Development of Microporosity in Mesoporous Carbons

Monolithic carbons with uniform and spherical mesopores can be easily obtained by filling the pores of colloidal silica monoliths with carbon precursors followed by carbonization and silica dissolution. In this study three different phenolic resin blends: resorcinol and crotonaldehyde (MC-RC), phenol and paraformaldehyde (MC-PP), and resorcinol and furfural (MC-RF) were used as carbon precursors. Subsequent heating and carbonization of the resulting silica–phenolic resin nanocomposites followed by silica dissolution afforded monolithic carbons with spherical mesopores matching the size of the silica colloids used. Development of microporosity in these carbons was achieved by post-synthesis KOH activation. This study shows that the combination of colloidal templating with post-synthesis activation affords monolithic micro–mesoporous carbons with large specific surface area and well-developed accessible porosity for adsorption, catalysis, environmental and energy-related applications.     

Synthesis of nitrogen-doped porous carbon from zeolitic imidazolate framework-67 and phenolic resin for high performance supercapacitors

An one-pot method has been developed to synthesize a new type of composite material, which can be used as carbon source to produce electrode material for supercapacitors. Specifically, zeolitic imidazolate framework-67 (ZIF-67) crystal was synthesized firstly in 2-methylimidazol aqueous solution, then silica primary particles (from hydrolysis of tetraethylorthosilicate) and phenolic resin (from aggregation of resorcinol and formaldehyde) co-condensed on the surface of ZIF-67 crystal in the same system. The key to realize one-pot method is that 2-methylimidazol aqueous solution shows alkalescence, which can catalyze the hydrolysis of tetraethylorthosilicate and the aggregation of phenolic resin. After carbonization and remove of silica, the N-doped porous carbon (Carbon-ZSR) with high degree of graphitization, wide pore size distribution and maximum specific surface area was obtained. When it is used for supercapacitors as the electrode material, the Carbon-ZSR shows excellent electrochemical properties, large specific capacitance (305 Fg⁻¹ at 1 Ag⁻¹), high rate performance (229 Fg⁻¹ keeps at 10 Ag⁻¹) and excellent electrochemical stability (the specific capacitance maintains 98.4% after 5000 cycles at 10 Ag⁻¹), which suggest that the ZIF-derived nitrogen-doped porous carbon is an outstanding electrode material for energy storage devices.     

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.     

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.     

铸型炭化法制备多孔炭材料的研究进展

铸型炭化法开辟了多孔炭材料制备研究的一个全新领域,近年来已成为能够最有效控制多孔炭材料结构的方法。本文概述了传统方法制备多孔炭材料的不足,重点综述了以硅胶、黏土、沸石和中孔硅分子筛为铸型制备多孔炭材料的最新研究进展,展望了铸型炭的应用前景,最后指出了铸型炭化法在制备多孔炭领域尚待开展的研究工作。     

Hierarchically Fe-doped porous carbon derived from phenolic resin for high performance supercapacitor

Supercapacitors are promising for high power application in the recent years. In particular, the conversion of simple and available carbon materials into economic and high performance electrical devices receives excellent scientific and technological interest. This paper reports a one-step strategy for synthesizing hierarchical porous carbon derived from phenolic resin (PR), which is then used to configure electric double-layer capacitors (EDLCs). Here, a carbon material with a flexible porous structure, large specific surface area, and high graphitization degree is prepared using potassium ferrate (K₂FeO₄) to catalytically activate PR and to realize synchronous carbonization and graphitization. This method overcomes the disadvantage of time-consuming, high-cost, and environmentally unfriendly. In addition, the as-prepared carbon material has a high specific surface area (1086 m² g^?1) and a large pore size (3.07 nm), which can increase the transfer rate of electrolyte ions. The specific capacitance of the obtained electrode material is 315 F g^?1 at 1.0 A g^?1, and the optimized electrode material has an ultra-long cycle lifetime (capacitance retention rate is 96.3% after 10,000 cycles). Thus, the hierarchically Fe-doped porous carbon material derived from PR material is expected to realize high rate capacitance for supercapacitor applications.     

Processing of strong and highly conductive carbon foams as electrode

Porous carbons were processed by the foaming of two-part polymer precursors with pre-loaded carbon powder (graphitic or amorphous), and then resin impregnation and carbonization to control both porosity and mechanical strength of the resulting foam. Electrical conductivity of the foams was improved by nickel-catalyzed graphitization. Different levels of graphitization were obtained for varied concentrations of nickel to the amorphous carbon foams. The presence of graphitic carbon improves the electrical conductivity by a factor of 50, compared to the amorphous counterparts. Electrochemical studies showed that graphitization of the amorphous structures increased the specific electrochemical surface area and electron transfer rate of the carbon electrodes.     

The use of organometallic additives to promote graphitization of carbons derived from furfuryl alcohol resins

The promotion of graphitization of carbons derived from furfuryl alcohol resins and phenolic resins, which had been modified by the addition of various organometallic (OM) compounds, was investigated. Of 15 different OM additives evaluated, the most effective at promoting graphitization were those which contained Ti, V or Zr. Resins doped with these additives yielded carbons whose L_c values were between 150 and 250 Å, as compared to values of less than 30 Å for control specimens. The OM compounds of Co, Fe, and Ni yielded carbons with L_c values of approximately 80 Å; the remaining additives had little, if any, effect. Because of the efficient dispersal of the dissolved OM compounds, additions representing as little as 0·1% metal in the precursor resin were usually sufficient to promote sample graphitization. Also investigated were mixtures containing OM-doped furfuryl alcohol resins and glassy carbon filler. Electron and optical microscopy revealed that reorganization of the amorphous filler particles takes place in preference to the moderately graphitic binder residue. The experimental data suggest that the promotion of graphitization is not the result of low-temperature structural modification to the precursor resins during crosslinking or carbonization, but that promotion occurs at higher temperatures and is consistent with the mechanism of catalytic graphitization of amorphous carbons by metals or metal carbides as proposed by Gillot et al. and Fitzer and Kegel.     

以硅凝胶网络结构为模板制备多孔炭材料的研究

分别以蔗糖和正硅酸乙酯(TEOS)作为炭和硅凝胶的前驱体,通过溶胶凝胶过程形成蔗糖聚合物和硅凝胶的复合物,经高温炭化后将硅模板刻蚀去除制备了一种多孔炭材料。研究发现,影响多孔炭孔结构的主要因素是原料的摩尔比,另外还与胶凝温度、炭化温度、刻蚀方式有关。     

Co-gelation synthesis of porous graphitic carbons with high surface area and their applications

An easy co-gelation route has been developed to synthesize porous graphitic carbons with high surface areas by using teraethylorthosilicate (TEOS), furfuryl alcohol (FA), and metal nitrates as precursors. Using a one-pot co-gelation process, a polyfurfuryl alcohol–silica interpenetrating framework with metal ions uniformly dispersed was formed during the polymerization of FA and the hydrolysis of TEOS within an ethanol solution of the three precursors. This synthesis process is simple and time-saving in comparison with the conventional preparation methods. During the heat treatment, Fe₇Co₃ alloy nanoparticles were produced by carbothermal reduction and they then catalyzed the graphitization of the amorphous carbon. The graphitic carbons obtained have a high crystallinity as shown by X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy analysis. The degree of graphitization can be controlled by the varying the loading amount of catalyst. The porous texture of the carbons combines miropores and bimodal mesopores, mainly originating from the silica template formed with different sizes and the loose packing of the graphite sheets. The carbons have large surface areas (up to 909 m²/g) and exhibit excellent electrochemical performance.     

Lignin-derived macroporous carbon foams prepared by using poly(methyl methacrylate) particles as the template

An efficient route for the synthesis of lignin-derived carbon foams by thermal decomposition of an organic colloid template is described. Lignin, resorcinol, and formaldehyde were reacted by polycondensation into a crosslinked phenolic resin network in the presence of colloidal poly(methyl methacrylate) microspheres as the sacrificial template. Subsequently, carbonization was carried out at 800 °C to fabricate carbon foams with porous structural frameworks. Lignin was used as an excellent candidate for replacing resorcinol or other phenolic substances in the phenolic resin due to its high carbon yield above 50%. The prepared lignin-derived carbon foams had partially open cell structures. The carbon foams had the bulk density and porosity of 0.37–0.60 g/mL and 68.5–82.8%, respectively. Furthermore, the addition of lignin increased the mechanical properties strength of carbon foams.     

溶胶凝胶法多孔炭材料的制备及其表征

以十六烷基三甲基溴化胺(CTAB)稳定过的商业硅溶胶为模板硅源、蔗糖为炭前体、运用溶胶凝胶法制备了多孔炭材料。并采用低温N2等温吸脱附、X射线衍射等对材料的结构进行了测试与表征。结果表明:CTAB的加入使所得的多孔炭孔径分布更加集中,由于炭化温度较低,所得的炭材料仍为无定形结构。     

Synthesis and characterization of nanostructured carbons with controlled porosity prepared from sulfonated divinylbiphenyl copolymers

A series of porous carbons have been prepared by the carbonization of spherical porous sulfonated divinylbiphenyl (DVBPh) copolymers. Carbons in spherical bead form were obtained by the pyrolysis of H⁺, Na⁺, Cs⁺, Cu²⁺, Co²⁺ and Fe³⁺ forms of the sulfonated DVBPh beads. Thermogravimetric analysis (TGA) in an inert nitrogen atmosphere (25-900 °C) was carried out on the DVBPh copolymer precursor, the sulfonated copolymer sample and various ionic forms of the resin. The TGA data provides evidence that the sulfonation process thermally stabilized the polymer resulting in a higher final carbon yield. It was found that the pyrolysis yield was ca. 40% for the sulfonic acid derivative and between 40% and 65% for the various sulfonic acid salts. The highest yield was observed for the monovalent sodium and cesium ionic forms of the sulfonated DVBPh copolymers. Low temperature nitrogen adsorption/desorption isotherms provided information on the porous structure of the polymer precursors and the carbons prepared from them. The pore structure in the carbons was found to a large extent to be similar to the porous structure of the starting sulfonated resin material, however, the metal form was found to impact on the micropore structure of the resulting carbons. The carbon materials prepared were characterized by X-ray photoelectron spectroscopy (XPS) to provide information on the form of the residual sulfur in the carbons. XPS results suggest that the ionic form of the sulfonic resin influences the amount and the form of the sulfur and this may be correlated with the yield of the final carbon.     

The effect of magnetic field on the catalytic graphitization of phenolic resin in the presence of Fe-Ni

The effect of an externally applied magnetic field on the Fe-Ni catalyzed graphitization of phenolic resin was investigated. The Fe and Ni doped phenolic resin was first carbonized at 800 °C and then graphitized at different temperatures (800-1200 °C). Both the carbonization and graphitization were carried out in a magnetic field and the crystal structure was characterized by X-ray diffraction and transmission electron microscopy. The externally applied magnetic field was found to promote the graphitization and to improve the orientation of the hexagonal carbon layers. In the presence of Fe-Ni, a high degree of graphitization could be achieved by applying a magnetic field. This resulted in a d₀₀₂ of 0.3355 nm and full-width at half maximum (FWHM) value of 0.103° after a 1200 °C heat treatment. In comparison, the absence of a magnetic field resulted in a d₀₀₂ of 0.3358 nm and FWHM of 0.305°.     

废弃棉短绒模板纤维素碳化机理的研究及多孔碳的制备

以废弃棉短绒为模板,采用溶胶凝胶技术制备出新型多孔碳模板,研究了纤维素碳化的机理。多孔碳的收缩率随着树脂/棉短绒复合体中树脂含量的增大而减小;所得多孔碳的气孔率随着树脂/棉短绒复合体中树脂含量的增大而减小,也随着碳化温度的升高而减小;多孔碳的弯曲强度随着树脂/棉短绒复合体中酚醛树脂含量的增大而增大,也随着碳化温度的升高而增大。     

Formation of graphitic rods in carbon/carbon composites reinforced with carbon nanotubes

The formation of graphitic rods with a carbon nanotube (CNT) in the center was observed in CNT-reinforced phenolic resin-based carbon/carbon composites heat treated at 2000 °C. TEM characterization indicated that the carbon surrounding the CNT has a much better degree of graphitization compared to the carbon in most of the matrix. The formation temperature (2000 °C) of the graphitic rod is lower than for stress graphitization and normal graphitization of phenolic resin.     

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.     

MnO nanoparticles with textured porosity supported on mesoporous carbons

Ordered mesoporous carbons doped with MnO nanoparticles (DCs) have been prepared by direct carbonization of a composite of a reverse copolymer-low-molecular-weight phenolic resin dipped in aqueous Mn(NO₃)₂ solution. The microstructure of the DCs was analyzed by the small-angle X-ray scattering, X-ray diffraction, nitrogen adsorption isotherms and transmission electron microscopy. The results showed that the size of MnO nanoparticles dispersed on the surface of DCs was about 10–50 nm and the pore size of DCs could be tailored from 4.9 to 9.3 nm as the amount of phenolic resin varied. Moreover, the structure of the DCs obtained was stripe-like at low amount of phenolic resin. However, the structure of the DCs becomes disordered as the amount of phenolic resin increases. Because of its nontoxic nature and cost-effective synthesis, these DCs exhibit properties that are needed for an environment-friendly catalyst and electrode materials.     

Carbon spheres prepared from zeolite Beta beads

Porous carbon beads were prepared from macroporous anion-exchange resin beads preliminary converted into resin-zeolite Beta composite or pure zeolite Beta spheres. Two synthesis procedures were used depending on the initial template employed. In a series of experiments, the resin from the resin-zeolite Beta composite was directly carbonized into carbon. In another series of experiments, the resin was removed by oxidation at 600 °C leaving behind self-bonded zeolite Beta beads, which were filled with carbon by chemical vapor deposition (CVD) of propylene. As a final step for both procedures, the zeolite was dissolved in hydrofluoric acid. All the carbons prepared inherited the macroscopic spherical shape of the template spheres as well as the morphology of the primary particles building up the beads. The synthesis procedure and the carbonization temperature or the temperature for CVD of carbon employed influenced the ordering and the pore structure of the produced carbons. The carbons prepared by direct carbonization showed relatively low surface areas, less than 1000 m² g⁻¹, and no zeolite structural regularity. The samples obtained via CVD maintained the zeolite ordering with a periodicity of 11.7 Å and had surface areas of over 2000 m² g⁻¹.     

The influence of carbon source on the wall structure of ordered mesoporous carbons

A series of ordered mesoporous carbons (OMCs) have been synthesized by filling the pores of siliceous SBA-15 hard template with various carbon precursors including sucrose, furfuryl alcohol, naphthalene and anthracene, followed by carbonization and silica dissolution. The carbon replicas have been characterized by powder XRD, TEM and N₂ adsorption techniques. Their electrochemical performance used as electric double-layer capacitors (EDLCs) were also conducted with cyclic voltammetry and charge-discharge cycling tests. The results show that highly ordered 2D hexagonal mesostructures were replicated by using all these four carbon sources under the optimal operation conditions. Physical properties such as mesoscopic ordering, surface areas, pore volumes, graphitic degrees, and functional groups are related to the precursors, but pore sizes are shown minor relationship with them. The sources, which display high yields to carbons, for example, furfuryl alcohol and anthracene are favorable to construct highly ordered mesostructures even at high temperatures (1300 °C). OMCs prepared from non-graphitizable sources such as sucrose and furfuryl alcohol display amorphous pore walls, and large surface areas and pore volumes. The functional groups in the precursors like sucrose and furfuryl alcohol can be preserved on carbon surfaces after the carbonization at low temperatures but would be removed at high temperatures. The graphitizable precursors with nearly parallel blocks and weak cross-linkage between them like anthracene are suitable for deriving the OMCs with graphitic walls. Therefore, the OMCs originated from sucrose and furfuryl alcohol behave the highest capacitances at a carbonization of 700 °C among the four carbons due to the high surface areas and plenty of functional groups, and a declination at high temperatures possibly attribute to the depletion of functional groups. Anthracene derived OMCs has the lowest capacitance carbonized at 700 °C, and a steady enhancement when heated at high temperatures, which is attributed to the graphitization. The OMCs derived from naphthalene have the stable properties such as relatively high surface areas, few electroactive groups and limited graphitizable properties, and in turn medium but almost constant capacitances.