Nitrogen-doped Microporous Carbons Research Articles

Facile synthesis of inherently nitrogen-doped PAN-derived microporous carbons activated with NaNH2 for selective CO2 adsorption and separation

N-doped porous carbons (PCs) are extensively researched for CO2 capture and separation under flue gas conditions, but their complex and expensive preparation methods hinder widespread industrial use. Herein, we present a direct approach for synthesizing N-doped PCs by utilizing polyacrylonitrile (PAN) and NaNH2 as precursors, without the need for any solvents. The utilization of NaNH2 as both a porogen and nitrogen supply during carbonization is primarily responsible for the formation of the well-developed pore structure and high specific surface area of N-doped PCs. The optimized sample “PN-3” demonstrated excellent textural features with an excellent specific surface area (SSA) of 2490 m2/g, a pore volume of 2.0559 cm3/g, a well-defined pore size distribution (PSD), and abundant micropores (<1 nm). In addition, PN-3 has the highest pyrrolic nitrogen content (∼40.1 at.%), resulting in a significant capacity for CO2 adsorption (7.15 mmol/g at 273 K/1bar, 4.56 mmol/g at 298 K/1 bar, 26.2 mmol/g at 298 K/ 40 bar). Furthermore, it exhibits an outstanding CO2/N2 selectivity (∼102) based on the ideal adsorbed solution theory (IAST) at 273 K, surpassing the performance of most of previously reported biomass and polymer-derived N-doped carbons in terms of CO2 adsorption and separation. In addition, the adsorption process is characterized by a modest heat of adsorption (39.10 kJ/mol) and a steady cyclic pattern of CO2 adsorption–desorption under flue gas settings (15 % CO2 and 85 % N2). This indicates that the adsorption is mostly governed by physisorption, which allows for an energy-efficient regeneration process. In summary, this study showcases the successful production of highly PCs that can effectively adsorb CO2, enlightening the way toward establishment of a cost-effective and facile synthetic protocol for achieving CO2 capture/separation at the commercial scale.

Nitrogen-doped microporous carbons as highly efficient adsorbents for CO2 and Hg(II) capture

Nitrogen-doped microporous carbon, which features a uniquely tunable porosity, exhibits promisingly high adsorption prospects in the greenhouse gas capture and water treatment. Herein, we propose a series of novel N-doped microporous carbons (CMPAn-C1000), and precisely tune their porosities via a direct pyrolysis of rigid conjugated microporous poly(aniline)s (CMPAn, n = 1, 2, 3) with pore size difference in a molecular level, as achieved by simply tuning their linkers with varying sizes, planarity, and symmetry. The CMPA3-C1000, with a satisfactory amount of nitrogen heteroatoms, high SBET of ∼800 m2 g−1, and large ultra-micropore volume of 0.25 cm3 g−1, has excellent CO2 capture ability (i.e., 5.1 mmol g−1 at 273 K, 1 atm) and Hg(II) adsorption performance (i.e., Qe = 571 mg g−1; k2 = 0.0031 g mg−1 min−1), respectively. CMPA3-C1000 might perform chemisorption towards Hg(II), according to calculations using density functional theory and experimental data; nitrogen atoms in porous carbon contributed to this excellent Hg(II) adsorption.

Base-type nitrogen doping in zeolite-templated carbon for enhancement of carbon dioxide sorption

Nitrogen-doped microporous carbons were synthesized via pyrolytic carbonization of pyrrole in a FAU zeolite template, using a carbonization temperature of either 600 or 700 °C. The carbon products, which were freed by dissolution of the template, all possessed a zeolite-like ordered pore arrangement with a high specific surface area of 2300–2500 m2 g−1 and a sharp distribution of pore diameters centered at 0.9 nm. The N content was similarly 5 wt%, but X-ray photoelectron spectroscopy analysis indicated that the 600 °C-pyrolized carbon had a relatively higher content of base-type N atoms (i.e., pyridinic and pyrrolic) than non-basic N (graphenic and oxidic), compared to the case at 700 °C. The 600 °C-pyrolized carbon exhibited an outstandingly high CO2 uptake. A breakthrough test with a CO2-H2O-N2 mixture at 1 bar indicated that the 600 °C-pyrolized carbon could capture CO2 effectively under humid conditions. This result suggests that it is important for CO2 capture, to achieve a high N content when doping with pyridinic or pyrrolic N as the major species. The high adsorption performance of zeolite-template carbon was attributable to the higher content of pyridinic N and pyrrolic N over graphitic N in the carbon, which provided basicity resulting in a strong chemisorption interaction with CO2.

Nitrogen-Doped Microporous Carbons Synthesized from Indole-Based Copolymer Spheres for Supercapacitors and Metal-Free Electrocatalysis

Indole-based copolymer spheres serve as a precursor for the facile and easily scalable synthesis of a series of nitrogen-rich microporous carbons. The influence of chemical activation and carboniza...

Enhanced CO2 capture in nitrogen-enriched microporous carbons derived from Polybenzoxazines containing azobenzene and carboxylic acid units

In this study, we prepared nitrogen-doped microporous carbons (NMCs) from two different benzoxazine monomers (AMBZ, AEBZ), each containing both azobenzene and carboxylic groups, through a simple and environmentally friendly process of ring-opening polymerization (ROP), calcination, and KOH activation. We synthesized the AMBZ and AEBZ monomers through Mannich condensations of 4,4′-diaminodiphenylmethane (M) and 4,4′-diaminodiphenyl ether (E), respectively, with paraformaldehyde and 4-(4-hydroxphenylazo)benzoic acid (Azo-COOH). Differential scanning calorimetry (DSC) revealed that the thermal curing temperatures of AMBZ and AEBZ (both ca. 230 °C) were lower than that of a typical Pa-type benzoxazine monomer (263 °C), suggesting that the azobenzene and COOH units acted as promoters and catalysts for the ROP of the benzoxazine units. In addition, after ROP of the benzoxazine units of AMBZ and AEBZ, the polymers PAMBZ and PAEBZ, respectively, displayed high glass transition temperatures (Tg) and high thermal stability, as evidenced using DSC and thermogravimetric analysis (TGA), due to their greater cross-linking densities. We used Brunauer–Emmett–Teller analysis, TGA, wide-angle X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy to examine the specific surface areas, porous structures, chemical compositions, and thermal stabilities of the resulting KOH-activated NMCs PAMBZ-A and PAEBZ-A. The CO2 capture abilities and thermal properties of these two highly-nitrogen-doped microporous carbons, synthesized from polybenzoxazine (PBZ) resins containing azobenzene and COOH groups, were excellent when compared with those of other N-doped porous carbons derived from other PBZ matrices.

Nitrogen-Doped microporous carbons derived from azobenzene and nitrile-functionalized polybenzoxazines for CO2 uptake

In this study we synthesized two nitrogen-doped microporous carbons (NMCs) from the benzoxazine monomers BZAPh and BZACN through a process of curing polymerization, calcination, and KOH activation. We prepared the benzoxazine monomers BZAPh and BZACN in high yield and purity through Mannich reactions of 1,3,5-tris(4-aminophenoxy)benzene (TriPh-3NH2), paraformaldehyde, and 4-phenylazophenol and 4-[(4-hydroxyphenyl)diazenyl] benzonitrile, respectively, in 1,4-dioxane. We employed differential scanning calorimetry (DSC), temperature-dependent Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) to characterize the ring opening polymerization and thermal stability of the uncured monomers BZAPh and BZACN and the products of their thermal treatment at various temperatures. In addition, we used TGA, wide-angle X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopies (XPS), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) analyses to examine the surface areas, porous structures, surface morphologies, chemical compositions, and thermal stabilities of these two highly N-doped NMCs. The NMC derived from the BZACN monomer, possessing both azobenzene and nitrile functionalities, exhibited superior thermal properties and CO2 capture ability because it contained a high crosslinking density of the triazine functional groups after thermal curing.

Environmental remediation by microporous carbon: An efficient contender for CO2 and methylene blue adsorption

Nitrogen-doped microporous carbons with extremely narrow pore size distribution were derived from sucrose and melamine with the molten LiCl/KCl salts acting as a template to generate pores. A high CO2 uptake of up to 197 mg/g at 273 K and 1 bar was observed, revealing the significance of the pore size (0.84 nm) for CO2 capture. Our findings demonstrate that the nitrogen-doped SMLK-1 has a large surface area (951 m2/g) and large micropore volume (0.42 cm3/g) with high nitrogen-content (11.2 at.%), but the adsorption capacity (180 mg/g at 273 K, 1 bar) is comparable to that of un-doped SMLK-0 (SBET = 520 m2/g, Vmicro = 0.26 cm3/g). The CO2 uptake capacity per pore volume and volume fraction of the pores (<0.84 nm) in total pore volume exhibit a straight-line graph with a high correlation coefficient of 0.93 revealing that the adsorption capacity of the carbonaceous adsorbents may strongly rely upon the fine pore size distributions. Moreover, the prepared materials were also investigated as adsorbents for methylene blue from an aqueous solution. The sample with a melamine-to-sucrose ratio of 0 (SMLK-0) exhibited the excellent dye adsorption, 134.7 mg/g for an initial methylene blue concentration of 25 × 10−2 mM and 31.1 mg/g for an initial concentration of 5 × 10−2 mM. Therefore, the fabrication method presented here permits the fine-tuning of the pore network to exploit the prepared materials both as CO2 and dye adsorbents for environmental remediation.

Tunable nitrogen-doped microporous carbons: Delineating the role of optimum pore size for enhanced CO2 adsorption

In the current study, a series of nitrogen-doped carbons was designed which possess high surface area (1047–3247 m2 g−1), ultra-micropores (<0.63 nm), high micropore volume (0.5718–1.6247 cm3/g) and optimum nitrogen content (2.07–13.8 at%). At 1 bar, all the prepared samples exhibits an outstanding CO2 uptake of 228–355 mg g−1 at 273 K and 162–218 mg g−1 at 298 K, which commensurate to the highest reported adsorption data for the carbon-based materials. The isosteric heat of adsorption (ΔHads) lies in the range (26.5–42.0 kJ/mol), suggesting the predominantly physisorption mechanism of adsorption. To investigate the effect of narrow micropores and nitrogen content on CO2 adsorption, the amount of CO2 adsorbed at 273 K/1 bar, micropore volume <0.63 nm and pyrrolic nitrogen content were normalized and compared. Results declared that the presence of micropores of about 0.63 nm in diameter were primarily responsible for CO2 adsorption by micropore filling mechanism with the pyrrolic content playing a secondary role.

Nitrogen-Doped Microporous Carbons Derived from Pyridine Ligand-Based Metal-Organic Complexes as High-Performance SO2 Adsorption Sorbents.

Heteroatom-doped porous carbons are emerging as platforms for gas adsorption. Herein, N-doped microporous carbon (NPC) materials have been synthesized by carbonization of two pyridine ligand-based metal-organic complexes (MOCs) at high temperatures (800, 900, 1000, and 1100 °C). For NPCs (termed NPC-1- T and NPC-2- T, where T represents the carbonization temperature), the micropore is dominant, pyridinic-N and other N atoms of MOC precursors are mostly retained, and the N content reaches as high as 16.61%. They all show high Brunauer-Emmett-Teller surface area and pore volume, in particular, NPC-1-900 exhibits the highest surface areas and pore volumes, up to 1656.2 m2 g-1 and 1.29 cm3 g-1, respectively, a high content of pyridinic-N (7.3%), and a considerable amount of SO2 capture (118.1 mg g-1). Theoretical calculation (int = ultrafine m062x) indicates that pyridinic-N acts as the leading active sites contributing to high SO2 adsorption and that the higher content of pyridinic-N doping into the graphite carbon layer structure could change the electrostatic surface potential, as well as the local electronic density, which enhanced SO2 absorption on carbon edge positions. The results show great potential for the preparation of microporous carbon materials from pyridine ligand-based MOCs for effective SO2 adsorption.

Organosilica-based ionogel derived nitrogen-doped microporous carbons for high performance supercapacitor electrodes

A new preparation process is developed to yield stable, yellowish and transparent organosilica ionogels, which after pyrolysis yields N-doped microporous carbon with remarkable capacity.

Directly synthesized nitrogen-doped microporous carbons from polybenzoxazine resins for carbon dioxide capture

Highly ordered nitrogen-doped microporous carbons as CO2 capturers from the cyano-functional benzoxazine monomer through thermal curing, carbonization, and KOH activation.

Controllable Nitrogen Doping of High-Surface-Area Microporous Carbons Synthesized from an Organic-Inorganic Sol-Gel Approach for Li-S Cathodes.

High-surface-area microporous carbons with controllable nitrogen doping were prepared via a novel organic-inorganic sol-gel approach, using phenolic resol and hexamethoxymethyl melamine (HMMM) as carbon precursors, and partially hydrolyzed tetraethoxysilane as silica template. The pore structures of microporous carbons were completely replicated from a thin silica framework and could be tailored greatly by changing the organic/inorganic ratio. The nitrogen atoms doped into the carbon framework were issued from high-nitrogen-content HMMM precursors, and the nitrogen content could be adjusted in a wide range by changing the phenolic resol/HMMM ratio. Moreover, the porous structure and nitrogen content could be simultaneously controlled, allowing the preparation of a series of microporous carbons with almost the same microstructures (BET surface areas of ca.1900 m(2)·g(-1)and pore volumes of ca. 1.2 cm(3)·g(-1), and the same pore size distributions) but with different nitrogen contents (0-12 wt %). These results provided a general method to synthesize nitrogen-doped microporous carbons and allowed these materials to serve as a model system to illustrate the role of nitrogen content on the performance of the carbons. When used as the supports for sulfur cathodes, only an appropriate nitrogen content of ca. 6.3 wt % was found to effectively improve sulfur utilization and cycle life of the sulfur cathodes. The resulting sulfur cathodes could deliver an outstanding reversible discharge capacity of 1054 mAh·g(-1) at 0.5 C after 100 cycles.

Effect of microporosity on nitrogen-doped microporous carbons for electrode of supercapacitor

Nitrogen-doped microporous carbons were prepared using a polyvinylidene fluoride/melamine mixture. The electrochemical performance of the nitrogen-doped microporous carbons after being subjected to different carbonization conditions was investigated. The nitrogen to carbon ratio and specific surface area decreased with an increase in the carbonization temperature. However, the maximum specific capacitance of 208 F/g was obtained at a carbonization temperature of <TEX>$800^{\circ}C$</TEX> because it produced the highest microporosity.

Chitosan derived nitrogen-doped microporous carbons for high performance CO2 capture

Nitrogen-doped microporous carbons were fabricated by a simple chemical activation strategy in which chitosan and K2CO3 were employed as the precursor and activation agent, respectively. The textural and chemical properties of the porous carbons could be easily tuned by changing the ratio of K2CO3/chitosan and activation temperature. Due to their large pore volume, well-defined microporosity and relatively high nitrogen content, these porous carbons were applied as adsorbents for CO2 capture and demonstrated excellent CO2 uptake performances. In particular, the sample prepared at 635°C with K2CO3/chitosan ratio=2 shows a CO2 uptake as high as 3.86mmolg−1 at 25°C, 1atm. Furthermore, the CO2 uptake remains almost constant in five consecutive adsorption–desorption cycles, indicating this material has great stability and recyclability as a CO2 sorbent. In addition, an extraordinary separation selectivity against N2 (CO2/N2 selectivity of ca. 21) was also observed.

Imine-Linked Polymer-Derived Nitrogen-Doped Microporous Carbons with Excellent CO2 Capture Properties

A series of nitrogen-doped microporous carbons (NCs) was successfully prepared by direct pyrolysis of high-surface-area microporous imine-linked polymer (ILP, 744 m(2)/g) which was formed using commercial starting materials based on the Schiff base condensation under catalyst-free conditions. These NCs have moderate specific surface areas of up to 366 m(2)/g, pore volumes of 0.43 cm(3)/g, narrow micropore size distributions, and a high density of nitrogen functional groups (5.58-8.74%). The resulting NCs are highly suitable for CO2 capture adsorbents because of their microporous textural properties and large amount of Lewis basic sites. At 1 bar, NC-800 prepared by the pyrolysis of ILP at 800 °C showed the highest CO2 uptakes of 1.95 and 2.65 mmol/g at 25 and 0 °C, respectively. The calculated adsorption capacity for CO2 per m(2) (μmol of CO2/m(2)) of NC-800 is 7.41 μmol of CO2/m(2) at 1 bar and 25 °C, the highest ever reported for porous carbon adsorbents. The isosteric heats of CO2 adsorption (Qst) for these NCs are as high as 49 kJ/mol at low CO2 surface coverage, and still ~25 kJ/mol even at high CO2 uptake (2.0 mmol/g), respectively. Furthermore, these NCs also exhibit high stability, excellent adsorption selectivity for CO2 over N2, and easy regeneration and reuse without any evident loss of CO2 adsorption capacity.

Synthesis of nitrogen doped microporous carbons prepared by activation-free method and their high electrochemical performance

Nitrogen-doped microporous carbons (N-MCs) were prepared by the carbonization of the polyvinylidene fluoride (PVDF)/melamine mixture without chemical activation. The electrochemical performance of the N-MCs was investigated as a function of PVDF/melamine ratio. It was found that, without additional activation, the N-MCs had a high specific surface area (greater than 560m2/g) because of the micropore formation by the release of fluorine groups. In addition, although the specific surface area decreased, nitrogen groups were increased with increasing melamine content, leading to an enhanced electrochemical performance. Indeed, the N-MCs showed a better electrochemical performance than that of microporous carbons (MCs) prepared by PVDF alone, and the highest specific capacitance (310F/g) was obtained at a current density of 0.5A/g, as compared to a value of 248F/g for MCs. These results indicate that the microporous features of N-MC lead to feasible ion transfer during charge/discharge duration and the presence of nitrogen groups as strong electron donor on the N-MC electrode in electrolyte could provide a pseudocapacitance by the redox reaction.