticipated in molecular clouds, this photoprocessing mechanism offers a plausible explanation for the measured S2/H2S ratio in comet 67P.

Collective dynamics of liquid sulphur across the polymerisation transition temperature probed by inelastic x-ray scattering

Inelastic x-ray scattering (IXS) experiments on liquid sulphur were carried out below (140 ∘C) and above (180 ∘C) the polymerisation temperature T λ of about 159 ∘C to investigate changes in the collective dynamics of this unique liquid, that exhibits a liquid–liquid transition. As reported earlier, broad longitudinal acoustic excitation signals were observed at both temperatures, and only the width of the quasielastic peaks slightly decreased when the temperature crossed the transition temperature. A model analysis was performed using a generalised Langevin formalism with a memory function having one thermal and two viscoelastic decay channels with the help of simple sparse modelling, and large positive deviations from the hydrodynamic sound velocity by 51%–54% were observed. The fast viscoelastic relaxation time τ µ is close to the correlation times of intermolecular stretching and bending motions of local sulphur connections in both ring and chain structures, and is similar to those of other molecular liquids. The small contrasts in the IXS spectra across the λ transition result in large changes in only the slow viscoelastic decay time τ α of the memory function. The τ α value at 140 ∘C matches the mixed internal/external torsional modes of S8 molecules well, whereas that at 180 ∘C has no corresponding molecular motion mode. The kinematic viscosity values at the Q→0 limit are much smaller than the minimum values of macroscopic shear viscosity, indicating that large changes in relaxation dynamics are expected with Q in the GHz and MHz excitation regimes.

First-Principles Investigation of Phosphorus-Doped Graphitic Carbon Nitride as Anchoring Material for the Lithium-Sulfur Battery.

The utilization of lithium-sulfur battery is hindered by various challenges, including the "shuttle effect", limited sulfur utilization, and the sluggish conversion kinetics of lithium polysulfides (LiPSs). In the present work, a theoretical design for the viability of graphitic carbon nitride (g-C3N4) and phosphorus-doping graphitic carbon nitride substrates (P-g-C3N4) as promising host materials in a Li-S battery was conducted utilizing first-principles calculations. The PDOS shows that when the P atom is introduced, the 2p of the N atom is affected by the 2p orbital of the P atom, which increases the energy band of phosphorus-doping substrates. The energy bands of PC and Pi are 0.12 eV and 0.20 eV, respectively. When the lithium polysulfides are adsorbed on four substrates, the overall adsorption energy of PC is 48-77% higher than that of graphitic carbon nitride, in which the charge transfer of long-chain lithium polysulfides increase by more than 1.5-fold. It is found that there are powerful Li-N bonds between lithium polysulfides and P-g-C3N4 substrates. Compared with the graphitic carbon nitride monolayer, the anchoring effect of the LiPSs@P-g-C3N4 substrate is enhanced, which is beneficial for inhibiting the shuttle of high-order lithium polysulfides. Furthermore, the catalytic performance of the P-g-C3N4 substrate is assessed in terms of the S8 reduction pathway and the decomposition of Li2S; the decomposition energy barrier of the P-g-C3N4 substrate decrease by 10% to 18%. The calculated results show that P-g-C3N4 can promote the reduction of S8 molecules and Li-S bond cleavage within Li2S, thus improving the utilization of sulfur-active substances and the ability of rapid reaction kinetics. Therefore, the P-g-C3N4 substrates are a promising high-performance lithium-sulfur battery anchoring material.

Ionization of sulfur clusters, S[formula omitted] (n = 2−8) by electron collisions

This article reports the electron scattering ionization cross sections for S2, S3, S4, S5, S6, S7, and S8 target molecules essential to many fields like radiation chemistry, atmospheric, astrophysical, and astrochemical modeling. The theoretical approach utilizes a complex scattering potential ionization contribution method. The computation is carried from the ionization threshold of the target molecule to 5000 eV to investigate the entire energy range, which is significant to the ionization process of the molecules. A simple additivity rule is applied to study complex and non-spherical cases. Further, screening correction is implemented within the molecular system to reduce the overestimation in cross section values due to the overlapping charge density. A high correlation was obtained for the maximum ionization cross section value and the square root of the ratio of polarizability to the target molecule’s ionization energy, indicating the present method’s accuracy. Besides the Astro modeling applications, the cross section values also find utility in industrial plasma, sulfur lamps, lithium-sulfur batteries, and mass spectrometry.

Adsorption mechanism study of sour natural gas and sulfur in high-sulfur carbonate rock gas reservoirs

As the world pivots towards green and renewable energy sources, natural gas stands out as a clean and efficient alternative. In particular, there has been an upsurge in the exploration and development of gas fields rich in hydrogen sulfide (H2S). However, an escalating issue of sulfur deposition is notably pronounced in carbonate rock reservoirs predominantly comprised of dolomite, as exemplified in China's Yuan Ba gas field. This study examines sulfur adsorption in high-sulfur gas reservoirs and its effects on carbonate rock formations. Molecular simulation analysis reveals that the sour natural gas density in 20 Å dolomite nanopore structure experiences an average increase of 30% at the nanoscale. Notably, CO2 and H2S manifested strong adsorption tendencies in smaller pore sizes, with CO2's strong adsorption state layer thickness measuring approximately 2.93 Å, and H2S's at about 1.871 Å. Additionally, it was found that the adsorption energy of sour natural gas decreases with rising temperature and pore size, and falling pressure, yet the temperature's effect on excess adsorption density is minor above 40 MPa. As the pore size reaches 160 Å, the strong adsorption states of CO2 and H2S dissipate. Beyond 160 Å, the influence of nanoscale dimensions is negligible, with only a 2.23% increase in adsorbed phase density compared to the bulk phase. The introduction of S8 molecules amplified the adsorption proclivities of CO2 and H2S, urging them closer to the pore wall. The study reveals that CO2 or H2S reinjection into formations could effectively mitigate sulfur deposition in pores smaller than 160 Å, offering valuable insights for the development of high-sulfur gas fields.

Rational Design of Novel Promising Infrared Nonlinear Optical Materials: Structural Chemistry and Balanced Performances.

ConspectusSecond-order nonlinear optical (NLO) materials are currently a hot topic in modern solid-state chemistry and optics because they can produce coherent light by frequency conversion. Noncentrosymmetric (NCS) structure is not only the prerequisite for NLO materials but also a challengeable issue because materials tend to be centrosymmetric (CS) in terms of thermodynamical stability. Among NLO materials, an excellent infrared (IR) candidate should simultaneously meet several strict key conditions including a large NLO coefficient, high laser-induced damage threshold (LIDT), phase-matchable (PM) behavior, and so on. Achieving a balance between the large NLO effect and high LIDT is difficult, as they have contradictory requirements for chemical bonds. Considering the urgent need of the high-power IR laser market and the drawbacks of the available ones, exploring new high-performance IR NLO crystals is necessary while challenging. In this Account, we first briefly introduce the status and advancement of IR NLO crystals and emphasize the criteria of an excellent candidate. Then, we will introduce five simple methods developed by us to discover practical NLO candidates through understanding of the chemical composition-structure-NLO performance relationship. (1) A rarely investigated system with simple chemical compositions as new-type NLO crystals, namely, adducts containing S8 molecules, are developed. Combining a chairlike S8 unit with other units through van der Waals forces has successfully obtained several high-performance NLO adducts. (2) The main trend in exploring new NLO crystals is that the chemical composition is more and more diversified and the structure is more and more complex, and expensive and chemically active alkaline and alkaline earth metals are usually introduced as counter cations. In contrast, the research on systems with simple chemical compositions, simple structures, and low costs has been continuously ignored. The binary M2Q3 (M = Ga, In; Q = S, Se) family with rich acentric modifications has been systematically investigated, and they all exhibit strong SHG effects and high LIDTs. (3) We first proposed the concept of inducing CS structures transformed to NCS ones by partial cation substitution to design novel NLO crystals. Considering the huge number of CS structures in the database compared to the number of NCS structures, it is an attractive method to apply CS structures as the parents to obtain potential NLO materials via partial-substitution-induced symmetry breaking. A series of chalcogenides with high NLO performances have been successfully obtained by us in this way. (4) We investigated the first NLO-active rare earth (RE) chalcophosphates and developed this family systematically, and they demonstrate wonderful comprehensive NLO properties. (5) We created a novel mixed-anion system for NLO applications, namely, chalcogenide borates. Usually, mixed-anion compounds can engender a synergistic effect to obtain desired IR NLO properties. Our recent progress on this system suggests that chalcogenide borates are potential candidates for IR NLO applications, although the study is still in its infancy. Finally, we state the current problems of IR NLO materials and give some perspectives for their future development.

Interplay between energy and geometry of parallel-displaced interactions in S8 dimer structures

Elemental sulfur exists in various allotropes, with the most stable form being the cyclic S8 allotrope. Although the orthorhombic α-S8 modification has been extensively studied, there has been no systematic analysis of noncovalent interactions between sulfur rings and their nature, geometries, and energies until now. To achieve this, we conducted a comprehensive study analyzing all crystal structures from the Cambridge Structural Database involving contacts between S8 molecules. Then, we combined those data with high-level quantum chemical calculations. The results revealed that the preferred orientation in the crystal structures is parallel-displaced. Quantum chemical calculations supported this finding, demonstrating that the most stable interaction in the S8 dimer occurs when two molecules adopt a parallel-displaced geometry resembling the one observed in the crystal structures. The interaction in the S8 dimer is very strong, with an energy of −8.70 kcal/mol, calculated at a highly accurate CCSD(T)/CBS level. In this stacking-like geometry, multiple S…S interactions can form, and the NCI analysis indicated an overlap of large surfaces of interacting molecules, significantly contributing to the system's stability. The SAPT2+(3) energy decomposition analysis showed that the predominant attractive force between two S8 molecules is dispersion, although the electrostatic component is also significant. This research holds importance in understanding the molecular assembly in solid sulfur and in systems that exhibit interactions between S8 molecules.

Tailoring short-chain sulfur molecules to drive redox dynamics for sulfur-based aqueous battery

Solid-solid reactions stand out in rechargeable sulfur-based batteries due to the robust redox couples and high sulfur utilization in theory. However, conventional solid-solid reactions in sulfur cathode always present slow reaction kinetics and huge redox polarization due to the low electronic conductivity of sulfur and the generation of various electrochemical inert intermediates. In view of this, it is crucial to improve the electrochemical activity of sulfur cathode and tailor the redox direction. Guided by thermodynamics analysis, short-chain sulfur molecules (S2-4) are successfully synthesized by space-limited domain principle. Unlike conventional cyclic S8 molecules with complex routes in solid-solid reaction, short-chain sulfur molecules not only shorten the length of the redox chain but also inhibit the formation of irreversible intermediates, which brings excellent redox dynamics and reversibility. As a result, the Cu-S battery built by short-chain sulfur molecules can deliver a high reversible capacity of 3,133 mAh g-1. To put this into practice, quasi-solid-state aqueous flexible battery based on short-chain sulfur molecules is also designed and evaluated, showing superior mechanical flexibility and electrochemical property. It indicates that the introduction of short-chain sulfur molecules in rechargeable battery can promote the development and application of high-performance sulfur-based aqueous energy storage systems.

A common mechanism for rapid transfer of zero-valent sulfur between microbial cells

Zero-valent sulfur is accumulated in the cytoplasm of certain sulfur-oxidizing or reducing microorganisms. When these microorganisms are unable to metabolize zero-valent sulfur, they produce sulfur globules that mainly consist of octasulfur (S8), a common species of elemental sulfur. The intracellular zero-valent sulfur was easily transferred to other bacteria and the yeast Saccharomyces cerevisiae for metabolism. After eliminating all known potential mechanisms of zero-valent sulfur transfer between cells, we hypothesized and tested whether S8 was directly transferred. S8 was shown to be soluble and enriched in membrane lipids. The transfer of S8 molecules occurred between live cells, inactivated cells, and liposomes via physical contact. Low-molecular thiols, such as glutathione, reacted with S8 in the cell membranes to produce glutathione persulfide that was soluble in the cytoplasm. In the recipient cells, glutathione persulfide was either metabolized by enzymes or spontaneously reacted with another glutathione to produce hydrogen sulfide and glutathione disulfide. The new mechanism of zero-valent sulfur transfer as membrane lipid-soluble S8 molecules is common among tested microorganisms and may also occur in the environment for microorganisms to share and use zero-valent sulfur.

Near-Infrared Transitions from the Singlet Excited States to the Ground Triplet State of the S2 Molecule

Intensity of transitions from the b1∑g+ and a1Δg states to the ground state X3∑g− in the near IR emission spectrum of the S2 molecule has been calculated by the multireference configuration interaction method taking into account spin-orbit coupling (SOC). The intensity of the b1∑g+ − X3∑g,Ms=±1− transition is largely determined by the spin interaction with the electromagnetic wave, which comes from the zero-field splitting of the ground X multiplet and the SOC-induced mixing between b and X3∑g,0− states. The Einstein coefficients for the experimentally detected 0−0, 0−1, 1−1 bands of the b1∑g+−X3∑g,Ms=±1− emission system are calculated in good agreement with observations. The Einstein coefficient of the a1∆g−X3∑g,Ms=±1− magnetic dipole transition is very low, being equal to 0.0014 s−1. Nonetheless, the weakest of all experimentally observed bands (the 0−0 band of the a-XMs=±1 transition) qualitatively corresponds to this calculation. Most importantly, we provide many other IR bands for magnetic dipole b1∑g+ − X3∑g,Ms=±1− and a1∆g−X3∑g,Ms=±1− transitions, which could be experimentally observable in the S2 transparency windows from a theoretical point of view. We hope that these results will contribute to the further experimental exploration of the magnetic infrared bands in the S2 dimer.

An efficient ring-opening copolymerization of thiiranes with elemental sulfur in the presence of the fluoride anion

Sulfurization of selected thiiranes such as 2-phenylthiirane (styrene sulfide), 2,3-tetramethylenethiirane (cyclohexene sulfide) and 2-(α-thienyl)thiirane was carried out, leading to sulfur-rich polymers. The activation of the S8 molecule was initiated by the fluoride anion (F−) delivered by tetrabutylammonium fluoride (TBAF) dissolved in tetrahydrofuran (THF). The opening of the thiirane ring, followed by the copolymerization process, was initiated by the fluoropolysulfide anions (FSx−) generated in situ. The anionic copolymerizations were carried out under mild conditions, below the floor temperature of S8 (159 °C), and a variable ratio of monomers (thiirane/sulfur) was applied to obtain polysulfides with a diversified sulfur content. Polysulfides were characterized using analytical (elemental analysis, gel permeation chromatography), spectroscopic (Raman spectroscopy, FTIR), and thermal (thermogravimetry (TGA), differential scanning calorimetry (DSC)) methods. Mechanistic interpretation of sulfur transfer in the anionic copolymerization of thiiranes with S8, in the presence of the fluoride anion, has been discussed.

Deposition mechanism of molecular S8 on the dolomite surface

Sulfur deposition threatens the production efficiency and mining safety in the development of high-sulfur natural gas reservoirs, but its occurrence in the pore throats remains unclear. The adsorption and migration mechanism of S8 molecules on the dolomite surface is studied by means of first-principles calculations and molecular dynamics simulations. The S8 molecule prefers to lie horizontally on the dolomite (104) surface, apt to slide, but hard to be exfoliated from the surface. Our calculations address the strong S8–surface interaction, which is however ignored in the in-use sulfur deposition models.

Neutron Diffraction with 34S/natS Isotopic Substitution Method on the Solvation Structure of S8 Molecule in Concentrated CS2 Solutions

Abstract Neutron diffraction measurements on 34S/natS isotopically substituted (natS: natural abundance) 6.9 mol% *S8 solutions in CS2 (natural abundance for both S and C atoms) have successfully been carried out in order to examine the possibility of the 34S/natS isotopic difference method neutron diffraction for liquid samples and to obtain novel structural insights into both intramolecular structure and the solvation structure of S8 molecule in concentrated CS2 solutions. Intramolecular structural parameters within the S8 molecule as well as the intermolecular parameters concerning the nearest neighbor *S⋯CS2 interaction have been determined through the least squares fitting analysis of the observed difference interference function, ΔS(Q), which has been derived from the numerical difference between scattering cross sections observed for *S8 with 34S-enriched and natural S solutions in natural CS2. MD simulations were performed with newly developed force field parameters for sulfur atoms in S8 molecule. The results derived by the simulations adequately agree with the neutron experiments.

Quantum-chemical modeling of reactions initiating sulfuric vulcanization of isoprene rubber

The quantum-chemical method of the density functional DFT B3LYP / 6-311G ** have been used for calculation of thermodynamic functions and changes in the total electronic energy during the initiation of sulfur vulcanization of isoprene rubber using the N - cyclohexyl - 2 benzthiazolyl sulfenamide accelerator in the presence of atmospheric oxygen. Since sulfur, in the process of vulcanization of rubber compounds, is in a larger amount in a dissolved state, unlike oxygen, it is concluded that in the presence of sulfur, the formation of a valid vulcanization agent (DAV) will occur, and oxidation will occur to a lesser extent. When comparing the values of the reaction energy with the addition of the S8 molecule, it was found that sulfur in the accelerator radical acceptance reactions is a more active acceptor than oxygen in similar reactions. The effect of the number of sulfur atoms on the activity of the radicals of the sulfidating complex arising upon the acceptance of sulfur by the radicals formed during the decay of the accelerator is analyzed. It was found that the cyclohexyl radicals of the accelerator are the most active, however, in subsequent reactions of DAV with rubber, the radicals of DAV obtained with the participation of benzthiazolyl fragments are more active. The study of the effect of the number of atoms on the energies of the reactions of the formation of persulfhydryl suspensions shows that the primary suspensions are most likely to contain 8 sulfur atoms formed in reactions involving biradicals formed during the decay of the eight-membered ring of a sulfur molecule

Crystal Growth of RuS2 Using a Chemical Vapor Transport Technique and Its Properties

In this work, we study the effect of increasing temperature on the structure parameters (lattice, sulfur–sulfur distance, and ruthenium–sulfur distance) and the energy gap of RuS2. However, it was very challenging to obtain a sample of RuS2 due to many factors, some of which are discussed in the introduction. To prepare the crystal growth of RuS2, we have used the chemical vapor transport technique. The crystals obtained show a pyrite structure, of which we studied its crystallographic structure, including the structure of crystals in surface (100). The sample was then characterized by X-ray diffraction and by microprobe analysis. We determine the relationship between the energy gap and the sulfur–sulfur distance. We analyzed the S-S bond compared with the S2 molecule.

MoO3/MoS2 flexible paper as sulfur cathode with synergistic suppress shuttle effect for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have become one of the most promising candidate systems for electronic energy storage applications. However, the shuttle effect, which is caused by the intermediate lithium polysulfide (LiPs) dissolving in the electrolyte and commuting between electrodes, is the main factor leading to the deterioration of the electrochemical performance of the Li-S batteries. Different from most single physical confinement or chemical adsorption, we report a hydrogen ion intercalated molybdenum trioxide (MoO3-HI) with embedded molybdenum disulfide (MoS2) flexible paper as S hosts not only restricted soluble LiPs passively with physical adsorption, but also accelerate actively the transformation rate of polysulfides with strong chemical affinity and catalytic activity. Furthermore, the theoretical calculation showed that the MoO3-HI/MoS2 equipped the ability of directly convert S8 molecules into LiS2 molecules, eliminating the formation of lithium polysulfide. Based on the new strategy of synergistic suppress shuttle effect, the Li-S battery with MoO3-HI/MoS2/S cathode achieved a capacity of 911.3 mAh g − 1 after 500 cycles with outstanding cycle stability. In addition, MoO3-HI/MoS2 paper as a flexible carrier for Li-S batteries can be folded repeatedly and keep the structure intact. Hence, the current work provides a novel paper electrode with active and passive dual synergistic inhibition of shuttle effect characteristics for high performance flexible lithium-sulfur batteries.

Outstanding long-cycling lithium−sulfur batteries by core-shell structure of S@Pt composite with ultrahigh sulfur content

Here we proposed a novel approach to greatly enhance the electrochemical performance of Li–S batteries by designing a composite electrode material composed of a core-shell structure of [email protected] composite (sulfur content, 85%) grown on the S surface. The platinum (Pt) nanosheets provide physical barrier and strong chemical binding to anchor LiPSs and improve the electronic conductivity of S. Significantly, by introducing carbon nanofibers (CNFs) as the interlayer, we achieved outstanding Li–S battery with a high initial discharge capacity of 1040 mAh g−1 at 1.0C and a reversible capacity of 742 mAh g−1 after 350 cycles, demonstrating its excellent long-term cycling stability with a low capacity decay rate of 0.08% per cycle. According to the density functional theory (DFT) calculations, we proposed that the superior performance is attributed to the cooperative effects of the strong interfacial interaction between Pt (111) surface and the S8 molecule, and very low reaction energy of decomposition, −6.4 ​eV.

Predicting the solubility of elemental sulfur in hydrogen sulfide through a molecular dynamics approach

Solubility reduction of elemental sulfur in H2S is the main reason of sulfur deposition in natural gas exploitation. In contrast to the usual approach in which the dissolution and diffusion processes of solid sulfur are simulated, a new computational model in which the aggregation process of S8 molecules starting with a well-dispersed solution is proposed to predict the solubility of S8 in H2S. Molecular dynamics simulations based on the new model produce reliable results compared to the measurements. Moreover, this model exhibits good efficiency and reproducibility, providing a useful tool for studying the sulfur deposition mechanism.

High resolution threshold photoelectron spectrum and autoionization processes of S2 up to 15.0 eV

VUV photoionization dynamics of the S2 molecule were re-investigated from threshold up to 15.0 eV, using synchrotron radiation coupled with double imaging photoelectron/photoion coincidence featuring high resolution capabilities. We measured the first threshold photoelectron spectrum of S2 achieving higher resolution than previous literature to derive accurate spectroscopic constants for a few electronic states of the cation including the X2ΠΩ,g ground state and the a4Πu, b4Σg–, and B2Σg– states. We also recorded the total ion yield for S2 up to a photon energy of 15.0 eV which, combined with the threshold photoelectron spectrum, led to the assignment of various autoionizing Rydberg series.