Nitrogen-doped Carbon Nanomaterials Research Articles

Effect of NH3 addition on the preparation of nitrogen-doped carbon nanomaterials by flame synthesis method

Effect of NH3 addition on the preparation of nitrogen-doped carbon nanomaterials by flame synthesis method

Nitrogen-doped carbon nanostructures embedded with Fe-Co-Cr alloy based nanoparticles as robust electrocatalysts for Zn-air batteries

Two types of nitrogen-doped carbon nanomaterials embedded with novel transition metal-based medium entropy alloy nanoparticles are synthesized via a simple, scalable, and cost-effective single-step pyrolysis route, by varying the stoichiometric ratio of iron and cobalt. The samples predominantly have bamboo-shaped nanotube morphology with some globular structures. The globules are core-shell type nanoparticles, i.e., containing the metallic-alloy nanoparticles encapsulated by the graphitic shell and embedded within defective amorphous-type carbon matrix. The electrochemical studies using these samples are conducted in basic medium to explore their potential for Zn-air batteries. Electrochemical measurements are carried out in 1 M and 0.1 M KOH, respectively, on a rotating disk electrode setup. The sample with higher cobalt content performs better for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) with regards to lower onset potential, lower Tafel slope and lower activation energy. However, the stability towards OER is better for the sample with higher iron content. The sample with higher cobalt content shows a better overall oxygen electrochemistry compared to the one with higher iron content, is at par with several state-of art electrocatalysts and is utilized for fabrication of a prototype Zn-air battery demonstrating its practical applicability.

Preparation of a three-dimensional bimetallic CoFex/ N-doped carbon nanomaterial used as modified electrode for the efficient electrochemical detection of l-tyrosine

The rapid and sensitive detection of l-tyrosine (L-Tyr) has become a vital issue in the fields of medicine and clinical analysis as lack or overdose of L-Tyr in human body could cause disease. In this paper, a three-dimensional cubic CoFex/N-doped carbon nanocomposite (CoFex-N,C) material was prepared by high-temperature calcination of CoFe-Prussian blue analogues (CoFe-PBA) in N2 atmosphere and then modified on glass carbon electrode (GCE) for L-Tyr detection. The prepared CoFex/N,C nanocomposite not only inherits the uniform morphology, and unique bimetallic active center of CoFe-PBA, but also possesses the high conductivity and large ratio area of nitrogen-doped carbon nanomaterials. Under optimum conditions, the CoFex/N,C nanocomposite electrode presented a broad linear scope of 0.8–354.84 μM, a low detection limit of 0.06 μM (S/N = 3), good anti-interference ability, and very high stability. In addition, the acceptable recoveries were obtained for real sample analysis.

Titanium metal–organic framework-derived nanocrystalline TiO2-supported nitrogen-doped carbon nanostructures as highly efficient antibiotic adsorbents

Metal-organic frameworks (MOFs) are explored extensively as a distinctive precursor for producing porous metal oxide-supported nitrogen-doped carbon nanomaterials. MOF-derived materials can offer tailored porosity, structure, and elemental composition so they are gaining prominence as a new-generation adsorbent for emerging antibiotic contaminant removal in aqueous solutions. In this study, we demonstrate the fabrication of nanocrystalline titanium dioxide-supported nitrogen-doped carbon nanostructures (TiO2@NC) obtained from a titanium metal–organic framework (NH2-MIL-125(Ti)) as a starting precursor. When applied as an adsorbent, TiO2@NC nanospheres efficiently removed high concentrations of tetracycline (TC) in aqueous solutions. The TiO2@NC adsorption process obeyed the Langmuir model and pseudo-second-order kinetics. The optimum adsorption capacity of the TiO2@NC nanospheres is estimated to be 1187.08 mg g−1, which is remarkably superior to several previously reported adsorbents for TC removal. The TiO2@NC adsorbent performs efficiently in a broad pH range (3–8) and shows excellent stability. The post-adsorption characterization signifies the crucial role of the adsorbent's nitrogen sites, surface area, and porous sphere morphology in achieving efficient TC removal through hydrogen bonding, π-π interactions, and surface complexation.

Structural Phase Transition of Mo2C for Enhancing Electrochemical Sensing of Hydrogen Peroxide

Regulating the electrocatalytic activity of metal carbides is the key to achieving highly sensitive electrochemical sensing. Molybdenum carbide (Mo2C) nanoparticles were anchored on the surface of nitrogen doped carbon nanomaterials (NC) through polymerization and calcination. By adjusting the calcination conditions, the crystal phase structure of Mo2C nanoparticles was successfully regulated, and two kinds of Mo2C nanoparticles with different crystal phase structure were obtained. The effect of the crystal structure of Mo2C on the electrocatalytic reduction of H2O2 was investigated. The results show that Mo2C with the hexagonal structure (H-Mo2C) has higher electrocatalytic activity for H2O2 reduction reaction, and the sensor based on H-Mo2C/NC could detect H2O2 in a wide linear range from 0.02 mM to 7.1 mM with a high sensitivity of 282.9 μA·mM−1·cm−2 and a low detection limit of 0.45 μM (S/N = 3). Moreover, the sensor can also accurately determine the content of H2O2 in disinfectant and milk samples. This study demonstrated Mo2C with the hexagonal structure as an effective sensing material for H2O2.

Mesoporous Nanocarbon-Based PGM-Free Electrocatalysts Prepared with MgO-Template for Anion-Exchange Membrane Fuel Cell

Anion-exchange membrane fuel cells (AEMFCs) are receiving more and more attention as a viable alternative to proton-exchange membrane fuel cells, because they permit the use of precious metal-free electrocatalysts for oxygen reduction reaction (ORR), such as transition metal and nitrogen-doped carbon nanomaterials, containing MNx ORR-active sites.1 However, in addition to active sites, the structure of the catalyst support material is also essential to ensure efficient mass transfer in the catalyst layer, especially in AEMFCs where mass transport issues are caused by the higher loading that PGM-free catalysts require.2 Easily removable inorganic particles like MgO offer a sustainable alternative to silica-based templates to achieve optimal porosity. The catalyst materials can be created via a template-directed synthesis, by pyrolyzing a carbon precursor with MgO or other thermally unstable magnesium compounds like acetate or citrate. The precursors break down by heat-treatment to create MgO nanoparticles, which are subsequently dissolved using dilute acids such as HCl.3 Unlike with silica-based templates, scaling up the method is significantly easier and more sustainable since no corrosive chemicals like hydrofluoric acid are used in the process.Using HoneyolTM (a mixture of alkylresorcinols) as the carbon source and magnesium acetate as the template precursor, we demonstrate a straightforward MgO template-assisted approach for obtaining mesoporous nitrogen and transition metal co-doped nanocarbon catalysts for AEMFCs.4 The effect of the mass ratio of Honeyol to magnesium acetate on the porosity and electrocatalytic activity of the catalysts was studied. The addition of Mg acetate increases the surface area of the materials, the prepared materials are mostly mesoporous with a broad pore size distribution. The catalyst with the highest electrocatalytic activity toward the ORR was synthesized using a 2:1 mass ratio of Honeyol to Mg acetate. The bimetallic FeCoNC-MgOAc catalyst displayed the highest electrocatalytic activity surpassing the benchmark Pt/C catalyst, showing a E 1/2 value of -0.14 V vs. SCE in the RDE test. The catalyst demonstrated excellent stability, only a minor decay was observed after 15,000 potential cycles (ΔE 1/2 = 10 mV). In AEMFC as the cathode catalyst, FeCoNC-MgOAc reached a peak power density of 0.92 W cm-2 (Figure 1), more than twice higher as the untemplated FeCoNC catalyst and slightly surpassing the benchmark Pt/C (20 wt.%). The catalyst also displayed promising durability in AEMFC with a minor voltage degradation rate of 0.0017 V h–1 after 24 h. References Osmieri, L.; Pezzolato, L.; Specchia, S. Recent Trends on the Application of PGM-Free Catalysts at the Cathode of Anion Exchange Membrane Fuel Cells. Current Opinion in Electrochemistry 2018, 9, 240–256.Dekel, D. R. Review of Cell Performance in Anion Exchange Membrane Fuel Cells. Journal of Power Sources 2018, 375, 158–169.Morishita, T.; Tsumura, T.; Toyoda, M.; Przepiórski, J.; Morawski, A. W.; Konno, H.; Inagaki, M. A Review of the Control of Pore Structure in MgO-Templated Nanoporous Carbons. Carbon 2010, 48 (10), 2690–2707.Kisand, K.; Sarapuu, A.; Douglin, J. C.; Kikas, A.; Treshchalov, A.; Käärik, M.; Piirsoo, H.-M.; Paiste, P.; Aruväli, J.; Leis, J.; Kisand, V.; Tamm, A.; Dekel, D. R.; Tammeveski, K. Templated Nitrogen-, Iron-, and Cobalt-Doped Mesoporous Nanocarbon Derived from an Alkylresorcinol Mixture for Anion-Exchange Membrane Fuel Cell Application. ACS Catalysis 2022, 12 (22), 14050–14061. Figure 1

(Invited) Recent Progress in the Synthesis of Functional and Three-Dimensional Carbon Nano-Composites By Gas-Liquid Interface Plasma

Carbon nanomaterials, such as fullerene, carbon nanotubes (CNT), graphene sheets, and so forth, play indispensable roles in nanotechnology research and applications. Due to their unique self-organized nanostructures and properties, various types of applications using them are expected and have been developed. Furthermore, in recent years, heteroatom-doped carbon nano-composite materials that exhibit catalytic activity are attracting much attention as non-platinum catalysts. Especially, nitrogen (N)-doped nanographene materials are well-known to have high catalytic activity. Pyridinic-N is known as a key component to express catalytic activity [1].There are two ways to obtain nitrogen-doped carbon nanomaterials. One is the addition of N into carbon nanomaterials during their synthesis, and the other is the post-nitridation after the synthesis, which often used nitrogen plasma. Especially in the latter case, the synthesis method of nanographene itself can be divided into two types of methods. One is the direct synthesis of the powder, and the other is the exfoliating from graphene oxide (GO) or bulk graphite in physical or chemical ways. Hydrothermal treatment using microwaves is one of the effective methods for simultaneous exfoliation, three-dimensional nanopore structuring, and nitrogen addition. While electronic device applications generally need high-quality graphene sheets synthesized by epitaxial growth, or chemical vapor deposition (CVD) methods at high temperatures up to 1,000°C, some kinds of applications, such as sensors, batteries, additives to polymers, and so forth, need a large amount of nanographene power. For that purpose, a reduction of GO is well known, but the quality of the synthesized graphene is not high enough.Recently, we have established a high-speed synthesis method of nanographene materials with high crystallinity by a plasma discharge at gas-liquid interfaces with alcohol sources. By this method, a synthesis rate of nanographene over 1 mg/min and higher crystallinity of nanographene than the reduced GO have been realized. On the other hand, there is a trade-off relationship between the synthesis rate and crystallinity, when different types of alcohols were used as a feedstock gas. When ethanol,1-propanol, and 1-butanol were used, it was found that the higher synthesis rates were obtained by the higher-molecular weight alcohols, while its crystallinity was lower. In the comparison between hexane (C6H14) and hexanol (C6H13OH), in the case of hexane, the synthesis rate is about twice as high as that in the case of hexanol, but the crystallinity is lowered. These results indicate that this trade-off relationship is attributed to a ratio of carbon (C) and oxygen (O) atoms. O-related radicals (O, OH, etc.) in plasma could have etching effects of amorphous or low-crystallinity carbon components. Actually, according to the results of plasma diagnostic measurements and residual liquid analyses, it was found that crystallinity of nanographene materials degraded with decrease in OH intensity in plasma. Furthermore, small radicals such as C2 and CHx contribute to the synthesis of nanographene rather than by-products with a six-membered ring structure. Furthermore, we have also found functionalization and structural control of nanographene materials by additive agents to alcohol sources at in-liquid plasma processes. Using an iron phthalocyanine with ethanol, size of carbon nanosheets increased up to micrometer. And they showed excellent catalytic characteristics thorough 4-electron reduction pathway. According to the verification results of dependence on synthesis conditions such as the type of additive, such the catalytic activity is induced by pyridinic C-N bonds. In the case of this way, to increase pyridinic C-N bonds and improve catalytic performance, iron phthalocyanine is much better than Hemin, even which also included Fe and N. These knowledges obtained in this study will open the way to the next-generation green energy solutions, such as high-performance catalytic electrode for the fuel cell.[1] D. Guo, R. Shibuya, C. Akiba, S. Saji, T. Kondo, and J. Nakamura. Science 351 (2016) 361–365.[2] J. Wang, W. Wu, H. Kondo, T. Fan, H. Zhou, Nanotechnology, NANO-132006.R1 (2022), online.[3] T. Hagino, H. Kondo, K. Ishikawa, H. Kano, M. Sekine, M. Hori, Appl. Phys. Express 5 (2012) 035101.[4] T. Amano, H. Kondo, K. Ishikawa, T. Tsutsumi, K. Takeda, M. Hiramatsu, M. Sekine, M. Hori, Appl. Phys. Express 11 (2017) 015102.[5] H. Kondo, R. Hamaji, T. Amano, K. Ishikawa, M. Sekine, M. Hiramatsu, M. Hori, Plasma Process. Polym. 19, (2022) 2100203.

Enhancing High-Capacity and High-Rate Sodium-Ion Storage through Synergistic N, S Dual Doping of Hard Carbon.

Hard carbon, as the most promising commercial anode materials of sodium-ion batteries (SIBs), has suffered from the coupling limitations on initial Coulombic efficiency (ICE), capacity, and rate capability. Herein, to break such coupling limitations, sulfur-rich nitrogen-doped carbon nanomaterials (S-NC) were synthesized by a synergistic modification strategy, including structure/morphology regulation and dual heteroatom doping. The small specific surface area of S-NC is beneficial for inhibiting excessive growth of solid electrolyte interphase (SEI) film and irreversible interfacial reaction. The covalent S can serve as active electrochemical sites by Faradaic reactions and provide extra capacity. Benefit by N, S co-doping, S-NC shows large interlayer spacing, high defects, good electronic conductivity, strong ion adsorption performance, and fast Na+ ion transport, which combined with a more significant pore volume result in speedier reaction kinetics. Hence, S-NC possesses a high reversible specific capacity of 464.7 mAh g-1 at 0.1 A g-1 with a high ICE of 50.7%, excellent rate capability (209.8 mAh g-1 at 10.0 A g-1), and superb long-cycle capability delivering a capacity of 229.0 mAh g-1 (85% retention) after 1800 cycles at 5.0 A g-1.

A multi-unit integrated electrochemical biosensor array for synergistic signal enhancing carbohydrate antigen 125 detection

Significant progress has been made in recent decades; however, the development of an accurate, portability and high-throughput electrochemical biosensor for quantifying trace biomarker in complex biological samples remains challenging. In this study, we described a novel 3 × 3 multi-unit portable integrated biosensor array, specifically designed for parallel and precise detection of trace levels of carbohydrate antigen 125 (CA-125) using multiplex synergistic signal amplification. The sensor array substrate was constructed on a planar printed circuit board (PCB) using printing technology, making them integrated, portable, affordable and disposable. The exceptional sensitivity of the biosensor is attributed to the nitrogen-doped mesoporous carbon (NMC) nanomaterial, which possesses a large surface area, superior conductivity and tunable pore size, enabling high affinity of and enzyme catalytic activity. The integrated biosensing array platform consists of individually controlled sensors, allowing for high-throughput tests of the same sample simultaneously, ensuring the reliability and accuracy of assay. The developed biosensor array system demonstrated excellent sensitivity and rapid CA-125 assay, achieving an impressive detection limit as low as 0.027 U/mL (S/N = 3). Meanwhile, the high-throughput multiplex test results (n = 9) were obtained within a short timeframe of 30 min. Ultimately, the biosensor array successfully quantified CA-125 in human serum, yielding results comparable to the enzyme–linked immunosorbent assay technique. This technology presents a highly promising strategy that can be potentially extended to detect other biomarkers for biological analysis and early disease diagnosis.

Nitrogen-doped porous carbon nanomaterials synthesized using a magadiite template as efficient peroxidase mimics for colorimetric detection of ascorbic acid as an antioxidant.

Nanomaterials with intrinsic enzyme-like activity have gained substantial scientific attention as viable substitutes to natural biological enzymes owing to their cheap price and great stability. Numerous artificial enzyme mimics have been employed effectively in sectors such as sensing, environmental processing, and cancer treatment. In this study, novel nitrogen-doped porous carbon nanomaterials (CPs) were produced by modifying polypyrrole with magadiite using chemical oxidative polymerization and calcination methods. The obtained nitrogen-doped porous carbon nanomaterials exhibited improved peroxidase-like activity, which catalyzed the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) to produce colorful compounds. Kinetic investigation revealed that the affinity for TMB of nitrogen-doped porous carbon peroxidase mimics was higher than that of genuine horseradish peroxidase (HRP). In addition, a sensitive assay with encouraging performance for the colorimetric detection of ascorbic acid (AA) was successfully fabricated employing nitrogen-doped porous carbon nanomaterials as peroxidase mimics. The results were satisfactory and demonstrated its potential application in antioxidant detection.

A Pentagonal Defect-Rich Metal-Free Carbon Electrocatalyst for Boosting Acidic O2 Reduction to H2O2 Production

Metal-free carbon-based materials are considered one of the most promising two-electron oxygen reduction reaction (2e- ORR) electrocatalysts for the green synthesis of hydrogen peroxide (H2O2). However, most reported carbon electrocatalysts perform much more effectively in alkalis than in acids. Herein, by creatively using fullerene (C60) as the precursor subject to ammonia treatment, we designed and synthesized a pentagonal defect-rich nitrogen-doped carbon nanomaterial (PD/N-C). It achieves outstanding ORR activity, 2e- selectivity, and stability in acidic electrolytes, surpassing the benchmark PtHg4 alloy catalyst. Impressively, the flow cell based on the PD/N-C catalyst achieves nearly 100% Faraday efficiency with a remarkable H2O2 yield, representing the best improvement among all the metal-free catalysts. Experimental and theoretical results reveal that such superb 2e- ORR performance of PD/N-C originates from the synergism between pentagonal defects and nitrogen dopants. This work presents an effective strategy for the design and construction of highly efficient acid-resistant carbon electrocatalysts for H2O2 production and beyond.

Metal–Organic Framework-Derived Co-Doped ZnO Nanostructures Anchored on N-Doped Carbon as a Room-Temperature Chemiresistive Hydrogen Sensor

The impending need to utilize H2 for multiple applications has surged the need to develop H2 sensors. Development of selective and rapid room-temperature H2 sensors is an uphill task without the doping of precious metals (Pd, Pt, and Au) in semiconductor metal oxide (SMO) sensors. Nanostructure of the SMOs could play a decisive role in gas sensing properties of the material. In this study, metal–organic framework (MOF)-derived Co–ZnO anchored on nitrogen-doped carbon (Co–ZnO–N/C) nanomaterial has been demonstrated as an effective rapid room-temperature H2 sensor. The pyrolysis of monometallic ZIF-8 (Zn) gave rise to amorphous ZnO stabilized on nitrogen-doped carbon (ZnO–N/C) and was found to be innocent for H2 sensing, whereas the pyrolysis of bimetallic ZIF(Co–Zn) resulted in the formation of Co–ZnO–N/C nanostructure with a high dispersion of Co on amorphous ZnO. Co–ZnO–N/C inherited the nanostructure of the parent precursor with rhombododecahedron particles of 200–300 nm and possessed subnanometer pores. Co inclusion into ZnO has converted the innocent amorphous ZnO–N/C into a rapid room-temperature H2 sensor (by measuring the dynamic change in the resistance with respect to time). Co–ZnO–N/C displayed a 3.7% response % with 17–26 s of recovery–response times for 1% concentration of H2 under room-temperature conditions. The unique nanostructure of Co–ZnO–N/C enhanced the signal transduction (via N-doped carbon support) and promoted H2 diffusion (through subnanometer pores). Higher-temperature H2 sensing studies were also conducted at 200 °C, wherein Co–ZnO–N/C displayed an increase in response to 5.7% with 8–16 s of response–recovery times. Co–ZnO–N/C chemiresistor is a rare example that does not contain precious metals yet exhibits room-temperature hydrogen sensing.

Adsorption characteristics of six bisphenol compounds on magnetic three-dimensional nitrogen-doped carbon nanomaterials and their use in effervescent reaction-assisted dispersive microextraction

Herein, we successfully prepared magnetic Co/Ni-based N-doped 3D carbon nanotubes and graphene nanocomposites (CoNi@NGC) using a simple high-temperature calcination method. The CoNi@NGC nanocomposites were used as adsorbents to study their adsorption performances and underlying kinetic mechanisms for six types of bisphenol compounds (BPs) in water. They were also used as extractants, and acid-base effervescent tablets were used to enhance extractant dispersion with the aid of vigorous CO2 bubbling. Thus, a novel pretreatment method was developed, denoted effervescent reaction-assisted dispersive solid-phase microextraction (ER-DSM), which was combined with high performance liquid chromatography-fluorescence detection (HPLC-FLD) to rapidly quantify trace-level BPs in several drinks. The morphology and structure of the CoNi@NGC adsorbent were characterized in detail using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption and desorption (BET-BJH), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The CoNi@NGC nanocomposites were successfully doped with N and exhibited large specific surface areas (109.42 m2/g), abundant pores, and strong magnetic properties (17.98 emu/g).Key parameters were rigorously optimized to maximize the adsorption performance of CoNi@NGC, including adsorbent dosage, solution pH, temperature, and time. Under the constant conditions of pH=7, 5 mg of CoNi@NGC, initial BP concentrations of 5 mg/L, and 5 min of shaking at 298 K, the adsorption percentages of bisphenol M (BPM) and bisphenol A (BPA) reached respective maxima of 99.01% and 98.21%. Remarkably, those of bisphenol Z (BPZ), BPA, and BPM reached almost 100% after 90 min. The adsorption between the BPs and CoNi@NGC was mainly governed by hydrogen bonds, electrostatic interactions, and π-π conjugation. The entire adsorption process was consistent with Freundlich adsorption and a quasi-second-order kinetic equation, representing spontaneous adsorption. Via integration with HPLC-FLD, ER-DSM was used to rapidly extract and analyze trace-level BPs in six types of boxed drinks. Critical factors were optimized individually, including the type of eluent and elution time and volume, which influenced the enrichment effect. Under the optimized extraction conditions (pH=7, 5 mg CoNi@NGC, elution with 2 mL acetone for 6 min), the limits of detection and quantification of the novel extraction method were 0.06-0.20 and 0.20-0.66 μg/L, respectively. The intra- and inter-day precisions spanned the ranges 1.44%-4.76% and 1.69%-5.36%, respectively, and the recoveries in the actual samples were in the range 82.4%-103.7%. Moreover, the respective residual levels of BPA and BPB in peach juice samples were 2.09 and 1.37 μg/L. Regeneration studies revealed that the CoNi@NGC adsorbent could be reused at least five times, which significantly reduced the cost of evaluation. In summary, compared to other methods, this method displays the advantages of a high sensitivity, rapid extraction, and environmental friendliness, thereby exhibiting considerable potential for use in conventional monitoring of trace-level BPs in food matrices.

Unexpected Room Temperature Ferromagnetism of a Ball-Milled Graphene Oxide-Melamine Mixture.

Nitrogen-doped carbon nanomaterial (NDCNM) was synthesized by grinding a mixture of graphene oxide and melamine in a planetary mill with both balls and milling chamber of zirconium dioxide. In the electron spin resonance spectrum of NDCNM, a broad signal with g = 2.08 was observed in addition to a narrow signal at g = 2.0034. In the study using a vibrating-sample magnetometer, the synthesized material is presumably a ferromagnet with a coercive force of 100 Oe. The specific magnetization at 10,000 Oe is approximately 0.020 and 0.055 emu/g at room temperature and liquid nitrogen temperature, respectively.

The facile detection and micromechanism of ATMP and DTPMP by fluorescence sensor based on nitrogen-doped carbon nanomaterials

In the present work, the N-doped fluorescent carbon nanomaterials (NCMs) were prepared. Fe3+ quenched the fluorescence of NCMs effectively, while the addition of different concentrations of ATMP or DTPMP can restore the fluorescence intensity of NCMs to different degrees. Therefore, the Fe-NCMs fluorescent probe can quantitatively detect ATMP or DTPMP, and the detection limit (LOD) of ATMP and DTPMP was 0.479 μΜ and 0.254 μΜ, respectively. The fluorescence quenching mechanism of NCMs by Fe3+ was revealed by UV–vis absorption spectra and the fluorescence lifetime analysis, the results showed that the fluorescence quenching was a combination of static and dynamic quenching. Moreover, based on Density Function Theory (DFT) calculation, basin analysis, topology analysis of atoms in molecules (AIM), electron localization function (ELF) analysis, and bond order density (BOD) analysis were firstly combined to reveal the difference in fluorescence restoration degree between the two organic phosphonates on Fe-NCMs. The detection mechanism of ATMP and DTPMP by Fe-NCMs was explained from a microscopic point of view.

Fe- and Co-Containing Nitrogen-Doped Nanocarbon Catalysts from 5-Methylresorcinol for Anion Exchange Membrane Fuel Cells

Replacing fossil fuels with alternative energy sources has a growing scientific and societal interest because of the the environmental concerns related with their utilization. Low-temperature polymer electrolyte fuel cells have become a subject of intense research as the future cornerstone of renewable energy-based economy.Platinum nanoparticles supported on high-area carbon materials (Pt/C) are commonly used as the cathode catalyst in low-temperature fuel cells. However, the high cost of precious metal-based catalysts limits the commercial viability of such fuel cells. Considerable effort has been directed to design efficient and cheap electrocatalysts through the last decades and transition metal-containing nitrogen-doped carbon nanomaterials have shown the most promising results. A simple strategy to prepare these catalyst materials is high-temperature pyrolysis of organic carbon precursors in the presence of nitrogen and metal sources, where carbonization and N-doping occur simultaneously.1 In this work, highly active oxygen reduction reaction (ORR) electrocatalysts from 5-methylresorcinol, dicyandiamide (DCDA) and Fe and/or Co salts were prepared by a simple one-pot synthesis procedure.2 It has been proposed that DCDA polymerizes into graphitic carbon nitride at around 550 °C, which acts as a reactive template during carbonization of organic precursors, decomposing above 750 °C to produce the micro- and macropores necessary for efficient mass transfer and yielding N-doped graphene-like carbon structures.3 The SEM and TEM analysis revealed that the materials are composed of wrinkled carbon structures doped with nitrogen and metals, and also contain metal nanoparticles encapsulated in N-doped carbon layers. According to the XRD analysis, these nanoparticles are mainly composed of Co, Fe/Fe3O4 and FeCo alloy for the CoNC, FeNC and FeCoNC catalysts, respectively. The specific surface area of the materials was between 290 and 410 m2 g−1. The XPS analysis revealed that the catalysts contain metal-coordinated N centers, while pyridinic nitrogen is the most abundant N species in all materials. Electrocatalytic activity for ORR in alkaline media was evaluated via the rotating disk electrode (RDE) method. The ratio of the precursors was optimized and bimetallic catalysts were found to be more active toward ORR than their monometallic counterparts. Acid treatment slightly increased the catalysts’ ORR activity. The acid-treated bimetallic catalyst (FeCoNC-at) showed exceptional ORR performance, comparable to that of commercial Pt/C (20 wt%) (Figure 1a). This can be attributed to the high surface metal and nitrogen contents, which at least partly are present as nitrogen-coordinated metal (M-Nx) centers, as confirmed by inhibition of ORR in the presence of cyanide ions. The catalyst also demonstrated a rather high stability in short-time tests (15000 potential cycles) and good tolerance to methanol. The FeCoNC-at catalyst was further tested in an anion exchange membrane fuel cell (AEMFC) with hexamethyl-p-terphenyl poly(benzimidazolium) (HMP-PMBI) membrane,4 where a high value of peak power density (P max= 415 mW cm–2) was achieved (Figure 1b).2 References Sarapuu, E. Kibena-Põldsepp, M. Borghei, K. Tammeveski, Electrocatalysis of oxygen reduction on heteroatom-doped nanocarbons and transition metal–nitrogen–carbon catalysts for alkaline membrane fuel cells, J. Mater. Chem. A 6, 776–804 (2018).Kisand, A. Sarapuu, D. Danilian, A. Kikas, V. Kisand, M. Rähn, A. Treshchalov, M. Käärik, M. Merisalu, P. Paiste, J. Aruväli, J. Leis, V. Sammelselg, S. Holdcroft, K. Tammeveski, Transition metal-containing nitrogen-doped nanocarbon catalysts derived from 5-methylresorcinol for anion exchange membrane fuel cell application, J. Colloid Interface Sci. 584, 263–274 (2021).-T. Ren, Z.-Y. Yuan, A universal route to N-coordinated metals anchored on porous carbon nanosheets for highly efficient oxygen electrochemistry, J. Mater. Chem. A 7, 13591–13601 (2019).G. Wright, J. Fan, B. Britton, T. Weissbach, H.-F. Lee, E. A. Kitching, T. J. Peckham, S. Holdcroft, Hexamethyl-p-terphenyl poly(benzimidazolium): a universal hydroxide-conducting polymer for energy conversion devices, Energy Environ. Sci. 9, 2130–2142 (2016). Figure 1

Synthesis of Nitrogen-Doped Wood-Based Carbon Materials and Their Application for Oxygen Reduction

Recently, great attention has been focused on biomass-derived electrocatalysts for the oxygen reduction reaction (ORR). In the present study, the wood-derived nitrogen-doped carbon nanomaterials with graphene-like structures have been synthesized from wood biomass using a chemical activation method with NaOH to achieve a high specific surface area (SSA). Then, the activated carbon materials have been doped with nitrogen using dicyandiamide (DCDA) as a cheaper nitrogen precursor. The synthesized catalyst's morphology, structure, and composition have been characterized using TEM, XPS, Raman Spectroscopy, and ICP-OES. The activity of the prepared catalysts was evaluated for ORR in the 0.1 M KOH solution employing the rotating disk electrode (RDE) method. The nitrogen-doped carbon materials have been shown a high electrocatalytic activity and stability for the oxygen reduction reaction. The number of electrons transferred per O2 molecule is close to 4.0.AcknowledgmentThis project has received funding under the Baltic Research Programme project “Sustainably produced nanomaterials for energy applications (SuNaMa)” (No. S-BMT-21-12, LT08-2-LMT-K-01-055).

Controllable synthesis of N-doped hollow mesoporous carbon with tunable structures for enhanced toluene adsorption

Mesoporous hollow carbon spheres have been considered as promising adsorbents for volatile organic compounds (VOCs) removal. However, the influence of the morphologies and structures on the adsorption performance of VOCs is still unclear. Herein, we developed a novel strategy for the controllable synthesis of nitrogen-doped mesoporous hollow carbon nanomaterials with adjustable morphologies and structures. By simply tuning tetraethyl orthosilicate addition time and ammonia amount in Stöber system, bowl-like, hollow, and yolk-shell carbon nanomaterials can be obtained. When used as toluene adsorbents, the bowl-like materials exhibited a capacity of 190 mg/g, higher than other carbon materials with different morphologies. The high adsorption capacity and fast adsorption rate of the bowl-like structures can be attributed to the high surface area, rich microporous/mesoporous structure and unique morphology. Our work provides a new strategy for the designed synthesis of novel VOCs adsorbents with advanced adsorption performance.

Highly stable N-containing polymer-based Fe/Nx/C electrocatalyst for alkaline anion exchange membrane fuel cell applications

A cost-effective electrocatalyst with high activity and stability was developed. The Fe-Nx and pyridinic-N active sites were embedded in nitrogen-doped mesoporous carbon nanomaterial by carbonization at high temperature. The electrocatalyst exhibited excellent electrochemical performance for the oxygen reduction reaction, with high onset potential and half-wave potential values (Eonset= 1.10 ​V and E1/2 ​= ​0.944 ​V) than 20 ​wt % Pt/C catalyst (1.04 and 0.910 ​V). The mass activity of the Schiff base network (SNW) based SNW-Fe/N/C@800° electrocatalyst (0.64 ​mA ​mg−1 @ 1 ​V) reached about half of the commercial Pt/C electrocatalyst (1.35 ​mA ​mg−1 @ 1 ​V). The electrocatalyst followed the 4-electron transfer mechanism due to very low hydrogen peroxide yield (H2O2 ​< ​1.5%) was obtained. In addition, this electrocatalyst with dual active sites showed high stability during cyclic voltammetry and chronoamperometry measurements. More importantly, the electrocatalyst also demonstrated the power density of 266 ​mW ​cm−2 in the alkaline anions exchange membrane fuel cell (AEMFC) test, indicating its prospective application for fuel cells.

Single-Atom Catalysts Boost Peroxidase-like Activity for Biosensing

Natural enzymes are one of the most important compounds in biosensing applications. However, their wide application is limited by expensive production costs and instability in complex conditions like high temperature or harsh pH environments. It is urgent to develop artificial alternatives with enzyme-like properties and activity for natural enzymes with high stability and low-cost biomedical applications. We designed various single-atom catalysts (SACs) with a high peroxidase-like activity that was able to work as efficiently as natural enzymes. Herein, single iron atoms embedded in nitrogen-doped carbon nanomaterials (with Fe-Nx active site),1 which mimic the active site of heme enzymes from an atomic/molecular structure perspective. The SACs are also more robust than natural enzymes, which show excellent stability under pH or temperature changes. The superior catalytic specificity of hydrogen peroxide paved the way for replacing natural peroxidase for high-sensitive biosensing. For investigating practical applying ability, electrochemical sensors, immunosorbent assays, intercellular nanoprobe, and lateral-flow immunoassay based on SACs were successfully developed for biosensing and bioimaging applications.2-4 Their unique electronic/geometrical have significant advantages in biocatalytic activity, stability, and selectivity, which offer massive potential in substituting natural enzymes for various biomedical applications.5 Reference Ding, S.; Lyu, Z.; Zhong, H.; Liu, D.; Sarnello, E.; Fang, L.; Xu, M.; Engelhard, M. H.; Tian, H.; Li, T.; Pan, X.; Beckman, S. P.; Feng, S.; Du, D.; Li, J.-C.; Shao, M.; Lin, Y., An Ion-Imprinting Derived Strategy to Synthesize Single-Atom Iron Electrocatalysts for Oxygen Reduction. Small 2021, 17 (16), 2004454.Ding, S.; Lyu, Z.; Fang, L.; Li, T.; Zhu, W.; Li, S.; Li, X.; Li, J.-C.; Du, D.; Lin, Y., Single-Atomic Site Catalyst with Heme Enzymes-Like Active Sites for Electrochemical Sensing of Hydrogen Peroxide. Small 2021, 17 (25), 2100664.Lyu, Z.; Ding, S.; Wang, M.; Pan, X.; Feng, Z.; Tian, H.; Zhu, C.; Du, D.; Lin, Y., Iron-Imprinted Single-Atomic Site Catalyst-Based Nanoprobe for Detection of Hydrogen Peroxide in Living Cells. Nano-Micro Letters 2021, 13 (1), 146.Lyu, Z.; Ding, S.; Zhang, N.; Zhou, Y.; Cheng, N.; Wang, M.; Xu, M.; Feng, Z.; Niu, X.; Cheng, Y.; Zhang, C.; Du, D.; Lin, Y., Single-Atom Nanozymes Linked Immunosorbent Assay for Sensitive Detection of A<i>β</i> 1-40: A Biomarker of Alzheimer’s Disease. Research 2020, 2020, 4724505.Jiao, L.; Xu, W.; Wu, Y.; Yan, H.; Gu, W.; Du, D.; Lin, Y.; Zhu, C., Single-atom catalysts boost signal amplification for biosensing. Chemical Society Reviews 2021, 50 (2), 750-765. Figure 1