Nitrogen-doped Carbon Spheres Research Articles

FeCo alloy nanoparticles supported on N-doped mesoporous carbon spheres for effective degradation of antibiotics and industrial dyes

Iron (Fe) is widely recognized for its effectiveness in the Fenton reaction and is commonly used in wastewater treatment. However, exploring other metals in similar Fenton-like reactions has been relatively limited. FeCo alloy nanoparticles (NPs), anchored on nitrogen-doped mesoporous carbon spheres (FeCo/NMCS), have been effectively synthesized and used as a Fenton-like catalyst in wastewater treatment under alkaline conditions. The NMCS exhibited spherical with an average diameter of 488.1 nm, while the FeCo alloy NPs, uniformly distributed over the NMCS, had an average diameter of 8.2 nm. The mesopores served as anchoring points for the NiCo alloy NPs, effectively preventing their possible agglomeration. The NMCS was composed of 3.91 wt% nitrogen. With 30 mg of FeCo/NMCS and 25 mM H2O2, more than 92% of tetracycline hydrochloride (TC) was degraded within 35 min at pH levels 7, 9, and 11. The remarkable degradation rate was attributed to the dual active sites present in the FeCo alloys. The rapid degradation of TC, even at pH 11, indicates the potential of FeCo/NMCS as a valuable solution for wastewater treatment under alkaline conditions. Industrial reactive (Y145, R195, B222A) and disperse dyes (O30, R167, B79) with a concentration of 10 ppm were degraded within 20 min when using 10 mg of the FeCo/NMCS catalyst and 25 mM H2O2 at pH 9. After five consecutive TC degradation cycles at pH 7 and 9, the FeCo/NMCS demonstrated consistent performance, emphasizing its reusability. FeCo/NMCS provides a promising solution to pollution control and wastewater treatment with stability, superior catalytic activity, magnetic separability, and recyclability.

Hollow Nitrogen-Doped Carbon Spheres as Zincophilic Sites for Zn Flow Battery.

Severe dendrite growth on Zn anodes poses a significant challenge to the development of Zn-based batteries. An effective strategy for inhibiting the formation of Zn dendrites involves electrode modification. In this study, hollow nitrogen-doped carbon spheres (HNCS) are synthesized and used as electrodes to regulate Zn deposition in Zn-based flow batteries. The electrochemical performance of HNCS reveals that the pyrrole nitrogen of HNCS changes the electrode surface state. Therefore, HNCS can inhibit the hydrogen evolution reaction and achieve uniform Zn deposition. HNCS can effectively inhibit dendrite growth and improve the reversibility of the Zn plating/stripping process to regulate the reversibility of Zn-based batteries. The zinc-bromine redox flow battery assembled with HNCS significantly reduces the hydrogen evolution reaction and exhibits a coulombic efficiency of 90 % and energy efficiency of 73 % at a current density of 60 mA cm-2. Similarly, an alkaline zinc-iron flow battery can maintain high Coulombic efficiency and energy efficiency of 83 %.

Nitrogen-doped mesoporous carbon spheres decorated with NiCo alloy nanoparticles for high-performance electrochemical supercapacitors

Nitrogen-doped mesoporous carbon spheres (NMCSs) decorated with NiCo alloy nanoparticles (NiCo/NMCS) were prepared and examined for their prospective role as high-performance electrode materials. The average size and BET surface of the NMCSs are 488.1 nm and 660.9 m2g−1. The N content of the NMCSs and NiCo/NMCS-50 (NMCSs with 50 wt% of NiCo alloy nanoparticles (NPs)) was 1.49 wt% and 2.9 wt%, respectively. The NiCo alloy NPs, with an average diameter of 9.6 nm, were evenly incorporated into NMCSs. The NiCo/NMCS-50 exhibited a specific capacitance of 585 F g−1 when tested in a 6 M KOH solution at a current density of 1 A/g. The superior electrochemical performance of NiCo/NMCS-50 is attributed to the synergistic effect of mesoporous carbon structure and NiCo alloy NPs by improving redox-related mass transport and electron transfer. Symmetric supercapacitor devices assembled using two NiCo/NMCS-50 electrodes had a maximum energy density of 30.0 Wh kg−1 at a power density of 187.5 W kg−1 with notable cycling stability, maintaining 60.1 % of capacitance, up to 5,000 cycles. These results suggest that NiCo/NMCS composites have significant potential for utilization in high-energy storage applications.

Photoelectrothermocatalytic reduction of CO2 to glycol via CdIn2S4-N/C hollow heterostructure mimicking plant cell

A series of novel semiconductor composites of CdIn2S4-N/C, in which CdIn2S4 is grown on hollow nitrogen-doped carbon spheres to mimic plant cells, were designed and applied to photoelectrothermocatalytic reduction of CO2. Our results reveal that the unique hollow structure and photothermal properties of N/C contribute to excellent performance of catalyst in CO2 reduction. Specifically, the optimal catalyst of CdIn2S4-N/C-2–800 demonstrates an outstanding catalytic activity with a formation rate of 168.5 µM h−1 cm−2 for carbon-based products and an electron selectivity for C2 products of 66.9 %. DFT calculations demonstrate that pyridine N and pyrrole N can reduce the energy barrier during CO2 reduction. Two important species of *=C=O and OC-COH* were detected by operando IR spectra and suggested to be key intermediates to C2 products via a carbene (*=C=O) coupling mechanism. CdIn2S4-N/C provides thermoelectrons and active sites like in the membrane of plant to enhance the probability of C-C coupling.

Lignin-derived nitrogen doped hierarchical porous carbon spheres for highly efficient dichloromethane adsorption

Biomass-prepared porous carbon materials are promising solid adsorbents for the removal of volatile organic compounds (VOCs). However, their application is hindered due to the insufficient number of pores and poor surface activity. In this study, a lignin-derived nitrogen-doped hierarchical porous carbon sphere (NHPCS-0.5) with abundant surface active sites was synthesised through spray drying and carbonisation–activation methods. The optimised NHPCS-0.5 displayed a high BET specific surface area (2961 m2·g−1) and total pore volume (1.57 cm3·g−1), developed hierarchical porous distribution with micro-/meso-/macropores and satisfactory surface nitrogen content. Moreover, it exhibited an excellent dichloromethane adsorption capacity of 156 mg·g−1 and maintained 86% of initial capacity after five regeneration cycles, indicating an outstanding regenerative ability. The nitrogen introduction improved the micropore volume and adsorption capacity. Adsorption mechanism reveals that micropore filling and enhanced van der Waals interaction of carbon surface with dichloromethane molecule by N-containing functional groups played a vital role in adsorption, and mesopores contributed to the high adsorption rates. The above results indicate the potential of NHPCS-0.5 as an adsorbent for VOC removal and provide new ideas for the utilisation of lignin and design of carbon sphere materials.

Impact of Low Catalyst Loading and Incorporation of Additives on Structure and Performance of PEM Electrolyzer Catalyst Layers

Polymer electrolyte membrane water electrolyzers (PEMWEs) are an important technology that can produce renewable hydrogen on demand, although with challenges posed by the slow kinetics of the anodic oxygen evolution reaction (OER) and degradation issues. The degradation of membrane electrode assemblies (MEAs) prepared with Ir-based catalysts is not well understood, especially with lower-loading catalyst layers and intermittent load inputs. This work investigates low-loading IrO2 catalyst layers made with different carbon-based additives, including high-surface-area carbon (HSC), graphitized HSC (gHSC), Vulcan, graphitic carbon nanofibers (gCNFs), graphitic nanoplatelets (gNPs), nitrogen-doped carbon spheres (NCs), Ti carbide (TiC) and Ti carbonitride (TiCN). While carbon-based supports have issues with corrosion at high oxidizing potentials, these materials provide a range of variations in morphology, shape, size, surface area, graphitization, and composition, allowing exploration of the impact of these parameters on catalyst layer structure to identify promising routes to improve catalyst layer structures. Catalyst layers were characterized with electron microscopy and x-ray spectroscopy to assess the distribution of catalyst, carbon additive, and ionomer. This information was correlated with electrochemical performance measurements to elucidate the impact on kinetic site access and mass transport. Selected samples were also subjected to more extended operation to investigate how the initial structures and their performance evolved.

Hollow Nitrogen-Doped Carbon Spheres with Presiding Graphitic Nitrogen for Oxygen Reduction Reaction

Hollow nitrogen-doped carbons, a class of metal free electrocatalysts, offer a wide range of modifications due to their tunable diameter and carbon wall thickness. Herein, hollow nitrogen-doped carbon spheres (HNCS-1000) with numerous structural defects, thin carbon wall of about 8 nm, high (sp2-sp3)/sp3 bond ratio of 3.11 and graphitic-N proportion of 71.4% are prepared using a double pyrolysis strategy. When employed as ORR catalyst in O2-saturated 0.1 M KOH solution, HNCS-1000 retains high onset and halfwave potentials of 1.03 V and 0.88 V, respectively. In addition, it also demonstrates excellent stability/durability with 90.25% current density retention after 84000 s continuous chronoamperometric operation and only 33 mV loss in halfwave potential after 7000 CV cycles. Overall, the ORR performance of HNCS-1000 surpasses most of the previously reported nitrogen-doped carbon catalysts, and it is among the best catalysts for ORR in alkaline environment.

Efficient nitrate removal by nitrogen-doped carbon spheres electrodes with interconnected architecture in novel stirring capacitive deionization: Dual promoting effect of facile mass transfer and additional active centers

Efficient nitrate removal by nitrogen-doped carbon spheres electrodes with interconnected architecture in novel stirring capacitive deionization: Dual promoting effect of facile mass transfer and additional active centers

Metal-organic framework derived hollow nitrogen-doped carbon sphere with cobalt phosphide in carbon nanotube for efficient oxygen evolution

The sluggish kinetics of the electrocatalytic oxygen evolution reaction (OER) pose a significant challenge in the field of overall water splitting. Transition metal phosphides have emerged as promising catalysts for OER by modulating the charge distribution of surrounding atoms. In this study, we employed self-sacrificing templates to fabricate hollow N-doped carbon spheres containing small-sized Co2P embedded within carbon nanotubes through high-temperature calcination and phosphorization, referred to as HNCS-CNT-CoP. The obtained HNCS-CNT-CoP electrocatalyst exhibited excellent OER performance in an alkaline electrolyte due to the optimization of OH* adsorption energy and the large specific surface area created by the hollow structure. It demonstrated a low overpotential of 302 mV at a current density of 10 mA cm−2 and a low Tafel slope of 68.5 mV dec−1, attributed to the electron transport facilitated by the in situ formed carbon nanotubes. Furthermore, theoretical calculations revealed a suitable reaction energy (1.17 eV) in the critical formation of Co2P-*OOH for HNCS-CNT-CoP, significantly lower than the the rate-determining step of HNCS-CNT-Co (10.08 eV). These findings highlight the significance of hollow structures and Co2P-doping in the design of highly active non-noble metal OER electrocatalysts, enabling the reduction of energetic reaction barriers for future applications.

Co3O4 nanoparticles-embedded nitrogen-doped porous carbon spheres for high-energy hybrid supercapacitor electrodes

This work synthesizes cobalt oxide (Co3O4)-embedded nitrogen-doped porous carbon spheres (Co3O4@NPCS) with inherent hierarchical structures through hydrothermal and pyrolysis processes. The synthesized material shows porous spherical carbon with nitrogen functionalities and contains Co3O4 nanoparticles on the surface of the carbon framework. The hybrid supercapacitor (HSC) is fabricated by Co3O4@NPCS and NPCS as anode and cathode, respectively, using aqueous KOH as electrolyte. The HSC displays exceptional electrochemical performance over the wide voltage window of 1.5 V with a large capacitance of 464 F g−1 at 1 A g−1, a high energy of 98.5 Wh kg−1, and power of 1500 W kg−1. Long charge-discharge cyclic stability demonstrates 87.2 % capacitance retention of the HSC over 10,000 cycles with almost 100 % coulombic efficiency. Additionally, first principles investigations show that the improved hybrid supercapacitors performance is as a consequence of the increased conductivity and the charge transfer. The proposed electrode and hybrid design show a potential for future high-energy storage.

Cooperative catalytic platinum species accelerating polysulfide redox reactions for Li-S batteries

The shuttle effect derived from diffusion of lithium polysulfides (LiPSs) and sluggish redox kinetic bring about poor cycling stability and low utilization of sulfur, which have always been the key challenging issues for the commercial application of lithium-sulfur (Li-S) batteries. Rational design of cathode materials to catalyze Li2S dissociation/nucleation processes is an appealing and valid strategy to develop high-energy practical Li-S batteries. Herein, considering the synergistic effect of bidirectional catalysis on LiPSs conversion and enhanced chemical immobilization for LiPSs by heteroatom doping, Pt nanoparticles loaded on nitrogen-doped carbon spheres (Pt/NCS composites) were constructed as cathode materials. According to the dynamic evolution of Pt catalysts and sulfur species, Pt0 and Pt2+ species were identified as active species for the accelerated dissociation and nucleation of Li2S, respectively. Meanwhile, in-situ Raman results demonstrated the expedited conversion of sulfur species resulted from bidirectional catalysis of active Pt species, corresponding to boosted redox kinetics. Consequently, Pt/NCS cathode exhibited improved long-term cyclability with high initial capacity, along with enhanced rate capability. This work provides a facile approach to construct cathode materials with bidirectional catalysis on Li2S dissociation/nucleation, and sheds light on a more global understanding of the catalytic mechanism of metal catalysts during LiPSs conversion.

Selectively oxygen reduction reaction and strongly suppressed CO poisoning on PtZn nanoalloys decorated on N-doped carbon sphere

The development of a high-performance oxygen reduction reaction (ORR) catalyst with a low Pt content, high activity, and long-term durability is crucial as it can become a core item in the fuel cell market. In this study, the amount of Pt used in the catalyst is reduced by more than three-fold compared with commercial catalysts. Concurrently, a PtZn alloy, which does not use expensive transition metals, is introduced as an active species. Nitrogen-doped carbon sphere (CS), which serves as an electron sink, is used as a support; it acts as a Lewis base site and facilitates H+ adsorption during the ORR. The analytical results reveal that the introduction of Zn is significantly more favorable for the ORR compared with N-doping. O2-pulse temperature-programmed desorption (TPD) reveals that most of the O2 molecules are adsorbed on Zn, and CO-pulse TPD demonstrates that Zn suppresses CO poisoning in the PtZn alloys. The mass and specific activities of the Pt1Zn1/N-CS electrode at 0.9 V are 5.94 A mg–1 and 0.79 mA cm–2, respectively, and a rotational frequency of 2.5 e-site–1 s–1 is achieved. The electrochemical performance remains unchanged even after 5000 cycles. The ORR on the Pt1Zn1/N-CS electrode does not occur randomly on Pt and Zn; Pt and Zn selectively attract and reduce *O, *OH, or *OOH which generated as intermediates.

Microwave and template assisted synthesis of atomically dispersed Co–N2 sites on carbon spheres for Fenton-like reaction

Recently, single atomic metals supported on carbon materials have attracted great interests because of their high catalytic activity and stability in peroxymonosulfate (PMS)-based Fenton-like process. Herein, we propose a convenient strategy to synthesize Co single atoms supported on nitrogen-doped carbon spheres (Co@MNC) via microwave treatment. The microwave irradiation can simultaneously induce the formation of carbon defects and immobilize the Co single atoms in N doped carbon support in a few minutes. The obtained Co@MNC can activate PMS for efficient catalytic oxidation of organic pollutants. The radical quenching tests and electron paramagnetic resonance (EPR) verify that Co (IV)-oxo species, 1O2, and O2•− are responsible for the remediation of organic pollutants. Density functional theory (DFT) calculations confirm that unique and low coordinated Co–N2 on void or edge defects are favorable for PMS adsorption. The electrons will then transfer from Co atoms to adsorbed PMS via the bonded N. Co (IV)-oxo species and other ROSs are therefore generated for pollutants degradation. This work provides a fast method for the synthesis of single atom catalysts for efficient Fenton-like reactions.

Efficient electrocatalytic two-electron oxygen reduction over aminophenol formaldehyde resin-derived carbon microspheres

The electrocatalytic 2-electron oxygen reduction reaction (2e-ORR) to hydrogen peroxide (H2O2) required cheap and efficient electrocatalytic materials. Herein cheap 3-aminophenol formaldehyde resin microspheres were synthesized at a large scale of about 15 g in one run. By annealing it, nitrogen-doped carbon spheres could be conveniently obtained, which was found to be efficient electrocatalyst for 2e-ORR with the highest H2O2 selectivity of about 94% at 0.4 V vs RHE. The electrolysis H2O2 production rate over N-doped carbon in 0.1 M KOH solution reached 48 mmol gcat-1h−1. Aminophenol formaldehyde resin-derived carbon provided a cheap and effective catalyst for electrocatalytic H2O2 production.

Hollow Nitrogen-Doped porous carbon spheres decorated with atomically dispersed Ni-N3 sites for efficient electrocatalytic CO2 reduction

Hollow nitrogen-doped porous carbon spheres (HNCS) with plentiful coordination N sites, high surface area, and superior electrical conductivity are ideal catalyst supports due to their easily access of reactants to active sites and excellent stability. To date, nevertheless, little has been reported on HNCS as supports to metal-single-atomic sites for CO2 reduction (CO2R). Here we report our findings in preparation of nickel-single-atom catalysts anchored on HNCS (Ni SAC@HNCS) for highly efficient CO2R. The obtained Ni SAC@HNCS catalyst exhibits excellent activity and selectivity for the electrocatalytic CO2-to-CO conversion, achieving a Faradaic efficiency (FE) of 95.2% and a partial current density of 20.2 mA cm−2. When applied to a flow cell, the Ni SAC@HNCS delivers above 95% FECO over a wide potential range and a peak FECO of 99%. Further, there is no obvious degradation in FECO and the current for CO production during continuous electrocatalysis of 9 h, suggesting good stability of Ni SAC@HNCS.

Highly dispersed ultrasmall iron phthalocyanine molecule clusters confined by mesopore-rich N-doped hollow carbon nanospheres for efficient oxygen reduction reaction and Zn-air battery

Iron phthalocyanine (FePc) has attracted extensive attention due to its unique planar symmetric Fe-N4 sites, which are considered to be the ideal active sites for oxygen reduction reaction (ORR) catalysis. However, the electrocatalytic performance of FePc is still unsatisfactory due to its low intrinsic activity, inadequate exposure and low utilization rate of Fe-N4 active sites. Herein, we synthesize a novel hybrid catalyst (FePc-NHCS-500) by coupling dispersed FePc molecule clusters into the defect-rich nitrogen-doped hollow porous carbon spheres (NHCS). Benefiting from the confining effect of mesopores in the NHCS, the well dispersed ultrasmall FePc molecule clusters exhibit excellent ORR performance with Tafel slope of 41 mV dec−1, half-wave potential (E1/2) of 0.94 V and kinetic current density (Jk) of 25.39 mA cm−2 at 0.9 V. Moreover, the as-assembled Zn-air battery (ZAB) using the FePc-NHCS-500 electrocatalyst as air electrode exhibits excellent performance, with open circuit voltage (OCV) of 1.524 V, peak-power density of 230 mW cm−2 and specific capacity of 808.7 mAh g−1. This work not only designs a non-noble metal catalyst with excellent ORR performance, but also makes reasonable guidance for the practical application of the catalyst in renewable energy storage and conversion.

Electrocatalytic reduction of nitrate by copper/iron oxides supported on nitrogen doped carbon spheres

In recent years, electrocatalytic reduction has gained attention as a promising method for environmentally friendly nitrate treatment. The key to this approach is finding cathode materials with high activity, N2 selectivity, and stability. Researchers are therefore focused on creating efficient catalysts. In this study, nitrogen-doped carbon spheres (NMCS) loaded with Cu and Fe3O4 were synthesized from non-precious metals Fe and Cu and tested for nitrate reduction in water. The bimetal combination effectively reduces the formation of toxic NO2− intermediates and improves material impedance, accelerating electron transfer during the reaction. The mesoporous structure with high surface area also supports metal nanoparticle loading and reduces metal leaching during the process. The resulting Cu/Fe-NMCS-1–3 catalysts showed excellent NO3− reduction (97.04%) and 100% N2 selectivity using electrochlorination. After four cycles, no decline in electrocatalytic performance was observed, suggesting good stability and potential for electrocatalytic nitrate removal.

Functional Interlayer with Highly Dispersed Co1–XS Embedded in N-Doped Carbon Spheres as Trapping-Catalyst Nanoreactors for Advanced Lithium–Sulfur Batteries

Shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPSs) have become the bottleneck in lithium–sulfur (Li-S) batteries. Herein, hierarchically porous nitrogen-doped carbon spheres with highly dispersed Co1–XS nanoparticles (CoXS-NC) as a trapping-catalyst interlayer for high-performance Li-S batteries is proposed. The nitrogen-doped hierarchically porous carbon spheres generate high specific surface area and large pore volume which provide adequate sites for the adsorption of LiPSs and facilitate the good dispersion of Co1–XS nanoparticles. Nitrogen doping and Co1–XS modification improve the polarity, which promotes the adsorption and rapid conversion of LiPSs. The exceptional properties of the CoXS-NC interlayer are confirmed with an exceeding low delay rate of 0.031% per cycle after 1000 cycles at 0.5 C and an outstanding retention rate of 78.7% over 300 cycles at 2 C. Even employed with high sulfur loading of 6 mg cm–2, it also delivers a high initial areal capacity of 5.74 mAh cm–2 at 0.1 C with capacity retention of 4.58 mAh cm–2 after 100 cycles. This research opens up possibilities for the construction of multifunctional interlayers for use in commercial Li-S batteries.

Ultra-high-performance aluminum-based hybrid supercapacitors prepared for nitrogen-doped micro-mesoporous carbon sphere

Aluminum-based devices are promising candidates for the next generation of energy storage due to the advantages of high energy density, high safety, and low cost. The aluminum ion batteries (AIBs) are based on the electrochemical intercalation/deintercalation reactions against the electrodes, but the selection of the cathode is limited to the present. The cathode reactions of cation-type AIBs are plagued by the poor kinetics of solid-state diffusion from high charge density of Al3+ and anion-type AIBs show poor capacity due to the intercalation of large-sized chloroaluminate (AlCl4−) active ions into the cathode. Here, we deliberately adopted a hybrid capacitor-battery mechanism and employed a nitrogen-doped micro-mesoporous carbon sphere of a high specific area as the cathode and aluminum as the anode to construct an aluminum-based energy storage device. After optimization, it exhibits an excellent discharge capacity of 224 mA h g−1 at a current density of 300 mA g−1, and exceptional cycling performance with a discharge capacity as high as 114 mA h g−1 at 10 A g−1 after 35000 cycles. The ultra-high-performance aluminum-based hybrid supercapacitor (Al-HSC) may lead to a new direction for the development of aluminum-based energy storage devices.

Mn-single-atom nano-multizyme enabled NIR-II photoacoustically monitored, photothermally enhanced ROS storm for combined cancer therapy

RationaleTo realize imaging-guided multi-modality cancer therapy with minimal side effects remains highly challenging.MethodsWe devised a bioinspired hollow nitrogen-doped carbon sphere anchored with individually dispersed Mn atoms (Mn/N-HCN) via oxidation polymerization with triton micelle as a soft template, followed by carbonization and annealing. Enzyme kinetic analysis and optical properties were performed to evaluate the imaging-guided photothermally synergized nanocatalytic therapy.ResultsSimultaneously mimicking several natural enzymes, namely peroxidase (POD), catalase (CAT), oxidase (OXD), and glutathione peroxidase (GPx), this nano-multizyme is able to produce highly cytotoxic hydroxyl radical (•OH) and singlet oxygen (1O2) without external energy input through parallel and series catalytic reactions and suppress the upregulated antioxidant (glutathione) in tumor. Furthermore, NIR-II absorbing Mn/N-HCN permits photothermal therapy (PTT), enhancement of CAT activity, and photoacoustic (PA) imaging to monitor the accumulation kinetics of the nanozyme and catalytic process in situ. Both in vitro and in vivo experiments demonstrate that near-infrared-II (NIR-II) PA-imaging guided, photothermally enhanced and synergized nanocatalytic therapy is efficient to induce apoptosis of cancerous cells and eradicate tumor tissue.ConclusionsThis study not only demonstrates a new method for effective cancer diagnosis and therapy but also provides new insights into designing multi-functional nanozymes.Graphical