Nitrogen Surface Groups Research Articles

Surface‐Modified Carbon Materials for CO2 Electroreduction

AbstractThe electrochemical reduction of CO2 to produce sustainable fuels and chemicals has attracted great attention in recent years. It is shown that surface‐modified carbons catalyze the CO2RR. This study reports a strategy to modify the surface of commercially available carbon materials by adding oxygen and nitrogen surface groups without modifying its graphitic structure. Clear differences in CO2RR activity, selectivity and the turnover frequency between the surface‐modified carbons were observed, and these differences were ascribed to the nature of the surface groups chemistry and the point of zero charge (PZC). The results show that nitrogen‐containing surface groups are highly selective towards the formation of CO from the electroreduction of CO2 in comparison with the oxygen‐containing surface groups, and the carbon without surface groups. This demonstrates that the selectivity of carbon for CO2RR can be rationally tuned by simply altering the surface chemistry via surface functionalization.

Catalytic reduction of NO over copper supported on activated carbon

Nitrogen oxides are involved in environmental pollution phenomena, making it important to develop techniques for treating the emissions of these gases. The selective catalytic reduction of NOx with carbon is an alternative technology to the more common reduction processes using NH3. This work's main objective is the synthesis of carbon catalysts, catalytically active in NO reduction. The activated carbons were subjected to appropriate treatments to modify their surface chemistry (introduction of nitrogen and oxygen functionalities and copper as metallic phase). Activated carbons prepared without metal do not show significant activity in the catalytic reduction of NO; therefore, the presence of copper in the catalysts is indispensable for obtaining high activities. The introduction of nitrogen surface groups further enhances their performance. An ideal copper-to-carbon mass ratio of 10% was obtained, with the highest NO reduction being observed for the AC_M_BM@10Cu sample, resulting in a 100% conversion for a temperature of 440 °C. For this type of catalyst, the presence of N2 and CO2 was confirmed; N2O and CO were not detected.The catalyst stability was evaluated by carrying out a long-term reaction test. Some catalyst deactivation was observed after 38 h of reaction. An ideal copper-to-carbon mass ratio of 10% was obtained, with the highest NO reduction being observed for the AC_M_BM@10Cu sample, resulting in a 100% conversion for a temperature of 440 °C. For this type of catalyst, the presence of N2 and CO2 was confirmed; N2O and CO were not detected.

Achieving ultrahigh electrochemical performance by surface design and nanoconfined water manipulation

The effects of nanoconfined water and the charge storage mechanism are crucial to achieving the ultrahigh electrochemical performance of two-dimensional transition metal carbides (MXenes). We propose a facile method to manipulate nanoconfined water through surface chemistry modification. By introducing oxygen and nitrogen surface groups, more active sites were created for Ti3C2 MXene, and the interlayer spacing was significantly increased by accommodating three-layer nanoconfined water. Exceptionally high capacitance of 550 F g–1 (2000 F cm–3) was obtained with outstanding high-rate performance. The atomic scale elucidation of the layer-dependent properties of nanoconfined water and pseudocapacitive charge storage was deeply probed through a combination of ‘computational and experimental microscopy’. We believe that an understanding of, and a manipulation strategy for, nanoconfined water will shed light on ways to improve the electrochemical performance of MXene and other two-dimensional materials.

Growing Tungsten Nanophases on Carbon Spheres Doped with Nitrogen. Behaviour as Electro-Catalysts for Oxygen Reduction Reaction

This work shows the preparation of carbon nanospheres with a high superficial nitrogen content (7 wt.%), obtained by a simple hydrothermal method, from pyrocatechol and formaldehyde, around which tungsten nanophases have been formed. One of these nanophases is tungsten carbide, whose electro-catalytic behavior in the ORR has been evaluated together with the presence of nitrogen surface groups. Both current and potential kinetic density values improve considerably with the presence of tungsten, despite the significant nitrogen loss detected during the carbonization treatment. However, the synergetic effect that the WC has with other electro-catalytic metals in this reaction cannot be easily evaluated with the nitrogen in these materials, since both contents vary in opposite ways. Nevertheless, all the prepared materials carried out oxygen electro-reduction by a mixed pathway of two and four electrons, showing remarkable electro-catalytic behavior.

The role of pore structure and nitrogen surface groups in the adsorption behavior of formaldehyde on resin‐based carbons

This study focused on the role of pore structures and nitrogen surface functional groups in the formaldehyde (HCHO) adsorption on the carbonized resin‐based materials (UFC). After comparing the optimal sample UFAC‐700 obtained by the activation of UFC at 700°C with the commercial activated carbon (CAC) and other UFC, the HCHO adsorption capacity for UFAC‐700 (12.30 mg g−1) is more than three times and 10 times of that for CAC and UFC, respectively. Abundant pore structures could provide more adsorption sites for the initial stage of HCHO adsorption. Moreover, according to the density functional theory (DFT) calculations, pyrrolic‐N could enhance the adsorption energy and polar interaction of HCHO due to electrostatic force between the positively charged H attached to the nitrogen group and the negatively charged O atoms in the HCHO molecule. This study introduced a novel way to specifically design the surface modifications for volatile organic compounds (VOCs) adsorption.

Adsorption mechanism of a cationic dye on a biomass-derived micro- and mesoporous carbon: structural, kinetic, and equilibrium insight

In this research, equilibrium, kinetics, and adsorption mechanism of methylene blue on a relatively large surface area (1437 m2 g−1) Azolla-derived micro- and mesoporous carbon has been investigated. The porous activated carbon was characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman and also X-ray photoelectron spectroscopy (XPS), N2 sorption, and high-resolution transmission electron microscopy. Remaining methylene blue solution revealed that the adsorption energy and adsorption capacity of the porous carbon are 21.76 kJ mol−1 and 1930 mg g−1, respectively. Based on the kinetics results, pseudo-second-order kinetic model is dominant during the adsorption process. Diffusion of methylene blue in the porosities and in the space between the graphitic planes of carbons is the rate-limiting parameters. Adsorption of methylene blue into the graphitic planes and the micro-porosities leads to some compressive stresses on the graphitic planes. The relative graphitization value of the prepared carbons will decrease during adsorption process. FTIR and XPS results demonstrate the effect of surface nitrogen groups on the adsorption of methylene blue. During the adsorption process, a relative percent of pyridinic nitrogen will decrease, pyrrolic and graphitic nitrogen of graphitic layers will eliminate and N-(C)3 and H-N-(C)2 nitrogen appear.

Screen-Printed Soft-Nitrided Carbon Electrodes for Detection of Hydrogen Peroxide.

Nitrogen-doped carbon materials have garnered much interest due to their electrocatalytic activity towards important reactions such as the reduction of hydrogen peroxide. N-doped carbon materials are typically prepared and deposited on solid conductive supports, which can sometimes involve time-consuming, complex, and/or costly procedures. Here, nitrogen-doped screen-printed carbon electrodes (N-SPCEs) were fabricated directly from a lab-formulated ink composed of graphite that was modified with surface nitrogen groups by a simple soft nitriding technique. N-SPCEs prepared from inexpensive starting materials (graphite powder and urea) demonstrated good electrocatalytic activity towards hydrogen peroxide reduction. Amperometric detection of H2O2 using N-SPCEs with an applied potential of −0.4 V (vs. Ag/AgCl) exhibited good reproducibility and stability as well as a reasonable limit of detection (2.5 µM) and wide linear range (0.020 to 5.3 mM).

Electrochemical and Electric Field Response Properties of Highly Sensitive Electrodes Based on Carbon Fiber With Oxygen and Nitrogen Surface Groups

In this paper, a high-sensitive carbon fiber electrode enriched oxygen and nitrogen groups were prepared using a method combining oxidation and graft modification. The surface compositions were analyzed by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The electrochemical results show that the modified carbon fibers have a better electric double layer performance and a lower capacitive impedance at the lower frequency. The offset potential of the electrode pairs is typically below 1 mV with a drift of less than $40~\mu \text{V}$ /day. Typical measured noise level is below 2 nV/rt (Hz) at 1 Hz. The modified carbon fiber electrode pairs exhibit a good response to the ac sine signal of amplitude 1 mV and frequency 1 mHz. The sensitivity is increased by 82% and 59%, respectively, in comparison with Ag/AgCl electrode pair. The possible mechanism of the electric field response is discussed by the model of the electric double layer. This carbon fiber electrodes could provide the potential candidate and the theoretical basis for the design of high-sensitivity marine electric field sensor.

A two-step method for the integrated removal of HCl, SO2 and NO at low temperature using viscose-based activated carbon fibers modified by nitric acid

Activated carbon fibers (ACFs) have been widely used as cost-effective integrated processes for the removal of nitrogen oxides, sulfur oxides and hydrogen chloride (HCl), while the competitive adsorption behaviors and the detailed interaction mechanisms have not been comprehensively investigated. In the current work, the adsorption capacities with one-step process and two-step method were compared, and the effects of HNO3 modification and ambient O2 concentration were simultaneously studied. Furthermore, the relative ratios of surface nitrogen groups, sulfur and chlorine compounds, as well as the soluble species on the ACFs surface, were respectively characterized by X-ray photoelectron spectroscopy and ion chromatography techniques. The results indicated that HCl, SO2 and NO were not able to be effectively removed with only one reactor due to the strong competitive adsorption behaviors, while the adsorption capacities of HCl, SO2 and NO were significantly improved by 30%, 280%, 230% in the two-stage reactors with HNO3 modification. Further investigation indicated interactions between HCl, SO2 and NO in the two-stage reactors are very complicated. The primary reactor can remove HCl and facilitate the catalytic removal of SO2/NO in the secondary reactor since HCl can severely inhibit the adsorptions of SO2 and NO, yet HCl adsorption can be suppressed by SO2. Simultaneously, nitro/nitroso groups derived of HNO3 treatment and NO oxidation can promote the chemisorption of HCl.

Role of sulfur and nitrogen surface groups in adsorption of formaldehyde on nanoporous carbons

S-doped nanoporous carbon, and commercial activated carbons, as received or modified by an incorporation of sulfur and nitrogen functional groups to their surface, were tested as low concentration formaldehyde (1 ppmv) adsorbents. The breakthrough capacities, in dry and wet conditions, were measured. The surface properties of the samples were evaluated using nitrogen sorption, potentiometric titration, thermal analysis, and XPS. The incorporation sulfur and/or nitrogen functional groups led to an increase in the amount of HCHO removed from air. These group (pyridines, amines, thiophenes, sulfones) when located in large pores increase the utilization of the carbon surface for formaldehyde adsorption providing chemical reactivity. In this aspect, rich in sulfur carbon of a relatively low surface was found as the most efficient formaldehyde adsorbent. Its HCHO adsorption capacity was 7.15 × 10−4 mg m−2 whereas on melamine modified carbon of a high surface area 4.23 × 10−4 mg m−2 were adsorbed. On the microporous carbon of basic nature reactions of HCHO with phenols block this carbon porosity and thus excluded the adsorption centers in ultramicropores for physical adsorption decreasing the adsorption capacity. Water in the system decreases the HCHO capacity between 10 and 30%, owing to its competitive adsorption on polar centers.

Role of different nitrogen functionalities on the electrochemical performance of activated carbons

Different oxidation, reduction and thermal methods are used for selectively obtaining each of the most common surface nitrogen groups (almost isolated) on the surface of a phosphorus-containing activated carbon (ACP), and their electrochemical performances are analyzed. Nitro- and amino-containing activated carbons show defined pseudocapacitive peaks, characteristic of redox processes, which can be associated to the formation of hydroxylamino groups (observed by means of XPS). Condensed structures of nitrogen, such as pyridinic and pyrrolic, additionally improve the ionic diffusion on the carbonaceous structure, increasing the specific capacitance of the carbon electrode up to 317 F g−1. The formation of poly (amido-amine) chains on ACP surface leads to an activated carbon with poor textural properties (ABET = 43 m2 g−1) but surprisingly high surface capacitances (ca. 3256 mF m−2) attributed to an enhancement of the carbon conductivity. Some of the activated carbons are submitted to a severe thermal treatment at 900 °C, yielding carbons with a developed porous texture, stable surface phosphorus groups and an increased proportion of quaternary nitrogen surface species. These activated carbons exhibit a faster development of the electric double layer, due to the more ordered carbon planes and the presence of charged functional groups.

Structural evolution of nitrogen-doped carbon nanotubes: From synthesis and oxidation to thermal defunctionalization

Mechanism of the oxidation and thermal defunctionalization of nitrogen-doped carbon nanotubes (N-CNTs) was studied. TGA-MS, low temperature nitrogen adsorption, Raman spectroscopy, TEM and XPS were used to trace the changes in the morphology, surface properties and defectiveness of N-CNTs during HNO3 treatment. The first hour of treatment resulted in the intensive oxidation of N-CNTs due to the transformation of surface nitrogen groups into oxidized pyridone ones. Complete destruction of segmented structure of N-CNTs and a decrease in both oxygen and nitrogen content was observed after prolonged oxidation. The changes in the defectiveness were confirmed by the increase in ID1/IG and the decrease in ID3/IG ratio in Raman spectra. The thermal stability of nitrogen species in N-CNTs was found to increase in the following sequence: pyridone, pyridine and graphitic nitrogen. Decomposition of pyridone nitrogen starts at 200–400°С resulting in the formation of pyridine and pyrrolic nitrogen species. Above 500 °C these two nitrogen species transform into graphitic nitrogen which decomposes at temperatures above 1000°С. NO release in different temperature ranges was associated with both the destruction of nitro-, nitrito-, nitroso-groups and oxidation of HCN. The mechanism of functionalization and thermal destruction of oxygen- and nitrogen-containing groups was proposed.

Synchrotron based NEXAFS study on nitrogen doped hydrothermal carbon: Insights into surface functionalities and formation mechanisms

Synchrotron-based Near-Edge X-ray Absorption Fine Structure (NEXAFS) studies have been conducted on two hydrothermally produced carbon (HTC) structures and their main surface structural features are reported. The two HTCs were produced respectively from sucrose, and sucrose with added (NH4)2SO4, under subcritical water conditions. The NEXAFS carbon K-edge spectra reveal the presence of CC, COC (furan), CO and COH functionalities on the surface of the sucrose derived HTC. For the nitrogen-doped HTC, the carbon K-edge spectra indicate an increase in CC and COH functionalities, as well as the inclusion of CN and CN functionalities. Additionally, the nitrogen K-edge for the doped hydrothermal carbon displayed characteristic peaks for pyridinic, pyrrolic and tertiary amine nitrogen surface groups. Furthermore, a mechanistic pathway to inclusion of nitrogen atoms in the HTC-SAS structure is postulated.

Adsorption of emerging pollutants on functionalized multiwall carbon nanotubes

Adsorption of three representative emerging pollutants – 1,8-dichlorooctane, nalidixic acid and 2-(4-methylphenoxy)ethanol- on different carbon nanotubes was studied in order to determine the influence of the morphological and chemical properties of the materials on their adsorption properties. As adsorbents, multiwall carbon nanotubes (MWCNTs) without functionalization and with oxygen or nitrogen surface groups, as well as carbon nanotubes doped with nitrogen were used. The adsorption was studied in aqueous phase using batch adsorption experiments, results being fitted to both Langmuir and Freundlich models. The adsorption capacity is strongly dependent on both the hydrophobicity of the adsorbates and the morphology of the adsorbents. Thermodynamic parameters were determined observing strong interactions between the aromatic rings of the emerging pollutant and the nitrogen modified adsorbents.

Generation of nitrogen functionalities on activated carbons by amidation reactions and Hofmann rearrangement: Chemical and electrochemical characterization

Nitrogen functionalization of a highly microporous activated carbon (BET surface area higher than 3000m2/g) has been achieved using the following sequence of treatments: (i) chemical oxidation using concentrated nitric acid, (ii) amidation by acyl chloride substitution with NH4NO3 and (iii) amination by Hoffman rearrangement. This reaction pathway yielded amide and amine functional groups, and a total nitrogen content higher than 3at.%. It is achieved producing only a small decrease (20%) of the starting microporosity, being most of it related to the initial wet oxidation of the activated carbon. Remarkably, nitrogen aromatic rings were also formed as a consequence of secondary cyclation reactions. The controlled step-by-step modification of the surface chemistry allowed to assess the influence of individual nitrogen surface groups in the electrochemical performance in 1M H2SO4 of the carbon materials. The largest gravimetric capacitance was registered for the pristine activated carbon due to its largest apparent surface area. The nitrogen-containing activated carbons showed the highest surface capacitances. Interestingly, the amidated activated carbon showed the superior capacitance retention due to the presence of functional groups (such as lactams, imides and pyrroles) that enhance electrical conductivity through their electron-donating properties, showing a capacitance of 83F/g at 50A/g.

Calorimetric study of functionalized carbonaceous materials

For this paper we conducted a calorimetric study of functionalized carbonaceous materials. The activated carbons were obtained by chemically activating the African Palm Stone with a mix of 2% CaCl2 solution and 32% H3PO4 solution. After the activation, the activated carbons were functionalized to increase the solids nitrogen content. In the study we determined the immersion enthalpies in benzene, water, NaOH, and HCl solutions. Additionally, the samples were characterized by N2 adsorption at 77K and Boehm titration. The calorimetric study showed that the immersion of different solids in respective solvents and solutions generated enthalpy values between −6.22Jg−1 and −173.2Jg−1. The immersion enthalpies of samples in the employed liquids varied with different functionalization processes to which the materials were subjected, showing changes in the carbons’ textural and chemical characteristics. Surface areas and pore volumes decreased with the functionalization process because of the nitrogen surface groups’ blocking the solids’ porosity.

Carbonized polyacrylonitrile fibers for the catalytic ozonation of oxalic acid

Textile polyacrylonitrile (PAN) fibers, which contain nitrogen, were carbonized at different temperatures and activated during 10h in order to assess their performance as ozonation catalysts in the oxalic acid degradation The fiber carbonized at 800°C shows the best performance due to its basic character and, mainly, the high concentration of nitrogen surface groups, particularly N-pyridinic (N6) groups. The carbonization of PAN fibers is a simple and effective method to prepare materials with good catalytic activity in ozonation processes

Comparison of melamine resin and melamine network as precursors for carbon electrodes

Nitrogen-rich carbons synthesized from two melamine-based precursors – a melamine resin (MR) and a melamine network (MN) – were compared based on their pore structure, surface chemistry and electrochemical performance. The effect of carbonization temperatures on carbon pore structure and surface chemistry was investigated by N2 and CO2 sorption analyses, potentiometric titration, elemental analysis (CHN) and X-ray photoelectron spectroscopy (XPS). The carbons prepared from melamine resin had higher surface areas and pore volumes than the carbons produced from the melamine network, with carbonization of the MN at temperatures of 700°C and higher leading to collapse of the MN pore structure. The electrochemical performances of the carbons were evaluated in 1M H2SO4. The changes in carbon surface chemistry after charge–discharge cycles were studied for the two melamine-based carbons carbonized at 800°C using Synchrotron XPS. This test demonstrated that in two-electrode 1M H2SO4 the redox reactions involving surface nitrogen groups are reversible and redox reactions involving COOH take place. The results revealed the impact of the initial structure of the melamine precursors on the porosity along with the surface chemistry of the carbon matrix on the capacitive performance.

Critical influence of surface nitrogen species on the activity of N-doped TiO2 thin-films during photodegradation of stearic acid under UV light irradiation

Atmospheric-pressure chemical vapour deposition (APCVD) was used to produce a series of nitrogen-doped titania (N-TiO2) thin-films using tert-butylamine as the nitrogen source. The films were deposited as the anatase phase on glass and quartz substrates and characterised using X-ray diffraction, optical and vibrational spectroscopy and electron microscopy. The nature and location of the nitrogen species present on the surface and bulk of the films was studied by X-ray photoelectron spectroscopy. Thorough comparison amongst films with similar structural and morphological features allowed the role of nitrogen species to be evaluated during photo-oxidation of a model organic pollutant (stearic acid). Sequential photocatalytic experiments revealed a drastic decrease in the UV activity of the films which were correlated with changes involving surface nitrogen groups. The existence of concomitant nitrogen species with similar binding energies (ca. 400eV) but different chemical nature is proposed, as well as the direct participation of at least one of these species in the oxidation reaction. A similar mechanism for the visible light activity of N-TiO2 materials is also suggested.

Interaction of Cobalt Nanoparticles with Oxygen- and Nitrogen-Functionalized Carbon Nanotubes and Impact on Nitrobenzene Hydrogenation Catalysis

The type and the amount of functional groups on the surface of carbon nanotubes (CNTs) were tuned to improve the activity of supported Co nanoparticles in hydrogenation catalysis. Surface nitrogen species on CNTs significantly promoted the decomposition of the cobalt precursor and the reduction of cobalt oxide, and improved the resistance of metallic Co against oxidation in ambient atmosphere. In the selective hydrogenation of nitrobenzene in the gas phase, Co supported on CNTs with the highest surface nitrogen content showed the highest activity, which is ascribed to the higher reducibility and the lower oxidation state of the Co nanoparticles under reaction conditions. For Co nanoparticles supported on CNTs with a smaller amount of surface nitrogen groups, a repeated reduction at 350 °C was essential to achieve a comparable high catalytic activity reaching 90% conversion at 250 °C, pointing to the importance of nitrogen species for the supported Co nanoparticles in nitrobenzene hydrogenation.