Varying Nitrogen Content Research Articles

Cover Caption

Foliar nutrient content plays a key role in mediating the interaction of plants and insect herbivores within and across generations. Here, the weed biological control agent Neolema abbreviate is depicted feeding on its host Tradescantia fluminensis during trials measuring performance across generations on hosts with variable nitrogen content. Our study concluded that adult traits such as oviposition selection, weigh gain and longevity were largely unresponsive to parental diet. Instead, offspring diet was more important in determining performance (see pages 361–374). Photo provided Frank Chidawanyika.

Chemical composition of food induces plasticity in digestive morphology in larvae of Rana temporaria.

ABSTRACTFood conditions are changing due to anthropogenic activities and natural sources and thus, many species are exposed to new challenges. Animals might cope with altered quantitative and qualitative composition [i.e. variable protein, nitrogen (N) and energy content] of food by exhibiting trophic and digestive plasticity. We examined experimentally whether tadpoles of the common frog (Rana temporaria) exhibit phenotypic plasticity of the oral apparatus and intestinal morphology when raised on a diet of either low (i.e. Spirulina algae) or high protein, N and energy content (i.e. Daphnia pulex). Whereas intestinal morphology was highly plastic, oral morphology did not respond plastically to different chemical compositions of food. Tadpoles that were fed food with low protein and N content and low-energy density developed significantly longer guts and a larger larval stomachs than tadpoles raised on high protein, N and an energetically dense diet, and developed a different intestinal surface morphology. Body sizes of the treatment groups were similar, indicating that tadpoles fully compensated for low protein, N and energy diet by developing longer intestines. The ability of a species, R. temporaria, to respond plastically to environmental variation indicates that this species might have the potential to cope with new conditions during climate change.

Effects of nitrogen content on pyrolysis behavior of nitrocellulose

Although the thermal decomposition of nitrocellulose (NC) has been comprehensively examined, the effects of nitrogen content on the pyrolysis behavior of NC have not been clearly elucidated. In this work, the macro- and microstructures of NC samples with varying nitrogen contents were qualitatively and quantitatively analyzed. Higher nitrogen contents in NC samples were found to be associated with an increased number of nitro groups and cracks in the fiber surface. To elucidate the NC pyrolysis process and provide a theoretical basis for enhancing its stability, the pyrolytic behavior of NC was examined using thermogravimetric analysis-Fourier transform infrared spectrometry and pyrolysis-gas chromatography-mass spectrometry. The pyrolysis of NC primarily occurred within a temperature range of 180–240 °C; however, the peak temperature of the mass loss rate decreased with increasing nitrogen content. The initial nitrogen oxide produced by pyrolysis was nitrogen dioxide (NO2). During the main stage of pyrolysis, a wider variety of gases was produced by NC having a higher nitrogen content, with more cyclization recombination forms occurring in the post-reaction stage of pyrolysis. Based on the findings of this study, a detailed process of NC pyrolysis has been proposed.

Dislocation density based modeling of three-stage work hardening behaviour of type 316LN SS with varying nitrogen content and its finite element implementation for different notch radii

Dislocation density based modified Kocks-Mecking approach has been employed to understand the influence of nitrogen on kinetics of dislocation storage and annihilation processes during tensile deformation of type 316LN stainless steel at 300 K. As compared to original Kocks-Mecking approach, the modified version based on the evolution of forest dislocation density and mean free path of dislocations provides better description of three-stage hardening behaviour of the steel at all the nitrogen content. The effect of increase in nitrogen on work hardening behaviour is clearly reflected in systematic increase in flow stress, mobile and forest dislocation densities and decrease in mean free path at a given plastic strain. The predicted decrease in mean free path with increasing nitrogen has not only influenced the enhancement of dislocation-dislocation interactions leading to higher storage of dislocation but also provides a large driving force for higher dynamic recovery in the steel. The material model is implemented into finite element code via user-defined material subroutine using implicit algorithm to study the influence of notch radius on tensile properties of type 316LN stainless steel for different nitrogen content. Detailed analysis showed that notch-strengthening effect increases with increase in nitrogen and decrease in notch radius in the steel.

Effect of nitrogen content on microstructure, mechanical properties, and corrosion behaviour of coarse-grained heat-affected zone of nitrogen-containing austenitic stainless steel

AbstractThe microstructures and properties of austenitic stainless steel with varying nitrogen content after welding thermal simulation were investigated. The results indicate that the nitrogen fraction has a considerable influence on the phase composition and properties. Low nitrogen fraction leads to formation of δ-ferrite. After a welding thermal cycle, the number of annealing twins of high nitrogen-containing steel decreases, M23C6 precipitates, and fine M23C6 are observed. For low nitrogen-containing steel, large-size M23C6 and elongated δ-ferrite are formed, which deteriorate the ductility. Meanwhile, equilibrium phase calculations also reveal the inhibiting effect of nitrogen on M23C6 and δ-ferrite. Furthermore, susceptibility to intergranular attack by 10 % oxalic acid solution was detected, and the synergistic effect of coherent twin boundaries, M23C6, and δ-ferrite leads to low resistance to corrosion for low nitrogen-containing steel.

Optical Properties of Isolated and Covalent Organic Framework-Embedded Ruthenium Complexes.

Heterogenization of RuL3 complexes on a support with proper anchor points provides a route toward design of green catalysts. In this paper, Ru(II) polypyridyl complexes are investigated with the aim to unravel the influence on the photocatalytic properties of varying nitrogen content in the ligands and of embedding the complex in a triazine-based covalent organic framework. To provide fundamental insight into the electronic mechanisms underlying this behavior, a computational study is performed. Both the ground and excited state properties of isolated and anchored ruthenium complexes are theoretically investigated by means of density functional theory and time-dependent density functional theory. Varying the ligands among 2,2′-bipyridine, 2,2′-bipyrimidine, and 2,2′-bipyrazine allows us to tune to a certain extent the optical gaps and the metal to ligand charge transfer excitations. Heterogenization of the complex within a CTF support has a significant effect on the nature and energy of the electronic transitions. The allowed transitions are significantly red-shifted toward the near IR region and involve transitions from states localized on the CTF toward ligands attached to the ruthenium. The study shows how variations in ligands and anchoring on proper supports allows us to increase the range of wavelengths that may be exploited for photocatalysis.

(Invited) Microfabrication and Electrochemical Activation of Amorphous Carbon Nitride a-CNx Working Electrode Integrated in Microfluidic Chip

a-CNx films are well-known polarizable interface materials with a large potential window (3 V-4 V [1]) interesting electrochemical reactivity [2] and tunable chemical surfacic composition [3]. Indeed, the surface structure, surface properties, number of grafting sites available are tunable according to the atomic percentage of nitrogen in the a-CNx [4]. High surface reactivity are highly dependent on the surface state and can be affected by synthesis (by varying the Csp3/sp2 ratio), and by pre-treatment (electrochemical or plasma). In this work, we elaborated a microfluidic chip integrating a-CNx as working microelectrodes. In brief, a titanium/ platinum (50/500 Å) underlayer was first deposited on the glass wafer and patterned as working microelectrodes for the future thin film a-CNx adhesion and conductivity. On the top of the working electrode, a 220 nm a-CNx (x=0.12), layer was deposited with DC magnetron sputtering (time =20 min, power=200 W) with a graphite target under a flow of nitrogen (PN2/Ptot =3%, Ptot =0.4 Pa). Then, a classical PDMS fluidic circuit was microfabricated and pre-treated with nitrogen plasma to favor its adhesion onto the glass slide containing the Ti/Pt/ a-CNx microelectrodes. The a-CNx microelectrodes were also electrochemically pre-treated in galvanostatic mode using 0.1 M KOH solution (anodic pre-treatment). The hydrodynamic properties of the fluidic channel a-CNx microelectrodes (as-grown and pre-treated) were screened with the [Fe(III)(CN)6]3−/[Fe(II)(CN)6]4− redox couple by cyclic voltammetry and impedance spectroscopy to provide a basis for further investigations such as the influence of a-CNx electrode pre-treatment on the DNA probe density issues in order to enhance the hybridization reaction efficiency with its specific DNA target. [1]. A. Lagrini, C. Deslouis, H. Cachet, M. Benlahsen, and S. Charvet. Elaboration and electrochemical characterization of nitrogenated amorphou scarbon films, Electrochem. commun., 6(3) (2004) 245–248. [2]. G Adamopoulos, C Godet, C Deslouis, H Cachet, A Lagrini, and B Saidani. The electrochemical reactivity of amorphous hydrogenated carbon nitrides for varying nitrogen contents: the role of the substrate. Diam. Relat. Mater.,12 (2003) 613– 617. [3]. R A Medeiros, A Benchick, R C Rocha-Filho, O Fatibello-Filho, B Saidani, C Debiemme-Chouvy, and C Deslouis. Simultaneous detection of ascorbic acid and dopamine with electrochemically pretreated carbon nitride electrodes: Comparison with boron-doped diamond electrodes. Electrochem. commun., 24 (2012) 61–64. [4]. M Faure, F Billon, A M Haghiri-Gosnet, B Tribollet, C Deslouis, A Pailleret, and J. Gamby. Influence of the atomic nitrogen content in amorphous carbon nitride thin films on the modulation of their polarizable interfaces properties. Electrochim. Acta, 280 (2018) 238-247.

Iodine sequestration using cyclophosphazene based inorganic-organic hybrid nanoporous materials: Role of surface functionality and pore size distribution

Cyclophosphazene based inorganic-organic hybrid nanoporous materials having triazine and pyrrolic functionality named as HNM-1 and CHNM-1, respectively, with varying nitrogen content, hierarchical pore size and high specific surface area have been explored for iodine sequestration application. The presence of electron rich functionality in the HNM-1 and CHNM-1 provides a large number of active sites for the adsorption of iodine. Maximum gravimetric iodine capture capacity of 223 and 120 wt% were estimated in HNM-1 and CHNM-1 specimens, respectively, under fuel processing condition i.e. 75 °C and ambient pressure. Moreover, both the specimens have shown very good iodine release behavior in organic solvents. The recyclability of HNM-1 and CHNM-1 for iodine sorption has shown the retention of adsorption capacity by 80 and 86%, respectively, even after five cycles. The iodine sorption both in vapor as well as solution phases is greatly influenced by the nitrogen content and pore size distribution of the framework materials.

Fabrication of nitrogen-doped hollow carbon nanospheres with variable nitrogen contents using mixed polymer brushes as precursors

Design and synthesis of heteroatoms-doped porous carbon model materials with controllable nitrogen contents and similar pore structure are of great importance for fundamental understanding of the correlation between their intrinsic properties and applications. Herein, we report a synthetic strategy for synthesis of nitrogen-doped hollow carbon nanospheres with variable nitrogen contents, similar pore structure and morphology by pyrolysis of mixed polymer brushes formed through surface-initiated atom transfer radical polymerization of monomer mixtures of styrene and 4-vinylpyridine. With increasing 4-vinylpyridine fractions in the monomer mixture, nitrogen contents in the final carbon products increase up to about 5.5 wt%. As example applications, electrocatalytic performance for oxygen reduction reactions in both basic and acidic media and carbon dioxide adsorption properties of the thus-formed materials are investigated to evaluate the synthetic approach. The results reveal that the higher nitrogen contents doped in carbon do not guarantee the better performance for either electrocatalysis or carbon dioxide adsorption. It is the fraction of pyridinic nitrogen that dominates the electrocatalytic activity and carbon dioxide adsorption capacity. The findings demonstrate that mixed polymer brushes are promising precursors for the formation of heteroatoms-doped carbon materials, particularly as model materials for fundamental understanding their structure–properties correlations.

Effect of nitrogen doping on surface morphology, microstructure, chemical composition and intrinsic stress of nickel thin films deposited by reactive sputtering

N-doped nickel thin films were fabricated by direct current reactive magnetron sputtering, with varying nitrogen contents (0%–20%) added to the sputtering gas (Ar). To investigate the effect of nitrogen contents on morphology, microstructure, chemical composition and intrinsic stress of nickel thin films, characterizations were carried out using grazing incidence X-ray reflectivity (GIXRR), X-ray scattering (XRS), atomic force microscopy (AFM), X-ray diffraction (XRD), cross-sectional transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and intrinsic stress measurements. GIXRR and AFM results showed that the roughness achieves minimum with 8% nitrogen, corresponding to minimum average grain size obtained by XRS and XRD measurements. XRD patterns simultaneously indicated that the position and intensity of the Ni(111) and Ni(200) peaks shifted. This is because Ni lattice structure changed after the introduction of N atoms at interstitial sites, which were octahedrally surrounded by Ni atoms. Cross-sectional TEM images confirmed that Ar + 8%N2 as sputtering gas can suppress the crystallization and effectively smoothen the surface of Ni film. Moreover, no nickel nitride was found in the N-doped Ni films by XPS analysis and the intrinsic stress remained unchanged after the addition of 8% nitrogen.

Assimilation of Global Total Chlorophyll OC‐CCI Data and Its Impact on Individual Phytoplankton Fields

AbstractThe coupled ocean circulation‐ecosystem model MITgcm‐REcoM2 is used to simulate biogeochemical variables in a global configuration. The ecosystem model REcoM2 simulates two phytoplankton groups, diatoms and small phytoplankton, using a quota formulation with variable carbon, nitrogen, and chlorophyll contents of the cells. To improve the simulation of the phytoplankton variables, chlorophyll‐a data from the European Space Agency Ocean‐Color Climate Change Initiative (OC‐CCI) for 2008 and 2009 are assimilated with an ensemble Kalman filter. Utilizing the multivariate cross covariances estimated by the model ensemble, the assimilation constrains all model variables describing the two phytoplankton groups. Evaluating the assimilation results against the satellite data product SynSenPFT shows an improvement of total chlorophyll and more importantly of individual phytoplankton groups. The assimilation improves both phytoplankton groups in the tropical and midlatitude regions, whereas the assimilation has a mixed response in the high‐latitude regions. Diatoms are most improved in the major ocean basins, whereas small phytoplankton show small deteriorations in the Southern Ocean. The improvement of diatoms is larger when the multivariate assimilation is computed using the ensemble‐estimated cross covariances between total chlorophyll and the phytoplankton groups than when the groups are updated so that their ratio to total chlorophyll is preserved. The comparison with in situ observations shows that the correlation of the simulated chlorophyll of both phytoplankton groups with these data is increased whereas the bias and error are decreased. Overall, the multivariate assimilation of total chlorophyll modifies the two phytoplankton groups separately, even though the sum of their individual chlorophyll concentrations represents the total chlorophyll.

The pygmy field mouse \u2014 what does influence food quality?

The dominant rodent species in Central European agricultural landscapes are granivorous mouse species and herbivorous common voles. Although our knowledge of European wood mice is relatively good, there is a distinct lack of information on pygmy field mice inhabiting Central and Eastern Europe and Central Asia. In this study, we examine the food quality of pygmy field mice in relation to environmental and population factors, and compare the food quality of related mouse species and common voles living in the same study plots. The dietary quality of the pygmy field mouse is similar to that of other mouse species; however, the food quality of pygmy field mice and common voles differed substantially, with mice having lower and more variable nitrogen content. For both rodent species, factors such as body size, age and sex had no influence on diet quality. Pygmy field mouse diet was mainly dependent on season, while total abundance had greatest influence on common vole diet.

Collagen functionalized graphene sheets decorated with in situ synthesized nano hydroxyapatite electrospun into fibers

We report the in situ synthesis of hydroxyapatite nanoparticles on 1–3 layers of colloidal collagen-graphene composites. Varying calcium and phosphate: graphene ratio two different composites were synthesized. Crystallite size, particle size and degree of crystallinity of hydroxyapatite nanoparticles changes with a change in graphene concentration. Transmission electron microscopy shows that these graphene composites change shape from spherical to elongated needle-like structures because of the varying nitrogen content in collagen-graphene. Fourier-transform Infrared Spectroscopy peaks suggests an interaction between calcium and the colloidal composites. X-ray Photo Electron spectroscopy data shows the interaction between graphene, collagen and hydroxyapatite through pyridinic N-oxide moiety. High-resolution lattice images confirm the co-existence of both graphene and hydroxyapatite. Anti-bacterial tests of the colloidal composites with two different bacteria S. Marcences and E. Coli show improved anti- bacterial property with increased graphene concentration. The colloidal composites were further electrospun into fibers, and their electrochemical stability in simulated body fluids estimated. The electrochemical test data show that the fiber made of composites would be extremely useful for biomedical applications such as internal bandages and burns.

Silicon nitride as anode material for Li-ion batteries: Understanding the SiNx conversion reaction

An extensive research effort is being made to develop the next generation of anode materials for lithium ion batteries. A large part of this effort has been related to silicon, primarily due to its considerable theoretical capacity; however, very limited cycling stability has prevented widespread commercial adoption. A potential solution for this is to use convertible sub-stoichiometric silicon nitride (a-SiNx), which goes through an irreversible conversion reaction during the initial lithiation cycle, producing active silicon domains in an inactive, lithium conducting matrix. Relative to pure silicon, the resulting composite material has gained cycle life at the cost of reduced specific capacity. The specifics of the conversion reaction, however, have not yet been determined; hence, the impact of varying nitrogen content remains uncertain. In this work we develop a model reaction which relates the reversible and irreversible capacities of an electrode to the composition of the conversion products. By fitting this model to experimental data from a large number of a-SiNx thin film electrodes with different thickness and composition, we determine with a high probability that the matrix composition is Li2SiN2. From this, the reversible and irreversible capacities of the material can be predicted for a nitride of a given composition.

Comparative study of activation methods to design nitrogen-doped ultra-microporous carbons as efficient contenders for CO2 capture

Microporous carbon materials are envisaged as efficient contenders for mitigating CO2 levels by virtue of their favorable surface chemistry, high specific surface area, tunable pore structures, moderate heat of adsorption, and facile regeneration. This study presents a solvent-free one-step polymerization and activation method for designing a series of nitrogen-enriched carbons to delineate the role played by nitrogen moieties and ultra-micropores on CO2 capture. Two activating agents were used at high temperature to fabricate microporous carbons with tunable pore structure and variable nitrogen content. The optimized material, MCKC-3, possesses high surface area (2060 m2/g) comprising of ultramicropores (<0.7 nm) and high nitrogen content (2.3 wt%). This material exhibit an outstanding CO2 uptake performance of 354 mg/g (8.03 mmol/g) at 273 K and 1 bar, comparable to the highest adsorption reported so far for carbon-based materials. In conclusion presence of both the ultra-micropores and nitrogen functionalities contribute a major role in CO2 adsorption, the former being predominant.

Nitrogen doped mesoporous carbon supported Pt electrocatalyst for oxygen reduction reaction in proton exchange membrane fuel cells

Nitrogen doped mesoporous carbons are employed as supports for efficient electrocatalysts for oxygen reduction reaction. Heteroatom doped carbons favour the adsorption and reduction of molecular oxygen on Pt sites. In the present work, nitrogen doped mesoporous carbons (NMCs) with variable nitrogen content were synthesized via colloidal silica assisted sol-gel process with Ludox-AS40 (40 wt% SiO2) as hard template using melamine and phenol as nitrogen and carbon precursors, respectively. The NMC were used as supports to prepare Pt/NMC electrocatalysts. The physicochemical properties of these materials were studied by SEM, TEM, XRD, BET, TGA, Raman, XPS and FTIR. The surface areas of 11 wt% (NMC-1) and 6 wt% (NMC-2) nitrogen doped mesoporous carbons are 609 m2 g−1 and 736 m2 g−1, respectively. The estimated electrochemical surface areas for Pt/NMC-1 and Pt/NMC-2 are 73 m2 g−1 and 59 m2 g−1, respectively. It is found that Pt/NMC-1 has higher ORR activity with higher limiting current and 44 mV positive onset potential shift compared to Pt/NMC-2. Further, the fuel cell assembled with Pt/NMC-1 as cathode catalyst delivered 1.8 times higher power density than Pt/NMC-2. It is proposed that higher nitrogen content and large pyridinic nitrogen sites present in NMC-1 support are responsible for higher ORR activity of Pt/NMC-1 and high power density of the fuel cell using Pt/NMC-1 cathode electrocatalyst. The carbon support material with high pyridinic content promotes the Pt dispersion with particle size less than 2 nm.

Binder-free production of 3D N-doped porous carbon cubes for efficient Pb2+ removal through batch and fixed bed adsorption

N-doped carbon cubes (NCCs) with varying nitrogen contents and different densities were fabricated using a simple and binder-free method that involved the curing of resorcinol-formaldehyde (RF) gel with different RF contents in the framework of a melamine sponge. In addition to the robust structure and nitrogen doping, the porosity of the NCCs could be tailored easily within the mesopores and ultra-micropores with a unique combination of macro, meso, and micropores. The prepared NCCs exhibited excellent uptake capacity, ranging from 32.1 to 39.3 mg/g Pb2+ ions, owing to their high surface area (up to 675 m2/g) and nitrogen doping (max. 4.9 wt. %). The Pb2+ adsorption property of NCC-10 was also compared with that of widely used commercial 3D carbon adsorbents. The weight and surface area-normalized Pb2+ adsorption capacity of NCC-10 was found to be 3.7 and 6.6 times higher, respectively than the commercial activated carbon granules. The continuous mode model data fitted with experimental fixed-bed results well, and showed 8.95 mg/g loading capacity, proving that NCC-10 is an effective 3D adsorbent. The prepared NCCs could be used as a practical adsorbent for the removal of Pb2+ ions because of their high adsorption capacity, easy regeneration, and exceptional stability maintained after longer reuse.

Influence of Cold Work on Sensitization Kinetics and Evaluation of Degree of Sensitization in Type 316LN Stainless Steels

The sensitization behavior of Type 316LN stainless steel (SS) with varying nitrogen content (0.07 wt% and 0.22 wt%) in 0% to 25% cold worked (CW) as well as in the as-received condition was evaluated. Time-temperature-sensitization diagrams were established for the cold worked Type 316LN SS (nitrogen content: 0.07 wt% and 0.22 wt%), using ASTM A262 Practice-E test. The time required for sensitization (ts) was found to decrease and critical cooling rates (CCR) increased up to 10% CW in the alloy with 0.07 wt% N. At higher CW, ts increased and CCR decreased. Similarly, ts decreased and CCR increased up to 15% CW in the alloy with 0.22 wt% N and at higher CW, ts increased and CCR decreased. To understand the sensitization behavior of Type 316LN SS with varying nitrogen content during thermal aging at 923 K for various durations, nondestructive electrochemical techniques like double loop electrochemical potentiokinetic reactivation (DL-EPR) technique and electrochemical reactivation technique (ERT) were adopt...

The effects of nitrogen partial pressure on the microstructure of amorphous carbon nitride films

ABSTRACTThe amorphous carbon nitride (a-CNx) films with varying nitrogen content were deposited on Si (100) wafers substrates using radio frequency magnetron sputtering (RFMS) from graphite target at different nitrogen partial pressure. The influence of nitrogen partial pressure on the microstructure and phase composition of a-CNx films were researched systematically. The films were characterized by atom force spectroscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). AFM results showed cluster structure in a range of tens to hundreds namometers existed on the surface of the films and the surface roughness increased with the increase of nitrogen partial pressure. Ratio of ID/IG increased with the nitrogen partial pressure, while the sp3 phase content from fitting results of XPS displayed reverse trend. The nanohardness of a-CNx films characterized by nanoindentation test decreased with the increase of nitrogen partial pressure, which consisted with the results of Raman and XPS. Thus high nitrogen partial pressure caused the mechanical properties of a-CNx films decrease.

Effects of nitrogen substitution in amorphous carbon films on electronic structure and surface reactivity studied with x-ray and ultra-violet photoelectron spectroscopies

We investigated the effects of incorporating a low percentage of nitrogen on the local and the electronic structures of amorphous carbon (a-C) using X-ray photoelectron spectroscopy and ultra-violet photoelectron spectroscopy (UPS). Nitrogen-doped amorphous carbon films (a-CNx) with varying nitrogen contents were prepared by a thermal decomposition method using a mixture of CH4 + NH3 under atmosphere. A slight shift of the C 1s core-level spectrum toward the higher binding energy side was detected in a-CNx as a function of nitrogen content, whereas a shift of the Fermi level (EF) cannot be confirmed from the UPS results. This was interpreted as a chemical shift between carbon and nitrogen atoms rather than as a shift of the EF. The C 1s peak shifts can be explained by the presence of two kinds of C–N local structures and the charge transferred bulk C–C components by nitrogen atoms. The two kinds of deconvoluted C 1s components could be well correlated with the two N 1s components. Two localized states were detected below the EF in UPS spectra of a-CNx, which could be assigned to defect bands. These defects played a significant role in the surface reactivity, and were stabilized in a-CNx. The adsorption and reaction of NO were carried out on a-CNx as well as a-C films. It was found that both defect sites and O2– species were responsible on a-C, while O2– species were selectively active for NO adsorption on a-CNx. We concluded that nitrogen doping reduces defect density to stabilize the surface of a-C, while at the same time inducing the selective adsorption capability of NO.