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.     

共聚物为模板制备草莓状二氧化硅空心球

成功地通过三嵌段共聚物聚乙二醇-聚丙二醇-聚乙二醇(PEG-PPG-PEG)为模板,正辛烷为壳材料来制备介孔外壳的草莓状二氧化硅空心球。其中正硅酸乙酯(TEOS)作为二氧化硅的前驱体。通过改变反应参数,我们发现当将反应最终溶液先室温下静置24h然后加热到较高温度12h可以获得草莓状结构。产物的表面形貌通过扫描电子显微镜(SEM)来分析;透射电子显微镜(TEM)表明空心球的平均直径为800nm,外壳为20nm;多孔性分析通过氮气吸附-解附法来测量,同时用Brunauer-Emmett-Tell-er(BET)的方法来测孔径大小。另外我们提出了二氧化硅的形成机理。     

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.     

Novel Two-Step Synthesis of Controlled Size and Shape Platinum Nanoparticles Encapsulated in Mesoporous Silica

Uniform shape and size platinum nanoparticles encapsulated in mesoporous silica (SBA-15) were prepared in the same solution by a novel two-step method. Platinum nanoparticles were prepared in aqueous solution of K₂PtCl₄, the reduction was carried out by bubbling hydrogen, the capping material was tri-block poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. The mesoporous silica was synthesized using the same copolymer as template from tetraethyl orthosilicate by hydrolysis in acidic conditions. The Pt-nanoparticles-in-mesoporous-silica system was characterized by a combination of low-angle powder X-ray diffraction, transmission electron microscopy and N₂ porosimetry. The platinum nanoparticles are encapsulated in the mesopores and retained their size and morphology. It appears that this hybrid material should be a superior three-dimensional high-surface-area catalyst for selective platinum-catalyzed reactions.     

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.     

CTAB含量对介孔空心微球结构的影响

介孔空心微球具有大的空心腔体和壳体上小的介孔结构,使得介孔空心微球结构材料作为一种新型功能材料有着广阔的应用前景。本文使用喷雾干燥法合成介孔空心微球,以CTAB作为致孔剂,TEOS作为硅源,系统研究了不同CTAB含量下产物的结构,发现n（CTAB）/n（TEOS）=0.2时,产物颗粒具有较好的空心结构,颗粒外壳上的介孔有序度高,当n（CTAB）/n（TEOS）的值增加时,产物中的空心颗粒含量减小,而且壳上的介孔的有序度下降,介孔孔壁厚度也减小。     

SBA-15介观相形成过程的耗散粒子动力学模拟

采用耗散粒子动力学方法（dissipative particle dynamics,DPD）,以介孔分子筛SBA-15的合成原料P123/TEOS/H₂O为研究体系,模拟了P123/TEOS超分子自组装行为,及剪切力作用下介孔分子筛SBA-15六角介观相的形成过程。结果表明：在水溶液中,P123与TEOS两相能够发生协同作用自组装形成超分子聚集体（胶束）,该胶束由疏水的PPO球核、亲水的PEO球壳以及聚集包裹在P123外部的TEOS组成;引入稳恒剪切力后,P123/TEOS超分子聚集体则会逐渐转变成规整的六角结构,并最终形成SBA-15六角介观相,这与实际材料的TEM电镜图片相吻合。可以说,DPD模拟方法是一个研究有序介孔分子筛SBA-15形成机理的有效手段,可为实验合成提供介观层面上的重要信息。此外,还拓展了DPD模拟在超分子自组装介观尺度研究方面的新应用。     

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.     

液相法合成ZrO2介孔材料

以工业化试剂聚氧丙烯聚氧乙烯嵌段型聚醚P123为模板剂,ZrOCl2为锆源,在不引入SO4^2-或PO4^3-进入骨架的情况下,利用溶胶-凝胶法合成了比表面积为156 m^2/g,孔径分布窄,孔径可调的ZrO2介孔材料.结果表明：乙酰丙酮的加入对合成ZrO2介孔材料有不利影响,会破坏孔道结构;陈化时间和搅拌温度的改变可以调节介孔ZrO2的孔径,影响孔道构型,而搅拌温度过高将不能形成介孔结构;提高焙烧温度,使孔径增大,比表面积下降,但孔道构型基本没有发生变化,仍为介孔结构.     

Fabrication and Pore Size Control of Large-Pore Mesoporous Silica Particles through a Solvent Evaporation Process

Large-pore mesoporous silica particles were synthesized through a solvent evaporation process using hydrophobic fumed silica particles and tetraethyl orthosilicate (TEOS) as silica sources. The solvent evaporation of an ethanol solution of fumed silica particles, TEOS, HCl and triblock copolymer (F127) resulted in mesoporous silica particles with pores with sizes of about 7 nm. In addition, the interplanar spacing of the mesoporous silica particles can be controlled by changing the solvent evaporation temperatures.     

The effect of silica template structure on the pore structure of mesoporous carbons

We have synthesized two kinds of mesoporous carbons using a spherical silica sol (SMC1 carbon) and an elongated silica sol (SMC3 carbon) as templates. Nitrogen isotherms and electrochemical experiments were performed to investigate the effect of the silica template structure on the pore structure of the resulting mesoporous carbons. When carbons produced using the same silica to resorcinol molar ratio were compared, both nitrogen isotherms and electrochemical studies revealed that the SMC3 carbons exhibit simpler pore connectivity than SMC1 carbons.     

Pore size control of wormholelike mesoporous carbons

A simple and efficient method to tailor the pore size of wormholelike mesoporous carbons (WMCs) has been developed by adding a proper amount of hydrofluoric acid (HF) during the sol-gel process of tetraethyl orthosilicate (TEOS). It was found that the pore size increased obviously from 3.1 to 8.5 nm when increasing HF/TEOS molar ratio from 0 to 1/7. Brunauer-Emmett-Teller surface area decreased accordingly. In addition, mesopore volume of WMCs basically kept unvaried due to their identical silica template amount.     

中孔炭材料的制备及吸附性能的研究

以正硅酸乙酯为模板硅源，酚醛树脂为炭前驱体，运用模板法制备了中孔炭材料。并用红外光谱（FT—IR）、扫描电镜（SEM）、低温N2自动吸附、甲醛和VB12饱和吸附等对样品形貌、孔结构和吸附性能进行了研究。结果表明：制备的炭材料孔径集中分布在2-7nm左右，且中孔孔隙率达到74．6％，比表面积达到1012m^2／g；材料对VB12大分子有较好的吸附性能。表明通过控制正硅酸乙酯的水解条件能制备孔径集中的中孔炭材料。     

Synthesis and fractionated crystallization of organic-inorganic hybrid composite materials from an amphiphilic polyethylene-block-poly(ethylene oxide) diblock copolymer

Mesostructurally ordered inorganic-organic hybrid composite materials were successfully synthesized by utilizing a low-molecular-weight amphiphilic polyethylene-block-poly(ethylene oxide) (PE-PEO) diblock copolymer as the directing agent. The hybrid composites were formed via the sol-gel reaction of inorganic precursor tetraethoxysilane (TEOS) in an acidic ethanol/water solution with various amounts of PE-PEO. In these composite materials, the hydrophobic PE block of the PE-PEO copolymer forms separate microphase on the nanoscales within the rigid matrix of silica network. The crystallization of the PE block is strictly restricted within the microphase by the rigid silica matrix and takes place through homogeneous nucleation under the nanoscale confinement environment.     

A simplified preparation of mesoporous carbon and the examination of the carbon accessibility for electric double layer formation

Mesoporous carbon was prepared from resol-type phenol-formaldehyde resin using mesoporous silica as template. By filling the resin into the pores of the template, followed by resin carbonization and template dissolution, mesoporous carbon preparation can be significantly simplified. Small-angle X-ray diffraction reflected the long-range ordering of the pores in the carbon. TEM and N₂-adsorption analysis showed that the carbon contained mesopores of different sizes and a high proportion of micropores. Electrochemical cyclic voltammetry was conducted in H₂SO₄ to examine the surface accessibility of the carbon for double layer formation. Microporous activated carbon, also from the resol resin, was prepared for comparison. Although the pore sizes are different, the double-layer capacitances per unit area for both carbons are similar at low potential sweep rates. However, the capacitance decline with the sweep rate was less significant for the mesoporous carbon. Upon gasification of the carbons to increase their surface area, the ultimate capacitance per unit carbon area was enhanced and the enhancement was slightly larger for the mesoporous carbon. It is suggested that the presence of mesopores has facilitated the electrolyte migration into carbon interior. A two-electrode capacitor assembled with the mesoporous carbon was shown to have a small resistance and still exhibited a capacitive behavior at high potential sweep rates.     

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。     

Synthesis of benzxazine-based nitrogen-doped mesoporous carbon spheres for methyl orange dye adsorption

In this work, nitrogen-doped mesoporous carbon spheres (NMCS) were synthesized through a hard template method by using benzoxazine resin as precursor and ordered mesoporous silica spheres as template. The obtained N-doped mesoporous carbons were amorphous spherical nanoparticles with worm-like mesoporous channels and possessed high surface area of 789 m²/g, large pore volume of 0.49 cm³/g and high nitrogen content of 3.50 wt.%. The adsorption capacity of methyl orange (MO) by NMCS could attain 352.1 mg/g at an optimal condition, while the adsorption capacity of MO by non-doped mesoporous carbon spheres (MCS) was 251.9 mg/g at the same condition. The adsorption process fitted the pseudo-second-order kinetic model and the Langmuir isotherm well. Thermodynamic analysis indicated that the removal of MO by NMCS was spontaneous, endothermic and feasible process. In addition, the adsorption capacity of regenerated adsorbent was 89.04% of the initial level after four regeneration cycles.     

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.     

Applications of Amine-functionalized Mesoporous Silica in Fine Chemical Synthesis

SBA-15 silica containing homogeneously distributed amine-functional groups and of fiber or platelet morphology was prepared through a modified co-condensation method using P123 copolymer as template under acidic condition. Synthetic factors which led to well-ordered mesoporous materials with high loadings of various amine groups were discussed. The resultant mesoporous materials were efficient base catalysts in Knoevenagel and Claisen–Schmidt addition reactions. The activities over SBA-15 materials with different amino-functional groups are compared. Moreover, the advantage of ordered large mesopores of SBA-15 in catalyzing liquid phase reactions was demonstrated, and the reaction rate could be further increased when SBA-15 was with platelet morphology and short mesochannels.     

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.