Heteroatom-doped carbon gels from phenols and heterocyclic aldehydes: Sulfur-doped carbon xerogels

Sulfur-doped carbon xerogels were obtained through carbonization of resorcinol/2-thiophenecarboxaldehyde organic gels. The acid-catalyzed sol–gel polymerization of resorcinol and 2-thiophenecarboxaldehyde leads to organic gels whose morphology and texture is dependent on the amount of catalyst used. As a result, monolithic organic gels with sulfur content of up to 19.6 wt.% and easily tailored properties can be produced. After carbonization, a substantial amount of sulfur is retained and porous carbon xerogels with S-content of up to 10 wt.% are produced (at 800 °C). Depending on the sol–gel synthesis conditions, monolithic S-doped carbon xerogels with controllable and enhanced mesoporosity, surface areas of up to 670 m²/g and enhanced mechanical integrity were obtained. Additional KOH activation of the organic or carbon xerogels enables production of micro–mesoporous carbons with surface areas of up to 2550 m²/g while retaining over 5 wt.% of sulfur. Preliminary CO₂ adsorption measurements were performed. On the basis of resorcinol/2-thiophenecarboxaldehyde gel synthesis a more general approach towards heteroatom-doped carbon gels is proposed: sol–gel polymerization of phenols and heterocyclic aldehydes. Thus a variety of heteroatom-doped porous carbon materials with a tailored pore texture and morphology are available via this procedure.     

Preparation of Polyaniline/Mesoporous Silica Hybrid and Its Electrochemical Properties

Polyaniline/mesoporous silica hybrids were prepared by chemical modification with aniline and their capacitances were examined for application to electrode of electrochemical capacitor. The chemical modification was performed by two kinds of processes, polymer insertion into pores and in-situ polymerization within pores. In the case of the polymer insertion process, since the mean pore sizes of the hybrid did not change, polyaniline molecules were not inserted. On the other hand, in the case of the in-situ polymerization process, the mean pore sizes decreased from that of mesoporous silica, while the XRD patterns became broad. Therefore, aniline molecules polymerized in the inside of pores, however, the mesoporous silica collapsed in part. Maximum capacitance measured in 1 mol/l H₂SO₄ aqueous solution was around 226 F per unit mass of polyaniline.     

Porous Silicon Oxycarbide Glasses

High-surface-area silicon oxycarbide gels and glasses were synthesized from mixtures of methyldimethoxysilane (MDMS) and tetraethoxysilane (TEOS) through acidic hydrolysis and condensation. A surface area of ∼275 m²/g and an average pore size of ∼30 Å was obtained for a 50% MDMS-50% TEOS glass at 800°C under a flowing argon atmosphere. The average pore size was increased by aging the precursor gels in ammonium hydroxide. The increased average pore size and the higher strength of the mesoporous gel network enhanced the surface-area stability of the glasses; in this case, surface areas >200 m²/g were retained at 1200°C under an argon atmosphere. ²⁹Si MAS NMR spectra revealed that an oxycarbide structure was established in the mesoporous glasses obtained after pyrolysis of the aged gels. The role of carbon was demonstrated by comparing the surface-area stability of the oxycarbide glasses with that of pure silica and that of oxycarbide glasses where all the carbon groups were removed through low-temperature plasma-oxidation treatments. In the absence of carbon, the thermal stability of the surface area decreased dramatically.     

A simple method to synthesize graphitic mesoporous carbon materials with different structures

Graphitic mesoporous carbon materials with different structure were synthesized by reversed replication method. SBA-15 was used as hard template and the synthesized aromatic polymers with different polymerization degree as the carbon sources. Adopting the impregnation method, the carbon source was assembled into the pore of the SBA-15. The silica/aromatic polymers system was carbonized under N₂ atmosphere (high polymerization degree aromatic polymers) and vacuum (low polymerization degree aromatic polymers) to produce the graphitic mesoporous carbon materials with structure of CMK-3 and CMK-5, respectively. It is a easy way to synthesize the graphitic mesoporous carbon materials, especial for the CMK-5 structure. The porous structure and composition of these carbon materials were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectrometry, and N₂ adsorption–desorption measurements.     

Synthesis of polyaniline/mesoporous carbon nanocomposites and their application for CO<Subscript>2</Subscript> sorption

Ordered mesoporous carbons (OMC), were synthesized by nanocasting using ordered mesoporous silica as hard templates. Ordered mesoporous carbons CMK-1 and CMK-3 were prepared from MCM-48 and SBA-15 materials with pore diameters of 3.4 nm and 4.2 nm, respectively. Mesoporous carbons can be effectively modified for CO₂ adsorption with amine functional groups due to their high affinity for CO₂. Polyaniline (PANI)/mesoporous carbon nanocomposites were synthesized from in-situ polymerization by dissolving OMC in aniline monomer. The polymerization of aniline molecules inside the mesochannels of mesoporous carbons has been performed by ammonium persulfate. The nanocomposition, morphology, and structure of the nanocomposite were investigated by nitrogen adsorption-desorption isotherms, Fourier Transform Infrared (FT–IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and thermo gravimetric analysis (TGA). CO₂ uptake capacity of the mesoporous carbon materials was obtained by a gravimetric adsorption apparatus for the pressure range from 1 to 5 bar and in the temperature range of 298 to 348 K. CMK-3/PANI exhibited higher CO₂ capture capacity than CMK-1/PANI owing to its larger pore size that accommodates more amine groups inside the pore structure, and the mesoporosity also can facilitate dispersion of PANI molecules inside the pore channels. Moreover, the mechanism of CO₂ adsorption involving amine groups is investigated. The results show that at elevated temperature, PANI/mesoporous carbon nanocomposites have a negligible CO₂ adsorption capacity due to weak chemical interactions with the carbon nanocomposite surface.     

Highly aligned,large pore ordered mesoporous carbon films by solvent vapor annealing with soft shear

Macroscopic alignment of block copolymer (BCP)-templated mesoporous carbon films is challenging, especially for large pores (>10 nm), due to the slow dynamics of the polymer segments that impede re-orientation of the ordered domains. Here, we demonstrate a facile method, solvent vapor annealing with soft shear (SVA–SS), to fabricate unidirectionally aligned, ordered mesoporous carbon films using two different BCP templates, poly(ethylene oxide)-block-poly(n-butyl acrylate) and polystyrene-block-poly(N,N-dimethyl-n-octadecylammonium p-styrenesulfonate), and we illustrate the efficacy of this technique for both cylindrical and spherical morphologies with relatively large accessible pores (≈15 nm). This alignment is preserved through the thermopolymerization of resol and carbonization. The alignment of the mesopores impacts several key properties of these carbon films, especially for the unidirectional cylindrical mesostructures. The highly aligned mesoporous carbon films exhibit a more narrow pore size distribution than the analogous unaligned ordered mesoporous carbon as determined by ellipsometric porosimetry. Moreover, the electrical conductivity becomes anisotropic with nearly 40% difference in conductivity between parallel and perpendicular directions of the cylindrical mesopores. In the parallel orientation, the electrical conductivity is over 20% greater than the analogous unoriented (random) films. These results illustrate the applicability of SVA–SS to obtain unidirectional aligned mesoporous carbon films over large areas without additional physical or chemical templating.     

介孔材料对乳液聚合稳定性的影响

研究了十二烷基硫酸钠(SDS)在不同介孔材料(MCM-41、MCM-48、SBA-15)存在下的临界胶束浓度(CMC),讨论了介孔材料对间歇乳液聚合的影响。研究表明:孔径最大的介孔材料SBA-15存在下SDS的CMC增加最多;在聚合体系中加入介孔材料对单体转化率没有影响,但增加了乳液聚合时的凝聚率,其中使用小孔径的MCM-41凝聚物较少,而颗粒较大的MCM-48凝聚物较多,同时所得乳液聚合物的分子量下降,分子量分布变宽。     

Development of polymer derived carbon coated monolith for liquid adsorption application by response surface methodology

The preparation of polymer derived activated carbon coated monolith is reported. The response surface methodology based on Box–Behnken design is used to find the optimal condition for synthesis of mesoporous carbon. The dominant parameters identified are the carbonization temperature, concentration, and molecular weight of pore former agent. Typical values for BET surface area are 341 m²/g _carbon and 20 m²/g _{supported carbon} with pores size distribution in the range of 4–400 nm. The highest pore volume obtained is 182.77 mm³/g _{supported carbon}.     

Preparation of Mesoporous Carbons from Acrylonitrile-methyl Methacrylate Copolymer/Silica Nanocomposites Synthesized by in-situ Emulsion Polymerization

Acrylonitrile-methyl methacrylate (AN-MMA) copolymer/silica nanocomposites were synthesized by in-situ emulsion polymerization initiated by 2,2'-azobis(2-amidinopropane) dihydrochloride absorbed onto colloidal silica particles, and the mesoporous carbon materials were prepared through carbonization of the obtained AN-MMA copolymer/silica nanocomposites, followed by HF etching. Thermogravimetric analysis of AN-MMA copolymer/silica nanocomposites showed that the carbon yield of copolymer was slightly decreased as silica particle incorporated. N₂ adsorption-desorption, scan electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the mesoporous carbon materials. Both SEM and TEM results showed that disordered mesopores were formed in the obtained carbon material mainly through templating effect of silica nanoparticles. The diameter of mesopores was mainly distributed in the range from 5 nm to 15 nm. The mean pore diameter and total pore volume of the material increased as the mass fraction of silica in the nanocomposites increased from 0 to 24.93%. The significant increase of the mean pore diameter and the decrease of surface area for the carbon material prepared from the nanocomposite with 24.93% silica were caused by partial aggregation of silica nanoparticles in the polymer matrix.     

Disordered mesoporous carbon as polysulfide reservoir for improved cyclic performance of lithium–sulfur batteries

Mesoporous carbon, which was templated by colloidal silica, was added to a sulfur cathode as a functional material to confine polysulfides to improve the cyclic performance of lithium–sulfur batteries. To investigate the effect of the pore size and the pore volume of mesoporous carbon on the absorption characteristics of the Li-polysulfides, mesoporous carbons with various pore sizes and total pore volumes were prepared by varying the size and the amount of colloidal silica templates. The results show that mesoporous carbon-containing sulfur cathode enhanced the cyclic performance of the batteries significantly. Comparable performances were observed regardless of pore size, suggesting that the pore size is not a critical factor affecting the absorption characteristics of the Li-polysulfides. However, the cyclic performance was affected by the total pore volume, suggesting that a certain pore volume is necessary to confine the majority of the soluble Li-polysulfides generated during cycling and to enhance sulfur utilization. The novel results obtained in this study will contribute to the consolidation of S electrochemistry and further development of high-energy lithium–sulfur batteries.     

A novel method for carbon modification with minute polyaniline deposition to enhance the capacitance of porous carbon electrodes

A novel method was developed for minute deposition of polyaniline onto microporous activated carbon fabric to enhance the capacitance of the carbon serving as electrodes for electrochemical capacitors. The deposition consisted of pre-adsorption of monomer into carbon micropores followed by electrochemical polymerization of the adsorbed monomer in a monomer-free H₂SO₄ solution at 0.85 V vs. Ag/AgCl. In comparison with the conventional polymerization in a monomer solution, the developed deposition resulted in a polymer framework distributed over the vast surface in carbon micropores, thus leading to a lower resistance for ion binding with the polymer in H₂SO₄ during charge-discharge. The lower resistance gave rise to a higher specific capacitance for the deposited polymer. In the assembled two-electrode capacitors, the usage of polyaniline redox reactions to store charges was more prominent for polymer-carbon composite electrodes from the developed method because of the higher electrode open circuit potentials. The present work has demonstrated that a capacitance enhancement of >50% in comparison with bare carbon can be achieved with minute polyaniline deposition (<5 wt.%) using the developed method, while only 22% was reached using the conventional method.     

Mesoporous carbon membranes from polyimide blended with poly(ethylene glycol)

The control of the mesoporous structure in a carbon membrane from a poly(ethylene glycol)/polyimide‐blended polymer was investigated. The size of the pores tends to become large with increase of the content of poly(ethylene glycol) against polyimide, that is, the mesoporous structure could be controlled by the composition of the blended polymers. On the other hand, the average molecular weight of poly(ethylene glycol) has little effect from the viewpoint of the control of the pore structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 836–841, 2001     

盐酸预处理对浒苔基活性炭电化学性能的影响

传统工艺制备的活性炭微孔足够,但中孔、大孔含量缺乏,导致其用作超级电容器电极材料时电化学性能水平较低。为解决这一问题,采用盐酸对炭化前浒苔原料进行预处理。酸处理去除了原料中大部分的杂质金属,其中,海藻酸钙与盐酸发生化学反应形成了蛋壳初始孔,酸溶性碱金属离子与盐酸发生置换反应形成了无规则初始孔隙,明显增加了活性炭的中孔含量。实验结果表明：盐酸预处理后的活性炭比表面积明显增加,由2273m²/g增至3166m²/g,孔容由2.10cm³/g增至3.82cm³/g,中孔率显著提高,改善了孔结构的连通性,促进了电解质离子在材料内部的扩散;当电流密度为0.1A/g时,经过酸洗处理的活性炭比电容高达359F/g,比原样活性炭比电容的293F/g增长了23%,超级电容器等效串联电阻很小,表现出良好的电化学性能。     

Simple preparation of ordered mesoporous carbons assisted by an organosilicate as a linking material

Ordered mesoporous carbon materials (OMCs) were prepared from a silica–carbon composite assisted by 3-mercaptopropyltrimethoxysilane (MPTMS) in an aqueous phase. The obtained OMCs have a high surface area, large pore volume and uniform pore structure. MPTMS plays an important role in linking the polymer part with silica part to form a mesoporous structure. Importantly, the amount of MPTMS used is an important determinant in the development of a uniform mesoporosity. The method described herein has some important advantages over existing methods, such as simplified synthesis steps for the preparation of OMCs, the fact that the aqueous phase can be used and that the resulting materials have a high surface area of more than 1700 m²/g.     

Enhanced capacitive deionization of graphene/mesoporous carbon composites

Capacitive deionization (CDI) with low-energy consumption and no secondary waste is emerging as a novel desalination technology. Graphene/mesoporous carbon (GE/MC) composites have been prepared via a direct triblock-copolymer-templating method and used as CDI electrodes for the first time. The influences of GE content on the textural properties and electrochemical performance were studied. The transmission electron microscopy and nitrogen adsorption-desorption analysis indicate that mesoporous structures are well retained and the composites display improved specific surface area and pore size distribution, as well as pore volume. Well dispersed GE nanosheets are deduced to be beneficial for enhanced electrical conductivity. The electrochemical performance of electrodes in an NaCl aqueous solution was characterized by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements. The composite electrodes perform better on the capacitance values, conductive behaviour, rate performance and cyclic stability. The desalination capacity of the electrodes was evaluated by a batch mode electrosorptive experiment and the amount of adsorbed ions can reach 731 μg g(-1) for the GE/MC composite electrode with a GE content of 5 wt%, which is much higher than that of MC alone (590 μg g(-1)). The enhanced CDI performance of the composite electrodes can be attributed to the better conductive behaviour and higher specific surface area.     

Preparation of mesoporous carbon templated by silica particles for use as a catalyst support in polymer electrolyte membrane fuel cells

Mesoporous carbons were prepared using commercial silica particles and a formaldehyde–resorcinol resin as a template and carbon precursor, respectively. By changing the molar ratio of template to carbon precursor, mesoporous carbons with different mesoporosities (MC-X, X represents the molar ratio of template to carbon precursor) were produced. The resulting MCs had a high-surface area and large pore volume. In particular, the highest mesoporosity was observed for MC-3. Pt catalysts-supported on MC-X were prepared using formaldehyde as a reducing agent for use as a cathode catalyst in a polymer electrolyte fuel cell (PEMFC). The size of Pt crystallite was dependent on the properties of corresponding carbon support. As a whole, a carbon support with a high-surface area and high-mesoporosity served the best in terms of a high-dispersion of Pt nanoparticles. In a unit cell test of the PEMFC, a Pt catalyst with a high-mesoporosity and fine dispersion of metal showed an enhanced performance. The findings indicate that the surface area combined with the mesoporosity had a positive influence on the metal dispersion and the distribution of ionomer, leading to the enhanced cell performance.     

Octadecyl grafted MCM-41 silica spheres using trifunctionalsilane precursors – preparation and characterization

MCM-41 silica spheres were prepared via the pseudomorphic route. Subsequent surface modification of the mesoporous silica spheres was achieved by two silylating agents, n-octadecyltrihydridosilane and n-octadecyltrimethoxysilane, which provided different surface coverages. The MCM-41 pore structure, surface properties and morphological features were examined by small angle X-ray scattering, nitrogen adsorption–desorption and scanning electron microscopy. The investigations revealed an influence of the silica source on the mesoporous structure, as reflected by a higher long-range order for the pores in MCM-41 spheres prepared from Kromasil silica. Surface modification is accompanied by a reduction of the surface area, pore diameter and pore volume of the MCM-41 materials, whereas the spherical morphology of the spheres is retained. The degree of grafting and cross-linking of the alkylsilanes was determined by ²⁹Si NMR spectroscopy. A higher degree of alkyl chain grafting was observed for the solvent extracted MCM-41 spheres and for samples prepared via surface polymerization.FTIR and ¹³C NMR spectroscopies were employed to study the conformational behaviour and mobility of the grafted octadecyl chains. The conformational order was found to strongly depend on the history of the MCM-41 supports (calcination, solvent extraction) and on the actual surface modification procedure. In general, a lower conformational order was observed for the present mesoporous alkyl modified silica spheres as compared to conventional C₁₈ modified silica gels which is mainly attributed to the lower surface coverage.     

Preparation and performances of mesoporous TiO2 film photocatalyst supported on stainless steel

Mesoporous TiO₂ film photocatalysts supported on stainless steel substrates were prepared using the sol–gel method with Ti(OC₄H₉)₄ as a precursor and poly ethylene glycol (PEG) as a structure-directing agent. Mesoporous TiO₂ film with a pore diameter of about 15 nm was obtained with the addition of PEG (molecular WEIGHT =400). The pore diameter of TiO₂film was varied with molecular weight of PEG additive. The structure-directing process was also discussed. Mesoscopically ordered inorganic/polymer composites were believed to form during the process. Compared to conventional TiO₂ film photocatalyst, the mesoporous TiO₂ film showed a good performance for the photo degradation of rhodamine B (RB) solution irradiated with UV light of 365 nm. The photo degradation constant of rhodamine B for mesoporous TiO₂ film photocatalyst can arrive at 22 times of that for conventional TiO₂ film photocatalyst. Also an excellent performance for the degradation of gaseous formaldehyde with mesoporous film photocatalyst was obtained. The photo degradation rate of gaseous formaldehyde for mesoporous TiO₂ film photocatalyst can arrive at six times of that for conventional TiO₂ film photocatalyst.     

中孔碳负载Pt催化剂用于抗氧剂7PPD合成反应

以纳米氧化锌为模板剂,酚醛树脂为碳源,通过硬模板法制备了中孔碳,并以其为载体制备了Pt/MC催化剂,通过BET、SEM、ICP、TEM等表征手段对中孔碳及其负载的Pt/MC催化剂进行表征。结果表明,可以通过模板剂有效调控中孔碳的比表面积和孔结构。将制备的Pt/MC催化剂用于抗氧剂7PPD合成反应,对比普通Pt/AC催化剂,p-ADPA的转化率由97.5%提高至100%,7PPD选择性由94.5%提高至99.5%,催化剂的稳定性明显提高。通过CO化学吸附、ICP、BET等对新鲜和使用十次后的催化剂进行表征,结果表明,催化剂载体的孔结构是影响催化剂稳定性的重要因素,平均孔径较小时,7PPD等大分子尺寸的分子容易堵塞孔道;平均孔径较大时,孔壁较薄,催化剂使用过程中容易磨损,活性组分流失。     

3D-Printed Poly(acrylic acid–vinylimidazole) Ionic Polymer Metal Composite Actuators

Ionic polymer–metal composites (IPMC)—constructed using an ionic polymer sandwiched between metal electrodes—have shown great potential for the fabrication of soft actuators. IPMC architectures have many advantages including low actuation voltage, fast response, basic control, and relatively light weight. Poly(acrylic acid) (PAA)-based ion exchange membranes are of particular interest for IPMC devices due to their large ion exchange capacity and ease of preparation; however, they suffer from relatively weak mechanical strength. Here, PAA-based soft actuators are synthesized with enhanced mechanical properties and proton conductivity through the incorporation of hydrogen bonding interactions with imidazolium groups via copolymerization with 1-vinylimidazole. In addition to examining the impact of composition on physiochemical (swelling, glass transition, decomposition, Young's modulus, etc.) and electrochemical (specific capacitance) properties, an additive manufacturing process, digital light projection (DLP), is utilized to fabricate complex geometries demonstrating the potential for the fabrication of IPMC devices with complex actuation modalities. Planar DLP 3D-printed IPMC actuators of varied polymer compositions are fabricated with activated carbon and copper electrodes, and their actuation performance is evaluated in air, where large bending deformation is observed (14°–37°).