Chemical States Of Nitrogen Research Articles

Tuning Nitrogen-Doped Carbon Electrodes via Synthesis Temperature Adjustment to Improve Sodium- and Lithium-Ion Storage

Structural imperfections, heteroatom dopants, and the interconnected pore structure of carbon materials have a huge impact on their electrochemical performance in lithium-ion and sodium-ion batteries due to the specific ion transport and the dominant storage mechanism at surface defect sites. In this work, mesopore-enriched nitrogen-doped carbon (NC) materials were produced with template-assisted chemical vapor deposition using calcium tartrate as the template precursor and acetonitrile as the carbon and nitrogen source. The chemical states of nitrogen, the volume of mesopores, and the specific surface areas of the materials were regulated by adjusting the synthesis temperature. The electrochemical testing of NC materials synthesized at 650, 750, and 850 °C revealed the best performance of the NC-650 sample, which was able to deliver 182 mA·h·g−1 in sodium-ion batteries and 1158 mA·h·g−1 in lithium-ion batteries at a current density of 0.05 A·g−1. Our study shows the role of defect sites, including carbon monovacancies and nitrogen-terminated vacancies, in the binding and accumulation of sodium. The results provide a strategy for managing the carbon structure and nitrogen states to achieve a high alkali-metal-ion storage capacity and long cycling stability, thereby facilitating the electrochemical application of NC materials.

A novel near-infrared fluorescent sensor for zero background nitrite detection via the “covalent-assembly” principle

Different chemical states of nitrogen are present in many freshwater and marine ecosystems, and nitrite ions are one of the most toxic water-soluble nitrogen species. Developing an effective and convenient sensing method to constantly detect the concentration of nitrite has become a wide concern. Here, a novel near-infrared fluorescent probe (AAC) was designed and synthesized via the “covalent assembly” principle, showing excellent selectivity and high sensitivity for nitrite. A new nitrite-quantitative method was established with the help of AAC, and the detection limit of nitrite using the new method was as low as 6.7 nM. AAC was successfully applied for the quantitative detection of nitrite in real-world environmental and food samples (including river water and Chinese sauerkraut), and the detection results were essentially identical to the results obtained from the traditional Griess assay. Moreover, AAC was successfully applied for tracking nitrite in Escherichia coli by fluorescence imaging. Since nitrite can have devastating effects, the method established with AAC allowed us to “see” effectively about the water quality, food quality, etc.

Electronic Structure of Polianylinine Modified by Copper and Zirconium Salts

The features of the electronic structure and chemical bonds of PANI/Me composites (Me–Cu, Zr) have been studied spectroscopically. X-ray absorption spectroscopy, x-ray photoelectron spectroscopy, and infrared spectroscopy have been used for the research. It has been found that polyaniline is in a partially oxidized form in composites regardless of the type of modifying additive used, but it is more oxidized in PANI/Zr than in PANI/Cu. The chemical states of nitrogen in composites have been determined and the ratio of neutral and charged nitrogen groups is different.

Electronic Structure of Nitrogen- and Phosphorus-Doped Graphenes Grown by Chemical Vapor Deposition Method.

Heteroatom doping is a widely used method for the modification of the electronic and chemical properties of graphene. A low-pressure chemical vapor deposition technique (CVD) is used here to grow pure, nitrogen-doped and phosphorous-doped few-layer graphene films from methane, acetonitrile and methane-phosphine mixture, respectively. The electronic structure of the films transferred onto SiO2/Si wafers by wet etching of copper substrates is studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy using a synchrotron radiation source. Annealing in an ultra-high vacuum at ca. 773 K allows for the removal of impurities formed on the surface of films during the synthesis and transfer procedure and changes the chemical state of nitrogen in nitrogen-doped graphene. Core level XPS spectra detect a low n-type doping of graphene film when nitrogen or phosphorous atoms are incorporated in the lattice. The electrical sheet resistance increases in the order: graphene < P-graphene < N-graphene. This tendency is related to the density of defects evaluated from the ratio of intensities of Raman peaks, valence band XPS and NEXAFS spectroscopy data.

Chemical bonding of nitrogen formed by nitridation of crystalline and amorphous aluminum oxide studied by X-ray photoelectron spectroscopy.

Numerous efforts have already been made to optimize nitridation of crystalline sapphire (c-Al2O3) substrates whereas very little attention has been paid to nitridation of amorphous aluminum oxide layers (a-AlOx). An extensive analysis of the reaction of amorphous aluminum oxide films with nitrogen species is thus needed to clarify the mechanisms of nitrogen incorporation into such layers and to control their properties. In this work X-ray photoelectron spectroscopy was used to determine the chemical state of nitrogen formed by nitrogen plasma treatment of c-Al2O3 and 15 nm thick a-AlOx layers grown by atomic layer deposition on Si and sapphire substrates. The results show that the nitridation proceeds significantly different for c-Al2O3 and a-AlOx samples, which we correlate with the initial stoichiometry of both materials. At the surface of sapphire O vacancies were found, which are necessary for the formation of AlN-type bonding via diffusion limited replacement of oxygen by nitrogen. This process was slow and involved formation of oxinitride AlN–O. After 80 min of nitridation only ∼3.4 at% of N was incorporated. In contrast, in a-AlOx layers Al vacancies were present before nitridation. This opened a new, more effective path for nitrogen incorporation via accumulation of N in the cation-deficient lattice and creation of the Al(NOy)x phase, followed by AlN and AlN–O formation. This scenario predicts more effective nitrogen incorporation into a-AlOx than c-Al2O3, as indeed observed. It also explains our finding that more N was incorporated into a-AlOx on Si than on sapphire due to supply of oxygen from the sapphire substrate.

Электронная структура полианилина, модифицированного солями меди и циркония

The results of spectroscopic studies of the electronic structure and chemical bonds of PANI - Me composites (Me - Cu, Zr) are presented. X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, IR spectroscopy were used for research. It was established that regardless of which modifying additive polyaniline is used in composites is in partially oxidized form, however, in PANI - Zr is more oxidized than in PANI - Cu. The chemical states of nitrogen in the composites are determined; a different ratio of neutral and charged nitrogen groups is observed.

Effect of nitrogen flow rate on the properties of nitrogen-doped Cu&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O

Cuprous oxide (Cu₂O) has the potential applications in photovoltaic and photocatalytic fields. Nitrogen-doping in Cu₂O can improve the conductivity by increasing hole concentration. However, the chemical states of nitrogen in nitrogen-doped Cu₂O have not been studied thoroughly.A series of nitrogen-doped Cu₂O samples are prepared by increasing nitrogen flow rates and simultaneously keeping the sputtering pressure and other parameters unchanged. The samples are characterized by X-ray diffraction (XRD), step instrument, scanning electron microscope (SEM), energy dispersive spectrometer, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), spectrophotometer and Hall effect et al. The results of Hall effect measurement show that nitrogen-doping can increase the hole concentration by one order of magnitude. The band gap width decreases with the increase of nitrogen flow rate. The nitrogen in Cu₂O is in three forms: β-N (nitrogen atom), α-N₂(molecular nitrogen, —N=N—)and γ-N₂(molecular nitrogen, N≡N). With the increase of nitrogen gas flow rate, the peak of binding energy of β-N increases while that of α-N₂ decreases. The sample prepared at the nitrogen flow rate of 2.0 sccm has the minimum resistivity among all samples.

Control of nitrogen doping in NaTaO3 synthesized by hydrothermal reaction and chemical state of nitrogen

Nitrogen‐doped NaTaO3 was synthesized through 1‐pot reaction, hydrothermal process using Ta3N5 as precursor. Changing concentration and amount of NaOH aqueous solution influenced nitrogen content in NaTaO3. Absorption edge of nitrogen‐doped NaTaO3 was extended at 570 nm, and absorbance in visible light region depended on nitrogen content in NaTaO3. Anodic photocurrent measured under visible light irradiation became larger with increasing nitrogen content in NaTaO3‐xNy. Under ultraviolet light irradiation (λ ≤ 400 nm), the highest anodic photocurrent was observed when nitrogen concentration was y = 0.024. It was possible to expand the wavelength range that can be effectively utilized for the photoelectrochemical reaction.

Synergistic interaction and controllable active sites of nitrogen and sulfur co-doping into mesoporous carbon sphere for high performance oxygen reduction electrocatalysts

Nitrogen and sulfur co-doped mesoporous carbon sphere (NSMCS) was prepared as a metal-free catalyst by an economical and facile pyrolysis process. The mesoporous carbon spheres were derived from sodium carboxymethyl cellulose as the carbon source and the nitrogen and sulfur dopants were derived from urea and p-benzenedithiol, respectively. The doping level and chemical states of nitrogen and sulfur in the prepared NSMCS can be easily adjusted by controlling the pyrolysis temperature. The NSMCS pyrolyzed at 900 °C (NSMCS-900) exhibited higher oxygen reduction reaction activity than the mesoporous carbon sphere doped solely with nitrogen or sulfur, due to the synergistic effect of co-doping. Among all the NSMCS samples, NSMCS-900 exhibited excellent ORR catalytic activity owing to the presence of a highly active site, consisting of pyridinic N, graphitic N, and thiophene S. Remarkably, the NSMCS-900 catalyst was comparable with commercial Pt/C, in terms of the onset and the half-wave potentials and showed better durability than Pt/C for ORR in an alkaline electrolyte. The approach demonstrated in this work could be used to prepare promising metal-free electrocatalysts for application in energy conversion and storage.

New-route synthesis of N-doped TiO2 via exposing the TiCl3 precursor to non-thermal quenched plasma at various times

The exposure of TiCl3 to the plasma electric discharge burned in moisten air lead to the formation of TiO2 nanopowder for short exposure time (<30 min). However, as expected for longer exposure time, the N-doped TiO2 was formed. The synthesized powder for three exposure times was characterized by X-ray diffraction (XRD), FTIR spectroscopy, and nitrogen physisorption. The nitrogen loading was confirmed by X-ray photoelectron spectroscopy (XPS) analysis and the redshift response of doped photocatalyst was evaluated through the discoloration of aqueous Remazol Brilliant Blue-R dye under daylight. As a result, the textural analysis revealed the mesoporous materials with a specific surface area of 157 m2 g−1. The chemical states of nitrogen have been assigned to N–Ti–O and O–N–O in the TiO2 lattice. The photo-degradation rates of RBB-R dye were 62; 76 and 81%, respectively, for the sample exposed during 20, 30 and 60 min. The observed enhanced photocatalytic activity is mainly attributed to the increasing amount of Nitrogen loaded that shift the photocatalytic response in the visible region of light.

Chemical State of Nitrogen in Nitrogen-Doped Hydroxyapatite Ceramics with Enhanced Bioactivity

The chemical state of nitrogen which was induced into crystal structure of hydroxyapatite by nitrogen-doping method (N-doping method) was examined. Determination of lattice constants by powder X-ray diffraction (XRD) showed that the nitrogen species induced by N-doping method substituted the OH- ion in the crystal structure of hydroxyapatite. In addition, Fourier transform infrared spectroscopy (FT-IR) and temperature programmed desorption-mass spectroscopy (TPD-MS) determined that the chemical state of nitrogen induced by N-doping method was N2O.

Influence of chemical states of doped nitrogen on photoluminescence intensity of hydrothermally synthesized carbon dots

Nitrogen-containing carbon dots were synthesized from glucose and glucosamine by hydrothermal treatment. The relation between the PL properties of the carbon dots and chemical states of nitrogen in them are discussed. The actual N/C ratio of synthesized samples increased from 0.00 to 0.08 as the nominal molar percentage of glucosamine/(glucose+glucosamine), xN, was increased from 0 to 100mol%. The samples were nanoparticles with microscopic local graphite structure. Some nitrogen atoms were doped in the graphite skeleton, and others were present as surface NH2 groups. The nanoparticles exhibited blue photoluminescence (PL) under near-ultraviolet excitation. The PL peak shifted to longer wavelength as the excitation wavelength increased. PL intensity was proportional to the absorbance of the carbon dots, and both increased with the amount of nitrogen doped in the graphite skeleton. Other carbon dots were synthesized using ammonium hydroxide as a nitrogen source instead of glucosamine. These samples possessed abundant surface NH2 groups, and exhibited no change in PL intensity with increasing NH2 content. Nitrogen doped in the graphite skeleton formed donor levels in the energy band of the carbon dots, increasing the amount of absorption centers and enhancing PL.

Morphology and chemical characteristics of micro- and Nano-particles in the haze in Beijing studied by XPS and TEM/EDX

X-ray Photoelectron Spectroscopy (XPS) is a useful surface sensitive tool to explore the particulate matter with different particle sizes. In this work, we report the analysis of elemental species in particulate matter with size ranging from 100nm to 10μm during the autumn haze of 2014 in Beijing. The size dependence of element composition and chemical state distribution on the particle surface was investigated. It was found that the number of investigated element species decreased from 8 (at stage 2) to 4 (at stage 10) with the decrease of particle sizes down to 100nm, which is in accordance with the result from Transmission electron microscopy (TEM/EDX) observations. Three chemical states of nitrogen, the amide group (399.9eV), the ammonium group (401.6eV), and the nitrate group (407.2eV), were confirmed according to the different binding energies. Nitrate was the main composition on the coarse particles, while the percentage of amide and ammonium at stage 3 (13.9% and 10.8% respectively) increased on the fine particles at stage 9 (46.8% and 38.8% respectively). The relative ratio of sulfate and ammonium (calculated 1:1) in the fine particles suggests that there is no enough NH4+ to neutralize the sulfuric acid and the surface of the PM is acidic. The result is useful to investigate the generation processes and the sources of collected particles.

Surface modification of graphene and graphite by nitrogen plasma: Determination of chemical state alterations and assignments by quantitative X-ray photoelectron spectroscopy

Multilayer graphene (MLGR) and its bulk analog, highly oriented pyrolytic graphite (HOPG), were treated by radio frequency activated low pressure N2 gas plasma (at negative bias 0–200V, for 5–20min). Surface composition and chemical-state alterations were delineated by X-ray photoelectron spectroscopy (XPS). Covalently bonded nitrogen of 5–15at% incorporated into the surface. The higher N concentration in MLGR below 100V is attributed to the larger number of defects. The equal N content at 200V indicates intensive formation of reactive sites. In-depth distribution of N is restricted to 2–4 monolayers. Model calculation resulted in 23at% N (at 100V) in the top graphene layers of HOPG. Three different chemical states of nitrogen (pyridine-type at 398.3eV, pyrrole- and triazine-type at 399.7eV and N substituting C in graphite-like network at 400.9eV) were determined from high-resolution N1s spectral region for all samples. Pyridine and pyrrole–triazine components increase preferentially with increasing bias. Alterations of the C1s and O1s spectra are discussed in a critical approach. The amount of reacted carbon was consistent with that required for the three different nitrogen and oxygen states, thus validating the proposed assignments.

Highly Durable Carbon Nanotube Composite Support By Pyrolysis of Conductive Polymer for Polymer Electrolyte Membrane Fuel Cell

Recently, there has been renewed of great interest in polymer electrolyte membrane fuel cells (PEMFCs) as promising alternative power generation systems due to higher efficiency and power density, lower operating temperature, and much less release of environmental pollutants than conventional energy conversion devices. Despite significant advances of PEMFCs, low durability is still key issues that should be addressed prior to their commercialization. The long-term performance loss of PEMFC mostly stems from the degradation of PEMFC catalysts and carbon supports. Although several types of Pt-based catalysts with enhanced catalytic activity or durability have emerged, they are still in development [1].Among various kinds of carbon materials, carbon nanotube (CNT) has emerged as a promising support for PEMFC catalysts due to its surface area, high electrical conductivity and excellent durability [2]. However, CNT has no enough binding sites for anchoring Pt particles, and the Pt/CNT catalysts thus have poor Pt dispersion and broad particle size distribution with large size, especially at high Pt loading [3]. One of facile approaches to solve this drawback is the use of heteroatom-doping to carbon supports, where the metal-carbon support interactions have been implicated in the enhanced electrochemical durability and activity in the modified system [4].Herein we present the fabrication of the nitrogen-containing carbon and CNT (NC-CNT) composite for PEMFC electrocatalysts and the enhanced durability of the Pt/NC-CNT composites by nitrogen doping. The NC-CNT composite has been synthesized by the polymer wrapping of the CNT with poly(styrenesulfonic acid) and in situ polymerization of pyrrole on CNT surfaces. Pyrolysis was performed at temperatures ranged from 400~1000 oC in an inert atmosphere of N2gas for 2 h. Uniform coating of polymer layer acing as linkers onto CNT surfaces was confirmed by UHR-FESEM/STEM. As shown in Figure 1(a), CNT was encapsulated by about 15 nm of coated polymer layers.For the as-synthesized NC-CNT composite, a new peak located at ~399 eV is observed, which indicates the presence of nitrogen atom. The atomic percentage of N-element in the NC-CNT composite is in the rage of 3.1~12.7 at.% by controlling the amount of conductive polymer and the heat-treatment temperature. As shown in Figure 1(b), high resolution N1s core level spectra of the heat-treated NC-CNT composite contain multiple components due to the presence of different chemical states of nitrogen. The peak at 400.9 eV is attributed to the graphite-like N, which is the most stable nitrogen species during the pyrolysis. The content of graphitic-N is in the range of 8.8~36.1% for NC-CNT composites.As shown in Figure 2(a), Pt nanoparticles were uniformly dispersed in the NC-CNT composites and their particle size was ~2.5 nm. Although Pt nanoparticles are distributed on CNT surfaces with a high density, they do not aggregate with each other as compared to Pt/unmodified CNT, resulting for the strong interaction with the NC-CNT composites via Pt-N-C bonding as well as the effective isolation of adjacent Pt nanoparticles by the coated polymer layers.The electrochemical durability of Pt/C catalyst has a significant influence on their long-term performance. As shown in Figure 2(b), the ECSA of Pt/NC-CNT only decreased by 15.0%, while Pt/unmodified CNT and commercial Pt/C (Pt 46.7%, TKK) catalysts lost about 40% and 65% of the initial ECSA, respectively. The result clearly demonstrates that Pt/NC-CNT is much higher stable than Pt/unmodified CNT and commercial Pt/C catalyst. The interaction between Pt and N-doped CNT composite was also analyzed by the XPS (not shown here). As compared to Pt/unmodified CNT, the shift in the Pt4f peak to a higher binding energy (~1 eV) observed in the Pt/NC-CNT composite is attributed to the strong interaction between Pt and N-containing moieties, thus creating stabilizing effect against the aggregation and dissolution of Pt nanoparticles. It should be also noted that Pt/NC-CNT composites show better durability with higher N-doping level and more graphitic N contents.In brief, the enhanced durability of the Pt/NC-CNT composite catalyst results from the polymer stabilization effect and strong interaction between Pt and support by nitrogen doping. The NC-CNT composites with different N-configuration can be also fabricated by controlling N-doping level and heat-treatment temperature. Our study also provides a design guide of highly durable Pt catalyst supports with a great potential for PEMFC.

The Tribological Chemistry of a Novel Borate Ester Additive and Its Interaction with ZDDP Using XANES and XPS

A novel borate ester containing heterocyclic group, 2,5-bis((2-((6-octadecyl-1,3,6,-dioxazaborocan-2-yl)oxy)propyl)thio)-1,3,4-thiadiazole (BDOT), was prepared and characterized. Its tribological properties and synergistic effect with zinc dialkyl dithiophosphate were evaluated using a four-ball tribometer. The results show that the novel borate additive possesses excellent anti-wear and friction-reducing properties compared with the performance of ZDDP. BDOT combined with ZDDP has a synergistic effect on the tribological properties, especially for the friction-reducing performance. The chemical state of nitrogen, boron and sulfur in thermal films and tribofilms was analyzed by XPS and XANES. XPS analysis suggests that the additive forms a protective film on the rubbing surfaces which is composed of B2O3, BN, FeSO4, FeS2 and Fe2O3. However, the B K-edge XANES shows that no BN was detected in the film. The synergistic effect between BDOT and ZDDP may be due to the formation of right concentration of FeS and FeSO4 in the tribofilm.

Supercapacitor performance of nitrogen-doped carbon nanotube arrays

Arrays of nitrogen-doped carbon nanotubes (N-CNTs) have been grown on Si substrates by thermolysis of vapors of acetonitrile and ferrocene. To change the content of incorporating nitrogen, carbonyls of Mo, W, and Cr were added in the reaction mixture. The products were comparatively studied using electron microscopy, Raman scattering, X-ray photoelectron spectroscopy, and charge/discharge cycling in an acidic electrolyte. Electrochemical characteristics of N-CNTs were correlated with nanotube length and chemical state of nitrogen. It is found that pyridinic nitrogen has determining effect on the N-CNT performance at low scan rates of potential. The density functional theory calculations of N-CNT models reveal that protonation of pyridinic nitrogen induces a net of negative charges on the neighboring carbon atoms that could increase the electrode capacitance. Cyclic voltammogram of nitrogen-doped carbon nanotube array at a scan rate of 2 mV s−1 in a 1 M H2SO4 aqueous solution and possible assignment of redox peaks.

Structural analysis of nitride layer formed on uranium metal by glow plasma surface nitriding

The nitride layer was formed on uranium metal by a glow plasma surface nitriding method. The structure and composition of the layer were investigated by X-ray diffraction and Auger electron spectroscopy. The nitride layer mainly consisted of α-phase U2N3 nanocrystals with an average grain size about 10–20nm. Four zones were identified in the layer, which were the oxide surface zone, the nitride mainstay zone, the oxide-existence interface zone, and the nitrogen-diffusion matrix zone. The gradual decrease of binding energies of uranium revealed the transition from oxide to nitride to metal states with the layer depth, while the chemical states of nitrogen and oxygen showed small variation.

High-performance charge storage by N-containing nanostructured carbon derived from polyaniline

Nitrogen-containing nanostructured carbon materials, C-nanoPANI, C-nanoPANI-DNSA and C-nanoPANI-SSA, were prepared by the carbonization of nanostructured polyaniline (PANI) doped with sulfuric acid, 3,5-dinitrosalicylic acid (DNSA), and 5-sulfosalicylic acid (SSA), respectively. The charge storage ability of these materials was investigated in alkaline solution. It was found that the specific capacitance increased in the order: C-nanoPANI-DNSA<C-nanoPANI<C-nanoPANI-SSA. The highest capacitance, amounting to 410Fg−1 at a scan rate of 5mVs−1, was found for C-nanoPANI-SSA. At a large rate of 10Ag−1, its capacitance displayed a stable value close to 200Fg−1. To explain the observed differences in charge storage properties, the materials were characterized by different techniques able to ascertain their morphology, elemental composition, nitrogen surface concentration, chemical state of nitrogen, pore structure and electrical conductivity. All materials were essentially microporous with relatively small fraction of mesopores and displayed conductivities in the range 0.32–0.83Scm−1. The best charge-storage performance of C-nanoPANI-SSA was attributed to its highest surface fraction of nitrogen, the highest surface content of pyridinic nitrogen groups, and the highest electrical conductivity, as well as to its well-balanced micro- and mesoporosity and highest content of mesopores.

Growth of nitrogen-doped carbon nanotubes and fibers over a gold-on-alumina catalyst

Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor decomposition of a N,C-precursor over a supported Au catalyst. Large quantities of carbon nanotubes with a compartmentalized structure containing ca. 5 at.% N were produced over a 1.5% Au/δ-Al 2O 3 catalyst with a mean diameter of Au particles equal to 2.8 nm under continuous flow conditions at 800 °С and 1 bar of the reaction gas mixture containing pyridine (Py) vapor (5 vol.%), Н 2 (10–20 vol.%) and Ar (balance). The majority of the N-CNTs obtained after 10 min have outer diameters (ODs) of 13–45 nm and closed tips without any encapsulated gold particles of the catalyst which indicates the “base-growth” mechanism of N-CNT formation. Carbon deposits synthesized for 30–135 min contain carbon fibers with OD values up to several micrometers, formed by self-assembling of N-CNTs, and individual N-CNTs. X-ray photoelectron spectra provide evidence for various chemical states of nitrogen (pyridinic, “quaternary” (graphitic) and pyrrolic nitrogen) in the N-CNTs, and these are discussed.