Oxygen-rich Material Research Articles

Seven white dwarfs with circumstellar gas discs II: tracing the composition of exoplanetary building blocks

ABSTRACT This second paper presents an in-depth analysis of the composition of the planetary material that has been accreted on to seven white dwarfs with circumstellar dust and gas emission discs with abundances reported in Rogers et al. The white dwarfs are accreting planetary bodies with a wide range of oxygen, carbon, and sulphur volatile contents, including one white dwarf that shows the most enhanced sulphur abundance seen to date. Three white dwarfs show tentative evidence (2–3$\sigma$) of accreting oxygen-rich material, potentially from water-rich bodies, whilst two others are accreting dry, rocky material. One white dwarf is accreting a mantle-rich fragment of a larger differentiated body, whilst two white dwarfs show an enhancement in their iron abundance and could be accreting core-rich fragments. Whilst most planetary material accreted by white dwarfs display chondritic or bulk Earth-like compositions, these observations demonstrate that core-mantle differentiation, disruptive collisions, and the accretion of core-mantle differentiated material are important. Less than 1 per cent of polluted white dwarfs host both observable circumstellar gas and dust. It is unknown whether these systems are experiencing an early phase in the disruption and accretion of planetary bodies, or alternatively if they are accreting larger planetary bodies. From this work there is no substantial evidence for significant differences in the accreted refractory abundance ratios for those white dwarfs with or without circumstellar gas, but there is tentative evidence for those with circumstellar gas discs to be accreting more water rich material which may suggest that volatiles accrete earlier in a gas-rich phase.

Chitosan/Graphene oxide/SiO2 Nanoadsorbents for the Removal of Cr(VI) from Wastewaters

The swift industrialization and urbanisation have led to the discharge of significant amounts of hazardous heavy metals into water environments. Heavy metal pollution is currently one of the most significant environmental challenges being addressed, attracting researchers due to its biotoxicity, and non-biodegradability even at minimal concentrations [1]. Chromium (Cr) is among the most prevalent heavy metal contaminants. Its oxidation state, Cr(VI), harms the environment yet has catastrophic consequences for human health [2]. It is removed by physical and chemical procedures such as ion exchange, chemical precipitation and electrochemical treatment. Yet, most of these procedures have downsides, such as the formation of hazardous sludge, causing disposal issues and the need for costly tools and monitoring systems [3]. Adsorption is regarded an appealing and favourable technology because to its ease of design, simplicity, and high efficiency. Carbon-based nanomaterials have been investigated as superior adsorbents in aqueous solutions for the separation of organic and inorganic contaminants. The current study recommends the usage of adsorbents based on graphene oxide (GO). GO is an oxygen-rich material that is produced during the oxidation of graphite. It features hydrophobic areas due to aromatic groups in the nanosheets' centres, along with a large number of hydrophilic functional groups such as hydroxy, aldehyde, epoxy, and carboxyl groups [4]. The latter allow GO to swell and perform electrostatic functions. Chitosan (Cs) is a great adsorbent since it is inexpensive, is biocompatible, and causes no secondary pollution. Its molecular chains include -NH2 and -OH groups, which can interact with heavy metal ions and give significant adsorption capacity [5]. Silicon dioxide (SiO2) nanoparticles with graphene oxide have better physical and chemical characteristics than graphene oxide-like surface area. Similar research has revealed that the presence of SiO2 increases the adsorbent's adsorption capacity for Cr(VI) [6]. The effect of the pH value, contact time and initial chromium concentration was examined in order to determine the feasibility of Cs/GO@SiO2. Its structure and the morphology were studied in detail by the application of BET, XRD, FTIR and SEM techniques. According to the results, the modification of Cs with GO@SiO2 enhanced the percentage removal of chromium ions, especially, in acidic conditions by using 0.5 g/L of the adsorbent. Experimental data of equilibrium were used to calculate adsorption isotherms. According to thermodynamics the spontaneous nature of their adsorption was confirmed. Overall, the results indicate that Cs/GO@SiO2 can be effectively employed for removal of chromium from aqueous solutions.

1100 days in the life of the supernova 2018ibb

Stars with zero-age main sequence masses between 140 and 260 M⊙ are thought to explode as pair-instability supernovae (PISNe). During their thermonuclear runaway, PISNe can produce up to several tens of solar masses of radioactive nickel, resulting in luminous transients similar to some superluminous supernovae (SLSNe). Yet, no unambiguous PISN has been discovered so far. SN 2018ibb is a hydrogen-poor SLSN at z = 0.166 that evolves extremely slowly compared to the hundreds of known SLSNe. Between mid 2018 and early 2022, we monitored its photometric and spectroscopic evolution from the UV to the near-infrared (NIR) with 2–10 m class telescopes. SN 2018ibb radiated > 3 × 1051 erg during its evolution, and its bolometric light curve reached > 2 × 1044 erg s−1 at its peak. The long-lasting rise of > 93 rest-frame days implies a long diffusion time, which requires a very high total ejected mass. The PISN mechanism naturally provides both the energy source (56Ni) and the long diffusion time. Theoretical models of PISNe make clear predictions as to their photometric and spectroscopic properties. SN 2018ibb complies with most tests on the light curves, nebular spectra and host galaxy, and potentially all tests with the interpretation we propose. Both the light curve and the spectra require 25–44 M⊙ of freshly nucleosynthesised 56Ni, pointing to the explosion of a metal-poor star with a helium core mass of 120–130 M⊙ at the time of death. This interpretation is also supported by the tentative detection of [Co II] λ 1.025 μm, which has never been observed in any other PISN candidate or SLSN before. We observe a significant excess in the blue part of the optical spectrum during the nebular phase, which is in tension with predictions of existing PISN models. However, we have compelling observational evidence for an eruptive mass-loss episode of the progenitor of SN 2018ibb shortly before the explosion, and our dataset reveals that the interaction of the SN ejecta with this oxygen-rich circumstellar material contributed to the observed emission. That may explain this specific discrepancy with PISN models. Powering by a central engine, such as a magnetar or a black hole, can be excluded with high confidence. This makes SN 2018ibb by far the best candidate for being a PISN, to date.

A precursor plateau and pre-maximum [O ii] emission in the superluminous SN2019szu: a pulsational pair-instability candidate

ABSTRACT We present a detailed study on SN2019szu, a Type I superluminous supernova at z = 0.213 that displayed unique photometric and spectroscopic properties. Pan-STARRS and ZTF forced photometry show a pre-explosion plateau lasting ∼40 d. Unlike other SLSNe that show decreasing photospheric temperatures with time, the optical colours show an apparent temperature increase from ∼15 000 to ∼20 000 K over the first 70 d, likely caused by an additional pseudo-continuum in the spectrum. Remarkably, the spectrum displays a forbidden emission line (likely attributed to λλ7320,7330) visible 16 d before maximum light, inconsistent with an apparently compact photosphere. This identification is further strengthened by the appearances of [O iii] λλ4959, 5007, and [O iii] λ4363 seen in the spectrum. Comparing with nebular spectral models, we find that the oxygen line fluxes and ratios can be reproduced with ∼0.25 M⊙ of oxygen-rich material with a density of $\sim 10^{-15}\, \rm {g\, cm}^{-3}$. The low density suggests a circumstellar origin, but the early onset of the emission lines requires that this material was ejected within the final months before the terminal explosion, consistent with the timing of the precursor plateau. Interaction with denser material closer to the explosion likely produced the pseudo-continuum bluewards of ∼5500 Å. We suggest that this event is one of the best candidates to date for a pulsational pair-instability ejection, with early pulses providing the low density material needed for the formation of the forbidden emission line, and collisions between the final shells of ejected material producing the pre-explosion plateau.

Inferring the Progenitor Mass–Kinetic Energy Relation of Stripped-envelope Core-collapse Supernovae from Nebular Spectroscopy

The relation between the progenitor mass and the kinetic energy of the explosion is a key toward revealing the explosion mechanism of stripped-envelope core-collapse supernovae (SESNe). Here, we present a method to derive this relation using the nebular spectra of SESNe, based on the correlation between [O i]/[Ca ii], which is an indicator of progenitor mass, and the width of [O i], which measures the expansion velocity of the oxygen-rich material. To explain the correlation, the kinetic energy (E K) is required to be positively correlated with the progenitor mass as represented by the CO core mass (M CO). We demonstrate that SNe IIb/Ib and SNe Ic/Ic-BL follow the same M CO–E K scaling relation, which suggests that helium-rich and helium-deficient SNe share the same explosion mechanism. The M CO–E K relation derived in this work is compared with the ones derived from early phase observations. The results are largely in good agreement. Combined with early phase observations, the method presented in this work provides a chance to scan through the ejecta from the outermost region to the dense inner core, which is important to reveal the global properties of the ejecta and constrain the explosion mechanism of core-collapse SNe.

Discrimination of phosgene from cyanogen chloride in recovered chemical munitions using tagged neutron interrogation with high-resolution gamma-ray spectroscopy

The associated particle (AP) technique has recently been used with a high-purity germanium γ-ray spectrometer to assess its capability to improve field identification of recovered chemical warfare (CW) materiel through prompt gamma-ray neutron activation analysis (PGNAA) measurements. A particularly challenging pair of CW agents commonly found in recovered munitions are phosgene (CG) and cyanogen chloride (CK), which have two of three elements in common, i.e. chlorine and carbon, but differ in the third being either oxygen or nitrogen. The detection of both latter elements is complicated by high oxygen concentration in the field environment which interferes with the small signal produced from the chemical agents. The matter is further complicated by the precautionary field practice of overpacking recovered munitions with vermiculite in larger steel multiple round containers (MRCs), which places additional oxygen-rich material in contact with the munition while further attenuating an already weak signal emitted from the munition center. This work reports quantitative results from realistic field measurements of CG and CK simulants in mock 4.2-inch (11 cm) mortar rounds overpacked with vermiculite in a large MRC. Results obtained with the AP technique are compared to those obtained with the traditional PGNAA approach for both overpacked- and bare-munition measurements. The AP technique is shown to provide a much more confident discrimination between the two chemicals, particularly for the more challenging field-relevant overpacked measurements, where a significant gain in sensitivity to all the key elements (chlorine, carbon, nitrogen and oxygen) is achieved.

Spectral modelling of Type IIb supernovae

We use the new non-local-thermodynamical-equilibrium (NLTE) light curve and spectral synthesis code JEKYLL to evolve a macro-scopically mixed ejecta model of a Type IIb supernova (SN) originating from a star with an initial mass of 12 M⊙ through the photospheric and nebular phase. The ejecta model is adopted from earlier work and has a mass of 1.7 M⊙, has a kinetic energy of 0.7 foe, and contains 0.075 M⊙ of 56Ni. The macroscopic mixing is simulated through a statistical representation of ejecta fragmented into small clumps but spherically symmetric on average. We compare our model with SN 2011dh and find that both the spectra and the light curves are well reproduced in both the photospheric and nebular phase, although there are also some differences. Our work further strengthens the evidence that this SN originated from a star with an initial mass of ~12 M⊙ that had lost all but a tiny (<0.1 M⊙) fraction of its hydrogen envelope, strongly suggesting a binary origin. We also investigate the effects of the macroscopic mixing by comparing macroscopically and microscopically mixed models and by varying the clumping geometry. In the photospheric phase, we find strong effects on the effective opacity in the macroscopically mixed regions, which affects the model light curves. The diffusion peak is considerably narrower (rise time decreased by 11%) in the macroscopically mixed case and differs strongly (rise time decreased by 29%) if the radioactive material in the helium envelope is allowed to expand more than in our standard model. The effect is mainly geometrical and is driven by the expansion of the clumps that contain radioactive material, which tend to decrease the effective opacity. In the limit of optically thick clumps, the decrease is roughly given by the product of the (volume) expansion and filling factors for the radioactive material, and in our models values up to ~8 are explored. These findings have implications for light curve modelling of stripped-envelope SNe in general, and the effect would increase the estimated ejecta masses. In the nebular phase, we find strong effects on the collisional cooling rates in the macroscopically mixed regions, which affects lines driven by collisional cooling, in particular the [Ca ii] 7291, 7323 Å and [O i] 6300, 6364 Å lines. The effect is mainly related to differences in composition between macroscopically and microscopically mixed ejecta. As these lines are often used for mass determinations, this highlights the importance of how and to what extent the calcium- and oxygen-rich material is mixed. As shown in this and earlier work, both NLTE and macroscopic mixing are essential ingredients for accurately modelling the light curves and spectra of Type IIb SNe throughout their evolution.

Statistical Properties of the Nebular Spectra of 103 Stripped-envelope Core-collapse Supernovae*

Abstract We present an analysis of the nebular spectra of 103 stripped-envelope (SE) supernovae (SNe) collected from the literature and observed with the Subaru Telescope from 2002 to 2012, focusing on [O i] λλ6300, 6363. The line profile and width of [O i] are employed to infer the ejecta geometry and the expansion velocity of the inner core; these two measurements are then compared with the SN subtypes, and further with the [O i]/[Ca ii] ratio, which is used as an indicator of the progenitor CO core mass. Based on the best-fit results of the [O i] profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of SESNe. There is a hint (at the ∼1σ level) that the distributions of the line profile fractions are different between canonical SESNe and broad-line SNe Ic. A correlation between [O i] width and [O i]/[Ca ii] is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive CO core. Such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. Further, when [O i]/[Ca ii] increases, the fraction of objects with Gaussian [O i] profile increases, while those with double-peaked profile decreases. This phenomenon connects ejecta geometry and the progenitor CO core mass.

Boosting the ultrahigh initial coulombic efficiency of porous carbon anodes for sodium-ion batteriesvia in situfabrication of a passivation interface

In this study we have prepared a nitrogen and oxygen rich porous carbon material (NOPC) and designed a uniform passivation layer of CMC on the material by using a one-step method, which suppresses the decomposition of electrolytes and results in an excellent ICE of 90%.

Hydrothermal synthesis of biobased carbonaceous composite from a blend of kraft black liquor and tannin and its application to aspirin and paracetamol removal

An alternative use for the Kraft Black liquor, the main byproduct of the pulping process, is presented in this work. It is a promising route for new biorenewable materials production, reducing dependence on petrochemicals. The synthesis of the novel biobased composites from a blend of tannin and Kraft black liquor involved a polycondensation reaction followed by a crosslinking process. This paper is the first one emphasizing the synthesis of a novel biobased composite from a blend of Kraft black liquor and tannin by performing the conventional and hydrothermal crosslinking. The hydrothermal conditions proved to be an effective strategy to obtain an oxygen-rich functional material. Besides being environmental-friendly, the hydrothermal process successfully replaced conventional curing, providing a higher yield and better chemical, functional, and structural properties. The role of two different processes, hydrothermal and pyrolysis, on the properties and adsorption performance of the final composites, was also assessed. RFA was obtained by hydrothermal conversion, processed at relatively mild conditions when compared to the pyrolysis performed to produce its carbon counterpart, RFC. Pyrolysis promoted a mesoporous structure on the RFC and the textural properties were improved. On the other hand, the severe thermal treatment degraded the RFC functional groups, increasing its basicity and decreasing the number of polar groups on the surface. RFA exhibited a smaller surface area than RFC, but it retained volatile organic matter and functional oxygen groups. These surface characteristics are known to be relevant in adsorption processes since the adsorbate-adsorbent chemical linkages and electrostatic interactions are favored. Paracetamol and aspirin adsorption onto RFA achieved the equilibrium at 480 and 720 min. On the other hand, the equilibrium for the adsorption onto RFC was achieved at 720 and 240 min. The maximum aspirin adsorption capacities onto RFA and RFC were 50.17 mg g−1 and 91.66 mg g−1, respectively. On the other hand, for paracetamol, the maximum adsorption capacities were 49.95 mg g−1 onto RFA and 73.58 mg g−1 onto RFC. The kinetic study suggested fast adsorption through a chemisorption process and the equilibrium implies the multilayer adsorption. Additionally, the major advantages of using the raw Kraft black liquor blended with tannin to synthesize the novel composites are their great availability and low cost, enabling the material large-scale production. Therefore, the results confirm the great potential of these new biomaterials as alternative adsorbents for wastewater treatment.

Hierarchically porous nitrogen, oxygen-rich carbons derived from filter paper for high-performance lithium ion battery anodes

A hierarchically porous nitrogen, oxygen-rich carbon material is developed by Mg(NO3)2 treatment of filter paper in a one-step pyrolysis. The obtained carbons exhibit high specific surface area (1031 m2 g−1), interconnected micro-, meso-, and macroporous conductive network and attractive heteroatom contents (2.84 at.% nitrogen and 13.82 at.% oxygen). The as-prepared carbon tested as anode for lithium ion batteries displays an excellent reversible capacity (1560 mAh g−1 at 0.1 A g−1), superior rate capability (501 mAh g−1 at 5 A g−1) and desired cycling performance (1538 mAh g−1 at 0.1 A g−1 and 1105 mAh g−1 at 1 A g−1after 100 cycles). Moreover, a full battery with an as-obtained carbon anode and a LiFePO4 cathode delivers a high discharge capacity of 165 mAh g−1 (the theoretical capacity of LiFePO4 was 170 mAh g−1) and good cyclability (156 mAh g−1 after 20 cycles).

MCM-41 supported nano-sized CuO-CeO2 for catalytic combustion of chlorobenzene

In this paper, MCM-41 was synthesized by a soft template technique and MCM-41 supported CuO-CeO2 nano-sized catalysts with different Cu/Ce molar ratios were prepared by a deposition-precipitation method. N2 adsorption, HRTEM-EDS, H2-TPR, XPS characterization, as well as catalytic activity and durability tests for the catalytic combustion of chlorobenzene (CB) were conducted to explore the relationship between the structure and catalytic performance of the catalysts. It is revealed that CuCe(6:1)/MCM-41 has the highest activity and can completely catalyze the degradation of CB at 260 °C. The reasons for the high activity of the catalysts are as follows: MCM-41, a type of mesoporous material which has large pore size and large specific surface area, is suitable as a catalyst carrier. The average diameter of nano-sized CuO and CeO2 particles is about 3–5 nm and adding CeO2 improves the dispersion of active component CuO, which are highly and evenly dispersed on the surface of MCM-41. Characterization results also explain why MCM-41 supported CuO-CeO2 with appropriate proportion can highly enhance the catalytic activity. The reason is that CeO2 acting as an oxygen-rich material can improve the mobility of oxygen species through continuous redox between Ce4+ and Ce3+, and improve the catalytic performance of CuO for CB combustion. Besides, CuCe (6:1)/MCM-41 also displays good durability for CB combustion, both in the humid condition and in the presence of benzene, making it a promising catalytic material for the elimination of chlorinated VOCs.

Hierarchical macro-/meso-/microporous oxygen-doped carbon derived from sodium alginate: A cost-effective biomass material for binder-free supercapacitors

Three-dimensional porous scaffolds doped with the heteroatoms show excellent performances in energy conversion and storage. Herein, we report a green synthesis approach to construct the oxygen-doped porous carbon electrodes by carbonizing the oxygen-rich biomass material, sodium alginate. By precisely controlling the carbonization temperature and increasing the mole ratio of α-L-guluronic acid units/β-D-mannuronic acid units in sodium alginate, the morphology, oxygen content and electrical conductivity of the as-obtained carbonaceous electrode are well balanced. This electrode material delivers capacitance of up to 424.6 F g−1 in 6 M potassium hydroxide (KOH) electrolyte at 1 A g−1, and good cyclic stability with the capacitance retention of >90% after 20,000 charge-discharge cycles. Such excellent electrochemical performance can be attributed to both the unique hierarchical macro-/meso-/microporous structure and the presence of abundant oxygen-containing functional groups in the as-prepared carbonized sodium alginate aerogels. The capacitance of our oxygen-doped porous carbon electrodes is at least twice greater than those of other carbonaceous electrodes produced from biomass precursors reported in literatures. This work provides a facile, effective and environmental-friendly approach for the fabrication of high-performance heteroatom-doped carbon-based electrodes for supercapacitor applications.

Laboratory evidence for co-condensed oxygen- and carbon-rich meteoritic stardust from nova outbursts

Although their parent stars no longer exist, the isotopic and chemical compositions and microstructure of individual stardust grains identified in meteorites provide unique constraints on dust formation and thermodynamic conditions in stellar outflows1–5. Novae are stellar explosions that take place in the hydrogen-rich envelope accreted onto the surface of a white dwarf in a close binary system6. The energy released by a suite of nuclear processes operating in the envelope powers a thermonuclear runaway, resulting in the ejection of processed material into the interstellar medium. Spectral fitting of features observed in the infrared spectra of dust-forming novae provided evidence of the co-condensation of both carbonaceous and silicate dust in stellar outflows within 50 to 100 days after explosion7–9. Although novae appear as prolific producers of both carbon- and oxygen-rich dust, very few presolar grains that can be attributed to novae have been found in meteorites thus far10–16. Here, we report the identification of an oxygen-rich inclusion, composed of both silicate and oxide nanoparticles, inside a graphite spherule that originated in the ejecta of a low-mass carbon- and oxygen-rich (CO) nova. This observation establishes laboratory evidence of the co-condensation of oxygen- and carbon-rich dust in nova outbursts and is consistent with large-scale transport and mixing of materials between chemically distinct clumps in the nova ejecta. Carbon-rich and oxygen-rich material coexist in a presolar grain originated by an outburst of a CO nova and found within the LaPaz Icefield 031117 meteorite. Condensation of both carbon and oxygen can thus happen in the same circumstellar environment, contrary to previous assumptions.

Enzymatic glucose/oxygen biofuel cells: Use of oxygen-rich cathodes for operation under severe oxygen-deficit conditions

A glucose/oxygen biofuel cell (BFC) that can operate continuously under oxygen-free conditions is described. The oxygen-deficit limitations of metabolite/oxygen enzymatic BFCs have been addressed by using an oxygen-rich cathode binder material, polychlorotrifluoroethylene (PCTFE), which provides an internal oxygen supply for the BFC reduction reaction. This oxygen-rich cathode component mitigates the potential power loss in oxygen-free medium or during external oxygen fluctuations through internal supply of oxygen, while the bioanode employs glucose oxidase-mediated reactions. The internal oxygen supply leads to a prolonged energy-harvesting in oxygen-free solutions, e.g., maintaining over 90% and 70% of its initial power during 10- and 24-h operations, respectively, in the absence of oxygen. The new strategy holds considerable promise for energy-harvesting and self-powered biosensing applications in oxygen-deficient conditions.

Synthesis and thermal decomposition behavior of nitrogen- and oxygen-rich energetic material N-trinitromethyl-4,5-dicyano-2H-1,2,3-triazole

N-trinitromethyl-4,5-dicyano-2H-1,2,3-triazole was readily synthesized from 4,5-dicyano-2H-1,2,3-triazole. Its crystal structure was obtained for the first time and its crystalline density in 296 K was 1.729 g cm−3. It shows high nitrogen and oxygen content up to 77.6%, high calculated solid heat of formation (564 kJ mol−1), and superior detonation pressure and detonation velocity (D = 8619 m s−1, P = 30.8 GPa). This new hydrogen-absent explosive shows high impact and friction sensitivities (IS: 1.25 J, FS: 32 N), which is lower than commercial primary explosive 2-diazonium-4,6-dinitrophenol (DDNP) (IS: 1 J, FS: 5 N). The relationship between intermolecular interaction and sensitivity as well as thermal stability of the title compound was investigated by Hirshfeld surface analysis and fingerprint plot. Its thermodynamic properties were studied by non-isothermal kinetic methods based on the results of differential scanning calorimeter. It is interesting that apparent activation energy (Ea) at Tp1 (210.89–214.17 kJ mol−1) is higher than those at Tp2 (133.90–134.87 kJ mol−1). In addition, gaseous product of this new energetic compound was analyzed by the rapid scanning Fourier transform infrared spectroscopy from 20 to 200 °C and its detonation products was theoretically predicted. Based on the decomposition products, its decomposition mechanism was discussed under inert atmosphere. It is undoubted that these significant physicochemical properties make N-trinitromethyl-4,5-dicyano-2H-1,2,3-triazole a potential hydrogen-absent primary explosive.

The very faint X-ray binary IGR J17062-6143: a truncated disc, no pulsations, and a possible outflow

We present a comprehensive X-ray study of the neutron star low-mass X-ray binary IGR J17062-6143, which has been accreting at low luminosities since its discovery in 2006. Analysing NuSTAR, XMM–Newton, and Swift observations, we investigate the very faint nature of this source through three approaches: modelling the relativistic reflection spectrum to constrain the accretion geometry, performing high-resolution X-ray spectroscopy to search for an outflow, and searching for the recently reported millisecond X-ray pulsations. We find a strongly truncated accretion disc at |$77^{+22}_{-18}$| gravitational radii (∼164 km) assuming a high inclination, although a low inclination and a disc extending to the neutron star cannot be excluded. The high-resolution spectroscopy reveals evidence for oxygen-rich circumbinary material, possibly resulting from a blueshifted, collisionally ionized outflow. Finally, we do not detect any pulsations. We discuss these results in the broader context of possible explanations for the persistent faint nature of weakly accreting neutron stars. The results are consistent with both an ultra-compact binary orbit and a magnetically truncated accretion flow, although both cannot be unambiguously inferred. We also discuss the nature of the donor star and conclude that it is likely a CO or O–Ne–Mg white dwarf, consistent with recent multiwavelength modelling.

Self-Healing Chemistry between Organic Material and Binder for Stable Sodium-Ion Batteries

Summary One of the major challenges for high-energy sodium-ion batteries is the mechanical fracture triggered by large volume change. To circumvent pulverization-induced capacity decay, self-healing chemistry between binder and active material is critical but is never reported. Here, we report a self-healing electrode with hydrogen bonding between an oxygen-rich active material, sodium rhodizonate dibasic (SRD), and a hydroxyl-rich binder, sodium alginate (SA). During the sodiation of microsized SRD, cracks induced by volume expansion expose a new oxygen-rich surface, whereas the SA binder fills these cracks under pressure generated by volume expansion and binds the pulverized SRD together by hydrogen bonding between SRD and SA. Self-healing between hydroxyl-rich binder and oxygen-rich active material is a universal strategy for mitigating the pulverization-induced capacity decay of active materials, as demonstrated by the longer cycle life of the SRD electrode with other hydroxyl-rich binders, polyacrylic acid, and xanthan gum than with hydroxyl-free polytetrafluoroethylene binder.

Coordination of Surface-Induced Reaction and Intercalation: Toward a High-Performance Carbon Anode for Sodium-Ion Batteries.

Oxygen-rich carbon material is successfully fabricated from a porous carbon and evaluated as anode for sodium-ion battery. With the strategy of optimal combination of fast surface redox reaction and reversible intercalation, the oxygen-rich carbon anode exhibits a large reversible capacity (447 mAh g-1 at 0.2 A g-1), high rate capability (172 mAh g-1 at 20 A g-1), and excellent cycling stability.

Microwave reduction of graphene oxide rationalized by reactive molecular dynamics.

Obtaining graphene (GRA) in industrial quantities is among the most urgent goals in today's nanotechnology. Elegant methods involve the oxidation of graphite with its subsequent solvent-assisted exfoliation. The reduction of graphene oxide (GO) is challenging leading to a highly-disordered oxygen-rich material. A particularly successful microwave-induced reduction of GO was reported recently (Science, 2016, 353, 1413-1416). We mimic the experiment by reactive molecular dynamics and establish the molecular mechanisms of reduction and their time scales as functions of temperature. We show that the rapid removal of oxygen groups achieved by microwave heating leaves GRA sheets intact. The epoxy groups are most stable within GO. They can rearrange into the carbonyl groups upon quick heating. It is important to avoid creating holes upon graphite oxidation. They cannot be healed easily and undermine GRA thermal stability and electronic properties. The edge oxygen groups cannot be removed by irradiation, but their effect is marginal on the properties of μm GRA sheets. We demonstrate that different oxygen groups are removed from GO at drastically different temperatures. Therefore, it is possible to obtain separate fractions, e.g. carbonyl-, hydroxyl- and carboxyl-free partially reduced GO. Our results guide the improvement of the GO reduction methods and can be tested directly by experiment.