Nitrogen Research Articles

Thermal treatment of sewage sludge: Impact of the sludge type and origin on the formation of recalcitrant compounds

In a municipal wastewater treatment plant, the thermal treatment of sludge can be an efficient way of increasing the final sludge cake dryness and boosting anaerobic digestion performances. However, such treatments generate refractory compounds which, once returned to headworks, can affect the quality compliance of effluent discharges, particularly concerning organic nitrogen. This study explores the effects of thermal hydrolysis (TH) and hydrothermal carbonization (HTC) of municipal sludge on the refractory organic compound production. A novel approach using ultra-performance liquid chromatography with size-exclusion chromatography and UV/fluorescence detection (UPLC-SEC-UV/Fluo) was employed to characterise recalcitrant dissolved organic matter (rDOM), which typically consists of Maillard reaction products (MRP). Specifically, UPLC-SEC-UV/Fluo was combined with principal component analysis (PCA) to enable a more thorough examination of the chemical diversity of MRPs produced. Greater temperatures during the thermal treatment step lead to increased production of rDOM and rDON. Protein-rich sludge with a great AS:PS ratio yields the greatest rDOM levels. MRP characteristics, such as molecular weight distribution and aromaticity, are primarily influenced by temperature and plant origin. UPLC-SEC-UV/Fluo provides information on the structures of MRPs useful to optimize the thermal treatment process and in understanding their fate in subsequent processes (chemical oxidation, biodegradation).These insights have practical implications for sludge treatment processes, including optimizing TH and HTC conditions to control rDOM production and adapt the sludge treatment line of a water resource recovery facility.

Coastal Supra-Permafrost Aquifers of the Arctic and Their Significant Groundwater, Carbon, and Nitrogen Fluxes.

Fresh submarine groundwater discharge (FSGD) can deliver significant fluxes of water and solutes from land to sea. In the Arctic, which accounts for ∼34% of coastlines globally, direct observations and knowledge of FSGD are scarce. Through integration of observations and process-based models, we found that regardless of ice-bonded permafrost depth at the shore, summer SGD flow dynamics along portions of the Beaufort Sea coast of Alaska are similar to those in lower latitudes. Calculated summer FSGD fluxes in the Arctic are generally higher relative to low latitudes. The FSGD organic carbon and nitrogen fluxes are likely larger than summer riverine input. The FSGD also has very high CO2 making it a potentially significant source of inorganic carbon. Thus, the biogeochemistry of Arctic coastal waters is potentially influenced by groundwater inputs during summer. These water and solute fluxes will likely increase as coastal permafrost across the Arctic thaws.

Nitrogen gas-bubble disease in two giant salamanders.

Gas-bubble disease (GBD)-a non-infectious disease in aquatic organisms caused by supersaturated levels of total dissolved gases (oxygen and nitrogen) in water-is well known in various species, including fish and amphibians, but has not previously been reported in giant salamanders. In the present study, macroscopic and histopathological examinations of 2 mature Andrias spp. (kept with 293 fish in an aquarium) were performed to characterize GBD pathology. Bubbles developed on the body surfaces of the salamanders and fish, with erythema specifically noted in the salamanders. Within 3 d of the bubbles appearing, both salamanders and more than 270 fish had died. On Days 1 and 2, dissolved oxygen levels were 75.5 and 86.9%, respectively, while dissolved nitrogen gas levels were 90.6 and 103.1%, respectively. The 2 salamanders exhibited identical lesions characterized by erythema, congestion, and numerous bubbles in the major veins of the body cavity. Histopathologically, congestion and gas embolism-like dilatations were observed in the small vessels and capillaries. These lesions were found in the parenchymal and gastrointestinal organs, skin, eyeballs, and surrounding stromal tissue. Based on these findings and that GBD occurs at dissolved nitrogen gas and oxygen levels above 120 and 200%, respectively, the salamanders were diagnosed with nitrogen GBD. The exact etiology of this disease remains unconfirmed but likely involves circulatory system dysfunction within the aquarium environment, highlighting the importance of routine inspections and maintenance of equipment.

Skeletal Editing via Transition-Metal-Catalyzed Nitrene Insertion.

Metal-nitrenes are valuable reactive intermediates for synthesis and are widely used to construct biologically relevant scaffolds, complexes and functionalized molecules. The ring expansion of cyclic molecules via single-nitrogen-atom insertion via nitrene or metal-nitrenoid intermediates has emerged as a promising modern strategy for driving advantageous nitrogen-rich compound synthesis. In recent years, the catalytic insertion of a single nitrogen atom into carbocycles, leading to N-heterocycles, has become an important focus of modern synthetic approaches with applications in medicinal chemistry, materials science, and industry. Catalytic single-nitrogen-atom insertions have been increasing in prominence in modern organic synthesis due to their capability to construct high-value added nitrogen-containing heterocycles from simple feedstocks. In this review, we will discuss the rapidly growing field of skeletal editing via single-nitrogen-atom insertion using transition metal catalysis to access nitrogen-containing heterocycles, with a focus on nitrogen insertion across a wide spectrum of carbocycles.

Impact of Transition-State Aromaticity on Selective Radical-Radical Coupling of Triarylimidazolyl Radicals.

Radical coupling reactions are generally known to have a low selectivity due to the high reactivity of radicals. In this study, high regio and substrate selectivity was discovered in the dimerization of triarylimidazolyl radicals (TAIR), a versatile photochromic reaction. When two different radicals, 2-(4-cyanophenyl)-4,5-diphenyl-1H-imidazolyl radical (CN-TAIR) and 2-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazolyl radical (OMe-TAIR), were simultaneously generated in situ, a hexaarylbiimidazole, formed by selective coupling at the nitrogen atom at position 1 of CN-TAIR and the carbon atom at position 2 of OMe-TAIR, was isolated with high selectivity as the main product among 24 possible radical dimer hexaarylbiimidazole derivatives. This high regio and substrate selectivity cannot be explained solely by the stability of the product and/or the electrophilicity and nucleophilicity of the radicals but originates from the aromaticity of the transition state in the radical-radical coupling reaction. To date, the selectivity of radical coupling reactions has been thought to be controlled by steric hindrance and radical spin density, but this study revealed a new factor for controlling radical coupling, that is, transition-state aromaticity. Aromaticity has been reported to have an important effect not only in the reactivity and structure of ground-state molecules but also on the electronically excited states and transition states in pericyclic reactions such as the Diels-Alder reaction and the Cope-Claisen rearrangement. This study demonstrated for the first time that radical coupling reactions can also be controlled by transition-state aromaticity.

Nitrogen substitution of bilayer penta-carbides: high solar-to-hydrogen conversion efficiency and excellent electrocatalytic activity for water splitting.

The shortage of fossil energy and environmental crises are two important issues in the 21st century, and the search for alternatives to fossil fuels, e.g. H2, is crucial. Herein, based on penta-germagraphene p-Ge2C4, bilayer penta-carbides of p-Ge4C8 and nitrogen substituted materials p-Ge4NnC8-n are proposed. The results indicate that gradually replacing the carbon atoms on the surface of p-Ge4C8 with nitrogen atoms can change the surface activities and electronic structures, and this is beneficial for both photocatalysis and electrocatalysis. The vertical intrinsic electric field in the two-dimensional materials can enhance photocatalytic water splitting of p-Ge2C4/Ge2N2C2 and break the conventional limitation of 1.23 eV for the band gap of photocatalysts. Therefore, solar energy conversion efficiency can reach 31%. The smaller effective mass and deformation potential of p-Ge2C4/Ge2N2C2 along the x and y directions lead to a huge electron mobility (425.64 × 103 cm2 V-1 s-1) at room temperature. Moreover, the overpotential for the hydrogen evolution reaction of p-Ge2C4/Ge2N2C2 is 0.074 V, which is beneficial for electrocatalysis. The external strain and electric field can also enrich the electronic properties. Surface modification achieved by introducing the nitrogen atoms can improve the catalytic performance of penta-carbides.

Enhanced warming and bacterial biomass production as key factors for coastal hypoxia in the southwestern Baltic Sea

Coastal ecosystems are affected by a multitude of anthropogenic stressors. As the Baltic Sea ecosystems rank among the most altered marine ecosystems worldwide, they represent ideal model regions to study ecosystem responses to anthropogenic pressures. Our statistical analysis of data including dissolved organic carbon and nitrogen, as well as bacterial abundance and -biomass production from the time-series station Boknis Eck in the southwestern Baltic Sea reveals that bacterial biomass production intensifies towards summer following the phytoplankton spring bloom. Moreover, warming, especially very high temperatures in summer, enhances stratification and bacterial biomass production despite long-term reduction in nutrient input. A strong decrease in oxygen in the bottom layer is possibly linked to this. We detect an increasing trend in bacterial biomass production along with intensifying warming and stratification, and more frequently occurring hypoxia despite ongoing restoration efforts. If this trend continues, the coastal Baltic Sea ecosystem is likely to be altered even further. Coastal ecosystems play pivotal roles in mitigating impacts of climate change but if destroyed, they may amplify climate change further calling for stronger ecosystem management strategies.

Influence of Granular Biostimulants on Growth and Yield Characteristics of Rice (Oryza Sativa) in New Alluvial Zone of West Bengal, India

Rice (Oryza sativa), the primary food source for over half of the global population, is critical to food security but faces productivity challenges from suboptimal fertilizer use and associated environmental degradation in India. Addressing these issues necessitates innovative strategies that enhance crop performance while maintaining ecological balance. Biostimulants, known for their role in enhancing nutrient efficiency and crop resilience, offer a promising solution for optimizing fertilizer use and improving soil health. This study evaluates the efficacy of AGMA Bio Stimulant Granules on the growth, yield, and soil health of rice during the kharif season of 2023 at Bidhan Chandra Krishi Vishwavidyalaya, Kalyani, West Bengal. A randomized block design with eight treatments and three replications was employed, including combinations of AGMA granules with 100% and 80% recommended NPK doses. Results demonstrated significant improvements in growth parameters, yield attributes, and soil nutrient availability with AGMA application. Treatments T2 and T5, integrating AGMA granules with 100% and 80% NPK, respectively, achieved the highest grain yields, with T5 showing a 19% yield increase over the control. Soil health indicators, including organic carbon and available nitrogen, phosphorus, and potassium, improved significantly, while electrical conductivity decreased. The study concludes that AGMA Bio Stimulant Granules enable a 20% reduction in NPK fertilizer use without compromising yields, underscoring their potential to support sustainable and environmentally friendly agricultural practices.

Combined application of biochar and silicon nanoparticles enhance soil and wheat productivity under drought: Insights into physiological and antioxidant defense mechanisms

Agricultural drought periods are enhanced by the change in global climate that threatens food security. One of the main factors affecting soil and wheat productivity worldwide is drought stress. Especially, in semi-arid climates, studies are not found about adding organic amendments may be a viable way to reduce the adverse impacts of drought on crops while enhancing soil qualities and water use efficiency. In this study, we aimed to explore the effects of combined application of biochar (BC = 5 %) and silicon nanoparticles (SiNP = 900 mg/L) on soil and wheat drought resistance. Drought stress was applied at the three most critical growth stages of wheat, tillering (DTS), flowering (DFS), and grain filling (DGFS) stages, then evaluated the soil nutrients and wheat drought physiological resistance under applied treatments (BC, SiNP, BC+SiNP). Results showed that combined treatment of BC and SiNP greatly reduced the adverse effects of drought by enhancing plant height (9.36 %), spike length (25.63 %), number of fertile tillers (29.26 %), grains per spike (10.86 %), thousand-grain weight (18.25 %), and biological yield (16.34 %) with comparison to the control application. Additionally, physiological measures like water use efficiency (20.58 %), stomatal conductance (29.26 %), chlorophyll a (16.25 %), chlorophyll b (18.96 %), transpiration rate (21.65 %), photosynthetic rate (22.94 %), electrolyte leakage (-17.77 %), MDA (29.25 %), hydrogen peroxide (-19.88 %), superoxide dismutase (11.19 %), catalase (9.26 %), peroxidase (18.59 %), nitrogen (14.81 %), phosphorus (13.89 %), and potassium (17.61 %) were also meaningfully improved by treated application. BC and SiNP also significantly amended the organic carbon, nitrogen, and minerals percentage in soil. In conclusion, using the synergistic application of BC and SiNP could be a successful strategy to promote the biological soil properties, plant growth, yield, and quality of wheat crops as compared to all other treatments via dropping the dangerous effects of drought stress.

Integrating isotope mixing and hydrologic models towards a more accurate riverine nitrate source apportionment

Nitrate (NO3–) is the major form of bioavailable nitrogen in most rivers, and its dramatic increase may lead to a number of serious environmental issues, such as eutrophication and biodiversity decline. Quantification of NO3– sources and fluxes in rivers is essential for effective management of NO3– pollution. Isotope mixing and hydrological models are proven practical tools for quantifying the sources of NO3– in rivers, yet both methods have severe limitations. To improve the accuracy and reliability of riverine NO3– source apportionment, this study proposed a protocol that integrates the strengths of both tools, capable of solving issues such as the calculation bias caused by isotope endmember overprinting in isotope mixing model and the lack of validation data for hydrological models. We applied the framework to a typical agricultural river, the Qihe River, and illustrated the effectiveness of the method in quantifying riverine NO3– sources. The proportional contribution of sewage simulated by the SWAT model approximated that estimated by the isotopic mixing model, yet the SWAT-based contributions of soil organic nitrogen and chemical fertilizer were 16.3 % lower and 14.0 % higher, respectively than the MCMC-based results. After integrating both models, we adopted the proportions of NO3– sources in the river from chemical fertilizer, sewage, and soil organic nitrogen as 45.1 %, 30.9 %, and 23.9 %, respectively. This study showed that coupling isotopic and hydrological models provided a new dimension for the accurate quantification of N sources in rivers.

Synthesis and Characterization of Two Sparfloxacin Crystalline Salts: Enhancing Solubility and In Vitro Antibacterial Activity of Sparfloxacin

Background: To improve the solubility and permeability of Sparfloxacin (SPX) and enhance its antimicrobial activity in vitro, two unreported pharmaceutical crystalline salts were synthesized and characterized in this paper. One is a hydrated crystal of Sparfloxacin with Pimelic acid (PIA), another is a hydrated crystal of Sparfloxacin with Azelaic acid (AZA), namely, SPX-PIA-H2O (2C19H23F2N4O3·C7H10O4·2H2O) and SPX-AZA-H2O (4C19H23F2N4O3·2C9H14O4·5H2O). Methods: The structure and purity of two crystalline salts were analyzed using solid-state characterization methods such as single-crystal X-ray diffraction, powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and infrared spectroscopy. Additionally, the interaction characteristics between two crystal salt molecules were examined by constructing Hirshfeld surfaces and mapping specific real-space functions through Hirshfeld surface analysis. The solubility under physiological conditions, diffusivity across simulated biological membranes, and in vitro antibacterial activity against specific bacterial strains of two crystalline salts were evaluated using established assays, including minimum inhibitory concentration (MIC) tests. Results: Single-crystal X-ray diffraction and Hirshfeld surface analysis indicate that SPX forms stable crystal structures with PIA through charge-assisted hydrogen bonds N1-H1e···O10 (1.721 Å, 173.24°), N5-H5a···O11 (1.861 Å, 169.38°), and with AZA through charge-assisted hydrogen bonds N5-H5B···O8 (1.810 Å, 154.55°), N4-H4B···O6 (1.806 Å, 174.97°). The binding sites of two crystalline salts were at the nitrogen atoms on the piperazine ring of SPX. Compared with SPX, the equilibrium solubility of the two crystalline salts was improved by 1.17 and 0.33 times, respectively, and the permeability of the two crystalline salts was increased by 26.6% and 121.9%, respectively. In addition, SPX-AZA-H2O has much higher antibacterial activity on Pseudomonas aeruginosa and Bacillus subtilis than SPX. Conclusions: This research yielded the successful synthesis of two crystalline salts of Sparfloxacin (SPX), significantly improving its solubility and diffusivity, and bolstering its antibacterial efficacy against targeted bacterial species. These breakthroughs set the stage for innovative advancements in the realm of antimicrobial drug development.

Ozone trends and their sensitivity in global megacities under the warming climate

Tropospheric ozone formation depends on the emissions of volatile organic compounds (VOC) and nitrogen oxides (NOx). In megacities, abundant VOC and NOx sources cause relentlessly high ozone episodes, affecting a large share of the global population. This study uses data from the Ozone Monitoring Instrument for formaldehyde (HCHO) and nitrogen dioxide (NO2) as proxy data for VOC and NOx emissions, respectively, with their ratio serving as an indicator of ozone sensitivity. Ground-level ozone (O3) reanalysis from the Copernicus Atmosphere Monitoring is used to assess the O3 trends. We evaluate changes from 2005 to 2019 and their relationship with the warming environment in 41 megacities worldwide, applying seasonal Mann-Kendall, trend decomposition methods, and Pearson correlation analysis. We reveal significant increases in global HCHO (0.1 to 0.31 × 1015 mol cm−2 year−1) and regionally varying NO2 (−0.22 to 0.07 × 1015 mol cm−2 year−1). O3 trends range from −0.31 to 0.70 ppb year−1, highlighting the relevance of precursor abundance on O3 levels. The strong correlation between precursor emissions and increasing temperature suggests that O3 will continue to rise as climate change persists.

Improving Molecular Arrangement and Alleviating Nonradiative Energy Loss Using a Chlorinated Pyrido[3,4‐b]Quinoxaline‐Core‐Based Acceptor for High‐Performance Organic Solar Cells

AbstractThe electron‐deficient A1 unit in A‐DA1D‐A structured acceptors is critical for optimizing the efficiency of organic solar cells (OSCs). Drawing inspiration from the high performance of the previously reported pyrido[2,3‐b]quinoxaline‐core acceptors, Py6, an isomer of Py1 is designed with a repositioned pyridine nitrogen atom, and further modified it by chlorinating Py6 to create Py7. Theoretical calculations show that chlorine incorporation strengthens intermolecular non‐covalent interactions and promotes the tighter molecular stacking, as confirmed by grazing‐incidence wide‐angle X‐ray scattering. Consequently, D18/Py7 device delivers the enhanced fill factor and short‐circuit current density, compared to D18/Py1 and D18/Py6 device. Notably, D18/Py7 device also yields a higher open‐circuit voltage of 0.871 V, significantly outperforming Py1 (0.764 V) and Py6 (0.723 V), due to the low nonradiative energy losses. Further studies reveal that introducing Cl directs hole density toward the central pyrido[3,4‐b]quinoxaline unit and decreases the charge transfer state ratio of D18/acceptor. This prompts triplet‐to‐singlet conversion and reduces non‐radiative recombination losses. Additionally, using a mutual donor–acceptor dilution strategy, the (D18:1wt.% Py7)/(Py7:1wt.% D18) device achieves an impressive efficiency of 19.60%. This work emphasizes the great potential of the Py‐series acceptors and demonstrates that chlorine incorporation effectively reduces non‐radiative losses.

Enhancing the solubility and antibacterial activity of novel molecular salts of enrofloxacin drug with isomeric pyridinedicarboxylic acids

Enrofloxacin (EFX) is a third-generation synthetic fluoroquinolone with a broad spectrum of antibacterial activity but suffers from low water solubility, affecting its bioavailability. This study attempts to enhance the physicochemical and biological properties of enrofloxacin by converting it into multicomponent forms using crystal engineering concepts. Cocrystallization of enrofloxacin with isomeric pyridine-2,n-dicarboxylic acids (n = 3,4,5,6) resulted in four new crystalline salts (1:1): EFX·Py2,3DCA, EFX·Py2,4DCA, EFX·Py2,5DCA·H2O and EFX·Py2,6DCA·H2O; two of these are monohydrates. The protonation of the nitrogen atom of the piperazine moiety and the presence of crystallization water molecules were confirmed by single-crystal X-ray diffraction and Fourier transform infrared spectroscopy. Thermogravimetric analysis provided information on the thermal behaviour of multicomponent forms. The biological studies showed that the obtained salts are characterized by high antibacterial activity against Gram-positive and Gram-negative bacteria, and their haemolytic activity is low. The new salts demonstrate significantly greater solubility in water compared to the parent drug, along with enhanced antibacterial activity; hence, pyridinedicarboxylic acids appear to be efficient cocrystallizing agents for improving the efficacy of pharmaceutical ingredients.

Improving visible light-driven CO2 conversion to high calorific fuels over sustainable highly crystalline and holey sulphur doped graphitic carbon nitrides

The effectiveness of CO2 reduction through g-C3N4 (CN) is considerably hindered by poor visible light absorption and the high rate of recombination of electron-hole (e−/h+) pairs. An effective method for increasing CO2 photoreduction efficiency is to incorporate non-metal components into the CN to modify its electronic properties and enhance its performance. This research presents the findings of our inquiry into sulfur-doped graphitic carbon nitrides (S–CN) for CO2 reduction through visible light. The XPS study reveals that the substitution of nitrogen atoms in the heptazine ring by sulfur (S) doping significantly influences the electronic configuration of CN, while the UV–visible absorbance spectra reveals that the CN band gap value 2.64 eV has reduced to 2.50 eV after S doping. Therefore, S–CN exhibits exceptional visible-light absorption, separation and migration of photoexcited e−/h+, corroborated by photoluminescence and transient photocurrent response experiments. Besides, S–CN demonstrated remarkable CO2 reduction capabilities without any cocatalyst or sacrificial agent, achieving CO/CH4 formation rates of 25/3 μmolg−1h−1, outperforming traditional CN. Our research highlights the relevance of impeding the e−/h+ recombination process to boost solar energy conversion output, suggesting potential for productive solar fuel generation using g-C3N4.

Spin Regulation of Nickel Single Atom Catalyst via Axial Phosphor‐Coordination Achieves Near Unity CO Selectivity in Electrochemical CO2 Reduction

AbstractThe engineering of the spin state and axial coordination of the metal center of single‐atom catalyst (SAC) represents an effective strategy for regulating the catalytic activity, selectivity, and stability toward electrocatalytic reduction of CO2 (ECO2R). However, rational design and deliberate fabrication of SACs with axial coordination of specified atoms remain challenging. Herein, Ni single atoms with axial coordination of phosphorus (NiP−N4−C) and four planar nitrogen atoms are fabricated, which induces reorientation of the 3d orbitals of the Ni atom and shift of the spin state from low (S = 0) to high (S = 2). The enhanced d−p orbital coupling between the Ni and the adsorbents enhances CO2 activation and reduces energy barrier for formation of *COOH, a key intermediate in the ECO2R to produce CO, enabling the high activity and near unity selectivity of CO in ECO2R in a broad potential range of 600 mV (−0.4–−1.0 V vs reversible hydrogen electrode vs RHE), achieving a turnover frequency of 37.2 s−1 at −1.0 V versus RHE. As a bifunctional cathode electrocatalyst, NiP−N4−C demonstrates a peak power density of 18.5 mW cm−2 and maintains cycling durability over 70 h in rechargeable Zn−CO2 batteries.

Interaction of Difluorocarbene with the Thiocyanate Anion: Access to a Silicon Reagent Bearing the Isothiocyanate Group.

The reaction between (bromodifluoromethyl)trimethylsilane (TMSCF2Br) and potassium thiocyanate providing TMSCF2NCS is described. The process involves the interaction of difluorocarbene with the nitrogen atom of the thiocyanate anion. The obtained silicon reagent served as a source of the fluorinated group and difluorocarbene in the reaction with N-alkyl imines, affording 2-(difluoromethylthio)-4-fluoroimidazoles.

RESULTS REGARDING THE INFLUENCE OF GREEN MANURE USAGE ON MAIZE CROP ON ACIDIC SOILS IN THE NORTHWEST OF THE COUNTRY

This paper presents the efficacy of green manures in raising soil fertility and enhancing crop productivity, on the Albic Luvisols in northwestern Romania.Green manures are cover crops that provide various benefits when added to the soil. Peas are especially effective at increasing organic nitrogen in the soil, leaving behind a significant amount of 471.74 kg N(a.s.) per hectare. Regardless of the pressure from the pathogen Fusarium spp. and the pest Ostrinia n. the maize yield was not affected. The incorporated green manures especially peas, significantly raises maize yield surpassing the control with almost 3000 kg. The quality of the maize crop, specifically starch content and hectoliter weight, was not influenced by either green manure or chemical fertilization.

Skeletal Nitrogen Functionalization of Isostructural 2D Conjugated MOFs for Enhancement of the Dual-Ion Storage Capacity.

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) are emerging as promising electrode materials for electrochemical energy storage. However, a viable path to realize superior dual-ion storage in 2D c-MOFs has remained elusive. Here, we report the synthesis of Cu2(Nx-OHPTP) 2D c-MOFs (x=0,1,2; OHPTP=octahydroxyphenanthrotriphenylene) with precise aromatic carbon-nitrogen arrangements, based on the π-conjugated OHPTP ligand incorporated with one or two nitrogen atoms. The skeletal nitrogen modification in Cu2(Nx-OHPTP) allows the synergistic introduction of additional redox sites, and thus substantially favors the unique dual-ion adsorption capacity. Consequently, the Cu2(N2-OHPTP) cathode exhibits a largely enhanced electrochemical performance for dual-ion storage (i.e., Li+ and Cl-) with a high specific capacity of 53.8 mAh g-1, which is twice that of Cu2(N0-OHPTP) and 1.3 times that of Cu2(N1-OHPTP). Furthermore, the Cu2(N2-OHPTP) electrode displays a favorable rate performance of 52% and good cycling stability of 96% after 1000 cycles. We identify N-centered redox sites as additional Li+ adsorption sites. In addition, calculations underline the synergistic enhancement of the Cl- adsorption energy by about 1.0 eV at the more electron-poor CuO4 linkages after N-incorporation. This work paves the way for the precise design of 2D c-MOFs with superior electrochemical properties, advancing their application in dual-ion storage applications.

Skeletal Nitrogen Functionalization of Isostructural 2D Conjugated MOFs for Enhancement of the Dual‐Ion Storage Capacity

Two‐dimensional conjugated metal‐organic frameworks (2D c‐MOFs) are emerging as promising electrode materials for electrochemical energy storage. However, a viable path to realize superior dual‐ion storage in 2D c‐MOFs has remained elusive. Here, we report the synthesis of Cu2(Nx‐OHPTP) 2D c‐MOFs (x=0,1,2; OHPTP=octahydroxyphenanthrotriphenylene) with precise aromatic carbon‐nitrogen arrangements, based on the π‐conjugated OHPTP ligand incorporated with one or two nitrogen atoms. The skeletal nitrogen modification in Cu2(Nx‐OHPTP) allows the synergistic introduction of additional redox sites, and thus substantially favors the unique dual‐ion adsorption capacity. Consequently, the Cu2(N2‐OHPTP) cathode exhibits a largely enhanced electrochemical performance for dual‐ion storage (i.e., Li+ and Cl‐) with a high specific capacity of 53.8 mAh g−1, which is twice that of Cu2(N0‐OHPTP) and 1.3 times that of Cu2(N1‐OHPTP). Furthermore, the Cu2(N2‐OHPTP) electrode displays a favorable rate performance of 52% and good cycling stability of 96% after 1000 cycles. We identify N‐centered redox sites as additional Li+ adsorption sites. In addition, calculations underline the synergistic enhancement of the Cl− adsorption energy by about 1.0 eV at the more electron‐poor CuO4 linkages after N‐incorporation. This work paves the way for the precise design of 2D c‐MOFs with superior electrochemical properties, advancing their application in dual‐ion storage applications.