Polymeric Nitrogen Research Articles

One-step Synthesis of Cubic Gauche Polymeric Nitrogen with High Yield Just by Heating

One-step Synthesis of Cubic Gauche Polymeric Nitrogen with High Yield Just by Heating

Achieving high-energy-density crown-like polymeric nitrogen cr-N via chelate CeN8

Achieving high-energy-density crown-like polymeric nitrogen cr-N via chelate CeN8

N18 ring: A building block for constructing 1D and 2D polymeric nitrogen frameworks

Exploring the fundamental building block is essential for constructing functional materials with extended topological configurations. In the polymeric nitrogen system, no fundamental building blocks have been reported so far. Here, we successfully synthesize the buckled 1-dimensional (1D) band-shaped and 2-dimensional (2D) layered polymeric nitrogen frameworks with N18 ring as a fundamental building block for the first time. Furthermore, the dimensions of the polymeric nitrogen frameworks can be regulated by pressure conditions. Bader charge analyses indicate that the charge transfer from the La atom to the low-order bonded nitrogen atom plays a crucial role in stabilizing these two low-dimensional polymeric frameworks. Both LaN16 and LaN8 are promising high-energy-density materials (HEDMs). This study reveals that the N18 ring can serve as a fundamental building block, analogous to thesix-membered ring in carbon-based materials, enabling the construction of novel polymeric nitrogen materials with extended frameworks.

All-Single Bonds Fused N18 Macro-Rings and N8 Cagelike Building Blocks Stabilized in Lanthanum Supernitrides.

Single-bonded polymeric nitrogen has gained tremendous research interest because of its unique physical properties and great potential applications. Despite much progress in theoretical predictions, it is still challenging to experimentally synthesize polynitrogen compounds with novel all-single-bonded units. Herein, we have synthesized two brand-new lanthanum supernitrides LaN8, through a direct reaction between La and N2 in laser-heated diamond anvil cells at megabar pressures. Our experiments and calculations revealed that two LaN8 phases had the R-3 and P4/n symmetry characterized by a unique 2D network with N18 macro-rings and cagelike N8 building blocks, respectively. Differing from known polynitrogen structures, these two polymers were composed of single-bonded nitrogen atoms belonging to sp3 and sp2 hybridizations. In particular, P4/n LaN8 possessed the longest N-N bond length among all of the experimentally reported metal nitrides, potentially being a high-energy-density material. The present study opens a fresh, promising avenue for the rational design and discovery of new supernitrides with unique nitrogen structures via the high-pressure treatment.

New compound XeN14 with high energy density

As a high-energy density material, polymeric nitrogen has attracted considerable attention, while the exceptionally high synthesis pressure hinders its studies and applications. A significant discovery indicates that the insertion of noble gas elements can effectively reduce the synthesis pressure of polymeric nitrogen compounds. This work utilized the particle swarm optimization algorithm and first-principles calculations to extensively explore the stoichiometry of Xe–N compounds under high pressures. Two phases of XeN14, P6mm and P-62m, have been discovered, which are energetically more stable than the basic mixture of Xe and N2. Evidence of charge transfer between Xe and N was found, verifying that Xe plays a crucial role in forming polymeric nitrogen compounds. These two compounds are kinetically stable at pressures ranging from 50 to 200 GPa and exhibit semiconductor properties. A unique channel-like structure was discovered in the P6mm phase. The energy densities of P6mm and P-62m phases are 7.39 and 7.59 kJ/g, respectively, significantly exceeding those of TNT (Trinitrotoluene) and HMX (Octogen), indicating their potential as high-energy density materials.

Pressure-Induced High-Energy-Density BeN6 Materials: First-Principles study

Recently, the use of polymeric nitrogen in the search for high-energy–density materials (HEDMs) has attracted widespread attention. However, synthesizing polymeric nitrogen materials is quite challenging; for instance, the synthesis of cubic gauche nitrogen requires a high pressure of 110 GPa. Previous theoretical predictions and experiments have shown that adding alkaline earth metals as cationic ligands can stabilize polymeric nitrogen and reduce the synthesis pressure. Using the USPEX structural prediction code and first-principles calculations, this study predicted 2 new nitrogen salt with nitrogen contents up to 89.80 %, namely α-BeN6 and β-BeN6, with their unique nitrogen chain structures, have energy densities as high as 3.32 and 3.59 kJ/g, respectively. The exceptional explosive properties reveal these two BeN6 are potential HEDMs. In addition, α-BeN6 is a direct bandgap semiconductor.

Evaluating the effect of antibiotics on aerobic granular sludge treatment of pharmaceutical wastewater.

Aerobic granular sludge (AGS) has been widely applied in pharmaceutical wastewater treatment due to its advantages such as high biomass and excellent settling performance. However, the influence of commonly found antibiotics in pharmaceutical wastewater on the operational efficiency of AGS has been poorly explored. This study investigated the effects of tetracycline (TE) on AGS treating pharmaceutical wastewater at room temperature and analyzed the related mechanisms. The results demonstrate a dose-dependent relationship between TE's effects on AGS. At concentrations below the threshold of 0.1 mg/L, the effects are considered trivial. In contrast, TE with more than 2.0 mg/L reduces the performance of AGS. In the 6.0 mg/L TE group, COD, TN, and TP removal efficiencies decreased to 72.6-75.5, 54.6-58.9, and 71.6-75.8%, respectively. High concentrations of TE reduced sludge concentration and the proportion of organic matter in AGS, leading to a decline in sludge settling performance. Elevated TE concentrations stimulated extracellular polymeric substance secretion, increasing polymeric nitrogen and polymeric phosphorus content. Intracellular polymer analysis revealed that high TE concentrations reduced polyhydroxyalkanoates but enhanced glycogen metabolism. Enzyme activity analysis disclosed that high TE concentrations decreased the activity of key enzymes associated with nutrient removal.

One-Dimensional Non-coplanar Nitrogen Chains in Manganese Tetranitride under High Pressure.

Transition metal nitrides have great potential applications as incompressible and high energy density materials. Various polymeric nitrogen structures significantly affect their properties, contributing to their complex bonding modes and coordination conditions. Herein, we first report a new manganese polynitride MnN4 with bifacial trans-cis [N4]n chains by treating with high-pressure and high-temperature conditions in a diamond anvil cell. Our experiments reveal that MnN4 has a P-1 symmetry and could stabilize in the pressure range of 56-127 GPa. Detailed pressure-volume data and calculations of this phase indicate that MnN4 is a potential hard (255 GPa) and high energy density (2.97 kJ/g) material. The asymmetric interactions impel N1 and N4 atoms to hybridize to sp2-3, which causes distortions of [N4]n chains. This work discovers a new polynitride material, fills the gap for the study of manganese polynitride under high pressure, and offers some new insights into the formation of polymeric nitrogen structures.

High-pressure Synthesis of Cobalt Polynitrides: Unveiling Intriguing Crystal Structures and Nitridation Behavior.

In this study, we conduct extensive high-pressure experiments to investigate phase stability in the cobalt-nitrogen system. Through a combination of synthesis in a laser-heated diamond anvil cell, first-principles calculations, Raman spectroscopy, and single-crystal X-ray diffraction, we establish the stability fields of known high-pressure phases, hexagonal NiAs-type CoN, and marcasite-type CoN2 within the pressure range of 50-90 GPa. We synthesize and characterize previously unknown nitrides, Co3N2, Pnma-CoN and two polynitrides, CoN3 and CoN5, within the pressure range of 90-120 GPa. Both polynitrides exhibit novel types of polymeric nitrogen chains and networks. CoN3 feature branched-type nitrogen trimers (N3) and CoN5 show π-bonded nitrogen chain. As the nitrogen content in the cobalt nitride increases, the CoN6 polyhedral frameworks transit from face-sharing (in CoN) to edge-sharing (in CoN2 and CoN3), and finally to isolated (in CoN5). Our study provides insights into the intricate interplay between structure evolution, bonding arrangements, and high-pressure synthesis in polynitrides, expanding the knowledge for the development of advanced energy materials.

Stable pressure-stabilized polymeric nitrogen in nitrogen-rich YNx (x = 6, 7) compounds

As shown in recent years, introducing exogenous elements (M) into nitrogen materials under pressure can form new multi-nitrogen structures (MNx) which are more stable and have milder synthesis conditions than pure nitrogen structures. We used the structure prediction software to search for the optimized components of transition metal yttrium nitrogen compounds, as well as for the stable crystal structures, by changing the chemical ratio and pressure conditions. We have predicted the six structures of yttrium nitrogen compounds: P1¯-YN4, C2/m-YN5, YN6 (C2/c phase, C2/m phase, P1¯ phase) and P1¯-YN7 under high pressure conditions, among them, the C2/c-YN6 and P1¯-YN7 are newly discovered in this paper. It was found that C2/c-YN6 and P1¯-YN7 can be synthesized by YN + N2 at high pressure. Molecular dynamics calculations show that the two structures are stable at high temperature. The structure analysis shows that the nitrogen atoms in the two structures are connected alternately by nitrogen single bond and nitrogen double bond, which is beneficial to energy storage of the structure. The energy density of these two structures is comparable to that of TATB and RDX, and the explosive velocity and explosive pressure are higher than those of TNT and HMX, so these two structures could be used as potential high energy density materials. The predicted structures of C2/c-YN6 and P1¯-YN7 may provide new clues for synthesis and exploration of novel stable polymeric nitrogen.

Interception of Layered LP-N and HLP-N at Ambient Conditions by Confined Template

We propose a feasible strategy of intercepting the layered polymeric nitrogen (LP-N) and hexagonal layered polymeric nitrogen (HLP-N) at ambient conditions by using the confinement templates. The stable mechanism of confined LP-N and HLP-N at ambient conditions is revealed, namely the synergistic effect of charge transfer and vdW confinement effect. The influence rule of interlayer spacing on the stability of LP-N is revealed. Most importantly, the nitrogen content and energy density of recoverable LP-N@graphene (70.59%, 8.15 kJ/g), LP-N@h-BN (70.59%, 7.96 kJ/g), HLP-N@graphene (68.97%, 9.31 kJ/g), and HLP-N@h-BN (69.57%, 8.05 kJ/g) refresh the new record for the confinement polynitrogen system.

High-pressure high-temperature induced polymerization of nitrogen molecules under restricted condition

Polymeric nitrogen has been recognized to be a new type of high-energy density material (HEDM). However, the polymeric nitrogen structure formed under high-pressure and high-temperature conditions is usually in poor thermodynamic stability. Confinement strategy is conductive to the stabilization of the high-pressure phase of polymeric nitrogen structures, providing a new modulation approach for realizing the polymerization of nitrogen. In this work, nitrogen molecules are confined into the boron nitride nanotubes (N<sub>2</sub>@BNNTs) under high-pressure condition. The pressure-induced polymerization of nitrogen in N<sub>2</sub>@BNNT samples with varying nitrogen content and the stabilities of polymeric nitrogen structure are characterized by high-pressure <i>in situ</i> Raman spectroscopy method. In the N<sub>2</sub>@BNNT sample with higher nitrogen content, the N<sub>2</sub> confined to boron nitride nanotubes exhibits different Raman spectral pressure response behaviors compared with that of non confined N<sub>2</sub>, but both of them are transformed into cg-N structure after laser heating at about 123 GPa. With pressure decreasing to 40 GPa, the unconfined cg-N decomposes and releases huge energy, which affects the stability and results in the decomposition of the confined cg-N. Under ambient conditions, the confined N<sub>2</sub> is stabilized in the liquid phase. In the N<sub>2</sub>@BNNTs sample with lower nitrogen content, the confined N<sub>2</sub> is transformed into new polymeric nitrogen structure, which possesses N=N double bonds with different bond lengths close to the those in the <inline-formula><tex-math id="Z-20240409215933">\begin{document}${\mathrm{N}}_3^- $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240173_Z-20240409215933.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240173_Z-20240409215933.png"/></alternatives></inline-formula> anion and <inline-formula><tex-math id="Z-20240409215942">\begin{document}${\mathrm{N}}_4^+ $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240173_Z-20240409215942.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240173_Z-20240409215942.png"/></alternatives></inline-formula> clusters, respectively, after laser-heating in the pressure range of 122–150 GPa. This polynitrogen structure is stable with pressure decreasing to 25 GPa. This work provides new insights into the synthesis and stabilization of polymeric nitrogen structures, opening up new avenues for developing these advanced structures.

Structurally Constrained Evolutionary Algorithm for the Discovery and Design of Metastable Phases.

Metastable materials are abundant in nature and technology, showcasing remarkable properties that inspire innovative materials design. However, traditional crystal structure prediction methods, which rely solely on energetic factors to determine a structure's fitness, are not suitable for predicting the vast number of potentially synthesizable phases that represent a local minimum corresponding to a state in thermodynamic equilibrium. Here, we present a new approach for the prediction of metastable phases with specific structural features and interface this method with the XtalOpt evolutionary algorithm. Our method relies on structural features that include the local crystalline order (e.g, the coordination number or chemical environment), and symmetry (e.g, Bravais lattice and space group) to filter the breeding pool of an evolutionary crystal structure search. The effectiveness of this approach is benchmarked on three known metastable systems: XeN8, with a two-dimensional polymeric nitrogen sublattice, brookite TiO2, and a high pressure BaH4 phase, which was recently characterized. Additionally, a newly predicted metastable melaminate salt, P1̅ WC3N6, was found to possess an energy that is lower than that of two phases proposed in a recent computational study. The method presented here could help in identifying the structures of compounds that have already been synthesized, and in developing new synthesis targets with desired properties.

Penta-MN8 family: First realization of type-5 pentagonal tessellation in 2D hexagonal crystals with intriguing properties

Tessellation of the Euclidean plane by congruent pentagons has long been of great interest. However, periodic pentagonal patterns realized in crystallography reported so far are limited to type-2 or type-4 tiling in typical square lattices. Based on the recently synthesized N18 macrocycles together with Hückel aromaticity and 18-electron rules, we design a family of pentagonal metal polynitrides, penta-MN8 (M = Mg, Ca, Sr, Ba; Sn, Pb; Cd; Mo, W), the first materials realization of type-5 mathematical pattern with novel pentagonal tiles in 2D hexagonal lattices. The penta-MN8 family exhibits rich stable phases (γ, α/α′, and β) and diverse Poisson's ratios ranging from 0.299 to -0.488. Among these nitrogen-richest monolayer nitrides hitherto, penta-MgN8 possesses firm stability up to 700 K and under low pressure originating from unique aromaticity over the polymeric nitrogen network, which could be synthesized under ∼50 GPa as confirmed by global structure search. Moreover, penta-MgN8 exhibits a fully flat band near Fermi level over the whole 2D Brillouin zone, deriving from the combination of pentagonal pattern and hexagonal lattice as verified with tight-binding model analysis. Such electronic structures fill in the blank of clear kagome flat bands in known kagome nitrides and pentagon-based materials, resulting in very heavy fermions with huge effective mass (55.7 m0) that are favorable to achieve quantum zero-field Wigner crystals. Our work presents a new pentagonal-materials class with unprecedented coordination, lattice symmetry, and physical properties compared to existing pentagon-based systems, which makes a breakthrough in exploring the materials realization of the mathematical models for pentagonal tessellation.

Coupling FeMgAl-LDH and sludge biofilm for simultaneous and effective removal of nitrate and ammonium in water

The existence of redundant nitrate (NO3−) and ammonium (NH4+) in water caused negative impacts on the ecosystem's stability while the simultaneous removal of these nitrogenous substances has become a challenging task. The intimately coupled photocatalysis and biodegradation (ICPB) system has shown great potential in the efficient removal of aquatic pollutants. In this study, the FeMgAl layered double hydroxide (FeMgAl-LDH) capable of removing NO3− and NH4+ concurrently through adsorption and photocatalysis was successfully synthesized based on the hydrothermal method. The characterization of the material has verified its lamellar structure and the inclusion of metal oxide phases. Then, the ICPB system was constructed by coupling FeMgAl-LDH and biofilm from activated sludge onto a polyurethane carrier. After 12-hour water treatment, the ICPB system could realize 54.45 % and 42.57 % of the NO3− and NH4+ removal rates at a pH of 7 and dissolved oxygen (DO) of 2 mg/L, which was superior to the single photocatalysis and biological treatment. The removal performances of the ICPB system under different pH and DO levels were assayed. Meanwhile, microbial activities, community variation, and relational genes were studied to analyze the microbial mechanisms. The microorganisms in the ICPB system possessed high activity to form extracellular polymeric substances (EPSs), nitrogen transformation, and electron transfer. In all, this study constructed a new ICPB system and revealed its mechanism to simultaneously remove the NO3− and NH4+ from the water.

Polymeric nitrogen in alkaline earth metal N-rich nitrides (MN2, M = Be, Mg, Ca, Sr, and Ba): A first-principles study

The distinctive chemical and physical characteristics of all-nitrogen salts have attracted significant interest. Some stable polymeric nitrogen with novel chemical bonding patterns are predicted using first-principles calculations and crystal structure prediction methods. However, the element effects of the chemical bonding pattern and structural stability are still unclear. Here, we select the cmcm-MgN2 structure, which is predicted to be free energy favorable between 5 and 40 GPa, and substitute the Mg atoms with other alkaline earth elements (beryllium, calcium, strontium, and barium) to systematically study the influence of the elements on the properties of the compound. We found that the N = N bonds are all covalent, but have metallic properties in BeN2 and BaN2, semiconductor properties in MgN2, CaN2, and SrN2 and the width of the indirect band gap increases with increasing pressure. The charge transfer between metal and N atoms is closely related to the electronegativity of metal elements. Furthermore, thermal stability is investigated based on the phonon spectrum and the imaginary phonons of unstable systems correspond to special vibrational modes of the N = N bond. The anisotropy of lattice constant compressibility is found to be a signal of structural thermal instability. Our results shed some light on the influence of elements on the physical properties of all-nitrogen salts under high pressure, thus accelerating the prediction of crystal structure.

Two Ultrahigh-Energy-Density Layered Cerium Polynitrides with Molecular Sieve Channel.

Two high-pressure stable phases (I41/a-CeN4 and R3̅m-CeN6) and two metastable phases (P6mm-CeN14 and P6mm-CeN17) were proposed in Ce-N compounds at 150-300 GPa. The polymeric nitrogen units include quadruple helical chains, N6 rings, and first reported layered molecular sieves structures. I41/a-CeN4 can be quenched to ambient conditions and its thermal stability can be maintained up to 500 K. P6mm-CeN14 is dynamically and mechanically stable at ambient pressure. The electronic properties analyses show that charge transfer between the Ce and N atoms makes a significant contribution to the structural stability by promoting the formation of Ce-N ionic bond and N-N covalent bond. The Ce atom provides a suitable coordination environment and an excellent bonding state for the fully sp3 hybridized layered molecular sieve to enhance the stability of P6mm-CeN14. Surprisingly, the energy density (8.45 kJ/g) and explosive performance of P6mm-CeN14 are the highest among all metal polynitrides, refreshing a new record for high-energy metal polynitrides.

High-pressure synthesis of fully sp2-hybridized polymeric nitrogen layer in potassium supernitride

Searching for fully sp2-hybridized layered structures is of fundamental importance because of their fascinating physical properties and potential to host topologically non-trivial electronic states. However, the synthesis of fully sp2-hybridized layered polymeric nitrogen structures remains a challenging work because of their low stability. Here, we report the synthesis of a fully sp2-hybridized layered polymeric nitrogen structure featuring fused 18-membered rings in potassium supernitride (K2N16) under high-pressure and high-temperature conditions. Bader charge analysis reveals that the potassium atomic layer stabilizes the unique sp2-hybridized polymeric nitrogen layers through the charge transfer effect in K2N16. The calculation of electronic structure indicates that K2N16 is a topological semimetal with multiple Dirac points and hosts higher-order Dirac fermions with cubic dispersion, which are contributed by the sp2-hybridized polymeric nitrogen layers arranged in P6/mcc symmetry. The high-pressure synthesis of the fully sp2-hybridized polymeric nitrogen layered structure provides promising prospects for exploring novel topological materials with effective stabilization routes.

Strain engineering of the electrocatalytic activity of nitrogen-rich BeN4 Dirac monolayer for hydrogen evolution reaction

The strong bond energy and short bond length of N≡N triple bond make it a challenging target for synthesizing nitrogen-rich compounds. However, recent research has successfully fabricated atomic-thick BeN4 layers under high pressure (Bykov et al., 2021). Beryllonitrene, a new 2D material, consists of a Be atom and polymeric nitrogen chains and has anisotropic Dirac cones located near the Fermi level. This distinguishes it from graphene, which has isotropic Dirac cones, bulk PtTe2 and 2D borophene, which have Dirac cones located far from the Fermi energy. The anisotropic Dirac cones in beryllonitrene result in ultrahigh carrier mobility and the potential for direction-dependent quantum devices. In this study, we systematically investigated the hydrogen evolution reaction (HER) catalytic activity of nitrogen-rich, non-precious BeN4 monolayer using first-principles DFT calculations. Our results demonstrate that BeN4 monolayer is thermally stable, and Be vacancy is the most energetically favorable site for hydrogen adsorption. We also found the Gibbs free energy (ΔGH∗) of H∗ coverage can be tuned to an optimal value of |ΔGH∗|≤ 0.2 eV through strain engineering, significantly enhancing the HER electrocatalytic activity of BeN4 monolayer. Furthermore, we examined both the homolytic Tafel reaction and heterolytic Heyrovsky reaction for HER mechanism using reaction kinetics and AIMD simulations. These findings can contribute to the development of high-performance, non-precious, and nitrogen-rich 2D catalysts for HER in future research.

Investigations of point defect and interface in cg-N under high-pressure

The properties of cg-N with point defects and an interface are investigated based on the first-principles method. Our results show that at 0 GPa, the stability of cavities depends on their size. A smaller cavity has higher stability than the larger case. The decomposition of N2 molecules mainly occurs on the (110) surface of the cavity. However, the decomposition process will be suppressed by applying high-pressure. For the interface constructed by (110) surfaces, N2 molecules will be released at low pressure, and polymerization of N2 molecules with surfaces is triggered by loading pressures of 80–100 Gpa, giving rise to a stable polymerized interface, which is also stable after decreasing the pressure to 0 GPa. The results indicate that the existence of polymeric nitrogen networks can enhance the polymerization of N2 molecules at low-temperature.