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.     

Preparation of three-dimensional ordered macroporous SiCN ceramic using sacrificing template method

Three-dimensional (3D) long range well ordered macroporous SiCN ceramics were prepared by infiltrating sacrificial colloidal silica templates with the low molecular weight preceramic polymer, polysilazane. This was followed by a thermal curing step, pyrolysis at 1250 °C in a N₂ atmosphere, and finally the removal of the templates by etching with dilute HF. The produced macroporous SiCN ceramics showed high BET surface areas (pore volume) in the range 455 m²/g (0.31 cm³/g)–250 m²/g (0.16 cm³/g) with the pore sizes of 98–578 nm, which could be tailored by controlling the sizes of the sacrificial silica spheres in the range 112–650 nm. The sphere-inversed macropores were interconnected by 50 ± 30 nm windows and 3–5 nm mesopores embedded in the porous SiCN ceramic frameworks, which resulted in a trimodal pore size distribution. The surface of the achieved porous SiCN ceramic was then modified by Pt–Ru nanoparticle depositing under mild chemical conditions.     

A simple approach for fabrication of interconnected graphitized macroporous carbon foam with uniform mesopore walls by using hydrothermal method

Three-dimensional (3D) highly interconnected graphitized macroporous carbon foam with uniform mesopore walls has been successfully fabricated by a simple and efficient hydrothermal approach using resorcinol and formaldehyde as carbon precursors. The commercially available cheap polyurethane (PU) foam and Pluronic F127 were used as a sacrificial polymer and mesoporous structure-directing templates, respectively. The graphitic structure of carbon foam was obtained by catalytic graphitization method using iron as catalyst. Three different carbon foams such as graphitized macro-mesoporous carbon (GMMC) foam, amorphous macro-mesoporous carbon (AMMC) foam and graphitized macroporous carbon (GMC) foam were fabricated and their physicochemical and mechanical properties were systematically measured and compared. It was found that GMMC possess well interconnected macroporous structure with uniform mesopores located in the macroporous skeletal walls of continuous framework. Besides, GMMC foam possesses a well-defined graphitic framework with high surface area (445 m²/g), high pore volume (0.35 cm³/g), uniform mesopores (3.87 nm), high open porosity (90%), low density (0.30 g/cm³) with good mechanical strength (1.25 MPa) and high electrical conductivity (11 S/cm) which makes it a promising material for many potential applications.     

A wormhole-structured mesoporous carbon with superior adsorption for dyes

A series of large-pore mesoporous carbon materials with a three-dimensional wormhole framework structure were synthesized by nanocasting using mesoporous silica as a hard template. Samples of hard-template mesoporous silica with pore diameters from 3.08 to 6.43 nm, pore volumes from 0.59 to 1.02 cm³ g⁻¹ and surface areas from 832 to 579 m² g⁻¹ were prepared from tetraethyl orthosilicate as the silica source and ionic liquid 1-butyl-3-methylimidazolium bromide as structure-directing agent through hydrothermal treatment at different temperatures (110–150 °C) followed by calcining at 550 °C. Subsequently, carbon materials with large pore diameters (2.76–6.70 nm), pore volumes (0.74–2.10 cm³ g⁻¹) and high surface areas (1074–1276 m² g⁻¹) were synthesized using the various mesoporous silicas synthesized at the different hydrothermal temperatures as a hard-template. The carbon material obtained at a hydrothermal temperature of 150 °C possesses outstanding adsorbility for amaranth and methylene blue dyes.     

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.     

Graphitic mesoporous carbons synthesised through mesostructured silica templates

In this paper the fabrication and characterization of graphitizable and graphitized porous carbons with a well-developed mesoporosity is described. The synthetic route used to prepare the graphitizable carbons was: (a) the infiltration of the porosity of mesoporous silica with a solution containing the carbon precursor (i.e. poly-vinyl chloride, PVC), (b) the carbonisation of the silica–PVC composite and (c) the removal of the silica skeletal. Carbons obtained in this way have a certain graphitic order and a good electrical conductivity (0.3 S cm⁻¹), which is two orders larger than that of a non-graphitizable carbon. In addition, these materials have a high BET surface area (>900 m² g⁻¹), a large pore volume (>1 cm³ g⁻¹) and a bimodal porosity made up of mesopores. The pore structure of these carbons can be tailored as a function of the type of silica selected as template. Thus, whereas a graphitizable carbon with a well-ordered porosity is obtained from SBA-15 silica, a carbon with a wormhole pore structure results when MSU-1 silica is used as template. The heat treatment of a graphitizable carbon at a high temperature (2300 °C) allows it to be converted into a graphitized porous carbon with a relatively high BET surface area (260 m² g⁻¹) and a porosity made up of mesopores in the 2–15 nm range.     

Facile preparation and unique H2 adsorption behavior of three-dimensional novel Pt–Ru hollow sphere assemblies

Three-dimensional long range ordered hollow Pt–Ru sphere assemblies were prepared using a sacrificial three-dimensionally ordered macroporous (3DOM) carbon template. Metallic salts, such as a mixture of RuCl₃ with H₂PtCl₆ were infiltrated into the carbon template, and a reduced Pt–Ru phase was produced on the surface of the 3DOM carbon template by a borohydride reduction reaction. The sacrificial template was then burnt off in air at 650 °C. The diameter of the hollow Pt–Ru spheres could be tailored using a different pore size 3DOM carbon template. Assemblies with an outer diameter of 550 nm showed high BET surface area of 584.3 m²/g. In addition, a high hydrogen adsorption stoichiometry (>0.5 H/M) was obtained on the Pt–Ru sphere assemblies, which indicated that most of the metal atoms on the surface were exposed.     

Sacrificial PSS-doped CaCO3 templates to prepare chitosan capsules and their deformation under bulk pressure

To prepare microcapsules composed of chitosan (CS), a templating method is developed using poly(styrene sulfonate) (PSS)-doped porous calcium carbonate (CaCO₃) templates as sacrificial templates. First, CS is absorbed onto PSS-doped porous CaCO₃ templates, and then the absorbed CS is covalently cross-linked with each other by using glutaraldehyde. Porous CaCO₃ templates are dissolved with disodium ethylenediaminetetraacetate dihydrate and the resultant CS capsules ranged from 2 to 5 μm in diameter. Nitrogen adsorption–desorption analysis are applied to characterize the porous CaCO₃ templates, the BET surface area and total pore volume are 220 m²/g and 0.36 cm³/g, respectively. Field-emission scanning electron microscopy and transmission electron microscopy were used to characterize the CS capsules morphology. Confocal laser scanning microscopy images reveal that the capsules have been labeled with green fluorescein isothiocyanate. The gradual deformation of capsule in response to bulk osmotic pressure created by CS solutions has also been discussed.     

Mesoporous Silica by Solution-Combustion Synthesis Followed by Etching

Mesoporous silica was synthesized through the solution-combustion process followed by etching with aqueous solution of sodium dodecyl sulfate (SDS). Combustion products were characterized by XRD, FTIR, SEM, TEM, HRTEM, and BET analysis. After etching, the specific surface, mean pore size, and volume of porous space in silica increased up to 390 m²/g, 15 nm, and 1.6 cm³/g, respectively. The synthesized mesoporous silica exhibited good performance in the tests on elimination of methylene blue from aqueous solution.     

Synthesis of Ordered Mesoporous Carbon Materials with Semi-Graphitized Walls via Direct In-situ Silica-Confined Thermal Decomposition of CH4 and Their Hydrogen Storage Properties

Ordered mesoporous carbons with semi-graphitized walls (OMCs-SGW) were successfully obtained by in situ silica-confined thermal decomposition of methane at low temperatures (800–1000 °C). This novel method, adopting ordered mesoporous silicas (OMSs) as hard templates, impregnating OMSs with small amounts of group VIII metal (Fe, Co, Ni) nitrates as catalysts, combining pore infiltration and carbonization/graphitization processes into a single step, provides an efficient way for the synthesis of OMCs-SGW. Methane, a special carbon precursor with small molecular size, is adopted because it allows complete penetration, and full carbon deposition inside the mesopores and is an easy graphitization process at low temperature assisted by catalysts. Two mesoporous silica materials, SBA-15 with hexagonal structure (p6m) and KIT-6 with cubic bicontinuous structure (Ia3d), were used as hard templates. SAXS patterns and TEM results show that the obtained carbon materials are faithfully replicated from the mesostructures of silica templates. Their pore walls are semi-graphitized and little structural shrinkage and negligible micropores are observed. The textural, structural properties and degree of graphitization of the OMCs-SGW can be conveniently tuned by controlling the temperature, namely, higher temperatures (e.g. 1000 °C) lead to products with more ordered and graphitized frameworks, but lower surface areas and pore volumes (about 390 m²/g and 0.45 cm³/g), while lower temperature (800 °C) results in products with less ordered and graphitized structures, but very high surface areas and pore volumes (up to 1200 m²/g and 2.08 cm³/g). OMCs-SGW can also be synthesized without catalysts. They have higher surface areas and pore volumes but much lower graphitized structures than the counterparts synthesized with catalysts. These OMCs-SGW show good hydrogen uptake capabilities (up to ~2 wt% at 10 bar and 77 K).     

Preparation of a carbon monolith with hierarchical porous structure by ultrasonic irradiation followed by carbonization, physical and chemical activation

A two-step direct and simple method for the preparation of a hierarchical porous carbon monolith with micropores, mesopores and macropores is described. The two stages give more flexibility in the preparation of a porous carbon monolith. In step I a macroporous interconnected carbon monolith is prepared by ultrasonic irradiation during sol-gel polycondensation. The effects of sol-gel temperature, catalyst concentration and ultrasonic power on the structure of the monolith are investigated. In step II, mesopores are induced in the monolith by Ca(NO₃)₂ impregnation followed by CO₂ activation. The effect of activation temperature is also studied. A hierarchical interconnected carbon monolith with mean pore size diameter of 1.2 μm, BET surface area of 624 m²/g, mesopore volume of 0.38 cm³/g and micropore volume of 0.22 cm³/g has been obtained from Ca(NO₃)₂ impregnation of the macroporous carbon monolith followed by CO₂ activation at 850 °C.     

The influence of preparation method on the physicochemical properties of titania–silica aerogels: Part two

Titania–silica aerogels with different titania content were prepared. Four preparation methods differing mainly in approach to precursors hydrolysis were applied, while only three of them allowed total hydrolysis of silica precursor before titania precursor was added. The preparation of mixed products of titania and silica hydrolysis precursors containing gels was followed by high temperature supercritical drying (HTSCD) and thermal treatment at 500 °C. Obtained mixed oxides in form of aerogels were characterized by BET surface areas up to 1000 m²/g, mesopore volumes up to 1.6 cm³/g and bulk densities as low as 0.04 g/cm³. Even 18 h lasting aging did not allow to produce narrow diameter range mesoporous materials, their broad pore diameter distributions resulted in average pore sizes varying from 10 to nearly 30 nm. XRD measurements proved the presence of anatase crystalline form of titania, while silica was present in amorphous form. SEM studies indicated presence of isolated titania particles on titania–silica surface while joint hydrolysis method was applied. Titania–silica aerogels obtained by the simultaneous hydrolysis of precursors and the impregnation method showed high photocatalytic activity in degradation of salicylic acid in water. Activities of these mesoporous photocatalysts were higher than commercial P25 Degussa TiO₂. Comparison of activity of pure TiO₂ (P25 Degussa) and aerogels indicates higher utilization of titania present in mesoporous mixed oxides.     

Magnetically-separable hierarchically porous carbon monoliths with partially graphitized structures as excellent adsorbents for dyes

Magnetically-separable hierarchically porous carbon monoliths with partially graphitized structures were synthesized through confinement self-assembly in polyurethane (PU) foam associated with a direct carbonization process from triblock copolymer F127, phenolic resol and ferric nitrate. It was observed that the magnetic Fe nanoparticles were embedded in the walls of graphitic porous carbon matrix, and the resulting materials exhibited hierarchically porous structure with macropores of 100–450 μm, mesopore size of 4.8 nm, BET surface area of 723 m²/g, pore volume of 0.46 cm³/g, and saturation magnetization of 3.1 emu/g. Using methylene blue as model dye pollutant in water, the carbon monolith materials showed high adsorption capacity of 190 mg/g, exhibiting excellent adsorption characteristics desirable for the application in adsorption of dyes and easy separation under an external magnetic field.     

Synthesis of a ferrocene-containing ordered mesoporous organosilica and its catalytic activity

A new ordered mesoporous organosilica has been synthesized through co-condensation of 1,1′-bis[2-(triethoxylsilyl)ethyl]ferrocene and tetraethyl orthosilicate under basic conditions using supramolecular templates of cetyltrimethylammonium bromide as structure directing agents. The templates were removed through solvent extraction to yield the ferrocene-containing ordered mesoporous organosilicas. The pore diameter, BET surface area, and pore volume of the extracted material were 2.2 nm, 1,085 m²/g and 0.67 cm³/g, respectively. The material also has been characterized by XRD, TEM, FT-IR, UV–Vis DRS, solid state ²⁹Si MAS NMR and ¹³C CP-MAS NMR etc. In the reaction of benzene hydroxylation to phenol, the ferrocene-containing ordered mesoporous materials show a comparable activity with the homogeneous ferrocene catalyst, giving 20.2% of yield and 65.3% of selectivity for phenol.     

Electron microscopy and nitrogen adsorption studies of film-type carbon replicas with large pore volume synthesized by using colloidal silica and SBA-15 as templates

Mesoporous carbons synthesized by the film-type replication of colloidal silica and SBA-15 templates are studied by electron microscopy and nitrogen adsorption. This synthesis strategy involves the formation of thin carbon film on the pore walls of these templates using resorcinol-crotonaldehyde polymer as carbon precursor. For the silica templates consisting of 20-80 nm colloids this synthesis affords carbons with extremely large pore volumes (5-9 cm³/g) and uniform spherical pores reproducing the size of the colloids used.     

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.     

Synthesis of macroporous ZrO2–Al2O3 mixed oxides with mesoporous walls, using polystyrene spheres as template

Macroporous ZrO₂–Al₂O₃ mixed oxides with mesoporous walls were synthesized. The three-dimensional interconnected macroporous structures, of inorganic zirconia–alumina mixed oxides containing different alumina compositions (25, 50, 100 wt%), were prepared by sol–gel method from inorganic precursors and using polystyrene microspheres with diameters of 685 and 1520 nm as templates. The final porous arrays with controllable pore size in the submicrometer range could be obtained by calcination of the organic template. The structural characteristics are discussed. The physicochemical characterization of the samples was carried out by N₂ physisorption (S_BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The shrinkage of pore diameter was approximately 35%, and the wall thickness of inorganic framework varied between 135 and 154 nm. The specific surface areas, of the samples, were between 123 and 287 m²/g, obtaining the largest surface area with the highest alumina contents and the smallest templates.     

Modification of Porous Silica with Activated Carbon and its Application for Fixation of Yeasts

Mixtures of small silica particles and activated carbon were heated at 1250–1450°C in an inert atmosphere to make nano- and macro-sized porous silica for incorporating yeast in the porous strucrure. Without activated carbon, porous silica of 45–60% porosity and 15–30 m pore diameter was produced with a specific surface area below 1 m²/g. By the addition of 8 wt% of activated carbon granules, the surface area of porous silica increased to 100 m²/g at 1250°C. It was confirmed that there were micropores(1.2 nm) and mesopores(4.0 nm) due to activated carbon granules in porous silica when granule type activated carbon was used. However, in the case of activated carbon fiber, its micro- and mesoporous structure was destroyed in the firing process. The fixation of Z. rouxii yeasts was promoted on the porous silica with activated carbon.     

Polyamide-silica gel hybrids containing metal salts: Preparation via the sol-gel reaction

The hydrolysis and condensation of tetramethoxysilane in a DMF solution of polyamides containing LiCl, CaCl₂ or ZnCl₂, both in presence and absence of polyoxazoline, resulted in the facile formation of polyamide-silica gel hybrids. Films were cast from the resulting mixtures and evaporation of the solvent resulted in the formation of clear, transparent hybrids with the salts dispersed at the molecular level. Pyrolysis of hybrids at 600 °C gave porous silica. Pore size and surface characteristics of these silica gel samples indicated a porous nature with a pore radius of 1.1 nm for silica gels obtained from hybrids HPA-6 (containing no salt) and HPA-9 (containing ZnCl₂) and a surface area of 213 m² g⁻¹ and 310 m² g⁻¹, respectively. Silica gel from hybrid HPA-7 (containing LiCl) had a pore radius of 1.9 nm and a surface area of 15 m² g⁻¹. The silica gel samples obtained from hybrids HPA-6, HPA-7 and HPA-9 exhibited narrow slit-like pores with a pore volume of 0.68 cm³ g⁻¹. Received: 7 January 1997/Accepted: 6 March 1997     

One-pot hydrothermal synthesis and supercapacitive performance of nitrogen and MnO co-doped hierarchical porous carbon monoliths

Nitrogen and MnO co-doped hierarchical porous carbon monolith (N-MnO-HPCM) materials were synthesized through a facile one-pot hydrothermal method. The resulting N-MnO-HPCM materials had hierarchical porous structure, high BET surface area (606 m²/g), large pore volume (0.33 cm³/g), and contained evenly dispersed MnO nanoparticles of about 6 nm in the carbon matrix. Their electrochemical performances as electrodes for supercapacitors were investigated. N-MnO-HPCM material exhibited an excellent electrochemical performance with a specific capacitance of 261.7 F/g at a current density of 1 A/g. It also showed a good rate capability with 74% capacity retention at high current density (5 A/g), indicating its potential applications in supercapacitors.