Nitrogen-doped Hollow Carbon Spheres Research Articles

Nitrogen-doped hollow carbon spheres for electrochemical detection of heavy metal ions

Nitrogen-doped hollow carbon spheres (N-HCSs) were successfully fabricated using silica sphere as template and resorcinol-formaldehyde resin as carbon precursor. Scanning electron microscopy and transmission electron microscopy demonstrated that diameters and shell thickness of N-HCSs were 325 and 25 nm, respectively. The N-HCS modified gold electrode was used for the square wave anodic stripping voltammetry for the individual determination of trace heavy metal ions (HMIs) such as Pb2+, Cu2+, and Hg2+ in drinking water. Electrochemical properties of modified electrode were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Moreover, the supporting electrolytes, pH, deposition potential, and deposition time were carefully studied. The N-HCS modified electrode exhibited the detection limit of 15, 17, and 2.35 nM for Pb2+, Cu2+, and Hg2+, respectively, which are significantly lower than the guideline values for drinking water quality provided by the World Health Organization. The electrochemical measurement results showed that the N-HCS structures exhibited wonderful adsorption and capacitive properties toward HMIs and were found to be useful for the simultaneous and selective electrochemical detection. Most importantly, herein we discussed the two types of test for simultaneous detection of Pb2+ and Hg2+, under the optimum experimental conditions. The sensitivity of Hg2+ increased in the presence of concentration range of Pb2+. Thus, this study provides a reliable method for online detection of low concentration Hg2+ and robust alternatives for heavy metal sensors.

Selective Low-Energy Carbon Dioxide Adsorption Using Monodisperse Nitrogen-Rich Hollow Carbon Submicron Spheres.

Monodisperse, nitrogen-doped hollow carbon spheres of submicron size were synthesized using hexamethoxymethylmelamine as both a carbon and nitrogen source in a short (1 h) microwave-assisted synthesis. After carbonization at 550 °C, porous carbon spheres with a remarkably high nitrogen content of 37.1% were obtained, which consisting mainly of highly basic pyridinic moieties. The synthesized hollow spheres exhibited high selectivity for carbon dioxide (CO2) over nitrogen and oxygen gases, with a capture capacity up to 1.56 mmol CO2 g-1. The low adsorption enthalpy of the synthesized hollow carbon spheres permits good adsorbent regeneration. Evaluation of the feasibility of scaling up shows their potential for large-scale applications.

Remarkable activity of nitrogen-doped hollow carbon spheres encapsulated Cu on synthesis of dimethyl carbonate: Role of effective nitrogen

A critical aspect in the improvement of the catalytic performance of Cu-based catalysts for the synthesis of dimethyl carbonate (DMC) is the development of an appropriate support. In this work, nitrogen-doped hollow carbon spheres (NHCSs), with 240 nm average diameter, 17 nm shell thickness, uniform mesoporous structure and a specific surface area of 611 m2 g−1, were prepared via a two-step Stӧber method. By varying the quantity of nitrogen-containing phenols used in the preparation it has been possible to control the nitrogen content and, consequently, the sphericity of the NHCSs. It was found that perfect spheres were obtained for nitrogen contents below 5.4 wt.%. The catalysts (Cu@NHCSs) were prepared by the hydrothermal impregnation method. The catalytic activity towards DMC synthesis was notably enhanced due to the immobilization effect on Cu particles and the enhanced electron transfer effect exercised by the effective nitrogen species, including pyridinic-N and graphitic-N. When the average size of the copper nanoparticles was 7.4 nm and the nitrogen content was 4.0 wt.%, the values of space-time yield of DMC and of turnover frequency (TOF) reached 1528 mg/(g h) and 11.0 h–1, respectively. The TOF value of Cu@NHCSs was 6 times higher than non-doped Cu@Carbon (2.1 h−1). The present work introduces the potential application of nitrogen-doped carbon materials and presents a novel procedure for the preparation of catalysts for DMC synthesis.

Efficient N-doping of hollow core-mesoporous shelled carbon spheres via hydrothermal treatment in ammonia solution for the electrocatalytic oxygen reduction reaction

Nitrogen-doped hollow core-mesoporous shelled carbon spheres (NHMCSs) are successfully synthesized via a simple, scalable hydrothermal treatment of hollow mesoporous carbon spheres (HMCSs) with ammonia water as the nitrogen source. This strategy not only efficiently introduces nitrogen atoms into the carbon framework, but also causes the fracture of some spheres and increases the shell thickness of hollow spheres. The subsequent pyrolysis at 900 °C in Ar results in the transformation of pyrrolic-N to graphitic-N. The resulting NHMCS-900 has a high BET specific surface area (648 m2 g−1), large pore volume (1.06 cm3 g−1), hierarchical mesoporosity (2–8, 43.9 nm), uniform shells and large hollow cores. The electrochemical experiments indicate that NHMCS-900 as a metal-free electrocatalyst possesses the improved ORR activity with a close four-electron reaction pathway (∼3.88) and a peroxide yield lower than 10% over a wide potential range in alkaline solution. Contrary to commercial Pt/C, NHMCS-900 is unaffected by the methanol crossover effect and exhibits excellent long-term durability with 97.0% of the initial current density after 5.56 h of continuous operation. The excellent activity of NHMCS-900 is mainly attributed to the high relative content of pyridinic-N and graphitic-N. Besides, the superior activity is also ascribed to its unique structural properties, promoting fast and efficient mass transfer and providing inner and outer surfaces with N-relative active sites for ORR.

Fabrication of hollow N-doped carbon supported ultrathin NiO nanosheets for high-performance supercapacitor

The polydopamine-assisted hierarchical composites of ultrathin NiO nanosheets uniformly coating on the surface of hollow nitrogen-doped carbon spheres (HNCS-NiO) were successfully fabricated via a facile synthesis method. The hierarchical HNCS-NiO composites as electrode materials for supercapacitors exhibit high capacitance of 550.4Fg−1 (880.6mFcm−2) at the current density of 0.5Ag−1 (0.8mAcm−2), and present a good rate capability. The composites display excellent improved electrochemical properties not only because their hierarchical hollow nanostructures can provide enough space to buffer the volume expansion during the reversible intercalation/deintercalation processes, but also because their larger specific surface areas can provide adequate active sites for the redox electrochemical reaction.

Nitrogen-doped hollow carbon spheres derived from amination reaction of fullerene with alkyl diamines as a carbon catalyst for hydrogenation of aromatic nitro compounds

Hollow carbon nanospheres have received much interest by virtue of the special shape, low density and large interior void space, allowing their many potential applications. Here we report a template-free route to produce nitrogen-doped hollow porous carbon spheres (denoted as N-HPCSs) through amination reaction of C60 with alkyl diamines and subsequent carbonization. The size of wall thickness and cavity of hollow carbon spheres could be easily regulated by the chain length of alkyl diamines. After carbonization in Ar atmosphere, the obtained N-HPCSs exhibited excellent activity and recyclability for hydrogenation of aromatic nitro compounds with hydrazine hydrate. The facile approach presented in this work provides a new way for preparation of doped hollow porous carbon spheres.

Nitrogen-Doped Hollow Mesoporous Carbon Spheres for Efficient Water Desalination by Capacitive Deionization

Water desalination performance of capacitive deionization (CDI) largely depends on electrode materials properties. Rational design and regulation of the structure and composition of electrode materials to acquire high CDI performance is of great significance. Herein, nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) were investigated as electrode material for CDI application. To understand the effect of structure and composition on CDI performance, another two CDI electrode materials, i.e., hollow mesoporous carbon spheres (HMCSs) and solid mesoporous carbon spheres (SMCSs) were prepared for comparison. The obtained N-HMCSs possessed unique hollow cavity and excellent nitrogen doping property, resulting in fast ion diffusion, good charge transfers ability and fine wettability. Compared with HMCSs and SMCSs electrodes, N-HMCSs electrode exhibited an improved electrosorption capacity and rate, demonstrating the dependence of CDI performance on the synergistic effect of hollow structure and nitrogen ...

Nitrogen doped porous hollow carbon spheres for enhanced benzene removal

Abstract In this work, nitrogen doped hollow carbon spheres (NHCS) were synthesized via modified “silica-assistant” route and further examined as adsorbents for the removal of benzene, which is a typical volatile organic compounds (VOCs). To understand the structure and composition on benzene removal, solid carbon spheres (SCS), nitrogen doped solid carbon spheres (NSCS) and hollow carbon spheres (HCS), were also prepared for comparison. The structure and morphology characterization revealed that the resultant carbon spheres possess uniform spherical shape, abundant micropores and mesopores with solid or hollow structure and high pore volume. Combined with Raman and XPS spectra, the composition of carbon spheres was successfully tailored via introduction of nitrogen atom into carbon matrix. To present the removal performance of carbon spheres for VOCs, the dynamic adsorption behavior was evaluated. Attributed to the combined effect of hollow structure and nitrogen doping, NHCS presents remarkable dynamic adsorption performance for benzene vapor with adsorption capacity of 766 mg/g. The enhancement on desorption behaviors resulting from hollow structure of HCS is confirmed when compared with SCS. Carbon spheres exhibit good regenerability based on desorption experiment. The mechanism of enhanced adsorption performance caused by nitrogen doping is clarified as the combined action of adjustment on porous structure and composition. These results indicate that NHCS would become a promising candidate for VOCs removal.

Hollow Nitrogen-Doped Carbon Spheres with Fe3O4 Nanoparticles Encapsulated as a Highly Active Oxygen-Reduction Catalyst

The development of nonprecious electrocatalyst with low cost and high efficiency for the oxygen reduction reaction (ORR) is a main challenge for electrochemical energy technology. In this work, a hierarchical hollow core-shell structured N-doped carbon spheres (N-HSCS), in which Fe3O4 nanoparticles are encapsulated (Fe3O4/N-HCSC) has been successfully prepared. The Fe3O4/N-HCSC electrocatalyst exhibits a remarkable catalytic performance toward ORR. The porous hollow core-shell structure and synergistic effect between Fe3O4 and protective nitrogen-doped graphitic layers are mainly responsible for such an excellent ORR catalytic property and stability. This work demonstrates a promising strategy of nanostructure-engineering to the future design and preparation of highly efficient non-noble metal electrocatalysts.

Silica-Assisted Assembly for Synthesis of Nitrogen-Doped Hollow Mesoporous Carbon Spheres as Supercapacitors

Nitrogen-doped hollow mesoporous carbon spheres (NHMCSs) are synthesized by a one-pot silica-assisted assembly process and applied in supercapacitors. SiO2 spheres act as interior cores, which is crucial to form the hollow structure. 3-Aminophenol/formaldehyde resin and tetraethylorthosilicate (TEOS) cross-link through hydroxyl groups, then together directly deposit and co-assemble with cetyltrimethylammonium bromide via electrostatic interactions leading to an outer carbon-silica shell surrounding the SiO2 spheres. In the preparing process, TEOS not only acts as silica-assisted material and assembles with 3-aminophenol/formaldehyde resin, but also creates more pores to improve the surface area. After carbonization and silica etching, the NHMCSs with spherical morphology, uniform mesoporous, hollow structure, high surface area and nitrogen content are obtained. The nitrogen-doped, hollow and mesoporous structure are conducive to improve the capacitance. As electrode materials, the NHMCSs exhibit a high capacitance (201 F g−1 at 1 A g−1) and a good cycling stability (83.3% after 5000 cycles). These results reveal that NHMCSs can be expected to be promising electrode materials for electrochemical capacitors.

Nitrogen-doped hollow mesoporous carbon spheres as a highly active and stable metal-free electrocatalyst for oxygen reduction

Nitrogen-doped hollow mesoporous carbon spheres (NHCSs) were successfully prepared via a simple, scalable hydrothermal method, followed by thermal treatment at 650 °C in ammonia atmosphere and subsequent high temperature annealing at 800–1000 °C in nitrogen, respectively. The resulting NHCSs with a particle diameter of ∼150 nm and a shell thickness of ∼20–25 nm have high specific surface areas (738–820 m2 g−1), large pore volume (0.50–0.56 cm3 g−1), bimodal pores system (3.9 and 51.6 nm) and adjustable N-doping levels (3.6–7.8 at.%) depending on the pyrolysis temperature. The unique structure of hollow spheres for NHCSs with uniform mesopores throughout the shells can both promote fast mass transfer and provide inner and outer surfaces with high density of N-related active sites, thus improving the reaction kinetics. The NHCS-1000 (annealed at 1000 °C) exhibited not only comparable ORR activity with a direct four-electron reaction pathway in terms of onset and half-wave potentials, and limiting current densities, but superior long-term durability and methanol-tolerance to commercial Pt/C catalyst, because it has the highest relative content of graphitic-N and pyridinic-N groups, indicating their crucial roles in ORR. The NHCS-1000 with excellent ORR performance is of potential to replace Pt/C catalyst for ORR in practical applications.

Nitrogen-doped hollow carbon spheres for supercapacitors

We present high nitrogen-doped hollow carbon spheres (HNHCSs) via cooperative template-directed coating method. The SiO2 spheres serve as hard template; ionic liquids, such as 1-hexadecyl-3-methylimidazolium bromide (CMMB), serve as cationic surfactant; resorcinol formaldehyde (RF) resins as carbon source; and melamine as nitrogen source. The CMMB used in the coating procedure improves the SiO2 spheres dispersion in the reaction media and introduces nitrogen atom into carbon skeleton. The CMMB, SiO2 spheres, and RF resins self-assemble into inorganic–organic core–shell structures through electrostatic interaction. After being treated with melamine, the nitrogen content of the sample further improved, which can enhance the performance of supercapacitor. Due to high nitrogen content, specific surface area, and unique hollow structure, the HNHCSs exhibit a reversible specific capacitance of 368 F g−1 at 0.2 A g−1 in 6 M KOH, and maintains a good high-class capacitance retention capability (85.1%) at 5.0 A g−1 for up to 5000 cycles. These results show that the HNHCSs with high nitrogen content, specific surface area, and hollow structure represent a promising alternative of efficient electrode material for supercapacitor.

Controllable synthesis of nitrogen-doped hollow mesoporous carbon spheres using ionic liquids as template for supercapacitors

We have demonstrated a facile and controllable synthesis of monodispersed nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) using resorcinol/formaldehyde resin as a carbon precursor, tetraethyl orthosilicate as a structure-assistant agent, ionic liquids (ILs) as soft template, partial carbon sources, and nitrogen sources. The sizes and the architectures including hollow and yolk-shell of resultant carbon spheres can be efficiently controlled through the adjustment of the content of ILs. Alkyl chain length of the ILs also has an important effect on the formation of N-HMCSs. With proper alkyl chain length and content of ILs, the resultant N-HMCSs show monodispersed hollow spheres with high surface areas (up to 1158m2g−1), large pore volumes (up to 1.70cm3g−1), and uniform mesopore size (5.0nm). Combining the hollow mesoporous structure, high porosity, large surface area, and nitrogen functionality, the as-synthesized N-HMCSs have good supercapacitor performance with good capacitance (up to 159Fg−1) and favorable capacitance retention (88% capacitive retention after 5000 cycles).

Nitrogen-doped hollow carbon spheres for supercapacitors application

Highly monodispersed nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) are prepared through a “silica-assisted” synthetic strategy with cetyltrimethylammonium bromide as cationic surfactant, 3-aminophenol/formaldehyde as carbon and nitrogen sources, tetraethyl orthosilicate as the structure-assistant agent. The particle sizes and shell thicknesses of the N-HMCSs can be easily tuned in the range of 130–290 nm and 17–42 nm, respectively, by simply modifying the ethanol-water volume ratio. The obtained N-HMCSs have high surface areas (750–1006 m2 g−1), large pore volumes (1.01–1.41 cm3 g−1), uniform mesoporous size of ∼3 nm, and high nitrogen loading content of 6.86 wt%. Due to these characteristics, the N-HMCSs exhibit a specific capacitance of 170 F g−1 at a current density of 1.0 A g−1 in 6 M KOH aqueous electrolyte. Besides, the capacitance still remains 94% after 5000 charge/discharge cycle, suggesting excellent cycling stability. The N-HMCSs may show promising prospects as electrode materials for electrochemical capacitors.

Hierarchical Nanocomposite of Hollow N-Doped Carbon Spheres Decorated with Ultrathin WS2 Nanosheets for High-Performance Lithium-Ion Battery Anode.

Hierarchical nanocomposite of ultrathin WS2 nanosheets uniformly attached on the surface of hollow nitrogen-doped carbon spheres (WS2@HNCSs) were successfully fabricated via a facile synthesis strategy. When evaluated as an anode material for LIBs, the hierarchical WS2@HNCSs exhibit a high specific capacity of 801.4 mA h g(-1) at 0.1 A g(-1), excellent rate capability (545.6 mA h g(-1) at a high current density of 2 A g(-1)), and great cycling stability with a capacity retention of 95.8% after 150 cycles at 0.5 A g(-1). The Li-ion storage properties of our WS2@HNCSs nanocomposite are much better than those of the previously most reported WS2-based anode materials. The impressive electrochemical performance is attributed to the robust nanostructure and the favorable synergistic effect between the ultrathin (3-5 layers) WS2 nanosheets and the highly conductive hollow N-doped carbon spheres. The hierarchical hybrid can simultaneously facilitate fast electron/ion transfer, effectively accommodate mechanical stress from cycling, restrain agglomeration, and enable full utilization of the active materials. These characteristics make WS2@HNCSs a promising anode material for high-performance LIBs.

Nitrogen-doped hollow carbon spheres wrapped with graphene nanostructure for highly sensitive electrochemical sensing of parachlorophenol

Owing to awfully harmful to the environment and human health, the qualitative and quantitative determination of parachlorophenol (PCP) is of great significance. In this paper, by using silica@polydopamine as template, nitrogen-doped hollow carbon spheres wrapped with reduced graphene oxide (NHCNS@RG) nanostructure was prepared successfully via a self-assembly approach due to the electrostatic interaction, and the obtained NHCNS@RG could exhibit the unique properties of NHCNS and RG: the NHCNS could impede the aggregation tendency of RG and possess high electrocatalytic activity; the RG enlarges the contacting area and offers many area-normalized edge-plane structures and active sites. Scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray diffraction and electrochemical method were used to characterize the morphology and structure of NHCNS@RG. Then, the NHCNS@RG hybrids were applied for the electrochemical sensing of PCP, under the optimized conditions, the detection limit of PCP obtained in this work is 0.01μM and the linear range is 0.03–38.00μM.

Ti4O7-Filled Nitrogen-Doped Carbon/Ti4O7 Double-Layer Spheres As Sulfur Host for Advanced Lithium Sulfur Batteries

Holding the largest market share, Li-ion batteries have been optimized for the post two decades, although their capacity is limited by the energy density of intercalation materials to ~300 mA h g-1. New chemistries are being sought as the next-generation energy storage device with higher energy density and reduced cost. Lithium-sulfur batteries, with their environmental benignity, competitive cost and high theoretical energy density (~2600 Wh kg-1), were intensively investigated in recent years as a promising candidate to replace the current lithium ion batteries. In this study, nitrogen-doped hollow carbon spheres (NC) with conducting Magnéli-phase Ti4O7 as the filling agent were designed delicately by employing one-step approach to reduce TiO2 and carbonize polydopamine on pre-synthesized SiO2 spheres as the sacrificial template, followed by the infiltration of sulfur at 155oC. The properties and performance of the composite (NC/Ti4O7/S) were examined and evaluated as the cathode material for lithium sulfur (Li-S) batteries. It was demonstrated that the sulfur particles could be well contained in the NC/Ti4O7 shells with the sulfur content being ~70%, while the particle size and thickness of the carbon shell can be easily tuned by controlling the reactant concentration and reaction time. The assembled battery exhibited an initial capacity of ~938 mAh g-1 at 0.5 C with a high retention rate of 94.8% after 100 cycles, which corresponds to a capacity decay of 0.052% per cycle. The NC/Ti4O7/S composite provides a promising cathode material for future lithium sulfur batteries. Figure 1

Mesoporous nitrogen-doped carbon hollow spheres as high-performance anodes for lithium-ion batteries

Nitrogen-doped mesoporous carbon hollow spheres (N-MCHSs) were prepared using mesoporous silica hollow spheres as template and dopamine as carbon precursor. The N-MCHSs demonstrate high specific surface area and vegetable sponge-like mesoporous shell with interconnected “carbon bridges”, facilitating continuous electron transport and Li ion diffusion, and making the whole structure more stable. The influence of N contents and N-bonding configuration on the Li storage of N-MCHSs is discussed. The N-MCHSs carbonized at 800 °C demonstrate high reversible capacity and excellent rate performance, delivering a capacity of 485 mAh g−1 at a current of 0.5 A g−1 after 1,100 cycles. Even up to 4.0 A g−1, a high capacity of 214 mAh g−1 can be remained. The high electrochemical performance of N-MCHSs can be ascribed to mesoporous carbon hollow spheres structure and high level pyridinic nitrogen doping.

Nitrogen-Doped Hollow Carbon Spheres As a Sensitive Electrochemical Sensor for Simultaneous Determination of Pb (II) and Hg (II)

Keywords: Electrochemical sensor; Hollow Carbon Spheres; Anodic stripping voltammetry (ASV); Heavy metal ions. Heavy metal ions (HMIs) pose a detrimental risk to human health and environment due to their higher toxicity [1]. Among those ions, both mercury and lead are the well-known toxic and relatively widespread water pollutants that could damage to the brain, heart, kidneys, lungs, and the immune system [2]. The electrochemical method as a promising and elegant technique has been widely used for trace detecting of HMIs due to the excellent sensitivity, low cost, short analysis time, and easy portability [3-4]. We fabricated a nanostructured nitrogen-doped hollow carbon spheres (N-HCSs), which was a kind of modified carbon nanomaterials and used in HMIs detection with enhanced performance for the first time. As-prepared N-HCSs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption and desorption analysis, X-ray photoelectron spectroscopy (XPS). Electrochemical properties of modified electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The operational parameters which have influence on the deposition and stripping of metal ions, such as supporting electrolytes, pH value, and deposition time were carefully studied. Under optimized conditions, the anodic stripping voltammetric performance toward HMIs were evaluated using square wave anodic stripping voltammetry (SWASV) analysis. The detailed study of the enhancing electrochemical response in stripping voltammetry for the individual and simultaneous detection of ultratrace Pb2+ and Hg2+ in drinking water was described. The detection limits achieved (15 nM and 2.35 nM for Pb2+ and Hg2+) are much lower than the guideline values in drinking water given by the World Health Organization (WHO)[5]. In addition, an interesting phenomenon of mutual interference between Pb2+ and Hg2+was observed. When the concentration of Pb is fixed, the sensitivity to Hg lowers a little and the response current of Pd doesn't change with the increasing concentration of Hg. Meanwhile, when the concentration of Hg is fixed, the sensitivity to Pb lowers a little and the response current of Hg does increase with the increasing concentration of Pb. This study provides a novel nitrogen-decorated hollow spheres carbon-based material for the construction of sensitive electrochemical sensors that meet the needs of environmental control.

Nitrogen-doped hollow carbon spheres with highly graphitized mesoporous shell: Role of Fe for oxygen evolution reaction

There are many studies portraying iron (Fe) and nitrogen (N)-functionalzed carbon as an electrocatalyst along with possible elucidation of catalytically active sites. Despite continuous controversial debate on the active sites/species, the presence of N is believed to be undeniably needed for the efficient catalysis, whereas the necessity and role of Fe are still debated. To clearly understand the role of Fe in Fe and N-functionalized electrocatalyst, N-doped hollow mesoporous shell carbon (N-HMSC) is prepared as a uniform model electrocatalyst by a simple template nanocasting using Fe phthalocyanine (FePc) as a single precursor for carbon, N, and Fe. It is found that the presence of Fe in N-HMSC leads to the efficient graphitization of N-HMSC structure, which can be beneficial for electrocatalytic oxygen evolution reaction (OER). Interestingly, it is observed that Fe is a must for the preparation of high efficient catalyst, but may not be necessary for OER.