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 carbon xerogel particles and fractal-like structures

A variety of dense and open-architecture amorphous carbon xerogel microspheres and folded fractal-like structures were synthesized by sol-gel polycondensation of resorcinol with formaldehyde in a slightly alkaline aqueous solution. Carbon structures were obtained by inverse emulsification of resorcinol-formaldehyde (RF) sol in cyclohexane containing a non-ionic surfactant Span-80, followed by its pyrolysis at 1173 K in nitrogen. We have investigated the effects of synthesis parameters including stirring time, resorcinol/catalyst (R/C) ratio and surfactant concentration on the structures. The average particle size of the carbon microspheres could be modulated from 5 to 46 μm by increasing the stirring time from 2 to 7 h and by varying the R/C ratio from 0.2 to 500. Particles agglomerated as the R/C ratio increases above 100. Increase in the surfactant concentration from 1% to 4% (v/v) produced smaller spherical particles with narrower size distribution. Further increase in the surfactant concentration from 10% to 50% (v/v) produced branched and folded fractal-like structures of large external area. Thus, RF sol-based precursor chemistry can be easily tuned to produce a spectrum of desired carbon particle morphologies with potential applications in printing technology, adsorbents, resonance-based solar cells, thermal detectors and carbon-based micro-electromechanical devices (C-MEMS).     

A low-temperature autoclaving route to synthesize monolithic carbon materials with an ordered mesostructure

Low-temperature autoclaving has been demonstrated to synthesize monolithic carbon materials with an ordered mesostructure by using triblock copolymer F127 as template, and resorcinol/formaldehyde resol as carbon precursor under acidic conditions. Transmission electron microscopy, small angle X-ray scattering, Fourier transform infrared spectroscopy and nitrogen adsorption measurements show that the crack-free carbon monoliths have a 2-D hexagonal pore system, a uniform pore size of ∼5.0 nm and a high surface area of ∼675 m² g⁻¹. The macroscopic morphology can be tuned by changing the diameter of the autoclave. The influence of the synthesis conditions including the autoclaving treatment time and the molar ratio of formaldehyde (F) to resorcinol (R) are discussed. It is found that while the F/R molar ratio ?2 and the autoclaving treatment time ?2 d, highly ordered mesoporous carbon monoliths can be obtained. In comparison, monolithic mesoporous carbon materials prepared through an evaporation-induced self-assembly strategy are partly cracked with a disordered wormhole-like mesostructure, suggesting that low-temperature autoclaving is an efficient way to prepare crack-free monolithic carbon materials with an ordered mesostructure.     

Carbon periodic cellular architectures

The first carbon periodic cellular architectures derived from 3D printing, in the form of new tetrakaidecahedra meshes, are reported and investigated in this paper. They were prepared in hydrothermal conditions by a template method based on polymer periodic structures of the same geometry, and fabricated by a 3D printer using photocurable resin. Several formulations based on resorcinol–formaldehyde were tested, and the best ones were those using low concentrations of resorcinol at 150 °C in a pressurised solution of nickel nitrate. After pyrolysis at 1000 °C, catalytic graphitisation was demonstrated by TEM, XRD and Raman studies. The higher was the amount of nickel, the higher was the resultant graphitisation level. Mechanical tests were also carried out on such extremely lightweight periodic carbon structures, showing that these new materials present a much higher modulus than carbon foams of similar bulk densities.     

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.     

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.     

Solvent annealing assisted self-assembly of hydrogen-bonded interpolymer complexes of AB block copolymer/C homopolymer in thin film

A simple process of solvent annealing has been shown to produce ordered self-assembly structures of poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP)/poly(4,4′-oxydiphenylenepyromellitamic acid) (POAA) block copolymer/homopolymer blends in thin film, where POAA chains selectively interact with P4VP blocks by strong interpolymer hydrogen-bonding. By simply exposing the thin film to benzene/NMP (0.97/0.03, in volume) vapor mixture, ordered microphase-separated structures with PS spherical microdomains distributed within P4VP/POAA complexes matrix were obtained. The formation of the microphase-separated structures could be attributed to the substantial mobility of PS blocks and P4VP/POAA complexes and enhanced repulsion between them under the benzene/NMP mixture vapor. When the volume ratio of benzene to NMP increased to 0.98/0.02, the increasing benzene in the mixture vapor induced the adhesive collision of spherical microphase-separated structures to form long “pearl necklaces”. With increasing volume ratio of benzene to NMP to 0.99/0.01, an ordered “pearl necklace” array oriented parallel to the film surface formed. The self-assembly structures were studied by FTIR spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Finally, possible mechanism of self-assembly and formation of microphase morphology was proposed.     

层层自组装法制备碳纳米管薄膜研究进展

综述了近年来通过层层自组装法制备碳纳米管薄膜的一些最新研究进展,重点介绍了通过物理吸附和化学吸附两种方式来制备碳纳米管组装膜,并对如何提高碳纳米管薄膜的电化学稳定性方面进行了论述。     

The growth of transparent amorphous carbon thin films from coal

Large-area, uniform, transparent amorphous carbon (a-C) thin films were synthesized through simple chemical vapor deposition using coal as the solid carbon source. The atomic force microscopy characterization showed that the synthesized carbon thin film has ∼5 nm thickness with ∼0.55 nm surface roughness. The optical transmittance spectrum showed that the carbon thin film has >96% optical transmittance over the spectral range from 350 nm to 900 nm. The carbon thin films can be transferred to various substrates, which show promise for applications in solar cell, optical and magnetic storage disks, light emitting diodes, photodiodes, and biomedical implants.     

Electrochemical synthesis of lamellar structured ZnO films via electrochemical interfacial surfactant templating

Interest in creating tunable, ordered mesoporous materials based on surfactant supramolecular templating has been increasing over the last decade. For the production of film-type mesoporous materials, the most common method currently used is sol-gel based dip-coating method, which utilizes evaporation induced self-assembly (EISA) of surfactants. A more recently developed method, electrochemical interfacial surfactant templating, exploits the interfacial surfactant assembly formed on the working electrode to electrodeposit inorganic mesoporous films. This method offers mechanisms for inorganic wall construction and amphiphilic assemblies that are quite different from those of the sol-gel dip-coating method. As a result, it offers new possibilities to produce mesoporous films that cannot be produced by other means. This paper reviews the recent advances in producing and tuning lamellar structured mesoporous zinc oxide films via electrochemical interfacial surfactant templating. The general principles of this method will be explained in comparison with other methods used for producing mesoporous films. This will be followed by discussions of the key synthesis conditions that govern the repeat unit, quality, and orientation of lamellar structures constructed during electrodeposition. This review will provide a useful foundation to further develop electrochemical interfacial surfactant templating as a versatile method to produce a broader range of mesoporous films.     

A moisture absorption and adhesion study of the process of blending film using p‐alkylphenol‐resorcinol‐formaldehyde and rubber latex

p‐alkylphenol‐resorcinol‐formaldehyde‐latex (ARFL) films were prepared by co‐condensation of p‐alkylphenols and resorcinol with formaldehyde to generate modified phenolic resins, followed by blending with rubber latex, aging, and finally curing. The weight‐gain of the ARFL films and the tensile force of the coated fiberglass were studied under different temperatures and various humidities. The surfaces of the ARFL films were further analyzed by measuring the static contact angle and the findings were confirmed by Fourier Transform Infrared Spectroscopy (FTIR) and X‐ray photoelectron spectroscopy (XPS) analysis. The adhesion between the coated fiberglass and neoprene rubber was evaluated using the H‐adhesion technique. The best hydrophobicity and the largest water contact angle were displayed on the surface of the p‐nonylphenol‐resorcinol‐formaldehyde‐latex (NRFL) film, with a weight‐gain percent that was 40.0% (wt %) lower and a static contact angle that was 22.6° more than that of the resorcinol‐formaldehyde‐latex (RFL) film. The NRFL‐coated fiberglass had a higher tensile force and H‐adhesion force than the RFL‐coated fiberglass. The shelf life of NRFL‐coated fiberglass can be raised significantly at 40°C and under 98% humidity. The mechanism of the dramatic drop in the tensile force of the coated fiberglass is also discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m²/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.     

Simultaneous synthesis of vertically aligned carbon nanotubes and amorphous carbon thin films on stainless steel

Carbonaceous nanostructures such as carbon nanotubes, graphene and transparent carbon-based thin films are envisioned to be part of the next generation of electronic devices, mechanical structures, and energy-storage systems. To synthesize these nanostructures on a large scale by chemical vapor deposition, large-area, flexible substrates are needed. Here, we studied the role of a metallic foil, stainless steel, as a self-catalytic substrate for carbon nanostructure synthesis. As a result, vertically aligned carbon nanotubes and amorphous carbon thin films were simultaneously obtained. We further showed that the evolution of the stainless steel foil during the different steps of the process played a critical role in carbon nanotubes and carbon thin film growth. A better understanding of how the growth of these carbon nanostructures is affected by stainless steel evolution under chemical vapor deposition conditions will enable the synthesis of hybrid carbon nanotubes/amorphous carbon nanostructures and pave the way to scale-up of their low-cost production.     

Double layer capacitance of high surface area carbon nanospheres derived from resorcinol–formaldehyde polymers

Micro-mesoporous bimodal carbon nanospheres with high surface areas were synthesized by a combined use of surfactant templating technique and BaO₂ chemical activation one. Starting spherical nanopolymer/surfactant composites were prepared by the NaOH-catalyzed reaction of resorcinol (R) and formaldehyde (F) in the presence of cetyltrimethylammonium bromide (CTAB) as a core template and 1,3,5-trimethylbenzene (TMB) and tert-butanol (t-BuOH) as cosurfactants. After pretreatment with hydrochloric acid, the composite materials were calcined at 1000 °C in N₂ coexistent with varying weight ratios of BaO₂ to RF polymer ranging from 0 to 11. It produced micro-mesoporous bimodal carbon nanospheres of 124–143 nm diameter, with specific surface areas as high as 1884 m² g⁻¹ or up to 3301 m² g⁻¹, in contrast to microporous ones with smaller surface areas obtained at low BaO₂-loadings. The electrochemical double layer capacitance of the resulting nanocarbons in 0.5 M H₂SO₄ showed a marked increase with specific surface areas, up to as high as 219 F g⁻¹ for the highest surface area carbon material.     

Vapor deposition of stable copolymer thin films in a batch iCVD reactor

This study demonstrates the deposition of poly(ethylhexyl acrylate-co-ethylene glycol dimethacrylate) (P(EHA-co-EGDMA)) copolymer thin films in a batch type initiated chemical vapor deposition (iCVD) reactor. Crosslinked copolymers are desired for many applications because of their high stable properties. iCVD polymers derived by monomers bearing only one vinyl bond are usually linearly structured polymers and hence they are not durable, which is unfavorable for many real-world applications. Robust crosslinked iCVD films can be produced with the help of crosslinkers. In a typical iCVD process, copolymer thin film is produced by constantly feeding monomer vapor and crosslinker into the reactor. The monomer/crosslinker ratio should be precisely controlled for fabrication of reproducible thin films. In order to eliminate problems caused by adjusting the flowrates of precursors, a closed-batch type iCVD reactor was used for the first time in this study to produce copolymer thin films. The variation of precursors' partial pressures allowed control over the copolymer thin film structures. As compared with homopolymer, copolymers showed the better chemical and thermal stable properties. Almost 40% of the copolymer thin film remained on the substrate surface at an annealing temperature of 300°C, whereas the homopolymer film was completely removed at an annealing temperature of 280°C.     

原料配比对介孔TiO2薄膜避光超亲水性的影响

采用蒸发诱导自组装法制备介孔TiO2薄膜,通过改变原料配比水解比H、抑制比p、TiO2与模板剂比s值控制合成介孔TiO2薄膜,考察原料配比对介孔TiO2薄膜避光超亲水性的影响.结果表明,随H、s值增大,介孔孔径和平均粒径先增大后减小,TiO2以锐钛矿型出现,TiO2薄膜避光超亲水性先增强后减弱;随p值增大,孔径和平均粒径逐渐减小,金红石含量增大,TiO2薄膜避光超亲水性逐渐降低.当H=15,p=2,s=188时,所制备的TiO2薄膜最大孔径为10.2nm,避光12 h后接触角仍小于5°.在所制备粒径范围内,介孔孔径对薄膜避光超亲水性的影响大于粒径的影响.     

Surface assisted laser desorption–ionization mass spectrometry on patterned nanoporous silica thin films

We describe the preparation and use of patterned nanocomposite silica thin films deposited on silicon for laser desorption-ionization mass spectrometry (LDI-MS) without the use of conventional matrices. Ordered nanocomposite silica thin films deposited on silicon substrates were prepared by evaporation induced self-assembly using Brij56 as the surfactant template. The films were then exposed to masked deep-UV light to selectively remove the template to yield isolated regions of ordered nanoporous silica in a field of nanostructured silica. The nanoporous regions act as isolated “wells” that allow for the mass spectral characterization of analytes by laser induced desorption–ionization MS using a commercial MALDI-TOF instrument. We demonstrate the utility of these patterned films for the mass spectral analysis of small organic molecules, such as amino acids, peptides and siderophores. No consistent background signal from the films was observed at laser intensities typically used to desorb/ionize analytes. We also show that the films remain active for over a year when stored at ambient laboratory conditions. Because these patterned nanocomposite films are straightforward to produce, readily modifiable and stable at ambient laboratory conditions, they provide a potentially useful alternative to currently available films and substrates for matrix-free LDI-MS analysis of small molecules.     

A new adsorption–desorption model for water adsorption in porous carbons

A new model is proposed to describe the adsorption and desorption branches of water adsorption in carefully synthesized mesoporous carbon materials. This model is an extension of a previous adsorption–desorption model proposed by Do et al. We prepared mesoporous resorcinol–formaldehyde carbon cryogels (RFCCs) by sol–gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution, followed by drying with freeze-drying and then carbonizing the RF cryogels at a high temperature under a nitrogen atmosphere. The resulting carbon materials have different surface and pore properties, which are valuable in the study of their effects on water vapor adsorption and desorption on RFCCs. The experimental data were used to test the model, and we have found that the model describes reasonably well all the data. We have also observed some interesting, but not unexpected, results in the analysis: the water cluster size in mesopore is larger than that in micropore, and the hysteresis loop of adsorption–desorption in mesopores is greater than that in micropores.     

EFFECT OF DRYING METHOD ON MESOPOROSITY OF RESORCINOL–FORMALDEHYDE DRYGEL AND CARBON GEL

Resorcinol–formaldehyde hydrogels were synthesized by sol–gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution. RF cryogels, RF xerogels, and RF xerogels (MW gels) were respectively prepared from RF hydrogels by freeze drying, hot air drying, and microwave drying. Carbon cryogels, carbon xerogels and carbon MW gels were subsequently obtained by pyrolyzing RF drygels in an inert atmosphere. Freeze drying and microwave drying were effective to prepare mesoporous RF drygels and carbon gels. RF cryogels and carbon cryogels showed high mesoporosity over wide ranges of the molar ratio of resorcinol to catalyst (R/C) and the ratio of resorcinol to water (R/W) used in sol–gel polycondensation. Although RF xerogels had a few mesopores, carbon xerogels had no mesopores. RF MW gels and carbon MW gels showed mesoporosity if appropriate values of R/C and R/W were selected.     

Simple hydrothermal synthesis of ordered mesoporous carbons from resorcinol and hexamine

Hexamine has been used as a release source of formaldehyde towards the self-assembly synthesis of resorcinol/formaldehyde (RF) resin-based mesoporous carbons under hydrothermal conditions. The obtained mesoporous carbons exhibit the micrometer-sized, sphere-like morphology and a high surface area. The use of hexamine instead of formaldehyde efficiently harnesses the organic–organic self-assembly of RF resin and block copolymer. Ordered mesostructures can be obtained over a wide range of hydrothermal temperature without the extra addition of inorganic bases or acids as catalysts. The method described here has the advantage of being a one-pot procedure and only involves the use of several organic precursors in an aqueous system.