Nitrogen-doped Reduced Graphene Oxide Research Articles

Lead–carbon hybrid ultracapacitors fabricated by using sulfur, nitrogen-doped reduced graphene oxide as anode material derived from spent lithium-ion batteries

Lead–carbon hybrid ultracapacitors fabricated by using sulfur, nitrogen-doped reduced graphene oxide as anode material derived from spent lithium-ion batteries

Sulfur or nitrogen-doped rGO supported Fe-Mn bimetal – organic frameworks composite as an efficient heterogeneous catalyst for degradation of sulfamethazine via peroxydisulfate activation

In this work, sulfur/nitrogen modified reduced graphene oxide (S/N-rGO) was employed as both electron shuttle and support to fabricate Fe-Mn bimetallic organic framework@S/N-rGO hybrids (BOF@S/N-rGO) via a facile two-step solvothermal route. Compared with the transition metal ions (Fe2+/Mn2+), the classical metal oxide catalyst (Fe2O3 and Fe3O4) and nano zero-valent iron (nZVI), BOF@S/N-rGO catalyst can more effectively activate peroxydisulfate (PDS) with ultra-low concentration (0.05 mM) to degrade sulfamethazine (SMT). Quenching experiments, electron paramagnetic resonance (EPR) measurement and linear sweep voltammetry (LSV) showed that the activation pathways of PDS between the two catalysts were different. In BOF@N-rGO+PDS system, the degradation of SMT was mainly attributed to the oxidation of radicals including SO4•− and •OH, especially SO4•− . However, in BOF@S-rGO+PDS system, in addition to the radical pathway, there are also non-radical pathways, namely 1O2 and direct electron transfer. Furthermore, the applicability of BOF@S/N-rGO used in the PDS-mediated advanced oxidation processes (AOPs) was systematically investigated in terms of the effects of operating parameters and coexisting substance (anions and humic acid (HA)), the degradation of other pollutants, as well as the stability and reusability of the catalyst. This study proved that BOF@S/N-rGO was a promising activator of PDS with ultra-low concentration for the degradation of SMT.

Characterisation of Novel Nitrogen Doped Reduced Graphene Oxide

The physical and electrochemical properties of a novel nitrogen-doped reduced graphene oxide (N-rGO) material were studied. The novel material was synthesized using biological microorganisms and non-toxic chemicals. In addition, the effect of the high shear treatment on material particle size and suspension stability was investigated. The material was characterized by particle size distribution analysis, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, and gas adsorption methods. The N-rGO material has low porosity but its specific surface area and total pore volume increased fourfold and tenfold, respectively, due to the high shear treatment. Electrochemical oxygen reduction activity measurements were conducted in 0.1 M HClO₄ and 0.1 M KOH solutions using rotating disc electrode and cyclic voltammetry methods.

Pd-Fe2O3 decorated nitrogen-doped reduced graphene oxide/CNT nanohybridas electrocatalyst for proton exchange membrane fuel cell

Many attempts are being made globally to synthesize and functionalize different nanomaterials to facilitate the commercial application of polymer electrolyte membrane (PEM) fuel cells. In this work, firstly nitrogen-doped reduced graphene oxide (NRGO) was synthesized and mixed with carbon nanotubes (CNT) followed by the incorporation of Pd- and Fe-content through a combined thermal annealing and polyol process to obtain a unique nanohybrid Pd-Fe2O3 decorated NRGO-CNT to be applied as an effective electrocatalyst. The experimental analyzes suggest thorough distribution of the Pd-Fe2O3 nanoparticles over NRGO and CNT layers. The electrochemical activity of the Pd-Fe2O3/NRGO-CNT nanohybrid showed the enhanced electrochemical active surface area (ECSA) of ~44.92 m2/g than that of Pt/C ~37.86 m2/g. The developed nanohybrid also displays remarkable enhancement in their stability in contrast to NRGO-CNT/Pd, NRGO/Pd and commercially available Pt/C catalyst. These interesting features make the developed nanohybrid suitable for fuel cell applications.

Three-dimensional nitrogen-doped graphene oxide beads for catalytic degradation of aqueous pollutants

Metal-free graphene-based catalysts have demonstrated excellent performance in advanced oxidation processes (AOPs). However, the recovery and reusability of these nanocatalysts are still a major issue. In this study, three dimensional (3D) nitrogen-doped reduced graphene oxide beads (NrGOb) were synthesized via a self-assembly method and then applied in heterogeneous activation of peroxymonosulfate (PMS) for the oxidation of hydroxybenzoic acid (HBA). The materials (NrGOb) were annealed at various temperatures ranging from 500 to 1000 °C, and the resulting NrGOb derived from 800 °C (NrGOb-800) exhibited the best performance for PMS activation. To avoid the challenging recovery, the degradation experiments were also performed in a packed-bed catalytic reactor. Various reaction parameters were investigated to optimize the efficiency of the system. Electron paramagnetic resonance (EPR) and quenching tests were carried out to differentiate the contribution of reactive radicals (SO4•-and•OH) in the degradation process and then aided in illustrating the degradation mechanism. Finally, the stability and reusability of the catalytic beads were investigated. The efficiency slightly declined with increased cycles; however, catalyst regeneration would be able to partially restore the active sites. The results suggest the feasibility of exploiting graphene-based macrostructures on the AOPs platform for the degradation of organic pollutants in commercial wastewater treatment plants.

Elaborate interface design of CoS2/Fe7S8/NG heterojunctions modified on a polypropylene separator for efficient lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered as the most promising energy storage system due to their high specific capacity and resource abundance. However, the low electronic conductivity of S8 and Li2S, shuttle effects of lithium polysulfides (LiPSs), and sluggish reaction kinetics hinder the advance of Li-S batteries. The key to addressing the issues mentioned above is to improve the electrical conductivity of the cathode, enhance the absorption of LiPSs and accelerate the conversion. Nevertheless, it is a great challenge to simultaneously optimize them all. In this study, by incorporating the virtues of the large lamellar structure and strong nonpolar adsorption of reducedgrapheneoxide (rGO), strong polar polysulfide adsorption of Fe7S8 and excellent catalytic polysulfide activity of CoS2, a CoS2/Fe7S8 heterostructure grown on the nitrogen-doped rGO (CoS2/Fe7S8/NG) was prepared. Besides, the experiments demonstrate that the designed CoS2/Fe7S8/NG possesses strong absorption and superior catalytic ability towards LiPSs. Subsequently, when applied as a modification layer for the polypropylene (PP) separator, the CoS2/Fe7S8/NG-PP coupled with CNT/S cathode exhibits a high initial discharge capacity (1459 mAh g−1 at 0.1 A g−1), a reversible capacity of 731 mAh g−1 after 100 cycles at 0.2 A g−1, and a robust cycling stability (0.058 % flowing rate at 1.0 A g−1). Moreover, the cathode with a high sulfur mass loading of ∼ 3.8 mg cm−2 can still display a reversible capacity of 663 mAh g−1 after 100 cycles at 0.2 A g−1. More importantly, the study shown herein shed light for the design of heterojunction to improve the electrochemical performance of Li-S batteries.

Facile synthesis of black N-TiO2 / N-RGO nanocomposite for hydrogen generation and electrochemical applications: New insights into the structure-performance relationship

Strenuous efforts have been dedicated to obtain efficient photocatalysts with an amplified hydrogen generation employing TiO2 and reduced graphene oxide (RGO). Accordingly, black - nitrogen doped TiO2/nitrogen doped reduced graphene oxide (BNTNG) has been strategically synthesized in low temperature/pressure, vacuum annealing process using ethanol for a better photocatalyst. The pyrrolic nitrogen stabilized photocatalyst (BNTNG-2 – 2h Ultrasonication) has found to show an augmented hydrogen generation and electrochemical potency than its 1 h and 3 h counterparts (BNTNG-1 and BNTNG-3) due to the attachment of C2H4 fragments from ethanol restoring sp2 hybridization in nitrogen doped reduced graphene oxide (NRGO). Meanwhile, reduction in hydrogen production and capacitance of BNTNGs than its white analogue can be substantiated to the presence of N-O species along with oxygen vacancies / Ti3+ in BNTNG promoting electron/hole recombination centers. The recyclability of the photocatalyst is ascertained over five consecutive cycles. Plausible mechanism has been proposed for the nuances of N-O moiety and restoration of sp2 graphitic structure in BNTNG-2.

A robust approach for designing N‐doped reduced graphene oxide/polyaniline nanocomposite‐based electrodes for efficient flexible supercapacitors

Abstract2D multilayered reduced graphene oxide (rGO) has received enormous research interest as a potential electrode material for flexible supercapacitor (FSC), owing to its excellent electrochemical and mechanical properties. However, rGO suffers from the restacking of graphene (GN) layers, lower electrical conductivity resulting from the residual oxygen functional groups and the relatively poor real‐time electrochemical performance. One of the finest ways overcoming the drawbacks of rGO by doping heteroatom into GN network and surface modification to enhance its electrochemical properties. In this work, a simple and robust approach for designing an efficient and high‐performance flexible electrode with nitrogen‐doped reduced graphene oxide (N‐rGO) framework coupled with surface modification through in situ chemical polymerization with aniline to form a long‐range interconnected polyaniline (PANI) nanostructure is presented. In a two‐electrode system, PANI/N‐rGO flexible electrode has delivered a higher specific capacitance of 322 F g−1 at a current density of 1 A g−1. Further, the composite exhibited notable cyclic stability over 1000 charge–discharge cycles. Surface‐modified in‐situ grown PANI nanostructures on N‐rGO nanosheets prevent the volume changes that occur in PANI during the charge–discharge process, and offer a higher charge transportation rate throughout the surface area. As a result of enhanced electrochemical properties, PANI/N‐rGO composites provide a feasible route for designing FSCs.

NiS1−xSex Nanoparticles Anchored on Nitrogen-Doped Reduced Graphene Oxide as Highly Stable Anode for Sodium-Ion Battery

Nickel sulfides are regarded as one of the promising anode materials for sodium-ion batteries (SIBs), but the sluggish electrodes kinetics and rapid capacity decay, caused by their intrinsic low electrical conductivity and high bulk expansion, greatly limit their practical application. To overcome these obstacles, nano-sized, selenium-doped, nickel sulfide particles, anchored on nitrogen-doped reduced graphene oxide composites (NiS1−xSex@N–rGO), are rationally synthesized. The broad Na+ diffusion channels, resulting from Se doping, as well as the short Na+ transferring path, attributed from nano-size scale of NiS1−xSex particles, endow NiS1−xSex@N–rGO composites with ultrafast storage kinetics. Moreover, strong coupled effect between the NiS1−xSex and N–rGO is beneficial to the uniform dispersion of NiS1−xSex nanoparticles, improving electrical conductivity and suppressing the volume variation in charge/discharge process. Furthermore, the cut-off discharge voltage is modulated to realize the smaller volume change during cycle process. As a result, the fabricated anode of SIBs based on NiS1−xSex@N–rGO composites exhibits a high specific capacity of 300 mAh g−1, at the current density of 1 A g−1, after 1000 cycles with almost no capacity degradation.

The organic contaminants degradation in Mn-NRGO and peroxymonosulfate system: The significant synergistic effect between Mn nanoparticles and doped nitrogen

A family of graphene-based activators including reduced graphene oxide (RGO), nitrogen doped reduced graphene oxide (NRGO), zero-valent manganese loaded reduced graphene oxide (Mn-RGO) and zero-valent manganese loaded N-doped reduced graphene oxide (Mn-NRGO) were fabricated to activate peroxymonosulfate (PMS) for bisphenol A (BPA) degradation. A significant synergistic effect between loaded manganese nano-particles (Mn-NPs) and doped N was revealed by comparing the apparent reaction rate constants with about 12.4, 7.6 and 10.5-folds enhancement when compared Mn-NRGO with RGO, NRGO, Mn-RGO, respectively. By integrating the results of chemical scavenger experiment, electron paramagnetic resonance test, galvanic oxidation process, PMS stoichiometric efficiency, linear sweep voltammetry and in-situ Raman spectrum, a predominant outer-sphere catalyst-PMS complexes mediated electron transfer pathway was uncovered. Based on kinetic studies, the specific contribution of synergistic effect was quantified to be at least 70%. The calculated Fermi level advanced by 0.03 eV in Mn-NG compared with that in NG, demonstrating that Mn-NG is more liable to donate electrons to PMS. The Eads and lO-O results pointed out that synergistic effect between Mn-NPs and doped N relied on the intimate affinity between Mn-NPs and HSO5– which triggered more uneven distribution of charge on the whole carbon sheets, and more adsorption of HSO5– on carbon framework. These newly created adsorption consequently reinforcing the formation of catalyst-PMS complexes and the elevation of mediated electron transfer pathway. Overall, this study firstly provides a comprehensive and definite insight of the synergistic effect between loaded Mn-NPs and doped-N on carbon materials for promoting PMS activation to degrade organics.

Facile synthesis of Fe-MoS2/NRGO composite material as effective electrocatalyst for high-efficiency hydrogen evolution reaction

Developing economical and efficient electrocatalysts with nonprecious metals for the hydrogen evolution reaction (HER), is pivotal for large-scale hydrogen production. With its many active sites and fast charge-transfer edges, earth-abundant MoS2 is a promising HER electrocatalyst in acidic solution. Here, we have synthesized an improved HER catalyst by exposing more active edge sites: iron-doped MoS2 was successfully supported on nitrogen-doped RGO (Fe-MoS2/NRGO). It shows significant catalytic advantages, with a very low overpotential of only 77.8 mV at 10 mA·cm−2, and a Tafel slope of 41 mV·dec-1. This capability is better than majority MoS2 electrocatalysts previously reported. Density functional theory (DFT) simulations show that the adsorption of Fe and N atoms decrease the energy barrier required to actuate the HER course and improve the internal activity of MoS2. In addition, DFT and experimental consequences showed the excellent electrocatalytic performance comes from the three-dimensional nanostructure, which fully exposes the active sites and affords a rapid charge transfer way for the electrolyzed water. The study will design advanced high-performance MoS2 catalyst to provide a potential method, which is achieved by regulating the activity of HER sites and electron transfer.

Gadolinium sesquisulfide anchored N-doped reduced graphene oxide for sensitive detection and degradation of carbendazim

Agriculture is having a major role in solving issues associated with food shortages across the globe. Carbendazim (CZM) is one of the fungicides which is commonly used in agriculture to grow crops in large quantities and fast. Monitoring CZM content is in high demand for environmental remediation. The present work deals with the synthesis of gadolinium sesquisulfide anchored Nitrogen-doped reduced graphene oxide (Gd2S3/NRGO) through a simple microwave-assisted method. X-ray diffraction and morphological studies confirm the formation of the nanocomposite. Gd2S3/NRGO showed enhanced activity both in electrochemical detection and light-driven degradation of CZM compared to Gd2S3 and NRGO. Gd2S3/NRGO modified glassy carbon electrode (GCE) exhibit a wide linear range of 0.01–450 μM CZM with 0.009 μM LOD using differential pulse voltammetry (DPV). Gd2S3/NRGO@GCE showed good selectivity, stability, and recovery (98.13–99.10%) in the river water sample. In addition, Gd2S3/NRGO has been explored towards the visible-light-induced degradation of CZM. The reactions conditions were optimized to achieve maximum efficiency. 94% of CZM was degraded within 90 min in presence of Gd2S3/NRGO. Mechanism of electrochemical redox reaction and degradation of CZM in presence of Gd2S3/NRGO has been explored to the maximum extent possible. Degradation intermediates were identified using LC-MS.

Enhanced electrochemical sensing performance for trace Hg(II) by high activity of Co3+ on Co3O4-NP/N-RGO surface

Constructing a highly sensitive and selective electrochemical interface is of great significance for the effective detection of Hg2+ in water and biological samples. Herein, Co3O4 nanopolyhedron (NP) anchored on nitrogen-doped reduced graphene oxide (N-RGO) is utilized as the electrode material for the detection of Hg2+ in the range of 0.1 μM–1.0 μM, with high sensitivity (1899.70 μA μM−1 cm−2) and low detection limits (0.03 μM) in natural water. Moreover, the Co3O4-NP/N-RGO modified electrode possesses reasonable anti-interference ability for Hg2+ in the presence of inorganic ions and glucose, which is the basis of its good response to trace Hg2+ in serum. Besides, combined with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, the electron transfer tendency is revealed. Additionally, combined with the electron state density of Co-p, it is speculated that Co3+ is an optimum active site for catalytic reaction. The above results elucidate an electrochemically sensitive interface is constructed to realize the efficient detection of Hg2+, which provides some theoretical guidance for the development of electrochemical sensors.

Flower-like three-dimensional bifunctional cathode catalyst for high-performance Li–O2 batteries: ZIF-67@3D-N/rGO

To accelerate the practical application of Li–O2 batteries. A catalyst with outstanding oxygen reduction reaction and oxygen evolution reaction catalytic activity is required. Here, in-situ growth ZIF-67 within three-dimensional nitrogen-doped reduced graphene oxide (3D-N/rGO) layers was used to investigate a bifunctional catalyst. The inner space is supported by ZIF-67 particles, while 3D-N/rGO extends a suitable three-phase reaction interface and enhances O2 adsorbability. When assembled battery with normal electrolyte, it delivered a high specific capacity of 12028 mAh g−1, and stabilised for 203 cycles at 200 mA g−1 with a limited capacity of 500 mAh g−1. When LiBr-gel polymer electrolyte (GPE) was used instead of electrolyte the lithium metal anode, the polarisation value of LiBr-GPE in Li/Li batteries was only about 0.0384 V after continuous working for 1600 h. When used as a cathode catalyst in Li–O2 batteries, the electrode performance was doubled compared with using the normal electrolyte. These findings pave the way for developing of all-encompassing battery materials with high capacity and long cycle life.

N-doped reduced graphene oxide/ZnO/nano-Pt composites for hydrogen peroxide sensing

An effective non-enzymatic H2O2 sensor electrode was fabricated, including nitrogen doped reduced graphene oxide (N-rGO) modified with different amounts of ZnO and incorporated by Pt nanoparticles. ZnO and Pt were fabricated on N-rGO with a hybrid synthesis consisting of hydrothermal and chemical synthesis. The Pt–N-rGO, Pt–10ZnO@N-rGO, Pt–20ZnO@N-r byGO and Pt–40ZnO@N-rGO composites as well as the effect of ZnO amount on the catalysts were studied the SEM (Scanning Electron Microscopy), EDX (Energy Dispersive X-ray Spectroscopy), TEM (Transmission Electron Microscopy), BET (Brunauer–Emmett–Teller method), XRD (X-ray Powder Diffraction). The electro-catalytic activity of the samples for H2O2 reduction was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and the amperometric method. Among the prepared catalysts, Pt–40ZnO@N-rGO was found to have higher sensitivity toward the reduction of H2O2 at ‒ 0.6 V (Ag/AgCl) because of the synergistic effect between ZnO and Pt nanoparticles that synthesized with the optimum mass ratio. It showed a linear response range from 0.1 μM to 0.1 mM with a low detection of 0.109 μM and a high sensitivity of 557 μA/mM−1. Furthermore, the fabricated sensor presented good selectivity to H2O2 with the existence of other interfering species.

CarbonIron Electron Transport Channels in Porphyrin-Graphene Complex for ppb-Level Room Temperature NO Gas Sensing.

It is a great challenge to develop efficient room-temperature sensing materials and sensors for nitric oxide (NO) gas, which is a biomarker molecule used in the monitoring of inflammatory respiratory diseases. Herein, Hemin (Fe (III)-protoporphyrin IX) is introduced into the nitrogen-doped reduced graphene oxide (N-rGO) to obtain a novel sensing material HNG-ethanol. Detailed XPS spectra and DFT calculations confirm the formation of carbon-iron bonds in HNG-ethanol during synthesis process, which act as electron transport channels from graphene to Hemin. Owing to this unique chemical structure, HNG-ethanol exhibits superior gas sensing properties toward NO gas (Ra /Rg = 3.05, 20ppm) with a practical limit of detection (LOD) of 500 ppb and reliable repeatability (over 5 cycles). The HNG-ethanol sensor also possesses high selectivity against other exhaled gases, high humidity resistance, and stability (less than 3% decrease over 30 days). In addition, a deep understanding of the gas sensing mechanisms is proposed for the first time in this work, which is instructive to the community for fabricating sensing materials based on graphene-iron derivatives in the future.

Metal-organic frameworks derived low-crystalline NiCo2S4/Co3S4 nanocages with dual heterogeneous interfaces for high-performance supercapacitors

Nickel cobalt bimetallic heterogeneous sulfides are attractive battery-type materials for electrochemical energy storage. However, the precise synthesis of electrode materials that integrate highly efficient ions/electrons diffusion with abundant charge transfer channels has always been challenging. Herein, an effective and concise controllable hydrothermal approach is reported for tuning the crystalline and integrated structures of MOF-derived bimetallic sulfides to accelerate the charge transfer kinetics, and thus enabling rich Faradaic redox reaction. The as-obtained low-crystalline heterogeneous NiCo2S4/Co3S4 nanocages exhibit a high specific capacity (1023 C/g at 1 A/g), remarkable rate performance (560 C/g at 10 A/g), and outstanding cycling stability (89.6% retention after 5000 cycles). Furthermore, hybrid supercapacitors fabricated with NiCo2S4/Co3S4 and nitrogen-doped reduced graphene oxide display an outstanding energy density of 40.8 Wh/kg at a power density of 806.3 W/kg, with an excellent capacity retention of 88.3% after 10000 charge-discharge cycles.

Exploring supercapacitance of solvothermally synthesized N-rGO sheet: role of N-doping and the insight mechanism.

We demonstrate the method of achieving excellent supercapacitance in nitrogen-doped reduced graphene oxide (N-rGO) sheets by controlling the amount of N-content through the use of different ratios of GO and urea during solvothermal synthesis. Here, urea plays a dual role in reducing GO and simultaneously doping nitrogen into the GO flakes forming exfoliated N-rGO sheets. The nitrogen content in N-rGO samples rises with an increase in the amounts of urea and saturates at a value of ∼14% for the GO : urea ratios beyond 1 : 8. The obtained N-rGO sheets with ∼ 5% N-content (obtained for GO : urea ratio of 1 : 3) were demonstrated as excellent supercapacitor materials. Using a 3-electrode setup, the maximum specific capacitance obtained for this sample was 514 F g-1 at a current density of 0.5 A g-1 (mass normalized current). The insights into the origin of this excellent supercapacitive behavior are explained through our results on optimum N-content, the relative amount of different N-environments, defects/disorders, and the degree of reduction of GO. Importantly, a proper stacking of rGO sheets with moderate N-content (∼5-6%) and a moderate amount of defects is the key to achieve high specific-capacitance. Furthermore, our 2-electrode device demonstrates the excellence of our samples with a Csp of 237 F g-1, a power density of 225 W kg-1, and an energy density of 6.7 W h kg-1 at 0.5 A g-1, exhibiting a high cyclic constancy with high capacitive retention of ∼ 82% even after 8000 cycles. Hence, our work provides a way to control the properties of N-rGO in achieving excellent supercapacitive performance.

Facile synthesis of Ni-incorporated and nitrogen-doped reduced graphene oxide as an effective electrode material for tri(ammonium) phosphate electro-oxidation

Drying well-mixed Ni(CH3COO)2-PVP solution results in incorporation of metal precursor NPs throughout the polymer sheets. Adjusting the metal salt content leads to produce N-doped and Ni-decorated rGO which is an effective electrocatalyst for H2 production from tri(ammonium) phosphate.

Enhanced Properties of Nitrogen-Doped Reduced Graphene Oxide for Electrochemical Energy Storage Through Hydrothermal Treatment and Composite Formation with Polyaniline

Enhanced Properties of Nitrogen-Doped Reduced Graphene Oxide for Electrochemical Energy Storage Through Hydrothermal Treatment and Composite Formation with Polyaniline