Search

It has been long believed that the FeMoS structure, where Fe is bonded with S, plays a pivotal role as a biomimetic catalyst for electrochemical nitrogen (N 2 ) fixation. Nevertheless, the structure of Fe bonded to heavier analogues (Se or Te) has never been explored for N 2 electrofixation. Here, we theoretically predict the electronic structure of FeMo(Se, Te) composed of tri-coordinated Fe species with open shells for binding with Se, which forms a joint electron pool for promoting N 2 activation. Guided by this interesting prediction, we then demonstrate a two-step procedure to synthesize such structures, which display remarkable N 2 electrofixation activities with an ammonia yield of 72.54 μg h -1  mg -1 and a Faradic efficiency of 51.67 % that are more than three times of the FeMoS counterpart. Further mechanism studies have been conducted by density function theory (DFT) simulations. This work provides new clues for designing versatile electrocatalytic materials for large-scale industrialization., (© 2022 Wiley-VCH GmbH.)

Hypothesis: Developing materials for thermally driven adsorption chillers and adsorption heat pumps is a growing research field due to the potential of these technologies to address up to 50% of the world's total energy demand. These materials must be abundant, easy to synthesize, hydrophilic, and low in cost. Bare carbon materials are hydrophobic and therefore usually not considered for these applications. However, by introducing heteroatoms and tuning their porosity, the hydrophilicity of carbonaceous networks can be increased significantly., Experimental: Herein, a series of highly nitrogen doped carbonaceous materials (CNs) have been synthesized by submitting uric acid to heat treatment at different temperatures in the presence of an inorganic salt mix as solvent and pore template. The effect of the thermal treatment on the materials composition, pore network, and water sorption capability has been studied., Findings: At 800 °C, a nitrogen depleted carbonaceous material with a maximal water uptake of 1.38g H2O g -1 is obtained. Condensation at 750 °C creates an ultra-hydrophilic CN with a water uptake of 0.8 g H2O g -1 at already much lower partial pressures. While the maximum uptake is mainly ascribed to the mesopore volume of the material, the differences in hydrophilicity can be controlled by functionality., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Layer-by-layer (LbL) assembly technique is applied for the first time for the preparation of nitrogen-doped carbon capsules. This approach uses colloid silica as template and two polymeric deposition components, that is, poly(ammonium acrylate) and a poly (ionic liquid) poly(3-cyanomethyl-1-vinylimidazolium bromide), which acts as both the carbon precursor and nitrogen source. Nitrogen-doped carbon capsules are prepared successfully by polymer wrapping, subsequent carbonization and template removal. The as-synthesized carbon capsules contain ≈7 wt% of nitrogen and have a structured specific surface area of 423 m(2) g(-1). Their application as supercapacitor has been briefly introduced. This work proves that LbL assembly methodology is available for preparing carbon structures of complex morphology., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Mesoporous nitrogen-doped carbon derived from the ionic liquid N-butyl-3-methylpyridinium dicyanamide is a highly active, cheap, and selective metal-free catalyst for the electrochemical synthesis of hydrogen peroxide that has the potential for use in a safe, sustainable, and cheap flow-reactor-based method for H(2)O(2) production., (© 2012 American Chemical Society)

Mesoporous nitrogen-doped carbon materials with high surface areas up to 1500 m(2) g(-1) were conveniently made by the carbonization of nucleobases dissolved in an all-organic ionic liquid (1-ethyl-3-methylimidazolium dicyanamide). Using hard templating with silica nanoparticles, this process yields high-surface-area nitrogen-doped carbon materials with nitrogen contents as high as 12 wt %, narrow mesopore size distribution of ca. 12 nm diameter, and local graphitic carbon structure. It is demonstrated that the resulting nitrogen-doped carbons show very high catalytic activity, even in the metal-free case in the oxygen reduction reaction (ORR) for fuel cells. Specifically, the as-prepared materials exhibit a low onset voltage for ORR in alkaline medium and a high methanol tolerance, compared with those of commercial 20 wt % Pt/C catalyst. We regard this as a first step toward an all-sustainable fuel cell, avoiding noble metals.

We present a simple and green one-step pathway towards nitrogen-doped carbon nanostructures with controlled mesoporosity through hydrothermal treatment of glucose in the presence of model proteins. Performing the reaction with different amounts of egg white ovalbumin protein (OvA), carbonaceous nanoparticles or continuous nanosponges with high specific surface areas can be efficiently produced. The nitrogen content of the structures is rather high (up to 8 wt%) and can be kept constant up to 950 degrees C, while oxygen elimination and graphitization of the carbon material occurs. We demonstrate here that sustainable natural resources can be efficiently used in the synthesis of pure high-potential nanomaterials.

We investigated semiconductor characteristics for polymeric carbon nitride as a metal-free photocatalyst working with visible light and have shown that the efficiency of hydrogen production by photochemical water reduction can be improved by approximately 1 order of magnitude by introducing the right type of mesoporosity into polymeric C(3)N(4). We anticipate a wide rang of potential application of C(3)N(4) as energy transducers for artificial photosynthesis in general, especially with a 3D continuous nanoarchitecture. Moreover, the results of finding photoactivity for carbon nitride nanoparticles can enrich the discussion on prebiotic chemistry of the Earth, as HCN polymer clusters are unequivocal in the solar system.

Herein we report the synthesis of a crystalline graphitic carbon nitride, or g-C(3)N(4), obtained from the temperature-induced condensation of dicyandiamide (NH(2)C(=NH)NHCN) by using a salt melt of lithium chloride and potassium chloride as the solvent. The proposed crystal structure of this g-C(3)N(4) species is based on sheets of hexagonally arranged s-heptazine (C(6)N(7)) units that are held together by covalent bonds between C and N atoms which are stacked in a graphitic, staggered fashion, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy.

The influence of structural modifications on the catalytic activity of carbon materials is poorly understood. A collection of carbonaceous materials with different pore networks and high nitrogen content was characterized and used to catalyze four reactions to deduce structure–activity relationships. The CO2 cycloaddition and Knoevenagel reaction depend on Lewis basic sites (electron‐rich nitrogen species). The absence of large conjugated carbon domains resulting from the introduction of large amounts of nitrogen in the carbon network is responsible for poor redox activity, as observed through the catalytic reduction of nitrobenzene with hydrazine and the catalytic oxidation of 3,3′,5,5′‐tetramethylbenzidine using hydroperoxide. The material with the highest activity towards Lewis acid catalysis (in the hydrolysis of (dimethoxymethyl)benzene to benzaldehyde) is the most effective for small molecule activation and presents the highest concentration of electron‐poor nitrogen species. [ABSTRACT FROM AUTHOR]

It has been long believed that the FeMoS structure, where Fe is bonded with S, plays a pivotal role as a biomimetic catalyst for electrochemical nitrogen (N2) fixation. Nevertheless, the structure of Fe bonded to heavier analogues (Se or Te) has never been explored for N2 electrofixation. Here, we theoretically predict the electronic structure of FeMo(Se, Te) composed of tri‐coordinated Fe species with open shells for binding with Se, which forms a joint electron pool for promoting N2 activation. Guided by this interesting prediction, we then demonstrate a two‐step procedure to synthesize such structures, which display remarkable N2 electrofixation activities with an ammonia yield of 72.54 μg h−1 mg−1 and a Faradic efficiency of 51.67 % that are more than three times of the FeMoS counterpart. Further mechanism studies have been conducted by density function theory (DFT) simulations. This work provides new clues for designing versatile electrocatalytic materials for large‐scale industrialization. [ABSTRACT FROM AUTHOR]

The potassium salt of polyheptazine imide (K–PHI) is a promising photocatalyst for various chemical reactions. From powder X–ray diffraction data an idealized structural model of K–PHI has been derived. Using atomic coordinates of this model we defined an energetically optimized K–PHI structure, in which the K ions are present in the pore and between the PHI–planes. The distance between the anion framework and K+ resembles a frustrated Lewis pair-like structure, which we denote as frustrated Coulomb pair that results in an interesting adsorption environment for otherwise non-adsorbing, non-polar gas molecules. We demonstrate that even helium (He) gas molecules, which are known to have the lowest boiling point and the lowest intermolecular interactions, can be adsorbed in this polarized environment with an adsorption energy of − 4.6 kJ mol−1 per He atom. The interaction between He atoms and K–PHI is partially originating from charge transfer, as disclosed by our energy decomposition analysis based on absolutely localized molecular orbitals. Due to very small charge transfer interactions, He gas adsorption saturates at 8 at%, which however can be subject to further improvement by cation variation. [ABSTRACT FROM AUTHOR]

As a new type of heterogeneous catalyst with "homogeneous‐like" activity, single‐site transition‐metal materials are usually treated as integrated but separate active centers. A novel grouping effect is reported for single Ni−N4 sites in nitrogen‐doped carbon (Ni/NC), where an effective ligand‐stabilized polycondensation method endows Ni/NC nanocatalysts with a high content of single‐site Ni up to 9.5 wt %. The enhanced electron density at each single Ni−N4 site promotes a highly efficient hydrogen transfer, which is exemplified by the coupling of benzyl alcohol and aniline into N‐benzylaniline with a turnover frequency (TOF) value of 7.0 molN‐benzylaniline molmetal−1 h−1; this TOF outpaces that of reported stable non‐noble‐metal‐based catalysts by a factor of 2. Herd instinct: A grouping effect is observed for single Ni−N4 sites in a Ni catalyst supported by nitrogen‐doped carbon (NC). A high 9.5 wt % Ni content was achieved with a ligand‐stabilized polycondensation method. An enhanced electron density effect manifests at each single Ni−N4 site, which decreases the binding energy of H radicals to Ni and promotes efficient coupling of benzyl alcohol and aniline to form N‐benzylaniline. [ABSTRACT FROM AUTHOR]

Abstract: The targeted thermal condensation of a hexaazatriphenylene‐based precursor leads to porous and oxidation‐resistant (“noble”) carbons. Simple condensation of the pre‐aligned molecular precursor produces nitrogen‐rich carbons with C2N‐type stoichiometry. Despite the absence of any porogen and metal species involved in the synthesis, the specific surface areas of the molecular carbons reach up to 1000 m2 g−1 due to the significant microporosity of the materials. The content and type of nitrogen species is controllable by the carbonization temperature whilst porosity remains largely unaffected at the same time. The resulting noble carbons are distinguished by a highly polarizable micropore structure and have thus high adsorption affinity towards molecules such as H2O and CO2. This molecular precursor approach opens new possibilities for the synthesis of porous noble carbons under molecular control, providing access to the special physical properties of the C2N structure and extending the known spectrum of classical porous carbons. [ABSTRACT FROM AUTHOR]

Abstract: Engineering the adsorption of molecules on active sites is an integral and challenging part for the design of highly efficient transition‐metal‐based catalysts for methanol dehydrogenation. A Mott–Schottky catalyst composed of Ni nanoparticles and tailorable nitrogen‐doped carbon‐foam (Ni/NCF) and thus tunable adsorption energy is presented for highly efficient and selective dehydrogenation of gas‐phase methanol to hydrogen and CO even under relatively high weight hourly space velocities (WHSV). Both theoretical and experimental results reveal the key role of the rectifying contact at the Ni/NCF boundaries in tailoring the electron density of Ni species and enhancing the absorption energies of methanol molecules, which leads to a remarkably high turnover frequency (TOF) value (356 mol methanol mol−1 Ni h−1 at 350 °C), outpacing previously reported bench‐marked transition‐metal catalysts 10‐fold. [ABSTRACT FROM AUTHOR]

Herein we introduce a straightforward, low cost, scalable, and technologically relevant method to manufacture an all-carbon, electroactive, nitrogen-doped nanoporous-carbon/carbon-nanotube composite membrane, dubbed 'HNCM/CNT'. The membrane is demonstrated to function as a binder-free, high-performance gas diffusion electrode for the electrocatalytic reduction of CO2 to formate. The Faradaic efficiency (FE) for the production of formate is 81 %. Furthermore, the robust structural and electrochemical properties of the membrane endow it with excellent long-term stability. [ABSTRACT FROM AUTHOR]

CO2 capture is a pressing global environmental issue that drives scientists to develop creative strategies for tackling this challenge. The concept in this contribution is to produce site-specific nitrogen doping in microporous carbon fibers. Following this approach a carbon/carbon heterojunction is created by using a poly(ionic liquid) (PIL) as a 'soft' activation agent that deposits nitrogen species exclusively on the surface of commercial microporous carbon fibers. This type of carbon-based biphasic heterojunction amplifies the interaction between carbon fiber and CO2 molecule for unusually high CO2 uptake and resistive sensing. [ABSTRACT FROM AUTHOR]

Porous TiN xO y-based particles were synthesized by an aerosol spray process. At first, the starting sol solution containing the metal precursor and the nitrogen source is sprayed to form an aerosol that is subsequently pyrolysed at different temperatures. The obtained dried particles are an amorphous coordination 'polymer' rich in carbon and nitrogen. These 'glassy' particles are finally thermally treated at 800 °C, promoting the crystallization of the particles and the release of a major part of the carbon. As the particles keep their original shape, carbon loss and density increase during the crystallization step and lead to the development of an accessible pore structure. The process was analyzed and extended to the synthesis of other metal nitrides, such as VN and W2N, thereby showing its general validity for the production of functional nanocrystalline nitride ceramics with high porosity still occupying a relatively small volume, and otherwise not easily accessible. [ABSTRACT FROM AUTHOR]

In this paper, the preparation of nitrogen-doped carbon fibers and thin films from mixtures of polyacrylonitrile (PAN) and a poly(ionic liquid) (PIL) by electrospinning and dip-coating is presented, respectively, followed by carbonization at distinct temperatures. The poor processability of the PIL into sub-micrometer fibers by electrospinning-originating from its high charge density and meanwhile low glass transition temperature-is successfully circumvented by using blends of PAN and PIL. The electrospun fiber mats exhibit a high surface-to-volume-ratio with an intrinsically macroporous through-pore structure and a uniform fiber diameter after carbonization. Physicochemical characterization of the N-doped carbons by means of scanning electron microscopy, algorithmic X-Ray diffraction analysis, nitrogen physisorption, thermogravimetry, elemental analysis, energy-dispersive X-ray, and X-ray photoelectron spectroscopy gives insight into their physical and electrical structures. Impedance measurements on carbonized PIL/PAN-blends reveal high electrical conductivities up to 320 S cm−1, which are attributed to the incorporation of predominantly quaternary-graphitic nitrogen atoms into the carbon network during carbonization. The results indicate that the electrical conductance of the N-doped carbons strongly depends on the chemical environment of the inserted nitrogen atoms, the microstructural evolution of π-conjugated carbon network-which in turn correlate with the carbonization temperature-and the chemical composition. [ABSTRACT FROM AUTHOR]

The article reports on the synthesis of a mesoporous nitrogen doped carbon supported platinum catalyst based on an ionic liquid as nitrogen/carbon precursor and the evaluation of the catalytics system for oxygen reduction reaction (ORR). It analyzes the long-term behavior of this new catalyst and compared it with commercial high surface area carbon (HSAC) supported platinum catalyst. It also illustrates the synthesis route for mesoporous nitrogen doped carbon supported platinum catalyst.

The hydrothermal synthesis of nitrogen-doped monolithic carbon aerogels derived from sustainable precursors (i.e.d-glucose and ovalbumin) is presented. The protein acts as nitrogen donor and surface stabilizing agent in this saccharide hydrothermal carbonization, to generate high surface area aerogels (＞240 m2g−1) composed of functional continuous large diameter mesopores with excellent hierarchical transport architecture. Post-carbonization treatment controls surface chemistry (e.g. C or N condensation), facilitating tuneable physicochemical properties on a unique continuous 3D carbonaceous pore structure. This highly flexible synthesis lays the basis for the development of a new generation of sustainable (heteroatom-doped) porous carbon aerogels suitable for a range of high value applications. [ABSTRACT FROM AUTHOR]

Production of ammonia is currently realized by the Haber–Bosch process, while electrochemical N2 fixation under ambient conditions is recognized as a promising green substitution in the near future. A lack of efficient electrocatalysts remains the primary hurdle for the initiation of potential electrocatalytic synthesis of ammonia. For cheaper metals, such as copper, limited progress has been made to date. In this work, we boost the N2 reduction reaction catalytic activity of Cu nanoparticles, which originally exhibited negligible N2 reduction reaction activity, via a local electron depletion effect. The electron-deficient Cu nanoparticles are brought in a Schottky rectifying contact with a polyimide support which retards the hydrogen evolution reaction process in basic electrolytes and facilitates the electrochemical N2 reduction reaction process under ambient aqueous conditions. This strategy of inducing electron deficiency provides new insight into the rational design of inexpensive N2 reduction reaction catalysts with high selectivity and activity. Electrocatalytic nitrogen reduction is promising for ammonia production, but electrocatalysts are limited by low efficiency and high cost. Here, the authors report electron-deficient copper nanoparticles, induced by rectifying contact with polyimide, for selective reduction of nitrogen to ammonia. [ABSTRACT FROM AUTHOR]

Review: 82 refs. [ABSTRACT FROM AUTHOR]

Mesoporous nitrogen-doped carbon materials with high surface areas up to 1500 m² g-1 were conveniently made by the carbonization of nucleobases dissolved in an all-organic ionic liquid (1-ethyl-3-methylimidazolium dicyanamide). Using hard templating with silica nanoparticles, this process yields high- surface-area nitrogen-doped carbon, materials with nitrogen contents as high as 12 wt %, narrow mesopore size distribution of ca. 12 nm diameter, and local graphitic carbon structure. It is demonstrated that the resulting nitrogen-doped carbons show very high catalytic activity, even in the metal-free case in the oxygen reduction reaction (ORR) for fuel cells. Specifically, the as-prepared materials exhibit a low onset voltage for OAR in alkaline medium and a high methanol tolerance, compared with those of commercial 20 wt % Pt/C catalyst. We regard this as a first step toward an all-sustainable fuel cell, avoiding noble metals. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon monoliths can be prepared from liquid, deep eutectic mixtures of urea and hexaketocyclohexane octahydrate, which are structured by chitosan as a natural in-situ scaffold and support. The as-formed polymer monolith can then be transformed into the respective nitrogen-doped carbon monolith with a high surface area, high mesoporosity and high nitrogen-content. The surface functionality as well as the access to the internal pore structure were demonstrated by carbon dioxide and dye sorption experiments. The applied synthetic procedure is simple, does not require additional activation steps and uses cheap and naturally abundant compounds avoiding typical and hazardous formaldehyde resins. Eventually, this offers a safe and sustainable alternative to current carbon monolith synthesis. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen-doped carbons were produced using hydrothermal carbonization of nitrogen-containing carbohydrates under mild temperature (180°C). The resulting materials contain significant amounts of nitrogen and display a high degree of aromatization. The nitrogen contents are also retained after further calcination at higher temperatures. All the resulting materials have been thoroughly characterized using X-ray photoelectron spectroscopy, solid state 15N and 13C-nuclear magnetic resonance, elemental chemical analysis, nitrogen adsorption, scanning and transmission electron microscopy. The nitrogen-doped materials proved to have superior performance with respect to their nitrogen-free counterparts in terms of electrical conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen-doped carbon particles were produced using the hydrothermal carbonization of a nitrogen-containing carbohydrate, namely glucosamine, under mild temperature conditions (180 °C) followed by further calcination under a stream of inert gas at 750 °C. The resulting materials contain significant amounts of nitrogen doping within their structure, mainly as quaternary N involved in an aromatized/graphitized carbon structure according to X-ray photoelectron spectroscopy. This nitrogen-doped material was dispersed with nanolatexes having a high affinity for carbon. The resulting hybrid dispersions could be conveniently cast into dense and stable films for thermal and electrical conductivity measurements. The conductivities were commensurate with technical carbon nanotube latex-based films. A morphological analysis of the dispersing mechanism suggests that the potential for high performance materials realized in this contribution is very competitive, but still far from being fully exploited. [Copyright &y& Elsevier]