Easy synthesis of ordered mesoporous carbon containing nickel nanoparticles by a low temperature hydrothermal method

Ordered mesoporous carbons (OMCs) with embedded metallic nickel (Ni) nanoparticles have been directly synthesized by a simple and low temperature (50 °C) hydrothermal method. The synthesis involved the use of a triblock copolymer Pluronic F127 as the mesostructure directing agent, resorcinol (R) and formaldehyde (F) as carbon precursors, and Ni(NO₃)₂·6H₂O as nickel source. It consisted in the self-assembly of F127, Ni²⁺ salt and RF polymer in an acidic medium and further carbonization, where the Ni²⁺ was captured by the network of F127/RF and further reduced into metallic Ni nanoparticles. The resultant Ni/carbon materials were characterised by X-ray diffraction, thermogravimetric analysis, transmission electron microscopy and nitrogen sorption. Ni/carbon materials with a highly ordered mesostructure were obtained using equal moles of resorcinol and formaldehyde molar ratio (R/F = 1/1), whereas an excess amount of formaldehyde (R/F = 1/2) was found to not form an ordered carbon structure. The results showed that nickel particles, with sizes of ∼10–50 nm, were homogeneously dispersed in the carbon matrices, while the pore mesostructure remained intact. The homogeneous Ni/carbon composites synthesized by this easy hydrothermal route have been demonstrated to be effective molecular adsorbents for magnetic separation.     

Lysine-assisted rapid synthesis of crack-free hierarchical carbon monoliths with a hexagonal array of mesopores

The rapid and scalable synthesis of hierarchical carbon monoliths with an ordered mesostructure and fully interconnected macropores has been demonstrated. Resorcinol and formaldehyde based polymers were used as the carbon precursor, triblock copolymer Pluronic F127 as the structural directing agent, and organic base lysine as both the polymerization catalyst and mesostructure assembly promoter. In the presence of lysine, homogeneous and crack-free polymer monoliths can be obtained through rapid gelation in 15 min at 90 °C. The polymer monoliths have a robust framework, which can be directly dried at 50 °C in air and carbonized at high temperature under a nitrogen atmosphere. The carbon monoliths are crack-free and have an ordered mesostructure with fully interconnected macropores. The surface area and the macropore volume are high with values up to 600 m² g⁻¹ and 3.52 cm³ g⁻¹, respectively. Further steam activation of the carbon monolith can significantly improve the surface area to 2422 m² g⁻¹ while still maintaining the ordered mesostructure.     

A two-step synthesis of ordered mesoporous resorcinol–formaldehyde polymer and carbon

A new two-step method is developed for the synthesis of resorcinol–formaldehyde polymer and carbon with highly ordered mesoporous structures. For this method, resorcinol and formaldehyde is pre-polymerized in the first step under the presence of a basic catalyst to produce resorcinol–formaldehyde resol. Then, the resorcinol–formaldehyde resol is mixed with Pluronic F127 solution followed by the addition of an acid catalyst to allow the rapid self-assembly and condensation in the second step. Compared with the early reported evaporation-induced self-assembly method as well as the one-step liquid phase self-assembly method, in the present two-step liquid method the self-assembly and condensation process can be carried out rapidly by using low amount of base and acid catalysts at room temperature. After the activation by CO₂, the carbon materials maintained ordered mesostructure, and the BET surface area enlarged to 2660 m²/g and total pore volume increased to 2.01 cm³/g. The CO₂ activation not only creates micropores within the carbon frameworks but also enlarges the mesopores by elimination of the carbon pore walls.     

Synthesis of ordered mesoporous silicon oxycarbide monoliths via preceramic polymer nanocasting

Highly ordered mesoporous silicon oxycarbide (SiOC) monoliths have been synthesized using liquid poly(hydridomethylsiloxane) (PHMS) as starting preceramic polymer and mesoporous carbon CMK-3 as direct template. Monolithic SiOC-carbon composites were generated via nanocasting of PHMS into CMK-3, pressing without any additive, cross-linking at 150 °C under humid air and subsequent thermolysis at 1000 or 1200 °C under argon atmosphere. The carbon template was finally removed by the thermal treatment at 1000 °C in an ammonia atmosphere, as a result of the generation of monolithic SiOC ceramics with ordered mesoporous structures. The products were characterized by scanning electron and transmission electron microscopes, X-ray diffraction, Fourier transformation infrared spectrometer, X-ray photoelectron spectroscope and nitrogen absorption-desorption analyzer. The as-prepared SiOC monoliths exhibited crack-free, ordered 2-dimentional hexagonal p6mm symmetry with high specific surface areas. With increasing the calcination temperature, the ordered mesoporous structure was still remained and the specific surface area just had a slight reduction from 616 to 602 m² g⁻¹. Moreover, the porous SiOC monoliths possessed good compression strengths and anti-oxidation properties.     

Preparation of highly mesoporous carbon membranes via a sol-gel process using resorcinol and formaldehyde

This paper reports the preparation of highly mesoporous carbon membranes, which are obtained by the pyrolysis of sol-gel derived mesoporous polymer membranes using resorcinol and formaldehyde (RF). Two series of RF carbon membranes were prepared by changing the resorcinol to catalyst molar ratio. The nitrogen adsorption-desorption measurement shows that the RF carbon membranes possess a well-developed mesoporous structure with controlled pore diameters of 5.48 nm and 13.9 nm. The helium and nitrogen permeances of both RF carbon membranes were independent of the feed pressure, indicating that there was no contribution of viscous flow and the membranes are initially crack-free. The gas permeation result showed that the dominant mechanism of gas transport through both the RF carbon membranes is Knudsen diffusion. With regard to the permeation of condensable gases such as CH₄ and CO₂, it was observed that the surface flow also contributes to the total permeation.     

Structure and electrochemical properties of resorcinol-formaldehyde polymer-based carbon for electric double-layer capacitors

A nano-porous carbon was prepared by carbonization of a novel synthetic resorcinol-formaldehyde (RF) polymer without any additional activation process, and used as electrode materials for aqueous electric double-layer capacitors (EDLCs). This novel RF polymer-based carbon shows high specific surface area with large carbonization yield (∼50%), and excellent specific dc capacitance over 200 F/g. The effect of R/CA ratio (i.e. molar ratio of resorcinol to curing agent) on the specific surface area, pore size distribution, nanostructure and electrochemical capacitance was studied, respectively. The results showed that a higher R/CA ratio yielded carbon with higher specific surface area, larger specific capacitance, and broader pore size distribution. The highest specific surface area of 825 m²/g and specific capacitance exceeding 200 F/g were found to occur at R/CA ratio of 50. The electrochemical behaviors were characterized by means of galvanostatic charging/discharging, cycle voltammetry and impedance spectroscopy. The correlation between electrochemical properties and pore structure was investigated. Due to the excellent capacitance properties, low cost and simple process, this RF polymer-derived carbon would be a promising material for EDLCs applications.     

Synthesis of ordered mesoporous carbon films, powders, and fibers by direct triblock-copolymer-templating method using an ethanol/water system

Morphology control of ordered mesoporous carbon was performed using an organic-organic interaction approach. Mesoporous carbons were synthesized from a resorcinol-phloroglucinol/formaldehyde polymer and triblock copolymer Pluronic F127 in ethanol-water solutions of different molar ratios. A face-centered orthorhombic Fmmm structure was formed in the film prepared by dip-coating method. A three-dimensional wormhole-like mesostructure was formed during powder preparation at EtOH/water molar ratios ranging from 0.5 to 1.25. When the molar ratio was further increased to 2.5, a hexagonal p6mm structure was obtained. The pore size of the mesoporous carbon powders increases with increasing EtOH/water molar ratio. A dual-templating approach was demonstrated to prepare mesoporous carbon nanofibers. Anodic aluminum oxide membranes were used as a hard template. A mesostructure with a short-range order was formed and oriented along the surface in different directions. The structural order became distorted in the interior region.     

Resorcinol-formaldehyde based porous carbon as an electrode material for supercapacitors

Porous carbon materials were prepared using resorcinol and formaldehyde catalyzed by KOH in a sol-gel process followed by carbonization, during which the KOH serves as an activating agent and generates pores mainly located in the micropore range. With an increase of mass ratio of KOH to resorcinol from 1 to 4, both the specific surface area and the pore volume of the carbons increased, from 522 to 2760 m²/g and 0.304 to 1.347 cm³/g, respectively, but the average pore diameter decreased from 4.4 to 2.5 nm. Samples were investigated as electrode materials in supercapacitors and the relevant electrochemical behavior was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and constant current charge-discharge experiments using 30% KOH aqueous solution as electrolyte. The highest specific capacitance of up to 294 F/g was obtained at a current density 1 mA/cm² for the sample with mass ratio of KOH to resorcinol of 2. Only a slight decrease in capacitance for the same sample, from 294 to 242 F/g, was observed when the current density increased from 1 to 30 mA/cm². The specific capacitance only decayed 3% at a current density 30 mA/cm² after 1000 cycles, which indicates that the sample possesses excellent power property and cycle durability.     

Bimodal, templated mesoporous carbons for capacitor applications

Several high capacitance ordered mesoporous carbon (OMC) materials, containing a bimodal pore distribution, were synthesized directly using hexagonal mesoporous silicas (HMS) as the template material. The HMS templates were formed using amine surfactants (C_nH_2n+1NH₂) with hydrophobic chain lengths containing 8-16 carbons (n = 8-16). These HMS structures were found to have an interconnected wormhole structure, high textural mesoporosity, a surface area ranging from 910 to 1370 m²/g, and a total pore volume of 1.09-1.83 cm³/g. Also, evidence for a change in structure from hexagonally ordered to layered (for surfactants of chain length with n > 12) was found. The resulting OMCs, formed using sucrose as the carbon precursor, contain bimodal pores 1.6-1.8 and 3.3-3.9 nm in diameter and have a very high surface area (980-1650 m²/g). The OMCs were evaluated as electrode materials for electrochemical capacitors using cyclic voltammetry in 0.5 M H₂SO₄ solution, giving a tunable gravimetric capacitance that increased linearly with BET area (and surfactant chain length), up to 260 F/g, among the highest yet reported for ordered carbon formed from an HMS templated precursor. All OMCs studied in this work displayed a specific capacitance of ∼0.15 F/m².     

One-pot synthesis of carbonaceous monolith with surface sulfonic groups and its carbonization/activation

The carbonaceous monoliths rich in surface sulfonic acid groups were synthesized by one-pot hydrothermal carbonization of the mixture of p-toluenesulfonic acid/glucose/resorcinol at 180 °C. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy characterizations confirmed the presence of surface sulfonic groups on these monoliths. The catalytic performance of this kind of carbonaceous material as a solid-acid catalyst was studied in the reaction of acetalization of benzaldehyde and the results showed that it has high activity and reusability. Then, these monoliths were further carbonized and activated to form monolithic carbons with high surface area and large pore volume. The surface area and pore volume per mass increased with prolonging the activation time (0–6 h) and the best results on 6-h activated samples were 2337 m²/g and 2.12 cm³/g. Due to the decrease in bulk density the volumetric surface area increased initially until maximum and then slightly dropped down during the activation. These carbonized and activated samples showed better oxidation resistance than one commercial activated carbon under air. Moreover, the adsorption capacity for dye molecules with different size on these activated samples was significant higher than that on commercial activated carbons and a synthetic ordered mesoporous carbon.     

Kilogram-scale synthesis of ordered mesoporous carbons and their electrochemical performance

An efficient post-cure approach has been demonstrated for the kilogram-scale synthesis of high-quality ordered mesoporous carbons (OMC) by using triblock copolymer Pluronic F127 as a template, phenolic resol as a carbon precursor and polyurethane foam as a sacrificial scaffold through an organic–organic self-assembly. The effects of the concentration and the loading amount of resol on the mesostructure of the carbons are systematically investigated. The small-angle X-ray scattering, nitrogen sorption and transmission electron microscopy results reveal that the resultant OMC in kilogram-scale quantities possesses high surface area (∼690 m² g⁻¹), large pore volume (∼0.45 cm³ g⁻¹) and uniform, large pore size (∼4.5 nm) as well as thick pore walls (∼6.5 nm). The OMC exhibits good electrochemical performance of about 130 F g⁻¹ in KOH electrolyte.     

Tubular structured ordered mesoporous carbon as an efficient sorbent for the removal of dyes from aqueous solutions

Tubular structured ordered mesoporous carbon CMK-5 was investigated for the adsorption of the industrial dyes reactive blue 19, acid red 57 and fuchsin basic in aqueous solutions at room temperature. It was found that CMK-5 exhibits an ultrahigh adsorption rate and superior adsorption capacities for these dyes. Its maximum adsorption capacities for reactive blue 19, acid red 57 and fuchsin basic were 733, 1131 and 1403 mg g⁻¹, respectively, and significantly greater than other literature reported results on porous carbons. Following adsorption of reactive blue 19, CMK-5 carbon could be regenerated by either ethanol extraction or thermal annealing at 600 °C, reaching ∼51% and ∼77%, respectively of the adsorption capacity of the original carbon. For comparison, ordered mesoporous carbon CMK-3 (rod structure), polymer based disordered mesoporous carbon, and steam and CO₂ activated commercial coconut carbons were investigated for the adsorption of reactive blue 19. The fast adsorption rate of CMK-5 carbon is due to its unique properties of tubular mesostructure, bimodal mesopore system and high surface area. In the case of requiring emergency removal of large amount of dyes in aqueous solution, CMK-5 would be an ideal choice.     

Simple synthesis of highly ordered mesoporous carbon by self-assembly of phenol–formaldehyde and block copolymers under designed aqueous basic/acidic conditions

In view of the low reactivity of phenol with formaldehyde under acidic condition in the synthesis of ordered mesoporous carbons, a strategy to accelerate the polymerization of phenol and formaldehyde by using designed aqueous basic/acidic conditions (first weakly basic condition then highly acidic condition) is developed. The first weakly basic condition benefits the formation of hydroxymethyl phenols at 313 K. The latter highly acidic condition mainly induces the condensation reaction between the formed hydroxymethyl phenols, as well as the self-assembly of phenol–formaldehyde and block copolymer template. After removal of the template, the obtained carbon exhibits highly ordered hexagonal mesostructure with a surface area of 760 m² g⁻¹, large pore volume (0.64 cm³ g⁻¹) and uniform pore size (3.32 nm). This developed strategy affords a simple and highly reproducible approach for the synthesis of ordered mesoporous carbon from the less expensive phenol under strong acidic condition, which also provides a wide and easily accessed synthesis condition for the further functionalization, such as the in situ introducing of metal ions.     

Fabrication and nano-structure control of carbon aerogels via a microemulsion-templated sol-gel polymerization method

Carbon aerogels were successfully fabricated by a microemulsion-templated sol-gel polymerization method. When a suitable molar ratio of surfactant to resorcinol (S/R) and an appropriate resorcinol-formaldehyde concentration were selected, the organic gels thus obtained could be dried with little shrinkage by heating at ambient pressure. The size of carbon nano-particles and the pore size of carbon aerogels thus produced decrease with an increase of S/R. The highest specific surface area and specific mesopore volume of the carbon aerogels prepared by our method were 620 m² g⁻¹ and 1.14 cm³/g, respectively.     

Carbon aerogels derived from cresol–resorcinol–formaldehyde for supercapacitors

The objective of the present paper is to demonstrate the possibility to synthesize mixed carbon aerogels (denoted C_mRF) from cresol (C_m), resorcinol (R) and formaldehyde (F), as an alternative economic route to the classical RF synthesis. These porous carbon aerogels can be used as electrode materials for supercapacitors with a high volume-specific capacitance. Organic precursor gels were synthesized via polycondensation of a mixture of resorcinol and cresol with formaldehyde in an aqueous alkaline (NaOH) solution. After gelation and aging the solvent was removed via drying at ambient pressure to produce organic aerogels. Upon pyrolysis of the organic aerogels at 1173 K, monolithic carbon aerogels can be obtained. By controlling the catalyst (Cat) molar ratio (C_m+R/Cat) in the range 200–500, up to 70% of the resorcinol can be replaced with the cheap cresol. The resulting homogeneous organic aerogels exhibit a drying shrinkage below 15% (linear). The shrinkage and mass loss upon pyrolysis of the mixed aerogels increase with increasing cresol content. Nitrogen adsorption at 77 K was employed to characterize the microstructure of the carbon aerogels. The data show that the porous structure of mixed carbon aerogels is similar to that of RF carbon aerogels. Cyclic voltammetry measurements show that the as-prepared C_mRF carbon aerogels exhibit a high volume-specific capacitance of up to 77 F/cm³.     

Template-free environmentally friendly synthesis and characterization of unsupported tungsten carbide with a controllable porous framework

Tungsten carbide (WC) with controlled pore size distribution was synthesized using a novel “precursor reassembly” method. The precursor crystal was assembled by mixing ammonium metatungstate (AMT) and ammonium carbonate (AC) in distilled water, followed by hydrothermal treatment. The mesostructure, crystal phase, and amount of deposited graphitic carbon can be conveniently tuned by controlling carburizing atmosphere (CO or a CO/H₂ mixture). Moreover, the influence of precursor preparation (AMT/AC mass ratio and hydrothermal temperature) on the materials was also investigated. The resultant materials with low carbon content were mesoporous WCs, which showed high specific surface areas (11.3-20.4 m² g⁻¹) and adjustable pore-size distributions (average pore size: 15.3-22.3 nm). A mechanism for the formation of WC with a controllable porous framework is proposed. Finally, cyclic voltammetry was used to investigate the inference of different mesoporous structure.     

PtCo supported on ordered mesoporous carbon as an electrode catalyst for methanol oxidation

A catalyst for methanol oxidation, PtCo supported on graphitized mesoporous carbon, has been synthesized and its electrochemical activity for methanol oxidation has been investigated. The graphitized mesoporous carbon support with ordered pore structure and high surface area of 585 m² g⁻¹ was prepared by one-step melt casting method using Al doped hexagonal mesoporous silica as hard templates and mineral pitches as carbon precursors followed by carbonization at 800 °C. The materials were characterized by X-ray diffraction, Raman spectra, field emission scanning electron microscopy, transmission electron microscopy and nitrogen sorption techniques. Cyclic voltammetry and amperometric i-t tests were adopted to characterize the electro-catalytic activities of the materials for methanol oxidation. The results show that the graphitized mesoporous carbon exhibits large electrochemical capacitance and good electric property. After supported with 20 wt%Pt or 20 wt%PtCo nanoparticles, the resultant mesostructured composites show 26-97% higher electrochemical catalytic activity for methanol oxidation than commercial catalyst 20 wt%Pt/C in mass activity (mA mg Pt⁻¹).     

Hierarchical porous carbons with controlled micropores and mesopores for supercapacitor electrode materials

Various porous carbons were prepared by CO₂ activation of ordered mesoporous carbons and used as electrode materials for supercapacitor. The structures were characterized by using X-ray diffraction, transmission electron microscopy and nitrogen sorption at 77 K. The effects of CO₂ treatment on their pore structures were discussed. Compared to the pristine mesoporous carbons, the samples subjected to CO₂ treatment exhibited remarkable improvement in textural properties. The electrochemical measurement in 6 M KOH electrolyte showed that CO₂ activation leads to better capacitive performances. The carbon CS15A6, which was obtained after CO₂ treatment for 6 h at 950 °C using CMK-3 as the precursor, showed the best electrochemical behavior with a specific gravimetric capacitance of 223 F/g and volumetric capacitance of 54 F/cm³ at a scan rate of 2 mV/s and 73% retained ratio at 50 mV/s. The good capacitive behavior of CS15A6 may be attributed to the hierarchical pore structure (abundant micropores and interconnected mesopores with the size of 3-4 nm), high surface area (2749 m²/g), large pore volume (2.09 cm³/g), as well as well-balanced microporosity and mesoporosity.     

Nitrogen-containing carbon spheres with very large uniform mesopores: The superior electrode materials for EDLC in organic electrolyte

We reported the electrochemical studies on mesoporous carbon spheres (MCS) enriched in nitrogen on frameworks serving as an electrode for electric double layer capacitor (EDLC) in an organic electrolyte. The preparation of the carbon spheres is involved in a facile polymerization-induced colloid aggregation method by using melamine-formaldehyde resin (MF) as the carbon precursor, and commercial fumed silica (Aerosil-200) as a hard template. After the carbonization of as-formed resin-template composites at 1000 °C under a nitrogen atmosphere, and the removal of silica template by HF treatment, monodisperse MCS with diameter size of ∼1.2 μm, high specific surface area (up to 1460 m²/g) and uniform pore size as large as 31 nm can be obtained. The MCS product presents a high specific capacitance as 159 F/g at 0.5 A/g. The high specific capacitance of the MCS is believed to be associated with its suitable nitrogen content that can afford pseudocapacitance as well as the high specific surface area. Furthermore, the specific capacitance of MCS can remain 130 F/g at high current density of 20 A/g. Our results show that the moderate nitrogen content can enhance the surface wettability and reduce the resistance, the large pore size can accelerate the diffusion process for the ions solvated with big organic solvent molecules in the pores. In view of the facts that precursors used in this simple process are commercially available low-cost chemicals, researches on the synthesis of such MCS materials templated by silica nanoparticles may not only be theoretically important, but also provide more options for economical and large-scale productions of mesoporous carbon materials with desired nanostructures, which might find practical applications in the fields of EDLC with high power performance.     

Synthesis and characterization of ruthenium-containing ordered mesoporous carbon with high specific surface area

A Ru-containing ordered mesoporous carbon with a high specific surface area of 2186 m²/g was synthesized through evaporation-induced multi-constituent co-assembly method, wherein soluble resol polymer is used as the carbon precursor, silicate oligomers as the inorganic precursor, triblock copolymer as the template, and RuCl₃ · 3H₂O as the Ru precursor. The resultant sample was characterized by X-ray diffraction, nitrogen sorption, transmission electron microscopy and scanning electron microscopy. The results showed that the carbon material exhibited highly ordered mesoporous structure, and the ruthenium particles with sizes of ∼2 nm were uniformly distributed in the carbon matrix. The sample was used to catalyze benzene hydrogenation, which displayed high efficiency for this reaction.