Synthesis and properties of mesoporous carbons with high loadings of inorganic species

A series of mesoporous carbons with high loading of silica has been synthesized by acid-catalyzed polymerization of resorcinol and formaldehyde in the presence of tetraethyl orthosilicate (TEOS), colloidal silica (silica source) and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (soft template) followed by carbonization. This synthesis route can be considered as a combination of soft-templating and hard templating strategies. The resulting mesoporous silica-carbon composites contained spherical silica colloids in addition to uniformly distributed silica originated from TEOS. Dissolution of silica led to high surface area carbons, which in addition to the primary mesopores formed by thermal degradation of block copolymer template possessed spherical mesopores after dissolution of silica colloids and fine pores after removal of TEOS-generated silica species. This approach can be used to incorporate other inorganic nanoparticles into mesoporous carbons with extra microporosity created after dissolving TEOS-generated silica species.     

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.     

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.     

One-pot preparation of functionalized nanostructured carbons

Functionalized nanostructured carbons were obtained by template method using sucrose as carbon precursor and silica gel SG60 as structure directing agent. To introduce acid groups into carbon a different amount of phosphoric acid was added to sucrose (impregnation ratio 0–1) before filling the pores of silica gel. After carbonization at 800 °C silica template was removed by dissolution in HF. Carbons were characterized by SEM/EDX, nitrogen adsorption at 77 K and acid–base titration. Pore size distributions (PSD) indicated that carbons obtained at impregnation (IR) of 0–0.75 have pores with size less than 4 nm due to crack during carbonization and activating action of phosphoric acid. Templated pores with 5.1 nm are observed in all carbons. PSD significantly changed at IR = 1 showing additional large mesopores of 8.2 nm. Acid–base titration revealed very high concentration of acid surface groups (4.1–4.7 mmol/g), significant amount of which (46 ± 3%) belongs to phosphate groups (pK = 2.3 ± 0.1). Another surface groups are weak carboxylic (pK = 5.9 ± 0.3), lactone and/or enol (pK = 7.2 ± 0.2, pK = 8.8 ± 0.3) and phenol groups (pK = 10.5 ± 0.3). SEM showed smooth carbon surface up to impregnation ratio 0.5 and increasing roughness at higher amount of phosphoric acid.     

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.     

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.     

Phase inversion membranes with an organized surface structure from mixtures of polysulfone and polysulfone—poly(ethylene oxide) block copolymers

Phase inversion precipitation of a polysulfone and polysulfone—poly(ethylene oxide) block copolymer solution yields a membrane with an organized surface structure. The poly(ethylene oxide) block of the polysulfone—poly(ethylene oxide) block copolymer segregates to the surface of the membrane. Measurement of the ¹H T_1ρ of the component materials, X-ray photoelectron spectroscopy, and differential scanning calorimetry reveal the organized surface structure of the membrane. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1353–1358, 1997     

A mesoporous composite template composed of self-assembled silica nanotube and multi-walled carbon nanotube

The multi-walled carbon nanotubes (MWNTs) were successfully embedded in the hexagonally-arranged silica tubular structure by the self-organization of two surfactant systems providing a MWNT-incorporated silica nancomposite template. The anionic surfactant (sodium dodecyl sulfate, SDS) adsorbed on the MWNT surfaces allowed the MWNTs to interact with the outer surface of the self-assembled non-ionic surfactant, poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer. Due to the hydrophilic–hydrophilic interaction between the PEO blocks and the sulfate group of SDS, the MWNTs were most possibly surrounded by the outer wall of the SBA-15 hexagonal tubes aligning in the longitudinal and transverse directions to the silica tube direction. According to the interplanar distances, electron microscopy images, and N₂ adsorption–desorption isotherms, the synthesized SBA-15/MWNT system exhibited the structural integrity of silica-tube arrangement and structural characteristics of MWNTs in terms of BET surface area and micropore volume. This work made it clear that the developed SBA-15/MWNT template could be used to synthesize various MWNT-incorporated 2-D replicas.     

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.     

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.     

Electrochemical study of double-walled carbon nanotube electrode/block polyether-lithium bis(trifluorosulphonyl)imide salt polymer electrolyte interface

Electrodes of double-walled carbon nanotubes functionalized with ∼5 mass% of carboxyl groups (DWCNT-COOH) were prepared as an entangled and porous mat structure to facilitate the infiltration of polymer electrolytes. A system composed by a block copolymer of polyethylene-b-poly(ethylene oxide) or PE-b-PEO with lithium bis(trifluorosulphonyl)imide salt was optimized with respect to salt concentration. The 25 mass% of polymer electrolyte-DWCNT-COOH composite showed typical electronic conductivity of carbon nanotube-based composites (i.e., conductivities of 10⁻² S cm⁻¹ were obtained). The Nyquist plots for the nanocomposite led to the assignment of separate semi-circles to the electronic transfer through the nanotube and at the polymer electrolyte–nanotube interface. A complete cell with two electrode nanocomposites and a polymer electrolyte layer was tested in a wide range of cell potentials and temperatures. The operation of this configuration at 100 °C and a 4 V window was demonstrated.     

Poly(ionic liquid) nanoparticles as novel colloidal template for silica nanocasting

Spherical poly(ionic liquid) (PIL) nanoparticles of different size (25–70 nm) were synthesized and applied as a novel colloidal soft template for the preparation of meso- and macroporous inorganics, here exemplified with silica and its metal nanoparticle doping via nanocasting. Pore size and pore architecture can be adjusted by appropriate choice of the template and the reaction conditions. Unexpectedly, it was found that the in situ generated methanol plays a very important role during the casting process. It enlarged the overall surface area by introducing a significant fraction of micropores and small mesopores. The largest specific surface area was obtained at an optimized ratio of tetramethyl orthosilicate (TMOS) to PIL nanoparticle. In addition, PIL nanoparticles pre-functionalized with Pt metal nanoparticles were used in the same manner as hybrid templates for nanocasting. The pyrolysis conditions were optimized to synthesize mesoporous silica functionalized with uniformly distributed metal nanoparticles of very small size in a one-pot process.     

A review of the control of pore structure in MgO-templated nanoporous carbons

Nanoporous carbons with a high surface area were directly prepared from various carbon precursors without any stabilization and activation processes. Various carbon precursors, including poly(vinyl alcohol), poly(ethylene terephthalate), polyimide, coal tar pitch, were used and MgO itself, Mg acetate, Mg citrate, Mg gluconate and Mg hydroxy-carbonate were employed as MgO precursor. Carbon precursor was mixed with MgO precursor in different ratios either in powder (powder mixing) or in solution (solution mixing), and heat-treated at 900 °C in inert atmosphere. MgO formed in the carbonization products was dissolved out using a diluted acid. BET surface area of the carbons obtained could be reached to high value, as high as 2000 m²/g, even though any activation process was not applied. Most carbons prepared through this method were rich in mesopores. Size of mesopores in the resultant carbons was tunable by selecting MgO precursor and relative volume between mesopores and micropores was controlled by carbon precursor.     

Esterification of hydroxylated polymers with 2-sulfobenzoic acid cyclic anhydride: A facile approach for the synthesis of near-monodisperse strong acid homopolymers and diblock copolymers

A convenient two-step route was developed to prepare a range of low polydispersity strong acid homopolymers and several examples of well-defined diblock copolymers. Atom transfer radical polymerization (ATRP) of either 2-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate or glycerol monomethacrylate afforded the corresponding near-monodisperse hydroxylated homopolymers, while several diblock copolymer precursors were prepared by either (1) the one-pot ATRP of 2-hydroxypropyl methacrylate and 2-(diethylamino)ethyl methacrylate using sequential monomer addition or (2) the ATRP of either 2-hydroxypropyl methacrylate or glycerol monomethacrylate using a poly(ethylene oxide)-based macro-initiator. Excess 2-sulfobenzoic acid cyclic anhydride was used to fully esterify the hydroxy groups of these homopolymers and diblock copolymers under mild conditions. The resulting zwitterionic diblock copolymers undergo micellar self-assembly on adjusting the pH of the solution, while one of the anionic poly(ethylene oxide)-based diblock copolymers formed colloidal polyelectrolyte complexes in aqueous solution when mixed with a cationic poly(ethylene oxide)-based diblock copolymer.     

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.     

Morphological and mechanical study of nanostructured epoxy systems modified with amphiphilic poly(ethylene oxide-b-propylene oxide-b-ethylene oxide)triblock copolymer

Thermosetting systems based on DGEBA epoxy resin and poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (EPE) triblock copolymer were prepared and investigated. Different mixtures were obtained by using different contents of EPE block copolymer in order to study the influence of the modifier on the properties of the final materials. All thermosetting systems were prepared without using any solvent and were cured at ambient temperature, taking into account the lower critical solution temperature (LCST) behavior of the block copolymer. DSC results indicated that the addition of block copolymer affected to the curing reaction time and to the glass transition temperature of the mixtures and also the miscibility of EPE triblock copolymer in the epoxy resin was proved. The morphologies studied by AFM and TEM showed clear nanostructuration up to 25 wt % EPE content. The addition of 5 and 15 wt % of EPE block copolymer led to a considerable improvement in the toughness of the materials. When EPE block copolymer was added to the epoxy resin, the surface became more hydrophilic and the UV–vis transmittance decreased slightly maintaining a high level of transparency.     

Functionalized organic nanoparticles from core-crosslinked poly(4-vinylbenzocyclobutene-b-butadiene) diblock copolymer micelles

Surface-functionalized polymeric nanoparticles were prepared by: a) self-assembly of poly(4-vinylbenzocyclobutene-b-butadiene) diblock copolymer (PVBCB-b-PB) to form spherical micelles (diameter: 15-48 nm) in decane, a selective solvent for PB, b) crosslinking of the PVBCB core through thermal dimerization at 200-240 °C, and c) cleavage of the PB corona via ozonolysis and addition of dimethyl sulfide to afford aldehyde-functionalized nanoparticles (diameter: ∼16-20 nm), along with agglomerated nanoparticles ranging from ∼30 to ∼100 nm in diameter. The characterization of the diblock copolymer precursors, the intermediate micelles and the final surface-functionalized crosslinked nanoparticles was carried out by a combination of size exclusion chromatography, static and dynamic light scattering, viscometry, thermogravimetric analysis, ¹H NMR and FTIR spectroscopy and transmission electron microscopy.     

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).     

Microstructure and performance of block copolymer modified epoxy coatings

The effects of two diblock copolymers, poly(ethylene-alt-propylene)-b-poly(ethylene oxide) (PEP–PEO) and poly(1,2-butadiene)-b-poly(2-vinyl pyridine) (PB–P2VP) on the mechanical properties of epoxy coatings were studied. Both modifiers self-assembled into spherical micelles of 10–20 nm diameter in cured bulk epoxy. This morphology was preserved in 15 μm thick coatings; however, micelle segregation to the coating/substrate interface was also observed. The critical strain energy release rate, G_1c, of bulk thermosets was enhanced by up to fivefold with the addition of block copolymers. Likewise, the abrasive wear resistance of thin coatings increased with modifier inclusion. The results showed that at 5 wt.% of loading, block copolymers were able to impart a 40% increase in abrasive wear resistance to modified coatings over neat ones. Block copolymer modifiers did not sacrifice the modulus and glass transition temperature of bulk thermosets and coatings, or the hardness and transparency of coatings.     

Preparation of mesoporous benzene–silica nanoparticles

Nanoparticles of periodic mesoporous organosilica (PMO) with benzene bridging groups were prepared using a 1,4-bis(triethoxysilyl)benzene organosilica precursor and mixed surfactant templates composed of a poly(ethylene oxide)–poly(dl-lactic acid-co-glycolic acid)–poly(ethylene oxide) (PEO–PLGA–PEO) triblock copolymer and a fluorocarbon surfactant under acidic conditions. Mesoporous organosilica particles clearly exhibited a nanoscale diameter of 50–1000 nm by scanning electron microscopy. Moreover, these particles possessed a mesostructure with uniform pores in the range of 6.3–6.6 nm and core-shell type spherical morphology, which were confirmed by Synchrotron small angle X-ray scattering, transmission electron microscopy, and nitrogen adsorption analysis. Benzene bridging groups linked covalently to Si atoms were analyzed by solid state ¹³C- and ²⁹Si MAS NMR.