Nitrogen-doped Carbon Spheres Research Articles

Molecular Level Design of Nitrogen-Doped Well-Defined Microporous Carbon Spheres for Selective Adsorption and Electrocatalysis.

Nitrogen-doped porous carbon spheres have attracted great interest in diversified fields owing to their unique physical and chemical properties. However, the synthesis of nitrogen-doped porous carbon spheres with hierarchical superstructures and refined micropore structures is still a challenge. Herein, we develop a molecular-scale silica templating strategy to prepare nitrogen-doped microporous carbon spheres (MCSSs) with high porosity and a well-defined micropore structure. Octa(aminophenyl) polyhedral oligomeric silsesquioxane is used as a building block in MCSS precursors to provide precise molecular-scale templating and nitrogen doping. The morphology of MCSSs can be easily tuned by choosing the proper solvent. The as-synthesized MCSS with a large surface area (2036 m2 g-1), narrow micropore size distribution, nitrogen doping, and hierarchical geometry can serve as an efficient selective adsorbent for CO2 and organic pollutants. Furthermore, the MCSS decorated with Fe-N-C active sites (MCSS-Fe) shows enhanced electrocatalytic ORR activity in alkaline solution. This novel approach may open a new avenue for controllable fabrication of porous carbon spheres with desired geometry and well-designed pore structure and show potential applications in selective adsorption and catalysis.

Self-templated formation of cobalt-embedded hollow N-doped carbon spheres for efficient oxygen reduction

The slow kinetics at the cathode of oxygen reduction reaction (ORR) seriously limits the efficiencies of fuel cells and metal-air batteries. Pt, the state-of-the-art ORR electrocatalyst, suffers from high cost, low earth abundance, and poor stability. Here a self-templated strategy based on metal-organic frameworks (MOFs) is proposed for the fabrication of hollow nitrogen-doped carbon spheres that are embedded with cobalt nanoparticles (Co/HNC). The Co/HNC manifests better ORR activities, methanol tolerance, and stability than commercial Pt/C. The high ORR performance of Co/NHC can be attributed to the hollow structure which provides enlarged electrochemically active surface area, the formation of more Co-N species, and the introduction of defects. This work highlights the significance of rational engineering of MOFs for enhanced ORR activity and stability and offers new routes to the design and synthesis of high-performance electrocatalysts.

Nitrogen doped carbon spheres with wrinkled cages for the selective oxidation of 5-hydroxymethylfurfural to 5-formyl-2-furancarboxylic acid.

Nitrogen doped carbon spheres with wrinkled cages (NCSWCs), which were used for the first time as metal-free catalysts, exhibited high catalytic activity and selectivity in the oxidation of 5-hydroxymethylfurfural (HMF) to 5-formyl-2-furancarboxylic acid (FFCA) under base-free conditions using tert-butyl hydroperoxide (TBHP) as the oxidant. The mechanistic studies found that this reaction was catalyzed by the synergy between NCSWCs and TBHP. The density functional theory (DFT) calculations further suggested that the hydroperoxyl radicals from TBHP adsorbed on the carbon atoms adjacent to the graphitic N atoms are the active sites.

Nitrogen-doped bagasse carbon spheres/graphene composite for high-performance supercapacitors

Carbon spheres have emerged as a promising material in energy storage, but preparing carbon spheres from raw biomass in a cost-effective way still remains as a great challenge. Here, for the first time, we directly transformed bagasse to nitrogen-doped carbon sphere through hydrothermal carbonization. Before carbonization, bagasse and graphene oxide was fully dissolved in NaOH/urea aqueous system. In the process of hydrothermal carbonization, graphene oxide acted as template and accelerant, and urea was acted as nitrogen source. The diameter of the prepared carbon spheres was about 200 nm, which were distributed on the graphene sheets and acted as spacer to prevent aggregation of graphene sheets. The nitrogen-doped bagasse-based carbon spheres/reduced graphene oxide composite exhibited 3D interconnected structures with high electrical conductivity, large specific surface areas, and active nitrogen-doped sites. Applied as electrode material for supercapacitor, the composite showed a higher specific capacitance, rate capability and better cycling stability compared to some traditional carbon spheres, active carbon and reduced graphene oxide. The specific capacitance is 226.8 F g−1 at the current density of 0.5 A g−1, which still retains 83.9% after 10,000 cycles. After 10,000 cycles, the composite maintains 83.9% of the initial capacitance. Furthermore, the possible formation mechanism of nitrogen-doped bagasse-based carbon spheres/reduced graphene oxide composite was discussed. This study achieved full solubility of bagasse in NaOH/urea aqueous system, not only providing a promising way to convert lignocellulosic raw biomass into carbon spheres directly, but also proposing an emerging strategy for synthesizing high capacitive and stable biomass-based electrode material.

Boosting sodium storage performance of Mo2C via nitrogen-doped carbon sphere encapsulation and rGO wrapping

As a model compound for transition metal carbides, Mo2C is considered as a promising anode material for sodium ion batteries (SIBs) due to its excellent electrical conductivity and low Na+ diffusion barriers. However, the low capacity and poor rate capability strongly limit its practical applications. Nanostructuralization of active materials combined with conductive matrix incorporation may address this issue. Inspired by this concept, we herein propose a rational strategy to create a special structure with ultrafine Mo2C nanoparticles encapsulated in porous N-doped carbon spheres wrapped by rGO. The well-defined double-carbon coating effectively limited the growth/agglomeration of Mo2C and provided highly conductive network to stabilize capacity. Theoretical calculations disclose hetero-interaction between components favorably promoted Na+ diffusion kinetics. Impressively, such composite with excellent cyclic stability showed a record high reversible capacity (332.9 mA h/g at 0.1 A/g) and rate capability (155.7 mA h/g at 5 A/g) of Mo2C based materials for SIBs.

An efficient ruthenium-based dual-electrocatalyst towards hydrogen evolution and oxygen reduction reactions

The development of highly efficient and durable catalysts for production and storage of clean energy remains a formidable challenge. Herein, a bifunctional electrocatalyst composed of ultrasmall ruthenium nanoparticles confined within a hollow nitrogen-doped carbon spheres (Ru/HNCS) was designed and synthesized through the pyrolysis of Ru3+ coordinated polydopamine layers. The as-synthesized Ru/HNCS with Ru content even below 0.1 wt% exhibited excellent catalytic activities towards both hydrogen production and oxygen reduction. When catalyzing hydrogen evolution reaction, a low overpotential of 39 mV was sufficiently to achieve the current density of 10 mA cm−2 in acidic media and the corresponding Tafel slope was only 30 mV dec−1. Furthermore, Ru/HNCS also exhibited outstanding oxygen reduction reaction activity with a half-potential of 0.72 V and an onset potential of 0.83 V, as well as high stability and palmary anti-poisoning capability for methanol in basic electrolyte. This Ru/HNCS might be a promising alternative to Pt-based electrocatalysts in energy conversion and storage.

Multistage Self-Assembly Strategy: Designed Synthesis of N-doped Mesoporous Carbon with High and Controllable Pyridine N Content for Ultrahigh Surface-Area-Normalized Capacitance

Nitrogen doping could improve the performance of carbon materials in electrocatalysis, CO2 adsorption, and energy storage. [1]However, the control of the doping type and the amount of nitrogen (N)-...

Palladium Nanoparticles Embedded in Yolk–Shell N-Doped Carbon Nanosphere@Void@SnO2 Composite Nanoparticles for the Photocatalytic Reduction of 4-Nitrophenol

Herein, a novel visible-light-driven yolk–shell nanoreactor has been fabricated, called as Pd/N–Cs@SnO2, which is consisted of movable nitrogen-doped carbon sphere (N–Cs) yolk, interlayer void, mesoporous tin oxide (SnO2) shell, and encapsulated palladium nanoparticles (Pd NPs). The obtained yolk–shell Pd/N–Cs@SnO2 nanoreactor can serve as an excellent catalyst in the visible-light-driven photocatalytic reduction of 4-nitrophenol (4-NP). More importantly, Pd/N–Cs@SnO2 exhibits a remarkable superior activity and higher reusability than core–shell Pd@SnO2 and yolk–shell Pd/N–Cs@mSiO2 nanoreactors. The fabulous character of Pd/N–Cs@SnO2 nanoreactor is attributed to (I) the mesostructured SnO2 shell provides a large surface area for the collection of light as well as the anchoring of Pd to avoid aggregating or leaching; (II) the interlayer void space improves the light absorption by multiple scattering, as well as favors the contact of active sites with reactants in the photocatalytic reactions; (III) the N–Cs allow more permeable visible-light absorption, and accelerate the photoexcited electrons transportation from SnO2 semiconductor to Pd NPs to suppress the electron–hole recombination. This enriches the electron density of Pd NPs surface and then facilitates the photocatalytic reduction of 4-NP. Both the structural advantages and enhanced synergy of Pd/N–Cs@SnO2 nanoreactor make it to be an efficient and stable photocatalyst, which can open an avenue for designing photocatalysts in a board range of organic reactions.

Aerosol-assisted preparation of N-doped hierarchical porous carbon spheres cathodes toward high-stable lithium-ion capacitors

Lithium-ion capacitors (LICs) are gradually emerging as one of the most indispensable hybrid energy storage devices. However, it is one main challenge to evade the mismatch of electrochemical kinetics and specific capacity between cathode and anode in LICs. Herein, we have proposed an efficient strategy to prepare the nitrogen-doped hierarchical porous carbon spheres (NHPCS) as cathode, which is synthesized by a simple aerosol-spraying pyrolysis using the low-cost phenolic resin as carbon source without any other catalyst or hard template. The NHPCS exhibits porous nanospheres structure with an appropriate nitrogen doping level (3.65 at.%). Benefitting from the two-pronged strategy of N-doped feature and nanostructure engineering, NHPCS achieves a high specific capacity of 74 mAh g−1 at a current density of 0.1 A g−1 and remains 86.5% of initial capacity even being subjected to a high rate of 50-fold. Furthermore, a high-performance LIC has been developed by coupling NHPCS cathode and hard carbon anode, which delivers a maximum energy density of 151 Wh kg−1 and excellent cycle stability (96.3% capacity retention after 3000 cycles). Significantly, such designed porous carbon could not only be convenient for scalable production, but also be served for many other energy storage devices. We have presented a larger-scale spray pyrolysis strategy to prepare nitrogen-doped hierarchical porous carbon spheres (NHPCS). A high-stable lithium-ion capacitor has been constructed by coupling NHPCS cathode with hard carbon anode, which exhibits a maximum energy density of 151 Wh kg−1 and capacity retention of 96.3% over 3000 cycles, showing great potential for the next-generation energy storage application.

5-Amino-2-mercapto-1,3,4-thiadiazole coated nitrogen-doped-carbon sphere composite for the determination of phenolic compounds

This study reports the simultaneous determination of phenolic antioxidant compounds of gallic acid (GA) and caffeic acid (CA). The composite probe was fabricated by electropolymerizing 5-amino-2-mercapto-1,3,4-thiadiazole (p-AMT) on nitrogen-doped carbon sphere (N-CS) modified glassy carbon (GC) electrode. The N-CS was derived by carbonizing poly(o-phenylenediamine) microspheres. The proposed p-AMT@N-CS/GC composite electrode exhibited lower operating voltage, good peak separation of 80 mV (for simultaneous GA and CA oxidation), and a dynamic concentration range detection of GA and CA. The kinetic parameters were calculated as follows: charge transfer coefficients of GA 0.80, CA 0.81 and electron transfer rate constants of GA 9.5 s−1, CA 3.3 s−1. The p-AMT@N-CS/GC composite electrode proved useful in the individual and simultaneous monitoring of GA and CA with wide dynamic concentration range (GA 5–1187 μM and CA 5–2082 μM), high sensitivity (GA 0.0251 μA μM−1 and CA 0.1024 μA μM−1), and low limit of detection (GA 0.58 μM and CA 0.143 μM). The p-AMT@N-CS/GC electrode revealed good interference tolerance ability with common interfering species, such as ascorbic acid, uric acid, hydroquinone, catechol, K+, Na+, Mg2+, Cu2+, Ni2+, NO3−, Cl−, SO42−, and glucose. Under optimized conditions, the p-AMT@N-CS/GC electrode was used in the simultaneous determination of GA and CA in grape juice samples.

Periodic Three-Dimensional Nitrogen-Doped Mesoporous Carbon Spheres Embedded with Co/Co3O4 Nanoparticles toward Microwave Absorption.

Although various bio-inspired materials with outstanding mechanical, acoustic, and optic properties have been developed, bio-inspired materials for microwave absorption applications are rarely reported. Herein, under the inspiration of the opal structure, for the first time, a kind of Co@Co3O4/nitrogen-doped (N-doped) mesoporous carbon sphere (Co@Co3O4/NMCS) with a periodic three-dimensional structure toward microwave absorption application was designed and synthesized. The microwave absorption performance was optimized with respect to the content of Co@Co3O4 nanoparticles. Co@Co3O4/NMCS with ∼20 wt % Co@Co3O4 achieves a reflection loss of -53.8 dB at 5.7 GHz. The simulated radar cross section demonstrated that the Co@Co3O4/NMCS can efficiently suppress the strong electromagnetic scattering from a metal groove structure, which further reveals its excellent absorbing performance. These periodic porous structures of N-doped mesoporous carbon spheres combined with the magnetic Co@Co3O4 nanoparticles contribute to the excellent microwave-absorbing performance.

RuP nanoparticles on ordered macroporous hollow nitrogen-doped carbon spheres for efficient hydrogen evolution reaction

The design of highly active, Earth-abundant and stable electrocatalysts is important for efficient water splitting. In this work, we report the fabrication of RuP and Ru2P nanoparticles supported on ordered macroporous N-doped carbon hollow spheres (RuP/H-NC and Ru2P/H-NC) through a facile and scalable space-confined pyrolysis process. The RuP/H-NC catalyst exhibits Pt-like activity in alkaline electrolyte, by means of the macroporous structure with a larger specific area and more exposed active sites, as well as the synergistic effect between the RuP nanoparticles and N-doped carbon. Specifically, the RuP/H-NC catalyst yields superior hydrogen evolution reaction activity in terms of low overpotential of 19 mV in 1 M KOH to achieve a current density of 10 mA cm−2 and excellent durability, outperforming Ru2P/H-NC and most of the reported non-Pt catalysts. Further density function theory calculation reveals that RuP is more intrinsically active with favorable hydrogen adsorption Gibbs free energy than that of Ru2P.

Nitrogen-doped carbon spheres decorated with CoSx nanoparticles as multifunctional electrocatalysts for rechargeable zn-air battery and overall water splitting

Developing non-precious multi-functional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) to replace noble metal (Pt, Ru, Ir, etc) is one of the most important directions in the field of energy conversion and storage. Herein, we successfully prepared CoSx nanoparticles loaded onto N-doped carbon spheres to form unique CoSx/NCS nanocomposites, showing good tri-functional activities for ORR, OER and HER. As the cathodic electrocatalyst in Zn-air battery, the CoSx/NCS shows a lower charge voltage of 2.1 V and a high power density of 72.7 mW cm−2 compared to Pt/C. CoSx/NCS also shows potentials in overall water splitting as the OER and HER electrocatalysts. The onset potential and overpotential at 10 mA cm-2 toward overall water splitting reaches 1.70 V and 1.83 V, respectively. The enhanced activity of CoSx/NCS should be ascribed to the synergistic effects of improved surface hydrophilicity, Co-N sites, pyridinic-N species, and Co-S bonds. This study provides a new strategy to synthesize active electrocatalysts with multiple functions in energy conversion and storage.

Bimetallic CoNi Alloy Nanoparticles Embedded in Pomegranate-like Nitrogen-Doped Carbon Spheres for Electrocatalytic Oxygen Reduction and Evolution

Electrocatalysts for oxygen reactions play a vital role in the applications of energy conversion devices, such as in fuel cells, water splitting, and metal–air batteries. Developing novel nonprecio...

Synthesis of amorphous and graphitized porous nitrogen-doped carbon spheres as oxygen reduction reaction catalysts

Amorphous and graphitized nitrogen-doped (N-doped) carbon spheres are investigated as structurally well-defined model systems to gain a deeper understanding of the relationship between synthesis, structure, and their activity in the oxygen reduction reaction (ORR). N-doped carbon spheres were synthesized by hydrothermal treatment of a glucose solution yielding carbon spheres with sizes of 330 ± 50 nm, followed by nitrogen doping via heat treatment in ammonia atmosphere. The influence of a) varying the nitrogen doping temperature (550–1000 °C) and b) of a catalytic graphitization prior to nitrogen doping on the carbon sphere morphology, structure, elemental composition, N bonding configuration as well as porosity is investigated in detail. For the N-doped carbon spheres, the maximum nitrogen content was found at a doping temperature of 700 °C, with a decrease of the N content for higher temperatures. The overall nitrogen content of the graphitized N-doped carbon spheres is lower than that of the amorphous carbon spheres, however, also the microporosity decreases strongly with graphitization. Comparison with the electrocatalytic behavior in the ORR shows that in addition to the N-doping, the microporosity of the materials is critical for an efficient ORR.

Design bifunctional nitrogen doped flexible carbon sphere electrode for dye-sensitized solar cell and supercapacitor

Developing a highly effective bifunctional electrode material is vital to the self-powered integrated electronics that combine the energy conversion unit of the dye-sensitized solar cell (DSC) and the energy storage unit of the supercapacitor. In this study, a nitrogen doped carbon sphere (NCS) is synthesized to promote the electrode activity as compared with that of the conventional solid carbon sphere (SCS) in both DSC and supercapacitor systems. In the DSC system, the rigid and flexible devices using NCS counter electrodes yield power conversion efficiencies of 8.64% and 6.73%, much higher than those of the devices using SCS counter electrodes (6.96% and 4.57%). As a supercapacitor working electrode, the NCS shows a remarkable specific capacitance of 224.6 F g−1, much higher than the counterpart value of the SCS electrode (124.9 F g−1) under the same conditions, which demonstrates capacitance improvement by 79.8%. Moreover, NCS preserves more than 90.0% of their initial capacitance after long term stability tests, suggesting a perfect cycle life. The enhanced activity of the NCS can be ascribed to the improved conductivity, charge transfer, and mass transport processes caused by nitrogen doping.

Preparation of nitrogen-doped porous carbon material by a hydrothermal-activation two-step method and its high-efficiency adsorption of Cr(VI)

Nitrogen-doped carbon spheres (CSs-N) were synthesized by a hydrothermal method with glucose as the carbon source and urea as the nitrogen source. The synthesized nitrogen-doped carbon spheres were activated by KOH to prepare high performance nitrogen-doped porous carbon material (PCM-N) for adsorption of Cr(VI). SEM, TEM, BET, Raman spectroscopy, XRD, XPS, Zeta potential and elemental analysis techniques were used to characterize the materials, and the properties of the materials were tested by a batch adsorption method. The results show that the specific surface area of PCM-N is 1600.67 m2/g, and the maximum adsorption capacity of Cr(VI) is 402.9 mg/g, and the performance was better than that of a similar materials (Longan seed and Fox nutshell and so on). Furthermore, the adsorption capacity will increase with increasing temperature. In this study, the kinetics and isotherm model of adsorption parameters are fitted, and it is found that the adsorption process is in accordance with the Pseudo-second-order kinetic model and Freundlich model, thermodynamic parameters show that the adsorption of Cr(VI) onto the PCM-N was spontaneous endothermic process. The regeneration adsorption experiment showed that PCM-N has good reusability and high application value.

Nitrogen-doped carbon sphere encapsulating antimony-cobalt antimony binary nanoseeds as promising anode material for high performance lithium ion battery

As a high capacity anode material, antimony and their alloys receive increasing research interest. However, the large volume change during cell cycling still hinders their practical application. Herein, a new type of nitrogen-doped carbon sphere encapsulating antimony-cobalt antimony binary nanoseeds is developed as anode material for Lithium ion batteries by a combined polydopamine coating and annealing method. The incorporation with CoSb2 and nitrogen-doped carbon matrix not only guarantees the high electronic conductivity, but could effectively alleviate the volume changes during cell cycling. The composites consisting of intermetallic CoSb2 electrode for LIBs exhibit the excellent charge/discharge rate capability of 320.2 mAh g−1 at 10.0 A g−1 and the high specific capacity of 878.2 mAh g−1 after 500 cycles at 1 A g−1, which offers a potential for the material design of the high performance of lithium-ion batteries.

Comprehensive understanding of the formation process on monodisperse resorcinol-formaldehyde polymer and carbon spheres and their use as substrates for surface-enhanced Raman spectroscopy

The synthesis of nitrogen-doped polymer (resorcinol-formaldehyde) and carbon spheres (denoted as N-RFS and N-CS, respectively) was carried out via an alkaline-based condensation reaction, with emphasis on high monodispersibility and precise size control. The particle size can be controlled in the range of 0.16–1.8 µm by simply adjusting the experimental conditions, i.e., the concentrations of the monomers including resorcinol and formaldehyde, the reaction temperature, the methanol volume fraction and the concentration of a catalyst/nitrogen source (ammonia hydroxide). The correlations between the synthetic conditions and the particle size are established and elucidate the mechanism of the particle size control, in turn enabling prediction of the particle size at a set experimental parameter. Due to the outstanding thermal stability of N-RFS, the converted N-CS can be generated uniformly with high yield. With their high monodispersity, versatile synthesis procedure and close-packing ability, both the N-RFS and their corresponding N-CS in this work may offer remarkable flexibility in the design of periodic arrayed substrates for surface-enhanced Raman spectroscopy (SERS).

A composite with botryoidal texture prepared from nitrogen-doped carbon spheres and carbon nanotubes for voltammetric sensing of copper(II)

Mercury-based electrodes have been employed for the electrochemical determination trace level of heavy metals. However, due to the toxicity of mercury, mercury-free materials are encouraged to develop for on-site monitoring of heavy metals. In this work, N-doped carbon spheres/multi-walled carbon nanotubes (N-CSs/MWCNTs) hybrid materials were successfully fabricated with a low-cost convenient method. The synthesized N-CSs/MWCNTs composites were used to fabricate chemically modified electrode for selective and sensitive determination Cu(II) by differential pulse anodic stripping voltammetry (DPASV). Under the optimized experimental conditions, the proposed electrode displayed a good linear dynamic range of 0.5–200 μg L−1 with a correlation coefficient of 0.99. Its limit of detection (LOD) was estimated to be 0.092 μgL−1. Moreover, the repeatability, reproducibility, and stability of the modified electrode were also explored. Finally, the proposed electrode can be applied to quantify Cu(II) content in lake water and human saliva samples.