SO3 formation from the X-ray photolysis of SO2 astrophysical ice analogues: FTIR spectroscopy and thermodynamic investigations

Highly Efficient Phosphazene-Derivative-Based Flame Retardant with Comprehensive and Enhanced Fire Safety and Mechanical Performance for Polycarbonate

Polycarbonate (PC) as a widely used engineering plastic that shows disadvantages of flammability and large smoke production during combustion. Although many flame-retardant PCs have been developed, most of them show enhanced flame retardancy but poor smoke suppression or worsened mechanical performance. In this work, a novel nitrogen-phosphorus-sulfur synergistic flame retardant (Pc-FR) was synthesized and incorporated into PC with polytetrafluoroethylene (PTFE). The extremely low content of PC-FR (0.1-0.5 wt%) contributes significantly to the flame retardancy, smoke suppression and mechanical performance of PC. PC/0.3 wt% Pc-FR/0.3 wt% PTFE (PC-P0.3) shows the UL-94 V-0 and LOI of 33.5%. The PHRR, THR, PSPR, PCO and TCO of PC-P0.3 decreased by 39.44%, 14.38%, 17.45%, 54.75% and 30.61%, respectively. The impact strength and storage modulus of PC-P0.1 increased by 7.7 kJ/m2 and 26 MPa, respectively. The pyrolysis mechanism of PC-P0.3 is also revealed. The pyrolysis mechanism of PC-P0.3 is stochastic nucleation and subsequent growth and satisfies the Aevrami-Erofeev equation. The reaction order of PC-P0.3 is 1/2. The activation energy of PC-P0.3 is larger than PC-0, which proves that the Pc-FR can suppress the pyrolysis of the PC. This work offers a direction on how to design high-performance PC.

Abiotic formation of alkylsulfonic acids in interstellar analog ices and implications for their detection on Ryugu

For the last century, the source of sulfur in Earth's very first organisms has remained a fundamental, unsolved enigma. While sulfates and their organic derivatives with sulfur in the S(+VI) oxidation state represent core nutrients in contemporary biochemistry, the limited bioavailability of sulfates during Earth's early Archean period proposed that more soluble S(+IV) compounds served as the initial source of sulfur for the first terrestrial microorganisms. Here, we reveal via laboratory simulation experiments that the three simplest alkylsulfonic acids-water soluble organic S(+IV) compounds-can be efficiently produced in interstellar, sulfur-doped ices through interaction with galactic cosmic rays. This discovery opens a previously elusive path into the synthesis of vital astrobiological significance and untangles fundamental mechanisms of a facile preparation of sulfur-containing, biorelevant organics in extraterrestrial ices; these molecules can be eventually incorporated into comets and asteroids before their delivery and detection on Earth such as in the Murchison, Tagish Lake, and Allende meteorites along with the carbonaceous asteroid Ryugu.

SOx-modified porous carbon as a highly active electrocatalyst for efficient H2O2 generation

A SOx-decorated porous carbon electrocatalyst that exhibits excellent 2e- oxygen reduction reaction activity is synthesized using UV-curing technology in combination with a pyrolysis process. The H2O2 selectivity using the SOx-porous C shows 95.1% at 0.4 V and delivers a H2O2 production rate of 604.2 mmol gcat-1 h-1. Density-functional theory calculations reveal the reasons for the improvement of catalytic performance.

Energetic electron irradiations of amorphous and crystalline sulphur-bearing astrochemical ices

Laboratory experiments have confirmed that the radiolytic decay rate of astrochemical ice analogues is dependent upon the solid phase of the target ice, with some crystalline molecular ices being more radio-resistant than their amorphous counterparts. The degree of radio-resistance exhibited by crystalline ice phases is dependent upon the nature, strength, and extent of the intermolecular interactions that characterise their solid structure. For example, it has been shown that crystalline CH3OH decays at a significantly slower rate when irradiated by 2 keV electrons at 20 K than does the amorphous phase due to the stabilising effect imparted by the presence of an extensive array of strong hydrogen bonds. These results have important consequences for the astrochemistry of interstellar ices and outer Solar System bodies, as they imply that the chemical products arising from the irradiation of amorphous ices (which may include prebiotic molecules relevant to biology) should be more abundant than those arising from similar irradiations of crystalline phases. In this present study, we have extended our work on this subject by performing comparative energetic electron irradiations of the amorphous and crystalline phases of the sulphur-bearing molecules H2S and SO2 at 20 K. We have found evidence for phase-dependent chemistry in both these species, with the radiation-induced exponential decay of amorphous H2S being more rapid than that of the crystalline phase, similar to the effect that has been previously observed for CH3OH. For SO2, two fluence regimes are apparent: a low-fluence regime in which the crystalline ice exhibits a rapid exponential decay while the amorphous ice possibly resists decay, and a high-fluence regime in which both phases undergo slow exponential-like decays. We have discussed our results in the contexts of interstellar and Solar System ice astrochemistry and the formation of sulphur allotropes and residues in these settings.

Chemical changes induced during heating of acetonitrile-rich ice pre-irradiated by X-rays and its implication in astrochemistry

In this work, we investigate the effects induced by the heating of acetonitrile-rich ice from 13 K to 350 K. Before the heating, the sample was irradiated at 13 K by broadband X-rays (6 eV to 2 keV), which trigger the production of new molecules, such as HCN, H₂CCNH, CH₄ and CH₃NC (see Carvalho and Pilling, 2020) and also induced desorption of frozen species to gas-phase. New spectra were collected during heating to investigate whether new species, not present before at lower temperatures, appear due to thermal processing. New infrared bands were identified at temperatures around 120 K and 300 K, from which it was possible to notice the possible presence of HCN/CN radical, ammonia and C₂N₂. It was also verified that acetonitrile has a thermal desorption peak between 120 K and 200 K, which yields to the vanishing of acetonitrile within the sample for temperatures of 200 K and above. Some infrared features assigned before solely to acetonitrile remain for sample temperatures >200 K, which indicates the presence of blended species with similar infrared features. From analyzing those blended peaks, we also perceived the possible presence of aminoacetonitrile.

Photolysis of CH3CN Ices by Soft X-rays: Implications for the Chemistry of Astrophysical Ices at the Surroundings of X-ray Sources

In this work, broad-band soft X-ray (6-2000 eV) was employed to irradiate frozen acetonitrile CH₃CN, at the temperature 13 K, with different photon fluences up to 1.5 × 10¹⁸ photons cm^-2. Here, acetonitrile is considered as a representative complex organic molecule (COM) present in astrophysical water-rich ices. The experiments were conduced at the Brazilian synchrotron facility (LNLS/CNPEM) employing infrared spectroscopy (FTIR) to monitor chemical changes induced by radiation. The effective destruction cross section of acetonitrile and effective formation cross section for daughter species formed inside the ice were obtained. The identified radiation products were HCN, CH₄, H₂CCNH, and CH₃NC showing that fragmentation and rearrangement contribute to acetonitrile destruction. Chemical equilibrium and molecular abundances at this stage were determined, which also includes the abundance estimates of unknown molecules, produced but not directly detected, in the ice. The chemical equilibrium was reached at fluence around 1.5 × 10¹⁸ photons cm^-2. Time scales for ices, at hypothetical snow line distances, to reach chemical equilibrium around compact objects, young stellar objects, and O/B stars and inside solar system were given. Among the obtained results are the time scales for reaching chemical equilibrium around different astronomical strong X-ray emitters, e.g., 14 days (for the Sun at 5 AU), 41 and 82 days (for O/B stars at 5 AU), 10⁹-10¹¹ years (for white dwarfs at 1 LY), 450 years (for Crab pulsar at 2.25 LY), around 10⁷ years (for Vela pulsar at 2.25 LY), and 7.5 × 10⁶ years (for Sagittarius A* at 3 LY).

Direct conversion of NO and SO2 in flue gas into fertilizer using ammonia and ozone

This study focused on the simultaneous removal of NO and SO₂ from an industrial flue gas stream. To evaluate the removal efficiency of NO and SO₂ using O₃ and NH₃, the consumption of two reactants (O₃ and NH₃) in line with the conversion of NO and SO₂ was quantified experimentally. In addition, NO and SO₂ were converted to valuable fertilizers, NH₄NO₃ and (NH₄)₂SO₄. To identify a principle strategy to enhance the generation of fertilizer, Fourier transform infrared spectroscopy was used to examine the reaction mechanisms for the formation of NH₄NO₃ and (NH₄)₂SO₄. Acceleration of SO₂ oxidation could be achieved effectively by adding NO to a gas mixture of SO₂, NH₃, and O₃. The formation of HNO₃ might be enhanced by the simultaneous feeding of NO and SO₂. Particle generation was also 10 times higher for NH₃/(NO + SO₂) than for NH₃/NO and for NH₃/SO₂, which is a prominent feature of this study. Moreover, the introduction of steam had a positive influence on particle generation. This method offers dual applications for NO and SO₂ removal from a flue gas stream and direct fertilizer generation.

Regeneration Mechanism of Sulfur Absorption Via Samarium-doped Cerium Adsorbents in the Gas Atmosphere of O2/N2

Sulfides existing in many high-temperature gas mixtures have a negative effect on various industrial applications. Ce-based adsorbents are becoming a hotspot in the high-temperature desulfurization process owing to their excellent thermal stability at high temperatures and regeneration capacity. In this study, we investigate the regeneration path of samarium-doped cerium (SDC) sorbent at high temperature. The SDC adsorbent showed a good sulfur removal ability and excellent regeneration capacity. Ce₂O₂S and Ce(SO₄)₂ are observed in the used adsorbent, and Ce₂O₂S is the main sulfur-containing species. The regeneration path of the Ce₂O₂S is the key to the regeneration mechanism of the adsorbent. There are two regeneration paths for the Ce₂O₂S at high temperature in O₂/N₂ gas mixture. In air stream, the Ce₂O₂S is oxidized to Ce₂O₂SO₄ and then decomposes into CeO₂ and SO₂. In a 2% O₂/N₂ gas condition, the Ce₂O₂S directly generates CeO₂ and elemental sulfur with O₂ assistance.

The influence of molecular vicinity (expressed in terms of dielectric constant) on the infrared spectra of embedded species in ices and solid matrices

In this theoretical work we evaluate how the chemical environment influences some features presented in the infrared spectrum, such as band intensities and band location of embedded species in icy matrices. The calculations were performed employing the Polarized Continuum Model (PCM) approach with the second-order Møller-Plesset perturbation theory (MP2) level using the Gaussian 09 package. Here, we simulate the effects of molecular vicinity around embedded species in terms of the effects of the dielectric constant (ε) of the icy and solid samples. Gas phase calculation was also performed for comparison purpose. The investigated embedded single molecules were CO, CO2, CH4, NH3, SO2 HCOOH, CH3OH and also H2O. The results suggest that for most vibrational modes, the strengths of IR bands show an increase with ε, which implies they also decrease with respect to porosity. The frequency shifts showed opposite behavior in relation to the band strengths, with few exceptions. A correlation between calculated band intensities with the band strengths A (taken from literature) was determined and described by a linear function I ∼ 6 × 1018 A [km mol-1], with A in unity of cm per molecule. In addition, an associative exponential function was adjusted to the studied dataset to characterize the evolution of frequency-shift and intensity-shift and band strength ratio as function of the dielectric constant. Since astrophysical ice mantles over cold dust grains can vastly vary in composition in space (having different dielectric constants) they are a challenge to be well characterized. Therefore, this work can help the astrochemistry community to better understand astrophysical ices and its observations in the infrared.

Photochemistry and desorption induced by X-rays in water rich astrophysical ice analogs: implications for the moon Enceladus and other frozen space environments

Soft X-rays are an important agent for chemical processing in the Solar System and in the interstellar medium. The photolysis and photodesorption processes of H2O-rich ices triggered by soft X-rays was, experimentally, addressed in this paper. The experiments were performed at the Brazilian synchrotron facility LNLS/CNPEN employing broadband radiation (from 6 to 2000 eV; mainly soft X-rays and a small fraction of VUV) in solid samples at temperatures of 20 and 80 K. The icy samples were monitored by infrared spectroscopy. We determined the effective destruction cross section (in the order 10-18 cm2) as well as the formation cross section for the new species produced after the irradiation. Among them, we list OCN-, CO, CO3, CH3OH, H2O2, HCOO-, NH4 +, HCONH2 and CH3HCO, mostly formed in the experiment at 80 K. The chemical equilibrium stage was characterized and molecular abundances were quantified. In addition, we discuss a methodology to estimate the amount of unknown species in the ice produced by photolysis. The samples reach chemical equilibrium at fluences around 2-3 × 1018 cm-2. Timescales for reaching chemical equilibrium in space environments illuminated by X-rays were given, as well as the desorption yields induced by X-rays. The astrophysical implication on the surface chemistry and desorption processes at the moon Enceladus are provided.