Nitrogen‐Doped Carbon Nanomaterials: Synthesis, Characteristics and Applications

Tailoring N and S Heteroatoms Through Rational Design in Carbon Nanotubes-Graphene Composites for Enhanced Zn-Air Battery Performance

Cathodic materials significantly influence the performance, durability, and sustainability of primary zinc-air batteries (ZABs). This study focuses on the rational design of highly active metal-free composites by tailoring the content of N and S heteroatoms in carbon nanotube-graphene (CNTG) composites. The oxygen reduction reaction (ORR) tests showed onset potentials (Eo) of 0.88 V (N-CNT) and 0.89 V (N-graphene) for individual materials and 0.92 V for the N-CNTG composite, highlighting the advantage of using a composite materialThe N content varied with dicyandiamide and urea, displaying changes in the surface area and N content (7.09 vs. 5.30 at. %), and in pyridinic and quaternary N species. The N content varied with dicyandiamide and urea, showing changes in the surface area and N content (7.09 vs. 5.30 at. %), and in pyridinic and quaternary N species. The abundance of pyridinic-N species in N-CNTG using urea enabled a higher ORR activity (Eo=0.92 V). The S incorporation through thiourea improved the Eo to 0.94 V (Pt/C=1.03 V). And, the combination of urea and thiourea resulted in a highly active and durable N,S-CNTG material, displaying a Eo of 0.96 V, and an activity loss of 8.7 % (Pt/C=25.4 %) after 2000 cycles. In ZAB mode, this material displayed a voltage of 1.35 V, a power density of 107 mW cm-2, and a specific capacity of 1060 mA h g-1.

Cobalt-Doped MnFe2O4 Spinel Coupled with Nitrogen-Doped Reduced Graphene Oxide: Enhanced Oxygen Electrocatalytic Activity for Zinc-Air Batteries

MFCO spinel anchored on N-rGO is synthesized by a two-step hydrothermal method as a bifunctional electrocatalyst. Its physicochemical properties have been characterized and tested, and it is applied to zinc-air batteries. The experimental and theoretical calculations show that the MFCO is uniformly distributed on the surface of N-rGO. When MFCO is anchored on the conducting N-rGO, a synergistic effect occurs between the Co-N bonds, which changes the arrangement of the C-N bonds from the sp2 orientation to the sp3 form. The ORR catalytic pathway of the MFCO/N-rGO electrocatalyst is dominated by 4-electron transfer, with a half-wave potential of 0.8003 V, an overpotential value of 352 mV, and a small potential difference (ΔE = 0.78 V). With a charge/discharge voltage difference of about 0.88 V, the voltage gap remains almost unchanged for a long period after 650 h, showing excellent stability. The improved catalytic performance is attributed to Co acting as an active site, and the doping of Co induces the Jahn-Teller effect, which alters the electronic structure of spinel, shifts the d-band center upward, enhances the adsorption of oxygen intermediates, and promotes the oxygen electrocatalytic reaction. This study provides a low-cost and promising bifunctional oxygen electrocatalyst for zinc-air batteries.

Nitrogen-doped hollow quadruple-shelled carbon-silicon nanosphere as a solid-phase microextraction adsorbent for the extraction of 19 polycyclic aromatic hydrocarbons in milk samples

In this study, nitrogen-doped hollow multi-shelled carbon-silicon nanospheres (NSiC-Homs-NS) were prepared using a template method and employed as a coating material for solid-phase microextraction (SPME) fibers. The extraction efficiency of single-, double-, triple-, and quadruple-shelled NSiC-Homs-NS coated fibers for polycyclic aromatic hydrocarbons (PAHs) were investigated, respectively. The NSiC-Homs-NS based SPME fiber coupled with gas chromatography-mass spectrometry was applied to detect 19 PAHs in milk samples. The extraction parameters of SPME were optimized using a central composite design methodology. Under the optimized conditions, the established method exhibited good linearity for the PAHs, ranging from 0.03 to 500 ng g-1, with coefficients of determination (r2) between 0.9952 and 0.9983. The limits of detection (S/N of 3) of the PAHs in milk samples ranged from 0.01 to 4.0 ng g-1. The relative standard deviations of the single-fiber repeatability (n = 5) and fiber-to-fiber reproducibility (n = 5) were all less than 12 %. The method recoveries of the PAHs in seven milk samples, evaluated at three different spiking concentrations, ranged from 80.4 % to 119 % with RSDs less than 12 %. The developed method exhibited good repeatability and accuracy.

Albizia Procera-Derived Nitrogen-Doped Carbon: A Versatile Material for Energy Conversion, Storage, and Environmental Applications

This review explores the diverse applications of nitrogen-doped carbon derived from Albizia procera, known as white siris. Native to the Indian subcontinent and tropical Asia, this species thrives in varied conditions, contributing to sustainable development. The nitrogen-rich leaves of Albizia procera are an excellent source for synthesizing nitrogen-doped carbon, which possesses remarkable properties for advanced technologies. This material demonstrates significant potential in energy conversion and storage systems, such as supercapacitors and batteries, due to its high surface area, electrical conductivity, and chemical stability. Nitrogen doping introduces active sites that enhance charge storage, making it ideal for renewable energy applications. Additionally, this material shows promise in environmental processes like water splitting and carbon dioxide capture, where its porous structure and chemical functionality enable efficient adsorption and remediation. The review discusses synthesis methodologies, including pyrolysis and activation, to optimize its properties for energy and environmental uses. Nitrogen-doped carbon derived from Albizia procera may expand into catalytic applications, enhancing its role in sustainable technologies. This review underscores the importance of utilizing natural resources like Albizia procera to develop materials that drive both environmental sustainability and technological innovation.

B,N-Doped Activated Carbon-Based Electrodes from Potato Peels for Energy Storage Applications

Potato peels (PPs) as waste biomass were selected as the biobased carbon source for this study, using urea as N precursor and boron trioxide as B precursor for the "in situ doping" via hydrothermal carbonization (HTC). During HTC, the feedstocks decompose over a wide range of complex chemical degradation mechanisms that finally form single B- and N- as well as B,N-co-doped hydrochars (HCs). Upon chemical ZnCl2 activation, the single B-doped activated carbon (AC) possessed a maximum B content of 0.2 wt%, whereas co-doped B,N-AC had the highest N content of 5.7 wt% with a B content of 0.1 wt%. The influence of single and B,N-co-doping on the physical-chemical material properties of the AC electrodes was analyzed and compared, in combination with its effect on the electrochemical performance for energy storage application. Compared to pristine AC derived from PPs, the B-doped and B,N-co-doped AC depicted increased electrical conductivity (EC) values of 50.3 S ⋅ m-1 and 34.0 S ⋅ m-1, respectively. In addition, the B,N-co-doped AC unveiled the highest average specific capacitances of 51.7 F ⋅ g-1 at 100 mV ⋅ s-1 and of 71.9 F ⋅ g-1 at 5 mV ⋅ s-1 outperforming the specific capacitance values of the reference material AC from peat.

Exploring Local Reactivity of Large Systems through Combining Conceptual DFT and the GFN2-xTB Method

This study evaluates the ability of the GFN2-xTB method and Conceptual Density Functional Theory-derived tools to predict local reactivity in large systems. Carbon-based systems such as C60, C70, Li+@C70, C240, C360, C648, and C720 have been used as test sets, and the orbital-weighted dual descriptor was employed to identify nucleophilic and electrophilic regions, providing a comprehensive analysis of their reactivity patterns. The results confirm that the GFN2-xTB method accurately reproduces reactivity profiles observed experimentally and at the DFT level, particularly in well-known fullerenes like C60 and C70. The addition of an endohedral Li+ cation to C70 demonstrated enhanced electrophilicity and reduced unfavorable nucleophilic regions, consistent with previous studies. For larger and less-studied systems, such as C240, C360, C648, and C720, the analysis revealed distinct reactivity features, including the localization of nucleophilic regions in -C≡C- units of C240/C648, the nucleophilic regions at the ends of the C360 nanoparticle model, and the emergence of electrophilic zones due to the reduction in aromaticity of the benzenoid rings in C720. These findings validate the GFN2-xTB method as a computationally efficient alternative for exploring the reactivity of large structures and contribute valuable insights into their potential applications in molecular design for material science and nanotechnology.

Fe3O4@nitrogen-doped carbon@Pd core-double shell nanotubes as a novel nanosorbent for ultrasonic assisted dispersive magnetic solid phase extraction of organophosphorus pesticides

In this study, an ultrasonic assisted dispersive magnetic solid phase extraction leveraging Fe3O4@nitrogen-doped carbon@Pd core-double shell nanotubes was developed for the extraction of organophosphorus pesticides (OPPs) in trace levels from real samples. Incorporation of Pd species into the structure of the nanosorbent could enhance its interactions with sulfur groups in the structure of OPPs. X-ray photoelectron spectroscopy and X-ray diffraction, brunauer-emmett-teller, field emission scanning electron microscopy, and high-resolution transmission electron microscopy were used to characterize the nanosorbent after its synthesis. Then, effective variables on the extraction efficiency of OPPs using the nanosorbent were optimized. These parameters included 2-propanol as the adsorption solvent; the sample pH of 7.0; the sorbent quantity of 10 mg; and the extraction and desorption times of 3 min. Under optimized conditions, linear ranges with determination coefficients (R2) higher than 0.99, low detection limits of 0.30 ng mL-1, high preconcentration factors (423-470) and relatively high extraction recoveries (84-94 %) were obtained. The proposed extraction system was then successfully applied to the analysis of OPPs in fruits, vegetables, water, and agricultural soil samples, yielding relative recoveries from 90.4 to 107 %.

Plasma-assisted fabrication of ultra-dispersed copper oxides in and on C-rich carbon nitride as functional composites for the oxygen evolution reaction

Significant efforts have been continuously devoted to the mastering of green catalysts for the oxygen evolution reaction (OER), whose sluggish kinetics prevents a broad market penetration of water splitting as a sustainable route for large-scale hydrogen production. In this extensive scenario, carbon nitride (CN)-based systems are in focus thanks to their favorable characteristics, and, whereas graphitic CN has been largely investigated, the potential of amorphous carbon nitride (a-CNx) systems remains almost entirely unexplored. In this regard, our study presents a novel two-step plasma-assisted route to a-CNx systems comprising ultra-dispersed, i.e. "quasi-atomic" CuxO (x = 1, 2). The target materials were fabricated using an original strategy consisting in the magnetron sputtering of a-CNx on conducting glasses at room temperature, followed by functionalization with low CuxO amounts by radio frequency (RF)-sputtering, and final annealing under an inert atmosphere. The tailoring of the CuxO co-catalyst content and spatial dispersion, as well as the overall composite features as a function of preparative conditions, enabled a direct modulation of the resulting OER performances, rationalized based on the formation of p-n CuxO/a-CNx heterojunctions. The amenable and scalable synthesis approach underscores the practicality of this method to develop (photo)electrocatalysts synergistically integrating the advantages of both constituents, yielding low-cost, green, and stable functional platforms that could contribute to the broader adoption of sustainable energy solutions.

Ultrasound-assisted fungal self-growth and heteroatom doping for the preparation of high-performance lignocellulose-based supercapacitor electrodes

Biomass materials are widely used as supercapacitor electrode materials due to their cost-effectiveness and eco-friendliness. In this work, ultrasound-assisted impregnation was employed for the thorough mixing of the liquid medium, and fungal treatment was conducted on the three main components of lignocellulose to prepare a fungi-modified heteroatom-doped lignocellulose-based carbon material (LCF-NP). The effects of heteroatom doping, the content of the three main components, and fungal modification on the electrochemical performance of lignocellulose-based carbon materials was investigated. The results revealed the synergistic effect of heteroatom doping and fungal treatment on the electrochemical performance. Compared with its counterpart free of fungal treatment, LCF-NP has a more reasonable pore structure and exhibits excellent electrochemical performance. LCF-NP porous carbon material has the highest specific surface area (792 m2/g), large pore volume (0.523 cm3/g), and ideal specific capacitance (1940 mF/cm2) under the conditions of 1.0 M Na2SO4 electrolyte and current density of 0.5 mA/cm2. After 10,000 cycles, there is almost no loss of capacitance. These results indicate that the joint utilization of heteroatom doping and fungal treatment has a promising application prospect in pore structure regulation and electrochemical performance improvement. This study provides a new strategy for the preparation of lignocellulose-based carbon electrode materials.

Self-Exfoliating Benzotristriazine Macrocyclic Network: A New 2D Material for High-Performance Electrochemical Energy Storage

Aza-fused aromatic π-conjugated networks are an important class of 2D graphitic analogs, which are generally constructed using aromatic precursors. Herein, the study describes a new synthetic approach and electrochemical properties of a self-exfoliating benzotristriazine 2D network (BTTN) constructed using aliphatic precursors, under relatively mild conditions. The obtained BTTN exhibits a nanodisc-like morphology, the self-exfoliation tendency of which is ascribed to the presence of structurally different macrocycles with high electronic repulsion between the layers. The benzotristriazine repeat units of BTTN is electroactive and holds higher carbon/nitrogen ratio when compared with the conventional graphitic aza-fused π-conjugated networks. The self-exfoliated BTTN nanodiscs show excellent electrochemical energy storage of 485 and 333 F g-1 at 1 A g-1 in three-electrode and two-electrode measurements, respectively. BTTN in a symmetric coin-cell architecture exhibits a high specific energy value of 46 Wh kg-1 at a power density of 1 kW kg-1 and shows excellent cyclic stability of 96% for 10 000 and 90% for 30 000 charge-discharge cycles at a higher current density of 5 A g-1, surpassing the device performance of most of the reported all-organic pseudocapacitive 2D networks.

Poly(ionic liquid)/Wood Composite-Derived B/N-Codoped Porous Carbons Possessing Peroxidase-like Catalytic Activity

The pursuit of efficient and cost-effective metal-free heterogeneous catalytic systems remains a challenging task in materials research. Heteroatom-doped carbonaceous materials are increasingly recognized as powerful metal-free catalysts, often demonstrating catalytic performance comparable to or even surpassing metal-based alternatives. This is attributed to their tunable physicochemical properties, tailorable structural features, and environmentally friendly profile. In a straightforward single-step synthetic approach, we utilized wood as an eco-friendly and renewable carbon source, in conjunction with a poly(ionic liquid) as a heteroatom source and pore-making agent. The combination of both biobased and synthetic polymers in this method yielded sustainable, high-performance catalysts characterized by enhanced stability and reusability. The inclusion of sacrificial pore-inducing templates resulted in the formation of abundant defects serving as catalytically active sites, while codoping with boron and nitrogen further enhanced these sites, significantly impacting catalytic activities, as established by peroxidase-like activity in this study. The optimized codoped porous carbon membrane exhibited excellent peroxidase-type activity and catalyzed the oxidation reaction of 3,3',5,5'-tetramethylbenzidine by hydrogen peroxide. This high activity was largely due to the dual heteroatom codoping effect and the mixed micro/macroporous structure of the membrane. Our work presents a versatile and eco-friendly method for fabricating hierarchically porous B/N codoped carbon membranes, offering a manageable, convenient, and recyclable biomimetic artificial enzyme with superior catalytic capabilities. This work introduces a practical and robust colorimetric method that can be used in healthcare and environmental rehabilitation.

Dopamine-Carbonized Coating PtCo Catalyst with Enhanced Durability toward the Oxygen Reduction Reaction

Stability is the main challenge for the application of PtCo catalysts because Co tends to leach during the electrochemical reaction. Herein, we immerse and adsorb dopamine to densely coat Pt0.8Co0.2 particles and subsequently thermally carbonize the coating into few-layer nitrogen-doped graphene to produce Pt0.8Co0.2@NC. This coating effectively hinders direct contact between Pt0.8Co0.2 particles and the electrolyte, thereby enhancing the stability of the catalyst by preventing Ostwald ripening and suppressing competitive adsorption of toxic species, while also bolstering its antipoisoning ability. Experimental results indicate that the thin coating does not compromise the oxygen reduction reaction activity of the catalyst, showcasing a half-wave potential of 0.81 V in alkaline electrolytes. Spectroscopic results suggest that a strong bonding interaction between Pt and the pyridinic N of N-doped graphene contributes to the generation of a dense coating. The coating layer does not affect the four-electron reaction mechanism of the Pt0.8Co0.2 alloy, and the coordinatively unsaturated carbon atoms on Pt0.8Co0.2@NC serve as active oxygen reduction reaction centers.

Robust Nitrogen-Doped Microporous Carbon via Crown Ether-Functionalized Benzoxazine-Linked Porous Organic Polymers for Enhanced CO2 Adsorption and Supercapacitor Applications

Nitrogen-doped carbon materials, characterized by abundant microporous and nitrogen functionalities, exhibit significant potential for carbon dioxide capture and supercapacitors. In this study, a class of porous organic polymer (POP) were successfully synthesized by linking Cr-TPA-4BZ-Br4 and tetraethynylpyrene (Py-T). The model benzoxazine monomers of Cr-TPA-4BZ and Cr-TPA-4BZ-Br4 were synthesized using the traditional three-step method [involving CH═N formation, reduction by NaBH4, and Mannich condensation]. Subsequently, the Sonogashira coupling reaction connected the Cr-TPA-4BZ-Br4 and Py-T monomers, forming Cr-TPA-4BZ-Py-POP. The successful synthesis of Cr-TPA-4BZ-Br4 and Cr-TPA-4BZ-Py-POP was confirmed through various analytical techniques. After verifying the successful synthesis of Cr-TPA-4BZ-Py-POP, carbonization and KOH activation procedures were conducted. These crucial steps led to the formation of poly(Cr-TPA-4BZ-Py-POP)-800, a carbon material with a structure akin to graphite. In practical applications, poly(Cr-TPA-4BZ-Py-POP)-800 exhibited a noteworthy CO2 adsorption capacity of 4.4 mmol/g, along with specific capacitance values of 397.2 and 159.2 F g-1 at 0.5 A g-1 (measured in a three-electrode cell) and 1 A g-1 (measured in a symmetric coin cell), respectively. These exceptional dual capabilities stem from the optimal ratio of heteroatom doping. The outstanding performance of poly(Cr-TPA-4BZ-Py-POP)-800 microporous carbon holds significant promise for addressing contemporary energy and environmental challenges, making substantial contributions to both sectors.

Work Function-Guided Electrocatalyst Design

The development of high-performance electrocatalysts for energy conversion reactions is crucial for advancing global energy sustainability. The design of catalysts based on their electronic properties (e.g., work function) has gained significant attention recently. Although numerous reviews on electrocatalysis have been provided, no such reports on work function-guided electrocatalyst design are available. Herein, a comprehensive summary of the latest advancements in work function-guided electrocatalyst design for diverse electrochemical energy applications is provided. This includes the development of work function-based catalytic activity descriptors, and the design of both monolithic and heterostructural catalysts. The measurement of work function is first discussed and the applications of work function-based catalytic activity descriptors for various reactions are fully analyzed. Subsequently, the work function-regulated material-electrolyte interfacial electron transfer (IET) is employed for monolithic catalyst design, and methods for regulating the work function and optimizing the catalytic performance of catalysts are discussed. In addition, key strategies for tuning the work function-governed material-material IET in heterostructural catalyst design are examined. Finally, perspectives on work function determination, work function-based activity descriptors, and catalyst design are put forward to guide future research. This work paves the way to the work function-guided rational design of efficient electrocatalysts for sustainable energy applications.

Recent Progress on Porous Carbons for Carbon Capture

High emission of carbon dioxide (CO2) has caused CO2 levels to reach more than 400 ppm in air and led to a serious climate problem. In addition, in confined spaces such as submarines and aircraft, the CO2 concentration increase in the air caused by human respiration also affects human health. In order to protect the environment and human health, the search for high-performance adsorbents for carbon capture from high and low concentration gas is particularly important. Porous carbon materials, possessing the advantages of low cost and renewability, have set off a boom in the research of porous adsorbents, which have the opportunity to be utilized on a large scale for industrial carbon capture in the future. In this review, we summarize the recent research progress of porous carbons for carbon capture from flue gas and directly from air in the last five years, including activated carbon (AC), heteroatom-modified porous carbon, carbon molecular sieves (CMS), and other porous carbon materials, with a focus on the effects of temperature, water content, and gas flow rate of industrial flue gas on the performance of porous carbon adsorbents. We summarize the preparation strategies of various porous carbons and seek environmental friendly porous carbon materials preparation strategies under the premise of improving the CO2 adsorption capacity and selectivity of porous carbon adsorbents. Based on the effects of real industrial flue gas on adsorbents, we provide new ideas and evaluation methods for the development and preparation of porous carbon materials.

Unlocking High-Current Performance in Silicon Anode: Synergistic Phosphorus Doping and Nitrogen-Doped Carbon Encapsulation to Enhance Lithium Diffusivity

The silicon (Si) offers enormous theoretical capacity as a lithium-ion battery (LIB) anode. However, the low charge mobility in Si particles hinders its application for high current loading. In this study, ball-milled phosphorus-doped Si nanoparticles encapsulated with nitrogen-doped carbon (P-Si@N-C) are employed as an anode for LIBs. P-doped Si nanoparticles are first obtained via ball-milling and calcination of Si with phosphoric acid. N-doped carbon encapsulation is then introduced via carbonization of the surfactant-assisted polymerization of pyrrole monomer on P-doped Si. While P dopant is required to support the stability at high current density, the encapsulation of Si particles with N-doped carbon is influential in enhancing the overall Li+ diffusivity of the Si anode. The combined approaches improve the anode's Li+ diffusivity up to tenfold compared to the untreated anode. It leads to exceptional anode stability at a high current, retaining 87 % of its initial capacity under a large current rate of 4000 mA g-1. The full-cell comprising P-Si@N-C anode and LiFePO4 cathode demonstrates 94 % capacity retention of its initial capacity after 100 cycles at 1 C. This study explores the effective strategies to improve Li+ diffusivity for high-rate Si-based anode.

Fe3O4@nitrogen-doped carbon core-double shell nanotubes as a novel and efficient nanosorbent for ultrasonic assisted dispersive magnetic solid phase extraction of heterocyclic pesticides from environmental soil and water samples

Fe3O4@nitrogen-doped carbon core-double shell nanotubes (Fe3O4@N-C C-DSNTs) were successfully synthesized and applied as a novel nanosorbent in ultrasonic assisted dispersive magnetic solid phase extraction (UA-DMSPE) of tribenuron-methyl, fenpyroximate, and iprodione. Subsequently, corona discharge ion mobility spectrometry (CD-IMS) was employed for the detection of the extracted analytes. Effective parameters on the extraction recovery percentage (ER%) were systematically investigated and optimized. Under optimal conditions, UA-DMSPE-CD-IMS demonstrated remarkable linearity in different ranges within 1.0 - 700 ng mL-1 with correlation coefficients exceeding 0.993, repeatability values below 6.9%, limits of detection ranging from 0.30 to 0.90 ng mL-1, high preconcentration factors (418 - 435), and ER% values (83 - 87%). The potential of the proposed method was further demonstrated by effectively determining the targeted pesticides in various environmental soil and water samples, exhibiting relative recoveries in the range 92.1 - 102%.

One-step preparation of magnetic N-doped sodium alginate-based porous carbon and efficient adsorption of bisphenol A

To resourcefully utilize algal biomass and effectively remove bisphenol A (BPA) from water, sodium alginate (SA) was prepared as the nitrogen-doped magnetic porous carbon material (SAC/N/Fe) with well-developed pore structure according to a one-step method using K2CO3, melamine, Fe(NO3)3·9H2O as the activator, nitrogen dopant, and magnetic precursor, respectively, in this study. The best product, SAC/N/Fe-0.2, was obtained by adjusting the mass ratio of raw materials, and its specific surface area and pore volume were 2240.65 m2 g-1 and 1.44 cm3 g-1, respectively, with a maximum adsorption capacity of 1248.23 mg g-1 for BPA at 308 K. SEM, XRD, XPS, VSM, and FT-IR characterization confirmed that the iron was successfully doped, giving the porous carbon a magnetic separation function. The adsorption process of BPA was more consistent with the Langmuir model and the proposed secondary kinetics, and the adsorption effect was stable and efficient in a wide pH range and under the interference of different metal ions. At the same time, the porous carbon was easy to separate and recover with good regeneration performance.

Tuning the Coordination Environment of Carbon-Based Single-Atom Catalysts via Doping with Multiple Heteroatoms and Their Applications in Electrocatalysis

Carbon-based single-atom catalysts (SACs) are considered to be a perfect platform for studying the structure-activity relationship of different reactions due to the adjustability of their coordination environment. Multi-heteroatom doping has been demonstrated as an effective strategy for tuning the coordination environment of carbon-based SACs and enhancing catalytic performance in electrochemical reactions. Herein, recently developed strategies for multi-heteroatom doping, focusing on the regulation of single-atom active sites by heteroatoms in different coordination shells, are summarized. In addition, the correlation between the coordination environment and the catalytic activity of carbon-based SACs are investigated through representative experiments and theoretical calculations for various electrochemical reactions. Finally, concerning certain shortcomings of the current strategies of doping multi-heteroatoms, some suggestions are put forward to promote the development of carbon-based SACs in the field of electrocatalysis.

A zeolite templating method for fabricating edge site-enriched N-doped carbon materials

N-doped carbon materials have attracted considerable attention as highly functional materials because nitrogen doping distorts the carbon lattice, changes the charge density, and introduces additional defects. Among various positions of N atoms in N-doped carbon compounds, pyridinic-N, pyrrolic-N, and valley-N, which are doped at edge sites, exhibit specific electrocatalytic activities during the oxygen reduction reaction (ORR). However, it is difficult to selectively introduce these N atoms into a carbon matrix because the synthesis procedure typically includes high-temperature heat treatment. In this study, we applied a zeolite templating method to synthesize edge site-rich N-doped carbon materials. The sample fabricated using a zeolite template possessed high concentrations of pyridinic-N and valley-N atoms, demonstrating a significantly higher ORR catalytic activity than the sample synthesized without a zeolite template. Additional experiments conducted using various zeolites confirmed the positive effect of N-doped carbons on the ORR catalytic performance. This work demonstrated that the zeolite templating method not only increased the specific surface area and the number of active sites but also selectively created edge sites and improved the quality of the active sites.

Iron carbide nanoparticles supported on an N-doped carbon porous framework as a bifunctional material for electrocatalytic oxygen reduction and supercapacitors

Highly active and durable bifunctional materials are of pivotal importance for energy conversion and storage devices, yet a comprehensive understanding of their geometric and electronic influence on electrochemical activity is urgently needed. Fe-N-C materials with physical and chemical structural merits are considered as one of the promising candidates for efficient oxygen reduction reaction electrocatalysts and supercapacitor electrodes. Herein, Fe₃C nanoparticles supported on a porous N-doped carbon framework (denoted as Fe₃C/PNCF) were readily prepared by one-step chemical vapor deposition under the assistance of a NaCl salt template. The experiment results revealed that the as-synthesized Fe₃C/PNCF nanocomposites successfully displayed attractive electrocatalytic oxygen reduction reaction (ORR) activity comparable to that of the Pt/C catalyst (E_1/2 of 0.84 V and 0.83 V, respectively), and a superior capacitance of 385.3 F g^-1 under 1 A g^-1 for a supercapacitor. It's proposed that the increased pyridinic and graphitic N coordination on the hydrophilic porous framework provides more electrochemical active surface area for the storage and transport of electrolyte ions. Additionally, an appropriate d-band center created by the optimized adsorption function endows Fe₃C/PNCF with excellent electrochemical properties. The results confirmed that the integration strategy of porous heterogeneous structure and accessible active sites balanced the complex relationship between geometry, electronic structure, and electrochemical activity. Our research provides a facile approach for fabricating multi-functional nanomaterials applicable in both ORR and supercapacitors in the future.

Effect of Modifying Carbon Materials with Metal Phthalocynines and Palladium on Their Catalytic Activity in ORR

Bimetallic catalysts based on multi-walled carbon nanotubes (MWCNT), graphene oxide (GO) and ultradispersed diamonds (UDD) supports for the process of electroreduction of oxygen from alkaline electrolyte were obtained using high-temperature synthesis. The materials were characterized by low-temperature nitrogen adsorption, Raman spectroscopy, scanning electron microscopy and X-ray structure analysis. The synthesized bimetallic catalysts contain meso- and micropores. Based on the study by Raman spectroscopy, it is shown that high-temperature synthesis of MWCNT with metal phthalocyanines leads to doping of this material with nitrogen and the appearance of significant defects in the structure. Carbon nanotube-based catalysts showed enhanced activity compared to other carbon materials. Moreover, bimetallic catalysts based on cobalt phthalocyanine and palladium (MWCNT_CoPc_Pd) are characterized by higher activity on all carbon supports compared to materials contain on copper and palladium. The specific current density in the diffusion region of the MWCNT_CoPc_Pd catalyst is comparable to a commercial platinum electrode (Pt(20%)/C) and equals to 2.65 mA/cm2. The area of the electrochemically active surface of all the obtained catalysts was calculated from the CV data in a nitrogen atmosphere. The MWCNT_CoPc_Pd catalyst is characterized by high corrosivity: after 2500 revolutions, the current density in the diffusion region decreases by 7%, and, also, an increase in the values of E1/2 and Eonset is observed.

Engineering at Subatomic Scale: Achieving Selective Catalytic Pathways via Tuning of the Oxidation States in Functionalized Single-Atom Quantum Catalysts

Regulating the catalytic pathways of single-atom sites in single atom catalysts (SACs) is an exciting debate at the moment, which has redirected the research towards understanding and modifying the single-atom catalytic sites through various strategies including altering the coordination environment of single atom for desirable outcomes as well as increasing their number. One useful aspect concerning the tunability of the catalytic pathways of SACs, which has been overlooked, is the oxidation state dynamics of the single atoms. In this study, iron single-atoms (FeSA) with variable oxidation states, dependent on the precursors, are harnessed inside a nitrogen-rich functionalized carbon quantum dots (CQDs) matrix via a facile one-step and low-temperature synthesis process. Dynamic electronic properties are imparted to the FeSAs by the simpler carbon dots matrix of CQDs in order to achieve the desired catalytic pathways of reactive oxygen species (ROS) generation in different environments, which are explored experimentally and theoretically for an in-depth understanding of the redox chemistry that drives the alternative catalytic pathways in FeSA@CQDs. These alternative and oxidation state-dependent catalytic pathways are employed for specific as well as cascade-like activities simulating natural enzymes as well as biomarkers for the detection of cancerous cells.

Progress in the use of organic potassium salts for the synthesis of porous carbon nanomaterials: microstructure engineering for advanced supercapacitors

Porous carbon nanomaterials (PCNs) are widely applied in energy storage devices. Traditionally, PCNs were mainly synthesized by activation and templating methods, which are time-consuming, tedious, corrosive and relatively high cost. Therefore, the development of easier and greener methods to produce PCNs is of great significance. Recently, organic potassium salts (OPSs) emerged as versatile reagents for synthesizing PCNs. The OPS-based synthesis of PCNs can avoid the use of large amounts of corrosive chemical agents. Potassium carbonate generated in situ from the decomposition of OPSs could serve as both a green activation agent and a water-removable template to produce nanopores. Potassium oxide and potassium formed at higher temperature could generate additional porosity, contributing to a highly porous architecture. The carbon-rich organic moiety could function as a carbon precursor and chemical blowing agent. This review aims to elucidate the multifunctionality of OPSs in the synthesis of PCNs and the capacitive performance of the corresponding PCNs. To this end, recent progress on the capacitive performance of PCNs synthesized from OPSs is summarized. This review provides constructive viewpoints for the cost-effective and green synthesis of PCNs with the aid of OPSs for application in supercapacitors.

Nitrogen-doped carbon nanotubes enhanced Fenton chemistry: Role of near-free iron(III) for sustainable iron(III)/iron(II) cycles

The sluggish kinetics of Fe(II) recovery strongly impedes the scientific progress of Fenton reaction (Fe(II)/H₂O₂) towards practical application. Here, we propose a novel mechanism that metal-free nitrogen-doped carbon nanotubes (NCNT) can enhance Fenton chemistry with H₂O₂ as electron donors by elevating the oxidation potential of Fe(III). NCNT remarkably promotes the circulation of Fe(III)/Fe(II) to produce hydroxyl radical (^•OH) with excellent stability for multiple usages (more than 10 cycles) in the NCNT/Fe(III)/H₂O₂ system. Although carbonyl on NCNT can act as the electron supplier for Fe(III) reduction, the behavior of NCNT is distinct from common reductants such as hydroxylamine and boron. Electrochemical analysis and density functional theory calculation unveil that nitrogen sites of NCNT can weakly bind with Fe(III) to elevate the oxidation potential of Fe(III) (named near-free Fe(III), primarily FeOH²⁺) at pH ranging from 2.0 to 4.0. Without inputs of external stimulations or electron sacrificers, near-free Fe(III) can promote H₂O₂ induced reduction of Fe(III) to initiate Fenton chain reactions for long-lasting generation of ^•OH. To our delight, it is a common property of N-doped carbon materials (e.g., graphene, carbon nanofibers, and acetylene black), our research thus provides a novel, sustainable, and green strategy for promoting Fenton chemistry.

N-doped nonalternant aromatic belt via a six-fold annulative double N-arylation

The design and synthesis of nitrogen (N)-doped molecular nanocarbons are of importance since N-doped nanocarbons have received significant attention in materials science. Herein, we report the synthesis and X-ray crystal structure of a nitrogen-inserted nonalternant aromatic belt. The palladium-catalyzed six-fold annulative double N-arylation provided an aromatic belt bearing six nitrogen atoms in one step from cyclo[6]paraphenylene-Z-ethenylene, the precursor of the (6,6)carbon nanobelt. The C_3i-symmetric structure of the aromatic belt in the solid state was revealed using X-ray crystallography. The multistep (electro)chemical oxidation behavior of the belt, which was facilitated by the six p-methoxyaniline moieties, was studied, and a stable dication species was successfully identified by X-ray crystallography. The present study not only shows the unique structure and properties of the N-doped nonalternant aromatic belt but also expands the scope of accessibility of synthetically difficult belt molecules by the conventional intramolecular contraction pathway.

Nitrogen-doped nonalternant aromatic belt was synthesized via palladium-catalyzed six-fold annulative double N-arylation reaction. The highly symmetric structure and multistep oxidation behavior of the N-belt were confirmed.

In situ fabrication of nitrogen doped graphitic carbon networks coating for high-performance extraction of pyrethroid pesticides

The tailor-prepare solid phase microextraction (SPME) coatings with stable and excellent properties to effectively extract analytes from sample matrix still remains a challenge. Herein, a nitrogen doped graphitic carbon networks (NG-CNTW) coated fiber was fabricated by direct carbonization of nanosized ZIF-67 crystals (nano-ZIF-67) that grown on stainless steel wire. The NG-CNTW coated fiber coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS) was applied for enrichment and determination of pyrethroids. The NG-CNTW coating exhibited high surface area and hierarchical porous structures that facilitate diffusion and accessibility of target molecules. Simultaneously, the nitrogen doped and highly graphitic structures endow the coating with high adsorption affinity for aromatic compounds. Under optimum conditions, the SPME-GC-MS/MS method presented wide range of linearity performance (0.08-200.0 ng g^-1), low limits of detection (0.02-0.5 ng g^-1) and good repeatability (RSD < 9.6%) for 8 kinds of pyrethroids. Furthermore, the proposed method was successfully applied in the determination of pyrethroids in grape and cauliflower samples, as the results were in the range of 3.16-15.06 ng g^-1and 2.08-9.29 ng g^-1, respectively. This work not only provides a new method by fabricating carbon nanomaterial coatings in situ derived from MOFs, but also shows great potential of MOFs derivative materials in environmental analysis field.

Design and Synthesis Strategies: 2D Materials for Electromagnetic Shielding/Absorbing

Two-dimensional (2D) materials possess special physical and chemical properties. They have been proved to have potential application advantage in the microwave absorption (MA) and electromagnetic interference (EMI) shielding. Particularly, they exhibit positive shielding and absorbing response to EMI. Here, the research progress of preparation, electromagnetic performance and microwave shielding/absorbing mechanisms of 2D composite materials are introduced. Effective preparation routes including introducing heteroatoms, constructing unique structures and 2D composite materials are described. Furthermore, the application prospects and challenges for the development of novel EMI materials are expatiated.

Microporous Carbon Nitride (C3 N5.4 ) with Tetrazine based Molecular Structure for Efficient Adsorption of CO2 and Water

Mesoporous carbon nitrides with C₃ N₅ and C₃ N₆ stoichiometries created a new momentum in the field of organic metal-free semiconductors owing to their unique band structures and high basicity. Here, we report on the preparation of a novel graphitic microporous carbon nitride with a tetrazine based chemical structure and the composition of C₃ N_5.4 using ultra-stable Y zeolite as the template and aminoguanidine hydrochloride, a high nitrogen-containing molecule, as the CN precursor. Spectroscopic characterization and density functional theory calculations reveal that the prepared material exhibits a new molecular structure, which comprises two tetrazines and one triazine rings in the unit cell and is thermodynamically stable. The resultant carbon nitride shows an outstanding surface area of 130.4 m²  g^-1 and demonstrates excellent CO₂ adsorption per unit surface area of 47.54 μmol m^-2 , which is due to the existence of abundant free NH₂ groups, basic sites and microporosity. The material also exhibits highly selective sensing over water molecules (151.1 mmol g^-1 ) and aliphatic hydrocarbons due to its unique microporous structure with a high amount of hydrophilic nitrogen moieties and recognizing ability towards small molecules.

Efficient Reduction of Selenite to Elemental Selenium by Liquid-Phase Catalytic Hydrogenation Using a Highly Stable Multiwalled Carbon Nanotube-Supported Pt Catalyst Coated by N-Doped Carbon

A stable catalyst, Pt/carbon nanotube (CNT) coated with N-doped carbon (Pt/CNT@CN), was designed to reduce selenite (Se(IV)) in water to elemental selenium by liquid-phase catalytic hydrogenation. Commercial Pt/C, pristine Pt/CNT, and carbon-coated Pt/CNT (Pt/CNT@C) were used for benchmarking. The Pt particles in Pt/CNT@CN were completely embedded beneath the coatings to minimize leaching and were not easily accessible to Se(IV). However, Schottky-Mott-type metal-carbon junctions that activate H2 were formed on the coated catalyst, facilitating effective reduction of Se(IV). The initial activity of Pt/CNT@CN (900.5 mg L-1 gcat-1 h-1) was two times higher than that of commercial Pt/C (448.6 mg L-1 gcat-1 h-1). The commercial Pt/C and uncoated Pt/CNT lost their initial activities during reuse and were almost inactive after 10 cycles due to significant Pt leaching (>90%) during the reaction and acid-washing regeneration processes. Pt/CNT@CN maintained 33% of the initial activity after the first cycle and stabilized over the following 9 cycles due to effective protection of Pt particles by carbon coatings. After 10 cycles, the activity of Pt/CNT@CN was over 20 times higher than that of Pt/C and uncoated Pt/CNT. Overall, catalytic hydrogenation using carbon-coated-supported Pt catalysts is an effective and promising approach to remove Se(IV) in water.

Ultrafine self-N-doped porous carbon nanofibers with hierarchical pore structure utilizing a biobased chitosan precursor

Ultrafine porous carbon nanofiber network with ~40 nm fiber diameter is realized for the first time utilizing a biobased polymer as carbon precursor. A simple one-step carbonization procedure is applied to convert the electrospun chitosan/poly(ethylene oxide) nanofibers to self-N-doped ultrafine hierarchically porous carbon nanofiber interconnected web. The pore formation process is governed by the immiscible nature of the two polymers and the sacrificial character of poly(ethylene oxide) with low carbon yield at the carbonization temperature (800 °C). The obtained porous scaffold has a high specific surface area (564 m² g^-1), high micro (0.22 cm³ g^-1) as well as meso/macropore volume (0.28 cm³ g^-1). Structural analysis indicates high graphitic content and the existence of turbostratic carbon typical for carbon fibers derived from otherwise synthetic polymer precursors. X-ray photoelectron spectroscopy confirms the presence of an N-doped structure with dominating graphitic N, together with a smaller amount of pyridinic N. The prepared electrode exhibits good electrochemical performance as a supercapacitor device. The excellent charge storage characteristics are attributed to the unique ultrafine hierarchical nanoarchitecture and the interconnected N-doped carbon structure. This green material holds great promise for the realization of more sustainable high-performance energy storage devices.

Nitrogen-Doped Carbons Derived from Imidazole-Based Cross-Linked Porous Organic Polymers

Nitrogen-doped and heteroatom multi-doped carbon materials are considered excellent metal-free catalysts, superior catalyst supports for transition metal particles and single metal atoms (single-atom catalysts), as well as efficient sorbents for gas- and liquid-phase substances. Acid-catalyzed sol-gel polycondensation of hydroxybenzenes with heterocyclic aldehydes yields cross-linked thermosetting resins in the form of porous organic polymers (i.e., organic gels). Depending on the utilized hydroxybenzene (e.g., phenol, resorcinol, phloroglucinol, etc.) and heterocyclic aldehyde variety of heteroatom-doped organic polymers can be produced. Upon pyrolysis, highly porous and heteroatom-doped carbons are obtained. Herein, polycondensation of phloroglucinol with imidazole-2-carboxaldehyde (and other, similar heterocyclic aldehydes with two heteroatoms in the aromatic ring) is utilized to obtain porous, N-doped organic and carbon gels with N-content of up to 16.5 and 12 wt.%, respectively. Utilization of a heterocyclic aldehyde with two different heteroatoms yields dually-doped carbon materials. Upon pyrolysis, the porous polymers yield ultramicroporous N-doped and N,S co-doped carbons with specific surface areas of up to 800 m2g-1. The influence of the initial composition of reactants and the pyrolysis temperature on the structure and chemical composition of the final doped organic and carbon materials is studied in detail.

Tuning the Nature of N-Based Groups From N-Containing Reduced Graphene Oxide: Enhanced Thermal Stability Using Post-Synthesis Treatments

The synthesis of N-containing graphene derivatives by functionalization and doping of graphene oxide (GO) has been widely reported as an alternative to tune both their chemical and physical properties. These materials are of interest for a wide range of applications, including biomedicine, sensors, energy, and catalysis, to name some. Understanding the role of the nature, reactivity, concentration, and distribution of the N-based species, would pave the way towards the design of synthetic routes to obtain improved materials for specific applications. The N-groups can be present either as aliphatic fractions (amides and amines) or becoming part of the planar conjugated lattice (N-doping). Here, we have modified the distribution of N-based moieties present in N-containing RGO samples (prepared by ammonolysis of GO) and evaluated the role of the concentration and nature of the species in the thermal stability of the materials once thermally annealed (500–1050 °C) under inert environments. After these post-synthesis treatments, samples underwent marked structural modifications that include the elimination and/or transformation of N-containing fractions, which might account for the observed enhanced thermal stability. It is remarkable the formation of pyridinic N-oxide species, which role in the properties of N-containing graphene derivatives has been barely reported. The presence of this fraction is found to confer an enhanced thermal stability to the material.

The Intrinsic Nature of Persulfate Activation and N-Doping in Carbocatalysis

Persulfates activation by carbon nanotubes (CNT) has been evidenced as nonradical systems for oxidation of organic pollutants. Peroxymonosulfate (PMS) and peroxydisulfate (PDS) possess discrepant atomic structures and redox potentials, while the nature of their distinct behaviors in carbocatalytic activation has not been investigated. Herein, we illustrated that the roles of nitrogen species in CNT-based persulfate systems are intrinsically different. In PMS activation mediated by nitrogen-doped CNT (N-CNT), surface chemical modification (N-doping) can profoundly promote the adsorption quantity of PMS, consequently elevate potential of derived nonradical N-CNT-PMS* complexes, and boost organic oxidation efficiency via an electron-transfer regime. In contrast, PDS adsorption was not enhanced upon incorporating N into CNT due to the limited equilibrium adsorption quantity of PDS, leading to a relatively lower oxidative potential of PDS/N-CNT system and a mediocre degradation rate. However, with equivalent persulfate adsorption on N-CNT at a low quantity, PDS/N-CNT exhibited a stronger oxidizing capacity than PMS/N-CNT because of the intrinsic higher redox potential of PDS than PMS. The oxidation rates of the two systems were in great linearity with the potentials of carbon-persulfate* complexes, suggesting N-CNT activation of PMS and PDS shared the similar electron-transfer oxidation mechanism. Therefore, this study provides new insights into the intrinsic roles of heteroatom doping in nanocarbons for persulfates activation and unveils the principles for a rational design of reaction-oriented carbocatalysts for persulfate-based advanced oxidation processes.