Hierarchically porous phenolic resin-based carbons obtained by block copolymer-colloidal silica templating and post-synthesis activation with carbon dioxide and water vapor

A series of hierarchically porous carbons was synthesized by self-assembly of polymeric carbon precursors and block copolymer template in the presence of tetraethyl orthosilicate (TEOS) and colloidal silica under acidic conditions. Resorcinol and formaldehyde were used as carbon precursors, poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer was employed as a soft template, and TEOS-generated silica and colloidal silica were used as hard templates. The carbon precursors were polymerized in hydrophilic domains of block copolymer, followed by carbonization and silica dissolution. This resulted in carbons possessing cylindrical (∼12 nm) and spherical (20 or 50 nm) mesopores created by thermal decomposition of the soft template and by the dissolution of colloidal silica, respectively; fine pores were also formed by the dissolution of the TEOS-generated silica (∼2 nm). A further increase in fine porosity was achieved by post-synthesis activation of the carbons with carbon dioxide and/or water vapor, which resulted in hierarchical carbons with a surface area and pore volume approaching 2800 m²/g and 6.0 cm³/g, respectively.     

The performance of electric double layer capacitors using particulate porous carbons derived from PAN fiber and phenol-formaldehyde resin

Activated carbon fibers are known to contain pores with a small resistance for electrolyte migration while possessing a large electrical resistance between the fibers. A carbon powder derived from pulverization of PAN-based carbon fibers was examined as an electrode for electric double layer capacitors using H₂SO₄ as the electrolyte solution. The performance of conventional-type activated carbon powders derived from phenol-formaldehyde resin char was also measured for comparison. The fiber-derived carbon exhibited an electrical resistance comparable to that of the conventional carbons while showed a larger specific capacitance as well as a lesser extent of capacitance decrease at high currents due to a smaller pore resistance. An ultimate capacitance as high as 290 F g⁻¹ can be reached for this fiber-derived carbon powder (with a BET surface area of ≈1300 m² g⁻¹). This large capacitance value was suggested to be associated with the high activity feature of the pore wall.     

Colloidal templating synthesis and adsorption characteristics of microporous–mesoporous carbons from Kraft lignin

Microporous–mesoporous carbons were synthesized via colloidal silica templating using Kraft lignin as a carbon precursor, which is a waste byproduct from paper industry. A unique feature of these carbons are uniform spherical mesopores achieved after dissolving colloidal silica used as a hard template, while micropores were created by post-synthesis CO₂ activation. The resulting activated lignin-based carbons possessed high specific surface area (up to 2000 m²/g) and microporosity and mesoporosity easily tunable by adjusting activation conditions and optimizing the amount and particle size of the colloidal silica used. The total pore volumes of activated carbons obtained by using 20 and 13 nm silica colloids as a hard template exceeded 1 and 2 cm³/g, respectively.     

Direct fabrication of mesoporous carbons using in-situ polymerized silica gel networks as a template

Mesoporous carbons were synthesized by in-situ polymerized silica gel networks as a template. The co-condensation of carbon precursor (sucrose) and silica precursor (sodium silicate) followed by heat treatment generated a carbon/silica nanocomposite. After etching the silica template, mesoporous carbons were obtained. Under optimum synthesis conditions a mesoporous carbon with a high surface area of >800 m²/g and a narrow pore size distribution centered at 3 nm was produced. The three-dimensionally interconnected silica structures effectively functioned as the template for the porous carbon materials.     

Magnetically separable bimodal mesoporous carbons with a large capacity for the immobilization of biomolecules

A method for the fabrication of carbon-based mesoporous magnetic composites with a large capacity for the adsorption/immobilization of biomolecules is presented. The composites consist of iron oxide spinel nanoparticles inserted into the pores of templated unimodal or bimodal mesoporous carbons. The deposition of the magnetic iron oxide nanoparticles was carried out following two synthetic routes: (1) the direct incorporation of nanoparticles into the pores of the templated carbons and (2) the insertion of nanoparticles into the mesopores of the carbon-silica composite followed by the selective removal of silica framework. The carbon-iron oxide magnetic composites prepared according to route 2 were found to have better textural properties (larger BET surface areas and pore volumes) and significantly higher capacity for the adsorption of hemoglobin and immobilization of lysozyme. The amounts of hemoglobin or lysozyme adsorbed/immobilized by these materials were 176 mg hemoglobin g⁻¹ support and 131 mg lysozyme g⁻¹ support using route 1 and 430 mg hemoglobin g⁻¹ support and 322 mg lysozyme g⁻¹ support by route 2. Furthermore, we have demonstrated that, when no inorganic nanoparticles are deposited, the bimodal mesoporous carbon shows exceptionally a large immobilization capacity for hemoglobin (830 mg g⁻¹ support) and lysozyme (510 mg g⁻¹).     

Synthesis of onion-like mesoporous silica from sodium silicate in the presence of α,ω-diamine surfactant

Mesoporous silicas with vesicular and onion-like morphologies were assembled through hydrogen-bonding pathway from sodium silicate as silica source and electrically neutral α,ω-diamine, Jeffamine D2000 surfactant (H₂NCH(CH₃)CH₂[OCH₂CH(CH₃)]₃₃NH₂) as template in aqueous media at different synthesis temperatures (25, 60 and 100 °C). Assembling the material at 100 °C afforded onion-like core shell mesoporous silica, while at relatively lower temperature, e.g. 25 and 60 °C, multilamellar vesicles were obtained. Mesoporous silica with onion-like morphology was also obtained by a two-step synthesis involving an aging period of 20 h at room temperature followed by a hydrothermal stage (1–12 h) at 100 °C. The heavily cross-linked (Q⁴/Q³ ratio of 4.43) onion-like mesophase silica exhibited high hydrothermal stability. The BET surface area, pore volume and KJS (Kruk-Jaroniec-Sayari) pore diameter of the onion-like mesoporous silica were found to be 464 m² g⁻¹, 1.16 m³ g⁻¹ and 7.2 nm, respectively.     

Physical adsorption and heat of immersion studies of microporous carbons

Physisorption and heat of immersion measurements have been made with two microporous carbons—a sample of charcoal cloth (BET area, 1250 m² g^?1; pore volume, 0.59 cm³ g^?1 having predominantly narrow micropores and a sample of Amoco carbon (BET area, 3700 m² g^?1; pore volume, 1.9 cm³ g^?1), having a wider distribution of micropores extending into the supermicropore range (pore width, ca. 1–2 nm). The adsorption isotherms of nitrogen and toluene are of Type 1 and reveal that the external surface of both samples is very small. The heat of immersion measurements were carried out with the aid of a Tian-Calvet microcalorimeter and with the following liquids: n-hexane, cyclohexane, neo-hexane, toluene, mesitylene and isodurene. A sample of non-porous graphitized carbon black (Vulcan 3G: BET area, 71.1 m² g^?1) was studied. Immersion calorimetry shows that in spite of the larger adsorptive capacity of the Amoco carbon, the sample of charcoal cloth has a higher adsorption affinity. The differences in the corresponding heats of immersion and in the adsorptive properties indicate that many of the pores in charcoal cloth are slit-shaped, whereas those in the Amoco carbon appear to be more cylindrical in shape.     

A combined salt–hard templating approach for synthesis of multi-modal porous carbons used for probing the simultaneous effects of porosity and electrode engineering on EDLC performance

A new approach, based on a combination of salt and hard templating for producing multi-modal porous carbons is demonstrated. The hard template, silica nanoparticles, generate mesopores (∼22 nm), and in some cases borderline-macropores (∼64 nm), resulting in high pore volume (∼3.9 cm³/g) while the salt template, zinc chloride, generates borderline-mesopores (∼2 nm), thus imparting high surface area (∼2100 m²/g). The versatility of the proposed synthesis technique is demonstrated using: (i) dual salt templates with hard template resulting in magnetic, nanostructured-clay embedded (∼27% clay content), high surface area (∼1527 m²/g) bimodal carbons (∼2 and 70 nm pores), (ii) multiple hard templates with salt template resulting in tri-modal carbons (∼2, 12 and 28 nm pores), (iii) low temperature (450 °C) synthesis of bimodal carbons afforded by the presence of hygroscopic salt template, (iv) easy coupling with physical activation approaches. A selected set of thus synthesized carbons were used to evaluate, for the first time, the simultaneous effects of carbon porosity and pressure applied during electrode fabrication on EDLC performance. Electrode pressing was found to be more favorable for carbons containing hard-templated mesopores (∼87% capacitance retention at current density of 40 A/g) as compared to those without (∼54% capacitance retention).     

An ordered hydrophobic P6mm mesoporous carbon with graphitic pore walls and its application in aqueous catalysis

A hydrophobic ordered mesoporous carbon with hexagonal arrays of rods was synthesized by a nanocasting process by using silica SBA-15 as a template and 2,3-dihydroxynaphthalene as a fused-aromatic carbon precursor. Impregnation of 2,3-dihydroxynaphthalene and its subsequent conversion into carbon occurred inside the mesopores of the silica template through a dehydration reaction between the surface silanols and hydroxyl groups of the carbon source and mild carbonization under inert atmosphere. After silica removal, X-ray scattering, transmission electron microscopy, pore size analysis and Raman spectroscopy showed that the resulting material was a negative replica of the silica template with a 2D-hexagonal P6mm ordered structure, possessing a large surface area (724 m² g⁻¹), a monomodal pore size distribution (3.4 nm) and a relative hydrophobic surface with graphitic pore walls. These features give the system substantial advantages to play a beneficial role in aqueous organometallic catalysis. The material appeared to be an excellent mass transfer promoter to enhance the overall reaction rate of the palladium-catalyzed cleavage reaction of water-insoluble allylundecylcarbonate (Tsuji–Trost reaction).     

Textural and Structural Properties of Mesoporous Silica Synthesized Under Refluxing Conditions

Mesoporous silica with pore sizes of 3–6 nm has been synthesized under refluxing and autogenous pressure conditions of hydrothermal synthesis from precursor gels having different alkaline pH. The mesoporous silica prepared is characterized by powder X-ray diffraction, nitrogen adsorption-desorption measurement and scanning electron microscopy. Thermal stability has been tested by XRD analysis of mesoporous silica after thermal treatment at 823 K, 6 h; 1023 K, 1 h and 1223 K, 1 h. The results indicate that the mesoporous silica prepared under refluxing condition from precursor gel of pH 11 has large surface area (ca.1103 m² g^{− 1}) and pore volume (ca. 0.868 cm³ g^{− 1}) and is thermally stable at 1223 K. The surface area, pore volumes and pore wall thickness increase as the pH of the precursor gel is increased for refluxing condition of synthesis. The comparison of textural properties revealed that the refluxing condition is advantageous over autogenous pressure condition for obtaining mesoporous silica with higher surface area (852 m² g^{− 1}), pore volume (0.894 cm³ g^{− 1}) and pore diameter > 4 nm with wall thickness of 1.59 nm, when synthesized from precursor gel of pH 9.2. The ²⁹Si NMR spectra showed that a great part of the Si atoms exists as silanol groups. The mesoporous silica made at the lower pH (9.2) under refluxing conditions have more condensed framework. In calcined mesoporous silica, the proportion of partly condensed silica (Q³) is higher than fully condensed silica (Q⁴).     

Preparation of hollow submicrocapsules with a mesoporous carbon shell

The preparation of carbon submicrocapsules with size up to 800 nm and a mesoporous shell by hard silica templating is reported. Washing and template synthesis conditions were varied to promote porosity and avoid deformation of the microcapsules. The silica template synthesis conditions analyzed were: silica nucleus formation time (0.25–6 h), octadecyltrimethoxysilane/tetraethylorthosilicate volume ratio for silica shell formation (0.2–0.6) and silica shell formation time (1–24 h). The samples were characterized by 77 K nitrogen adsorption/desorption, mercury porosimetry and electron microscopy. Under all the washing conditions tested the carbon submicrocapsules were deformed due to the large size of the hollow core and the thickness of the shell. Changes in the silica template synthesis conditions did not result in substantial improvement of the strength of the microcapsules. The synthesis of a silica template with a double shell allowed us to obtain thick shell carbon submicrocapsules without significant deflation and with higher porosity. The characterization of these microcapsules showed that they have a BET surface area of 1541 m²/g and a pore size distribution with peaks centered at 0.75, 0.86, 1.0 nm in the micropore range and 3.5 nm in the mesopore range. The pore volume in the 2–80 nm range was 1.7 cm³/g.     

Monodispersed nanoporous starburst carbon spheres and their three-dimensionally ordered arrays

Controlled syntheses of highly monodispersed nanoporous carbon spheres via a nanocasting route are described. Previously reported monodispersed super-microporous or mesoporous silica spheres with hexagonally ordered pore channels were used as sacrificial templates, and the effect of pore sizes of the templates on the porous properties of the nanocast carbon spheres was comprehensively studied. The resultant carbon spheres exhibited a unique starburst structure derived from radially-aligned pore channels in the silica template, and had a BET surface area of over 1000 m²g^?1. It was found out that the radial alignment and sufficiently large pore size of hexagonally ordered pore channels in the silica spheres were effective to enhance the degree of order of the starburst structure in the nanocast carbon spheres and that ordered nanoporous carbon spheres could be obtained even from the MCM-41-type mesoporous silica. The diameters of the nanoporous carbon spheres were controlled in the sub-micrometer range by changing the sizes of silica templates. Furthermore, three-dimensionally ordered arrays consisting of nanoporous carbon spheres were successfully fabricated via the self-assembly of mesoporous silica/carbon composite spheres and the subsequent dissolution of the silica templates.     

KOH activation of ordered mesoporous carbons prepared by a soft-templating method and their enhanced electrochemical properties

Ordered mesoporous carbon (COU-2) was synthesized by a soft-templating method. The COU-2 mesoporous carbon was activated by using KOH to improve its porosity. The mesopore size of COU-2 was 5.5 nm and did not change by the KOH activation. But, the BET surface area of COU-2 largely increased from 694 to 1685 m²/g and total pore volume was increased from 0.54 to 0.94 cm³/g after the KOH activation. The large increase of micropore volume is due to the increase of the surface area. Electrochemical cyclic voltammetry measurements were conducted in aqueous (1 M sulfuric acid) and organic (1 M tetraethyl ammonium tetrafluoroborate/polypropylene carbonate) electrolyte solutions. The KOH-activated COU-2 carbon shows superior capacitances over the COU-2 carbon and a commercial microporous carbon both in aqueous and organic electrolyte solutions. These results suggest that the carbons having regularly-interconnected uniform mesopores and micropores in thin pore walls are desirable for the electrodes in electrochemical double-layer capacitors.     

Synthesis of nitrogen-doped porous graphitic carbons using nano-CaCO3 as template,graphitization catalyst,and activating agent

Nitrogen-doped porous graphitic carbons (NPGCs) with controlled structures were synthesized using cheap nano-CaCO₃ as template, melamine-formaldehyde resin as carbon precursor, and dilute HCl as template removing agent. In addition to its use as a template, the nano-CaCO₃ acted as an internal activating agent to produce micro- and mesopores, as an adsorbent to remove the released hazardous gases (i.e. HCN, NH₃), and as a mild graphitization catalyst. The obtained NPGCs with hierarchical nanopores contained as high as 20.9 wt% of nitrogen, had surface areas of up to 834 m² g^–1, and also exhibited high thermal stability with respect to oxidation. Using carbohydrate or phenolic resin as the carbon precursor, this simple approach was also capable of producing hierarchical porous graphitic carbons with high surface area (up to 1683 m² g^–1) and extremely large pore volumes (>6 cm³ g^–1). X-ray diffraction and infrared spectroscopy suggested that the intermediate CaCN₂ or CaC₂ generated during the carbonization plays a critical role in the formation of the graphitic structure.     

Preparation and pore control of highly mesoporous carbon from defluorinated PTFE

Porous carbon having more than 2000 m²/g of BET specific surface area was synthesized by defluorination of polytetrafluoroethylene (PTFE) at 473 K using sodium metal. The porous carbon as-prepared had a large amount of narrow mesopores 2-3 nm in pore width, together with micropores. Control of the pore structure was attempted by simple heat-treatment of the carbon in nitrogen, and change of the porous structures was characterized by nitrogen adsorption techniques. As a result, it was found that the ratio between micro- and mesopores was easily varied. Electric double layer capacitance was measured as one of the applications for the mesoporous carbon with specific porosity, and the effect of pore control on capacitance was investigated.     

Capacitive performance of mesoporous carbons derived from the citrates in ionic liquid

Mesoporous carbons with different pore structures are prepared via a simple pyrolysis process using citrate salts as precursors. BaC-T carbons derived from barium citrate possess large pore volume and typical multimodal pore size distribution (PSD), while MgC-T carbons derived from magnesium citrate possess high specific surface areas due to their dominant small mesopores and micropores. The capacitive performance of the prepared carbons is investigated in ionic liquid and high specific capacitances (maximum of 180.3 F g⁻¹ for MgC-700) are achieved. Experimental data demonstrate that porosity and surface chemistry corporately determine the capacitive performance. BaC-700 and BaC-800 present good rate performance, and exhibit energy densities of about 50 Wh kg⁻¹. The good capacitive performance of these carbons is attributed to their bimodal PSD with large pore size and appropriate surface properties. The MgC-800 and BaC-800 carbons present good durability of capacitance during three thousand of charge/discharge cycles.     

Carbide-derived-carbons with hierarchical porosity from a preceramic polymer

Synthesis of carbon by extraction of metals from carbides has been successfully used to produce a variety of micro-porous carbide-derived carbons (CDCs) with narrow pore size distributions and tunable sorption properties. This approach is of limited use when larger mesopores are targeted, however, because the relevant synthesis conditions yield broad pore size distributions. Here we demonstrate the porosity control in the 3-10 nm range by employing preceramic polymer-derived silicon carbonitride (SiCN) precursors. Polymer pyrolysis in the temperature range 600-1400 °C prior to chlorine etching yields disordered or graphitic CDC materials with surface area in the range 800-2400 m² g⁻¹. In the hierarchical pore structure formed by etching SiCN ceramics, the mesopores originate from etching silicon nitride (Si₃N₄) nano-sized crystals or amorphous Si-N domains, while the micropores come from SiC domains. The etching of polymer-derived ceramics allows synthesis of porous materials with a very high specific surface area and a large volume of mesopores with well controlled size, which are suitable for applications as sorbents for proteins or large drug molecules, and supports for metal catalyst nanoparticles.     

Green synthesis of templated porous carbons

Porous carbon materials such as activated carbons are widely used industrially for the purposes of purification, decolourization, deodorization, and gas storage, among others. Routes for the synthesis of these materials employing templates have increasingly attracted attention due to the ease of manipulating the characteristics of the final product. In the present work, a simple synthesis method was applied for the production of highly porous carbon materials using commercial sugar as the carbon source, Aerosil silica as a template, and deionized water. The synthesis procedure was as follows: (I) Gel formation; (II) carbonization of the gels; (III) removal of the silica template; (IV) activation. The materials were characterized by N₂ and CO₂ physisorption, Raman spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy, and thermogravimetric analysis. The aging time had an important influence on the specific area and porosity of the material, with physisorption analysis revealing a high specific area and pore volume. The activation procedures further contributed to significantly increasing the specific area (up to 1158 m² g⁻¹) and pore volume (up to 1.65 cm³ g⁻¹). The X-ray diffractograms and Raman spectra identified the formation of semi-crystalline structures in the material, with the presence of a random distribution of graphite and graphene oxide, in addition to amorphous carbon. FTIR analysis showed the presence of bands corresponding to aromatic groups. The results demonstrated that it was possible to obtain materials with excellent potential for use in different industrial sectors using simple raw materials and a technique that is easy to reproduce.     

Porous nitrogen doped carbon foam with excellent resilience for self-supported oxygen reduction catalyst

Fabrication of graphitized carbon materials (e.g. carbon nanotubes and graphene) normally entails the assistance of transition metal catalyst. In this paper, a nitrogen doped carbon foam (NCF) with both graphitized and porous carbon structure was fabricated by direct pyrolysis of melamine foam (MF) without using any transition metal catalyst. The graphitized carbon structure was possibly attributed to the triazine moieties in the MF precursor. The introduction of oxygen groups in the oxidation step resulted in the formation of large amount of micro- and mesopores and therefore high specific surface area. The NCF exhibited a three-dimensional cellular network consisting of carbon microfiber with abundant micro- and mesopores and giving rise to a specific surface area over 980 m² g⁻¹. Due to such graphitized porous structure, the NCF was demonstrated to have superior resilience, excellent electrocatalytic activity and good durability for oxygen reduction.