Distribution Of Heteroatoms Research Articles

Regulating Sodium Deposition Behavior by a Triple-Gradient Framework for High-Performance Sodium Metal Batteries.

An efficient method for the synthesis of a self-supporting carbon framework (denoted Gra-GC-MoSe2) is proposed with a triple-gradient structure-in sodiophilic sites, pore volume, and electrical conductivity-which facilitates the highly efficient regulation of Na deposition. In situ and ex situ measurements, together with theoretical calculations, reveal that the gradient distribution of Se heteroatoms in MoSe2, and its derivatives tailor the sodiophilicity, while the gradient distribution of porous nanostructures homogenizes the Na+ diffusion. Therefore, Na deposition occurs from the bottom to the top of the Gra-GC-MoSe2 framework without dendrite formation. In addition, the gradient in electrical conductivity ensures the stripping process does not lead to dead Na. As a result, a Gra-GC-MoSe2 modified Na anode (Na@Gra-GC-MoSe2) shows impressive cycling stability with a high average Coulombic efficiency in an asymmetric cell. In symmetric cells, it also exhibits a long cycling life of 2000h with a low polarization voltage and works stably even under a large capacity of 10mAhcm-2. Moreover, a Na@Gra-GC-MoSe2|| Na3V2(PO4)3 full cell delivers a high energy density with an excellent cycling performance.

Molecular characteristics of eight lignites based on the big data obtained from Orbitrap mass spectrometry

Eight lignites from different regions were selected for thermal dissolution (TD) sequentially using cyclohexane, methanol and ethanol. The TD extracts of the eight coal samples were characterized using atmospheric pressure chemical ionization source (APCI)-Orbitrap mass spectrometry (MS). Chemometric methods were employed to deeply explore the molecular structural and composition information of the organic compounds detected by Orbitrap MS. The longest distance method in systematic clustering of chemometrics was employed to ascertain the optimal number of groups, which was found to be 7 by clustering 24 soluble portions (SPs) using Euclidean distance. Taking one group as an example, the similarities and differences of SPs within the group were derived based on the compositional class of O1N1, N1, O2N1 and O2, and heteroatom distribution patterns of the SPs were proposed and compared. The integration of high-resolution MS data and chemometric methods not only exposes the existence of heteroatomic compounds in lignite but also furnishes evidence for the origin and evolution of lignite, as well as a methodology for the high-value utilization of lignites from different sources.

Green-Emitting Extended B3,N2-Doped Polycyclic Aromatic Hydrocarbon with Multiple Resonance Structure.

An air-stable B3,N2-PAH (B3N2; nine annulated six-membered rings) was synthesized from 1-X-2,6-di(azasilaanthryl)benzenes (X = Cl, I) via lithiation/borylation, electrophilic aromatic borylation, and Si/B exchange. The heteroatom distribution in B3N2 meets the requirements for multiple resonance thermally activated delayed fluorescence (MR-TADF). Indeed, B3N2 emits green light (λem = 523 nm; ΦPL = 85%; CHCl3) with a small fwhm of 0.15 eV. Lifetimes for prompt (7.8 ns) and delayed (60 μs) fluorescence were measured in PMMA.

Facile synthesis of ultrahigh-surface-area and hierarchically porous carbon for efficient capture and separation of CO2 and enhanced CH4 and H2 storage applications

Ultrahigh surface area and hierarchically microporous carbons functionalized with heteroatoms are critical for many applications, particularly gas storage and separation. However, the facile synthesis of such carbons remains challenging. Herein, we present a single-step activation strategy for producing porous polymer-based ultrahigh surface area carbons through melamine-mediated potassium oxalate activation. As prepared carbon possesses a uniform distribution of heteroatoms and hierarchical micropores, and exhibits a maximum specific surface area of 3463 m2/g, which is among the best reported for carbon materials. The presence of heteroatoms (N and O), along with its ultra-high surface area and hierarchical microporous structure, plays a significant role in storing large amounts of CO2 (22.8 mmol/g at 298 K/25 bar), CH4 (10.1 mmol/g at 298 K/25 bar) and H2 (5.2 wt% at 77 K/50 bar). Furthermore, it demonstrates a selective capture of CO2 over N2, CH4 and H2. The developed carbon is highly suitable for gas storage and the separation of CO2 from flue gas and syngas.

Enhanced flexibility and ablative performance of silicone rubber by constructing an interpenetrating zirconium-containing polysiloxane double network

To achieve uniform distribution of heteroatoms in silicone rubber, further simultaneously improving the flexibility and ablation resistance, polydimethylsiloxane with an interpenetrating zirconium-containing double-network (Zr-PDMS) was prepared. Compared to pure PDMS, the tensile strength and elongation-at-break of Zr-PDMS with interpenetrating double-network were increased by 615.33% and 124.23%, respectively, exhibiting significantly enhanced flexibility. Ablation analysis indicated that Zr-PDMS showed excellent anti-ablation performance, exhibiting obviously decreased mass ablation rate and charring rate. Most importantly, different from the crisp charred layers of pure PDMS as well as ZrO2 blends, Zr-PDMS formed stable and coherent charred layers after ablation tests. The improvement correlated to the in-situ formation of tetragonal ZrO2 in the char layer of Zr-PDMS, which could avoid the generation of defects in the ZrO2 blends char layer were discussed in detail. This work provided a new strategy of high flexible silicon rubber with excellent ablative performance, which can be expected to be well applied in the hypersonic spacecrafts.

Best Practices for Analysis of Carbon Fibers by Atom Probe Tomography

AbstractCarbon fiber technology drives significant development in lightweight and multifunctional applications. However, the microstructure of carbon fibers is not completely understood. A big challenge is to obtain the distribution of heteroatoms, for instance nitrogen, with high spatial resolution in three dimensions. Atom probe tomography (APT) has the potential to meet this challenge, but APT of carbon fibers is still relatively unexplored. We performed APT on three types of carbon fibers, including one high modulus type and two intermediate modulus types. Here, we present the methods to interpret the complex mass spectra of carbon fibers, enhance the mass resolution, and increase the obtained analysis volume. Finally, the origin of multiple hit events and possible methods to mitigate multiple hit events are also discussed. This paper provides guidance for future APT studies on carbon fibers, and thus leads the way to a deeper understanding of the microstructure, and consequently advancements in wide applications of carbon fibers.

The analysis of the BAS OH band in zeolites

The zeolite frameworks ( FER , TON , CHA , and IFR ) with a large diversity of the IR band shapes in the OH stretching region were investigated by combined use of FT-IR spectroscopy and DFT calculations. The analysis of various isolated Brønsted acid sites was performed with a model based on Boltzmann weighted relative energies and OH frequencies obtained by the ω/r correlation method. This approach has recently been used to reveal the non-statistical incorporation of aluminum into the H- MOR framework. The model correctly predicts the band shapes of H- FER and H- TON zeolites in the free OH region of the FT-IR spectra. For H-C HA and H- IFR , however, the mutual BAS interactions cannot be ignored even for high Si/Al ratios, which renders the concept of isolated BAS inadequate. Thus, the periodic calculations of adsorption and catalytic properties of zeotype frameworks should always be carried out with extended models mimicking real heteroatom distribution in these materials. • FER , TON , CHA , and IFR high-silica zeolites with a large diversity of the OH band shapes were investigated. • A combined use of FT-IR spectroscopy and periodic DFT calculations provided rationalization of observed spectral features. • Analysis of 44 different BAS in zeolites was carried out with the ω/r correlation method. • The statistical model of the BAS OH band in high-silica H- CHA was proposed based on empirical FF simulations. • Two mechanisms for the formation of free OH BAS in IFR were identified by analysis of 20 Al pairs at the DFT level.

Promising N, P Co‐doped Porous Carbon Materials as Metal‐Free Electrocatalyst for Oxygen Reduction Reaction in Alkaline Medium

AbstractDeveloping an efficient metal‐free electrocatalyst to compete with the noble metal‐based catalysts for oxygen reduction reaction (ORR) is of great significance in the field of energy storage and conversion. We have designed a metal‐free electrocatalyst via dual doping of nitrogen and phosphorus in a porous carbon structure from a cyclotripolyphosphazene (CTP)‐based polymer. The optimized material (CTP‐800) demonstrates an excellent ORR catalytic performance with an onset potential of 0.89 V, a high limiting current density of 4.58 mA cm−2, and a favorable 4‐electrons mediated reaction mechanism in the KOH electrolyte. Moreover, the electrochemical stability, as well as methanol compatibility of CTP‐800, are superior to the commercially available Pt/C catalyst. The remarkable electrocatalytic performance of CTP‐800 can be credited to the high surface area with rich micropores/mesopores and homogenous distribution of heteroatoms.

Characterization of biochar-derived organic matter extracted with solvents of differing polarity via ultrahigh-resolution mass spectrometry

In recent years, biochar, a porous carbon-based material, has gained attention for its application prospects in contaminated soil remediation and soil improvement. Biochar-derived organic matter has a key role in influencing the migration and transformation of soil elements and pollutants. However, existing research concerning the molecular characteristics of biochar-derived organic matter is limited. Here, we used four polar solvents — dichloromethane (CH2Cl2), acetone (CH3COCH3), methanol (CH3OH), and distilled water (H2O) — to extract organic matter from soybean straw biochar and wheat straw biochar by accelerated solvent extraction (ASE). We characterized the extracts using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). We found considerable differences in organic matter according to the extraction solvents; such differences were related to the polarity of the solvent, as well as intermolecular forces between the solvent and organic matter. CH3OH extracted the most biochar-extractable organic matter components because CH3OH can weaken or destroy oxygen bridge bonds in biochar and form hydrogen bonds with small-molecule organic compounds. CH3OH and H2O have strong extraction capacity for compounds containing heteroatoms. CH2Cl2-extractable organic matter is relatively labile and bioavailable, while CH3OH- and H2O-extractable organic matters are relatively stable. In addition, the binding capacity of biochar-derived organic matter for minerals and pollutants differed among fractions, in part because of differences in molecular weight, atomic O/C and H/C ratios, heteroatom distribution, and biomolecular compounds present in biochar-derived organic matter. The findings in this study help to select appropriate extractants to analyze biochar-derived organic matter for various research purposes, and provides a theoretical basis for biochar-based remediation of contaminated soil.

Surface Reconstruction of Ni‐Rich Layered Cathodes: In Situ Doping versus Ex Situ Doping

The structural instability and sluggish Li+ diffusion kinetic of the nickel‐rich LiNixCoyMn1−x−yO2 (NCM) cathode still hinder its further commercialization for lithium‐ion batteries. Doping heteroatoms are widely studied as an effective strategy to maintain structural and thermal stability for improving the capacity retention of NCM during cycling. Herein this work, in situ Zn2+‐doped NCM (in situ Zn‐NCM) is successfully designed by atomic layer deposition (ALD) combined with annealing. In comparison to ex situ Zn2+‐doped NCM (ex situ Zn‐NCM), in situ Zn‐NCM can better enhance the layered structure stability and reduce the generation of surface defects due to that it has lower migration energy barrier and more uniform distribution of heteroatoms. As a result, at a high cutoff voltage of 4.5 V, in situ Zn‐NCM with the obvious advantages of lower cation mixing, better phase transition stability, as well as more efficient charge transfer displays higher reversible capacity (i.e., 203.2 mAh g−1 at 50 mA g−1) and initial Coulombic efficiency (85%) compared to ex situ Zn‐NCM and the pristine NCM. Therefore, in situ doping is a novel and universal strategy to enhance battery performance of high‐energy‐density NCM cathodes for lithium‐ion batteries.

Effect of postsynthesis preparation methods on catalytic performance of Ti-Beta zeolite in ketonization of propionic acid

Heteroatom metal-zeolite, with heteroatom metal (oxide) dispersed in the zeolite framework, enables the reactions typically catalyzed by bulk metal oxide counterpart but with maximized the atomic utilization. However, the distribution of heteroatoms in the framework is strongly influenced by the preparation method. In this work, Ti-Beta zeolites were postsynthesized using the recrystallization (Ti-Beta-Re) and solid-state ion-exchange (Ti-Beta-SSIE) methods. Characterizations showed that more Ti species were incorporated in the tetrahedral framework site of Ti-Beta-Re to form Lewis acid sites than in that of Ti-Beta-SSIE. In addition, intra-crystallite mesopores were developed in Ti-Beta-Re due to partial dissolution of BEA framework during alkaline etching and subsequent recrystallization of the etched framework. These zeolites were then tested for ketonization of biomass derived propionic acid at 350 °C and atmospheric pressure. The turnover frequency of ketonization was found to be 25% higher on Ti-Beta-Re (0.25 min−1) than on Ti-Beta-SSIE (0.20 min−1), whereas the apparent activation energy of 80 kJ/mol on Ti-Beta-Re is lower than 95 kJ/mol on Ti-Beta-SSIE. Moreover, the selectivity of 3-pentanone kept > 95% on Ti-Beta-Re while it dropped to ∼63% on Ti-Beta-SSIE with increase of reaction time at a space time of 2 h. This work demonstrated that the tetrahedrally coordinated Ti species are the active sites and the presence of intra-crystallite mesopores facilitates selective ketonization of carboxylic acids.

Heteroatom-Doped Graphites Oxygen Reduction Catalysts for Anion Exchange Membrane Fuel Cells

Catalysts for the oxygen reduction reaction (ORR) are crucial for electrochemical energy conversion and storage devices. The development of active, ultra-low-cost, critical raw materials-free catalysts is vital for the success of the anion exchange membrane fuel cell (AEMFC) technology [1]. In this work, we present metal-free oxygen reduction catalysts based on heteroatoms (I, N, S or B)-doped graphites by a scalable and reproducible one-step planetary ball milling protocol [2]. The distribution and the morphology of these ultra-low cost catalysts are characterized by advanced electron microscopy showing uniform distribution of heteroatoms in the graphite matrix. We have tested the catalysts for ORR in 0.1 M KOH solution in a rotating ring disk electrode (RRDE) and doped-graphites showed enhanced ORR performance relative to the pristine graphite. Among these, the N-graphite exhibiting the highest ORR onset potential of 0.87 V with a low peroxide yield of 15%@0.1 V. Good ORR kinetic (jk,s ) and mass (ik,m ) activities were also obtained. The catalysts also show remarkable stability in both RDE stress and corrosion tests. Finally, we showed good performance in operando H2-O2 AEMFC, reaching ~350 mW cm‒ 2 at 60 oC with a high voltage efficiency. These results encourage further development of metal-free ultra-low-cost and stable catalysts, easily scalable for AEMFC cathode production.

Molecular Characterization of NSO Compounds and Paleoenvironment Implication for Saline Lacustrine Oil Sands by Positive-Ion Mass Spectrometry Coupled with Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry.

NSO compounds mainly exist in geological bodies in the form of nonhydrocarbons and asphaltenes with abundant geological and geochemical information. Combined with the gas chromatography mass spectrometry (GC–MS) technology, positive-ion electrospray ionization Fourier-transform ion cyclotron resonance MS (FT-ICR MS) was used to understand the composition and distribution characteristics of NSO compounds in the oil sands of the Dongpu Depression and to explore their paleoenvironmental significance. The results show that n-alkanes are characterized by an even carbon number and phytane dominance, suggesting a saline lacustrine environment. Certain abundance of nC37 and β-carotane, high gammacerane content, and low diasterane content are detected in the analyzed samples, reflecting the saline-reducing paleoenvironment for the organic matter. Nine types of heteroatom compounds are detected: N1, N1O1, N1S1, O1, O1S1, O2, O2S1, S1, and S2. The main compounds are S1 and N1 compounds, followed by O1S1 compounds. The double-bond equivalent (DBE) value of S1 compounds is mainly distributed between 3 and 12, and the carbon number is mainly distributed between 18 and 35. The DBE value of N1 compounds is mainly distributed between 4 and 14, and the carbon number is mainly distributed in the range 15–35. Among the S1 compounds, DBE3 compounds (thiophenes) have relatively more sulfur-containing carotenoids (C40). The abundance of C40 S1 and the ratio of pyridine and its homologue DBE4–8/DBE9–12 N1 compounds show a good contrast with the paleoenvironment indicators of gammacerane/C30 hopane and diasterane/regular sterane. They can be used as a reference for the paleoenvironment index. Maturity is another factor affecting the distribution of NSO heteroatoms in the oil sands. NSO compounds are enriched in the DBE area with higher condensation, and the main peak carbon shifts forward. As the maturity increases, the relative abundance of N1 compounds increases, the aromatization intensifies, and carbon is broken into short chains. The research results shed light on the potential application of NSO compounds in petroleum exploration based on FT-ICR MS.

Gripper-like Silicon Species for Efficient Synthesis of Crystalline Metallosilicates with Spatially Homogeneous Heteroatoms in the Framework

Heteroatoms determine the functionalities of zeolites. Facile and effective incorporation of heteroatoms into the framework of zeolites remains an important and challenging goal. We report a strategy for efficient and simple synthesis of crystalline metallosilicates with spatially homogeneous distribution of heteroatoms and free of extra-framework metal species via the crystal dissolution and crystallization process (CDC process). This method succeeds in the synthesis of a wide range of crystalline metallosilicates with the MFI topology including TS-1, Al-MFI, Fe-MFI, Sn-MFI, and Nb-MFI zeolites as well as with other topologies such as TS-2, Ti–Al–beta zeolite, and so forth. The gripper-like silicon species, which is condensed matter of silicon species in Q2 and Q3 states (detected by 29Si NMR), was identified for the first time to be the key to the effective incorporation and spatially homogeneous distribution of heteroatoms during the CDC process. Such silicon species could bond heteroatoms efficiently to form stable and isolated Si–O–M structural units in the synthetic sol, and such structural units remain unchanged under the “protection” of silicon species during the whole liquid-phase transformation and crystallization process. In addition, the gripper-like silicon species could be obtained not only by dissolving the crystal under high basicity but also by dissolving/polymerizing amorphous silicon species under the same conditions. The CDC process for synthesizing crystalline metallosilicates with spatially homogeneous distribution of heteroatoms in the framework by controlling the state of silicon species opens up a new perspective for the synthesis of heteroatomic zeolites.

Control of location and distribution of heteroatoms substituted isomorphously in framework of zeolites and zeotype materials

Well-controlled incorporation of heteroatoms in frameworks of zeolites and zeotype materials has been achieved by a variety of new synthetic approaches, generating outstanding catalysts compared to uncontrolled materials.

A treasure map for nonmetallic catalysts: optimal nitrogen and fluorine distribution of biomass-derived carbon materials for high-performance oxygen reduction catalysts

The intrinsic laws of the catalytic performance and heteroatom distribution of a nonmetallic biomass-derived carbon material were revealed systematically, providing a new idea for high-throughput screening of heteroatom-doped catalysts.

Spatial distribution of metallic heteroatoms in soot nanostructure mapped by aberration-corrected STEM-EELS

Soot from the thermochemical conversion of solid and liquid fuels can be infused with metallic heteroatoms originating from the fuel – these heteroatoms alter the nanostructure and the reactivity of the soot. Here, we investigate the spatial distribution of metallic heteroatoms in soot generated by biomass gasification, using aberration-corrected Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy (STEM-EELS). The technique allowed for the mapping of heteroatom distribution in soot at the nanoscale, and thereby for the direct correlation of heteroatom concentration with the graphitic nanostructure. Spherical soot particles were coated with a thin layer of silicon, possibly in the form of quartz that may be linked to minor distortions of the nanostructure of the graphitic shell of the particles. Further results on non-spherical soot and inorganic-carbon fused aggregates suggest that the chemistry of formation was affected by the presence of gaseous ash-forming elements, especially calcium, with carbon-oxygen functional groups forming as intermediates in the graphite-inorganic reaction; i.e., prior to the formation of the thermodynamically stable carbonate bonds. The analytical approach demonstrated here can potentially help select fuel additives or aid in the design of fuel blends that minimize the formation of similar, hybrid carbon nanoparticles in combustion or gasification systems.

Hydrogen adsorption of O/N-rich hierarchical carbon scaffold decorated with Ni nanoparticles: Experimental and computational studies

Hierarchical carbon scaffold (HCS) with multi-porous structures, favoring hydrogen diffusion and physisorption is doped with 2–10 wt % Ni for storing hydrogen at ambient temperature. Due to N- and O-rich structure of melamine-formaldehyde resin used as carbon precursor, homogeneous distribution of heteroatoms (N and O) in HCS is achieved. 2 wt % Ni-doped HCS shows the highest hydrogen capacity up to 2.40 wt % H2 (T = 298 K and p (H2) = 100 bar) as well as excellent reversibility of 18.25 g H2/L and 1.25 wt % H2 (T = 298 K and p (H2) = 50 bar) and electrical production from PEMFC stack up to 0.7 Wh upon eight cycles. Computations and experiments confirm strong interactions between Ni and heteroatoms, leading to uniform distribution small particles of Ni. This results in enhancing reactive surface area for hydrogen adsorption and preventing agglomeration of Ni nanoparticles upon cycling. Ni K-edge XANES spectra simulated from the optimized structure of Ni-doped N/O-rich carbon using DFT calculations are consistent with the experimental spectra and suggest electron transfer from Ni to hydrogen to form Ni–H bond upon adsorption. Considering low desorption temperature (323 K), not only chemisorbed hydrogen is involved in adsorption mechanisms but also physisorption and spillover of hydrogen.

Insights into the structural characteristics of four thermal dissolution extracts of a subbituminous coal by using higher-energy collisional dissociation

In coal chemistry, thermal dissolution (TD) is an effective processing technique to obtain soluble components from coal by using organic solvents under a certain pressure and temperature. Exploring molecular structures of the TD extracts of low-rank coal is of great importance for eco-friendly and value-added utilization in chemical industry. To well elucidate the structural information of components in coal, higher-energy collisional dissociation (HCD) specific to Orbitrap mass spectrometry was applied to analyze four TD extracts of a subbituminous coal. Alkyl chains of aromatic compounds can be removed from aromatic cores during a HCD process, allowing determination of the distribution of heteroatoms in either aromatic cores or alkyl chains. Both double bond equivalent value and carbon number of precursor ions (whole molecules) and the corresponding fragment ions (aromatic cores) obtained via a HCD process were used to evaluate the relationship between aromatic cores and alkyl chains for compounds in coal. With the increase of molecular weight, compounds in coal exhibited different distributions for aromatic cores and alkyl chains. From 200 Da to 300 Da, the increase of carbon number mainly contributed to the formation of condensed aromatic cores. However, from 300 Da to 400 Da, it was attributed to the formation of both aromatic cores and alkyl chains. In addition, heteroatom distribution index indicated that a higher TD yield of heteroatom-containing compounds would be obtained via solvents with a smaller molecular size and nitrogen-containing aromatics would be enriched by using TD solvents containing aromatic ring.

Quantitative Analysis Method for Nitrogen Electron Energy-Loss Near-Edge Structures in Nanocarbons Based on Density Functional Theory Calculations and Linear Regression

Nonmetallic heteroatoms found in carbon nanomaterials act as active sites and exhibit excellent catalytic performance. Owing to structural complexity and the limitations of characterization technology, the identification of active sites in nanocarbon is challenging and controversial. Electron energy-loss spectroscopy is an electron microscope technique with high spatial resolution and a powerful tool for identifying the arrangement of heteroatoms. However, structural information regarding the configuration and distribution of heteroatoms is difficult to obtain using existing analytical methods. Herein, we have developed a method for the quantitative analysis of electron energy-loss near-edge structures to identify accurately nitrogen species in nanocarbon. Based on this approach, the relative amounts of nitrogen species were obtained from linear regression with calculated spectra. The concentration distribution of nanocarbon obtained by this method was consistent with the result of X-ray photoelectron spectroscopy analysis at different depths. Therefore, this fitting method can be used for the quantitative analysis of nitrogen K-edge structures. This provides a new strategy for studying the structure–activity relationships of carbon-based materials and the further design of custom nanocarbon catalysts with high active site densities.