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XPS spectra of N-doped graphene and schematic illustration of nitrogen functional groups. XPS spectra of N-doped graphene converted from GO with different oxygenic groups (a-e). Schematic illustration of nitrogen functional groups in the carbon lattice (f).
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Few-layer nitrogen doped graphene was synthesized originating from graphene oxide functionalized by selective oxygenic functional groups (hydroxyl, carbonyl, carboxyl etc.) under hydrothermal conditions, respectively. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observation evidenced few-layer feature of the graphene oxi...
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The research is focus on manufacturing graphene nanosheets by electrochemical exfoliation method (EC-graphene). Through tuning the synthetic parameters, such as the composition of electrolytes, concentration of electrolyte, KOH/H2SO4 ratio as well as applying voltages and current density to study the relationship between characterization and synthe...
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... However, controlling and analyzing the nitrogen doping process in GO, which involves the reduction of oxygen-bound and vacancy defect sites, poses more challenges due to its defective and poorly ordered structures [30,31]. Additionally, numerous experimental and theoretical studies have explored the bonding natures and evolution of nitrogen-doped sites on pure graphene [32][33][34][35]. Recent research has highlighted that defects in the conjugated graphene network significantly influence the N-doping mechanism and, consequently, the doping efficiency of the material [36][37][38][39]. ...
Nitrogen-doped graphene has been increasingly utilized in a variety of energy-related applications, serving as a catalyst or support material for fuel cells, and as an anode material for lithium-ion batteries, among others. The thermal reduction of graphene oxide (GO) in nitrogenous sources to incorporate nitrogen, producing nitrogen-doped reduced graphene oxide (NRGO), is the most favored method. Controlling atomic configurations of nitrogen-doped sites is the key factor for tailoring the physico-chemical properties of NRGO, but major challenges remain in identifying detailed atomic arrangements at nitrogen binding sites on highly defective and chemically functionalized GO surfaces. In this paper, we present atomistic-scale modeling of the nitrogen doping process of GO with different types of vacancy defects. Molecular dynamics simulations using a reactive force field indicate that the edge carbon atoms on defect sites are the dominant initiation location for nitrogen doping. Further, first-principles calculations using density functional theory present energetically favorable chemical transition pathways for nitrogen doping. The significance of this work lies in providing important chemical insights for the effective control of the desired properties of NRGO by suggesting a detailed mechanism of the nitrogen doping process of GO.
... Fig. 2bshows the components with C 1 s binding energy: a main peak of C--C, of sp 2 graphitic domains, C-N/ C-O and C--N/C--O, of single and double bonds with heteroatoms, respectively, and O--C-O, of residual carboxyl groups[38,39]. The positions and proportions (at%) of each carbon chemical environment are presented in the table inserted inFig. ...
... Here it is shown that NGO consists of different C-N bond types, including pyridinic, pyrrolic-N and graphitic-N and these bond types have profound effects on the NGO properties and applications. The N level and N species could be controlled by tuning the experimental parameters such as mass ratio between dopant and GO source, reaction time and hydrothermal temperature [76,77]. In addition, the N content and N types with different amount can depend greatly on the amount and type of oxygen functionalities present on the GO surface. ...
... In addition, the N content and N types with different amount can depend greatly on the amount and type of oxygen functionalities present on the GO surface. For example, GO modified with more carboxyl groups (GO-OOH) had high N content compared to GO modified with −OH and −C=O functionalities under similar conditions due to the reduction in epoxy groups as the carboxyl groups introduced increases (Fig. 7) [76]. Therefore, an increase in the carboxyl groups enhances the surface activity of GO. ...
... This presumption was made due to the absence of N observed in the elemental analysis when GO was annealed with urea at 700 °C. Additionally, Mou et al. [77] and Chen et al. [76], stated that carboxyl Review groups which provide active sites on the GO are the main oxygen functionalities responsible for the reaction with N atoms. Chen et al. also added that at high-temperature and alkaline conditions the carbonyl groups are transformed into carboxyl groups, which reacted with NH 3 and favoured N-doping. ...
This review covers recent advances on production techniques, unique properties and novel applications of nitrogen-doped graphene oxide (NGO). The focal point is placed on the evaluation of diverse methods of production for NGO and reduced nitrogen-doped graphene oxide (NrGO) nanosheets using GO and graphite as carbon precursors. Variation in chemical composition of GO with variable N content, C–N bonding configurations and chemical reactive functionalities of NGO allow tuneable properties that render NGO a suitable material for various applications such as lithium-ion batteries, biosensors, supercapacitors and adsorption processes. NGO and NrGO exhibit significantly different performances compared to GO even with small amounts of N-doping. The type of C–N bonding and surface chemistries on the NGO are responsible for their unique electrical, mechanical, adsorption, chemical reactivity, photocatalytic activity, and optical properties. Various investigative techniques used to study NGO nanomaterials are also reviewed. Finally, future perspectives of NGO in this rapidly developing area are discussed.
Graphical abstract
Methods of synthesis of N-doped graphene oxide nanosheets and their advantages and disadvantages.
... 42 The overlap may be due to the fact that there is sufficient carbonyl in FGO, which favors the electron attraction, resulting in a low number of charges on the C�C atom. 42,43 Overall, the FTIR data clearly show the successful preparation of FGO. Quantitative analysis of FGO3, FGO10, and FGO20 was carried out by XPS. ...
... This is because the amount of carboxylate moieties converted from the C6 primary hydroxyls of cellulose increases in accordance with the amount of TEMPO involved in the reaction. This observation complies with the characteristic absorption spectra obtained by Shao et al. [23]. ...
To design a new system of novel TEMPO-oxidized cellulose nanofibrils (TOCNs)/graphene oxide (GO) composite, 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation was utilized. For the better dispersion of GO into the matrix of nanofibrillated cellulose (NFC), a unique process combining high-intensity homogenization and ultrasonication was adopted with varying degrees of oxidation and GO percent loadings (0.4 to 2.0 wt%). Despite the presence of carboxylate groups and GO, the X-ray diffraction test showed that the crystallinity of the bio-nanocomposite was not altered. In contrast, scanning electron microscopy showed a significant morphological difference in their layers. The thermal stability of the TOCN/GO composite shifted to a lower temperature upon oxidation, and dynamic mechanical analysis signified strong intermolecular interactions with the improvement in Young’s storage modulus and tensile strength. Fourier transform infrared spectroscopy was employed to observe the hydrogen bonds between GO and the cellulosic polymer matrix. The oxygen permeability of the TOCN/GO composite decreased, while the water vapor permeability was not significantly affected by the reinforcement with GO. Still, oxidation enhanced the barrier properties. Ultimately, the newly fabricated TOCN/GO composite through high-intensity homogenization and ultrasonification can be utilized in a wide range of life science applications, such as the biomaterial, food, packaging, and medical industries.
... The oxidized functional group ratios of hydroxyl, carboxyl, and epoxy groups are 1.05:0.9:1.0 ∼ 1.0:1.2:0.96, which is comparable to the experimental value of 1.05:0.9:1.0 ∼ 1.0:1.2:0.96 [29,30]. The nanoscale and rectangle-shaped GQDs are studied in terms of current computation ability, as in previous simulation studies [6,7,14]. ...
Although spatially heterogeneous oxidation is pivotal to the cellular translocation process of graphene quantum dots (GQDs), the dynamical road to the thermodynamically stable translocation conformation remains hazy. In this study, we illuminate the bio-interface doctrine involving the cellular translocation of Janus-shaped oxidized GQDs by performing multi-dimensional pathway computations predicated on coupled microsecond-long molecular dynamics and well-tempered metadynamics simulations. The oxidation nanodomains of Janus-shaped GQDs spontaneously yield hydrogen-bonds with polar lipid heads, while their pristine graphene nanodomains hy-drophobically associate with nonpolar lipid tails, and thus respond as self-propelled nanomotors across biological membranes. Hydrophobic-associations and hydrogen-bondings are found to be competitively coordinated, which dictates the dynamic pathway and thermodynamic states for cellular translocation, particularly modulating the adaptive self-propelling activity. The translocational phase diagram is drawn, demonstrating that GQDs with moderately square-patterned oxidation and thin thickness facilitate excellent translocation and minimal biological nanotoxicity. Importantly, intermolecular mechanochemistry is discovered to play a crucial role in energy transduction and nanomechanical interactions, which in turn affect the spatial rotation pathways of GQDs, as well as the membrane perturbations. Overall, this study provides an intuitive insight into the dynamics and thermodynamics of spontaneously translocating GQDs, opening up brand-new avenues for developing GQD-enabled nanocarriers or antibiotics.
... Graphene has intensively drawn interest due to its physicochemical features, such as chemical stability, excellent electric conductivity, and high surface area. Nitrogen doping in graphene is one of the most popular and has been proven to be an effective way to tailor the properties of pristine graphene [2]. The doped nitrogen atoms can modify the surface chemical state and electronic structure. ...
Graphitic nitrogen-doped graphene (g-NG) with significantly high nitrogen content, i.e., 18.79 at.%, could be produced by the electrical discharge in liquid, so-called “solution plasma”, with a single dielectric barrier. The proposed system could reduce the excessive current, resulting in stabilizing the glow plasma and maintaining the overall temperature. It could promote the preservation of nitrogen atoms from evaporation during the synthesis process and the formation of a graphitic carbon framework. Moreover, the influence of the precursors, i.e., six-membered ring organic molecules with and without the substitution of nitrogen atoms and the nitrogen-based functional groups, was also investigated to provide the guideline for the synthesis of g-NG via this proposed method. The substitution of nitrogen atoms in the benzene ring could be used to synthesize g-NG with higher nitrogen dopants, compared to the benzene ring with only nitrogen-based functional groups.
... Carbon materials with pyridinic N prepared without metal substrates have been reported [46,47], but the actual percentages of pyridinic N in the structures are uncertain due to the wide full width at half maximum (FWHM) of N1s X-ray photoelectron spectroscopy (XPS) spectra and the insufficient structural analysis (Fig. 1b). By top-down methods, carbon materials synthesized from N-containing hydrocarbon precursors other than ones with pyridinic N have also been reported, but the percentages of pyridinic N in these materials are as low as 73% [48], 70% [49], 60-70% [50], and 45% [51]. We have also attempted to introduce pyridinic N and other N-containing functional groups without using catalysts [52][53][54][55]. ...
Nitrogen-doped carbon materials, especially pyridinic nitrogen, have attracted attention because of the high performance for various applications such as electrodes for fuel cells and other catalytic reactions. However, the selective introduction of pyridinic nitrogen without using catalysts and the mass production of such carbon materials are challenging. In this work, carbon materials with selectively introduced pyridinic nitrogen were synthesized by just simple heat treatment of aromatic compounds containing pyridinic nitrogen in the absence of catalysts. Dibenzacridine isomers, C21H13N, with different molecular frameworks such as either zigzag or armchair edges were selected as precursors to investigate the influence of edges on the percentage of pyridinic nitrogen. The percentage of pyridinic nitrogen of precursors heated at 973 K was in the order of dibenz[c,h]acridine (DCHA) (80%) > dibenz[a,h]acridine (60%) > dibenz[a,j]acridine (39%) > dibenz[a,i]acridine (33%). The percentage of pyridinic nitrogen of DCHA was further enhanced to 94% at 923 K. Experimental X-ray photoelectron, infrared, and Raman spectra combined with calculation of spectra and formation energy and calculation of carbonization reaction pathways by molecular dynamics simulation with reactive force field (ReaxFF) precisely revealed the reasons why the high percentage of pyridinic nitrogen was attained. The steric hindrance generated by the bay structure of DCHA provided the high formation energy of C–N bond (tertiary nitrogen) and N–H bonds (secondary nitrogen), avoiding the side reactions such as the formation of tertiary nitrogen and secondary nitrogen.
Graphical abstract
... 70,71 The O 1s peak ( Figure 4E,H,K) after deposition of copper featured two supplementary species, which were a cupric oxide (CuO) at 529.7 eV and a cuprous oxide (Cu 2 O) at 530.3 eV. Figure 4C shows the deconvolution of the N 1s peak into four nitrogencontaining species: a pyridinic (N-6) at 398.80 eV, a pyrrolic (N-5) at 399.8 eV, a quaternary/graphitic (N-Q) at 401.8 eV, and an oxidic (N-Ox) at 404.2 eV. 48,66,72,73 Figure 4F,I,L shows Cu 2p peaks, which were fit into the five species: a copper, a cuprous oxide, a cupric oxide, a copper hydroxide (CuOOH), and a copper sulfate (CuSO 4 ). 32,74,75 The contribution from copper sulfate after annealing was negligible and was therefore omitted in the further analysis. ...
Low-cost enzyme-free glucose sensors with partial flexibility adaptable for wearable Internet of Things devices that can be envisioned as personalized point-of-care devices were produced by electroplating copper on locally carbonized flexible meta-polyaramid (Nomex) sheets using laser radiation. Freestanding films were annealed in nitrogen and nitrogen/air working environments, leading to the formation of Cu microspheroids and CuO urchins dispersed on the substrate film. The aggregation mechanism, crystallographic properties, surface chemistry, and electrochemical properties of the films were studied using scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. Cu microspheroids and CuO urchins attained activity for glucose detection and showed improvement of amperometric sensitivity to 0.25 and 0.32 mA cm–2 mM–1, respectively. The CuO urchin film retained its chemical composition after amperometric testing, and, by rinsing, allowed multiple repetitions with reproducible results. This study opens the possibility for the fabrication of durable composite biosensors with tailored shape, capable of implementation in flexible carriers, and microfluidic systems.
... In the N 1s XPS spectrum ( Figure S4b, Supporting Information), the three deconvoluted peaks located at 400.1, 403.4, and 406.9 eV can be assigned to pyridine N, pyrrolic N, and sorbed N. [33] It is also notable that the presence of pyridine type N atoms can increase the electron conduction, thus favoring the rate performance of the electrode. [34] From the above discussion, the enhanced-compressively strained interface in N-Pd/A-Co(II) was successfully constructed. ...
The development of palladium‐based catalysts for alkaline hydrogen evolution reaction (HER) is highly desired for renewable hydrogen energy systems, yet still challenging due to the strong palladium–hydrogen bond. Herein, the bottleneck is largely overcome by constructing a nitridation‐induced compressively strained‐interface N‐doped palladium/amorphous cobalt (II) interface (N‐Pd/A‐Co(II)), which dramatically boosts HER performance in alkaline condition. The optimized catalyst with the compressive strain of 2.7% exhibits the higher activity with an overpotential of only 58 mV to achieve the current density of 10 mA cm⁻², much better than those of pure Pd (327 mV), and the state‐of‐art Pt/C (78 mV). Notably, it also shows excellent stability with negligible decline during a 30 h stability test. Detailed analyses reveal that the strong absorption of Hads on Pd can be efficiently reduced via the compressively strained N‐doped Pd. And the amorphous Co(II) component accelerates the water dissociation. Consequently, the cooperative effect between the compressed N‐doped Pd and amorphous Co(II) creates the impressive HER performance in alkaline condition, highlighting the importance of the functional interface to develop efficient electrocatalysts for HER and beyond.
