The self-assembly of gold nanoparticles in large-pore ordered mesoporous carbons

Simple encapsulation of 3 nm gold nanoparticles in ordered mesoporous carbon with large pores of 17 nm and thick pore walls of 16 nm was achieved by a metal-ligand coordination assisted-self-assembly approach.Polystyrene-block-polyethylene-oxide (PS-b-PEO) diblock copolymer with a large molecular weight of the PS chain and mercaptopropyltrimethoxysilane were used as the template and the metal ligand,respectively.Small-angle X-ray scattering,X-ray diffraction,transmission electron microscopy,and X-ray photoelectron spectroscopy showed that monodispersed aggregation-free gold nanoparticles approximately 3 nm in size were partially embedded in the large open pore structure of the ordered mesoporous carbon.The strong coordination between the gold species and the mercapto groups and the thick porous walls increased the dispersion of the gold nanoparticles and essentially inhibited particle aggregation at 600 ℃.The gold nanoparticles in the ordered mesoporous carbon are active and stable in the reduction of nitroarenes involving bulky molecules using sodium borohydride as a reducing agent under ambient conditions (30 ℃) in water.The large interconnected pore structure facilitates the mass transfer of bulky molecules.     

Pore structure and graphitic surface nature of ordered mesoporous carbons probed by low-pressure nitrogen adsorption

Ordered mesoporous carbons (OMCs) were produced by pyrolysis of sucrose adsorbed in two different silica matrices (MCM-48 and SBA-15), followed by dissolution of the matrix in hydrofluoric acid. Subsequently, some of these OMCs were heat-treated at temperatures of up to 1600 °C. The OMC pore structure was studied by low-pressure nitrogen adsorption. Information on the graphitic order of the surface of the mesopore walls was also obtained from the nitrogen adsorption data. These results were correlated to the order of the graphene layers at the outer surface, which was studied by X-ray photoelectron spectroscopy (XPS).

The OMCs were predominantly mesoporous, but they also contained micropores. For OMCs produced in an SBA-15 matrix, the micropore volume decreased upon heating. After heating to 1600 °C, nearly all micropores had disappeared. Furthermore, upon heating the width of the mesopores increased from 35 to 50 Å. All these changes can be explained by a shrinking of the OMC framework upon heating. A different behavior was found for OMCs derived from MCM-48. Upon heating these materials at increasingly high temperatures, the width of the mesopores first decreased, and for temperatures above 1100 °C it increased again. For all OMCs studied the graphitic order of the mesopores and the order of the graphene layers at the outer surface increased upon heating. For a given temperature, the graphitic surface order of OMCs derived from SBA-15 and MCM-48 was similar.     

CO2 capture by adsorption with nitrogen enriched carbons

The success of CO₂ capture with solid sorbents is dependent on the development of a low cost sorbent with high CO₂ selectivity and adsorption capacity. Immobilised amines are expected to offer the benefits of liquid amines in the typical absorption process, with the added advantages that solids are easy to handle and that they do not give rise to corrosion problems. In this work, different alkylamines were evaluated as a potential source of basic sites for CO₂ capture, and a commercial activated carbon was used as a preliminary support in order to study the effect of the impregnation. The amine coating increased the basicity and nitrogen content of the carbon. However, it drastically reduced the microporous volume of the activated carbon, which is chiefly responsible for CO₂ physisorption, thus decreasing the capacity of raw carbon at room temperature.     

Surface chemistry of ordered mesoporous carbons

Ordered mesoporous carbons (OMC) were produced by pyrolysis of hydrocarbons adsorbed in two different silica matrices (MCM-48 and SBA-15), followed by dissolution of the matrix in either hydrofluoric acid or sodium hydroxide. Some carbons were subsequently heat treated at temperatures of up to 1600 °C. The chemistry of the external surface was studied by X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectroscopy (SIMS). Information on the graphitic order of the surface of the mesopores was obtained from low-pressure nitrogen adsorption data. The external and internal surface of the OMC has a polyaromatic, graphite-like character. This character increases considerably with increasing pyrolysis and/or post-pyrolysis temperature, as expected. According to the XPS and the nitrogen adsorption data, this increase was especially pronounced for temperatures above 1100 °C. In spite of the different pore structures, only small differences in the polyaromatic character were found for OMC synthesised either in a MCM-48 or in a SBA-15 matrix. Differences exist for the non-carbon elements. When hydrofluoric acid is used for dissolution of the silica matrix, organic fluorine compounds are formed. Their concentration is higher when a MCM-48 matrix as opposed to a SBA-15 matrix was used. Dissolution of the silica matrix in sodium hydroxide yielded a less contaminated OMC as compared to dissolution in hydrofluoric acid.     

MnO nanoparticles with textured porosity supported on mesoporous carbons

Ordered mesoporous carbons doped with MnO nanoparticles (DCs) have been prepared by direct carbonization of a composite of a reverse copolymer-low-molecular-weight phenolic resin dipped in aqueous Mn(NO₃)₂ solution. The microstructure of the DCs was analyzed by the small-angle X-ray scattering, X-ray diffraction, nitrogen adsorption isotherms and transmission electron microscopy. The results showed that the size of MnO nanoparticles dispersed on the surface of DCs was about 10–50 nm and the pore size of DCs could be tailored from 4.9 to 9.3 nm as the amount of phenolic resin varied. Moreover, the structure of the DCs obtained was stripe-like at low amount of phenolic resin. However, the structure of the DCs becomes disordered as the amount of phenolic resin increases. Because of its nontoxic nature and cost-effective synthesis, these DCs exhibit properties that are needed for an environment-friendly catalyst and electrode materials.     

高比表面磁性有序介孔炭的合成及对亚甲基蓝的吸附性能

具有高比表面积、大孔容的铁磁性有序介孔炭(Fe/OMCs)对含染料废水的处理提供了一种简单有效的方法。采用苯酚树脂作炭源,三嵌段共聚物F127为模板剂,正硅酸乙酯为硅前驱体,硝酸铁为磁源,通过软模路线合成了Fe/OMCs。利用X射线衍射仪(XRD),氮气吸附仪,透射电镜(TEM)和综合物性测试仪研究了硝酸铁加入量对Fe/OMCs的相态、孔结构参数和磁性的影响;并以亚甲基蓝(MB)为染料探针分子,研究了Fe/OMCs对MB的吸附行为。结果表明材料有序性、比表面和孔容随着硝酸铁加入量的增加而降低,而饱和磁化强度明显增强。Fe/OMCs对MB有快速吸附能力,其行为符合Sips吸附方程。     

Quenched solid density functional theory method for characterization of mesoporous carbons by nitrogen adsorption

Quenched solid density functional theory (QSDFT) model for characterization of mesoporous carbons using nitrogen adsorption is extended to cylindrical and spherical pore geometries. The kernels of theoretical isotherms in the range from 0.4 to 50 nm are constructed accounting for different possible variations of the pore shapes in micropore and mesopore regions. The results of QSDFT method are illustrated with experimental data on adsorption on novel CMK-3 and 3DOm carbons. The proposed method is recommended for pore size distribution calculations for micro–mesoporous carbons obtained through various templating mechanisms.     

Avoiding structure degradation during activation of ordered mesoporous carbons

Hierarchical micro–mesoporous carbons with high porosity development and ordered structure were prepared. The innovative proposal consists in developing microporosity in ordered mesoporous carbon by chemical activation in template presence in order to minimize the structural damage. Thus, we have directly carried out the chemical activation of a mesoporous carbon/silica composite with KOH. The effect on mesoporous ordered structure of both KOH/carbon ratio and activation temperature has been studied. Following chemical activation the specific surface area is increased from 341 to 1757 m²/g and the micropore volume becomes almost six times larger than initial value. Although a slight widening of the mesopore distribution and an increase in the mesopore volume has been observed during activation, TEM and XRD results reveal an excellent conservation of the ordered mesoporous structure during activation even at conditions well above the limits that a CMK-3 type carbon can resist.     

Superior electric double layer capacitors using ordered mesoporous carbons

This paper reports for the first time superior electric double layer capacitive properties of ordered mesoporous carbon (OMCs) with varying ordered pore symmetries and mesopore structure. Compared to commercially used activated carbon electrode, Maxsorb, these OMC carbons have superior capacitive behavior, power output and high-frequency performance in EDLCs due to the unique structure of their mesopore network, which is more favorable for fast ionic transport than the pore networks in disordered microporous carbons. As evidenced by N₂ sorption, cyclic voltammetry and frequency response measurements, OMC carbons with large mesopores, and especially with 2-D pore symmetry, show superior capacitive behaviors (exhibiting a high capacitance of over 180 F/g even at very high sweep rate of 50 mV/s, as compared to much reduced capacitance of 73 F/g for Maxsorb at the same sweep rate). OMC carbons can provide much higher power density while still maintaining good energy density. OMC carbons demonstrate excellent high-frequency performances due to its higher surface area in pores larger than 3 nm. Such ordered mesoporous carbons (OMCs) offer a great potential in EDLC capacitors, particularly for applications where high power output and good high-frequency capacitive performances are required.     

Adsorption of vitamin B12 on ordered mesoporous carbons coated with PMMA

Ordered mesoporous carbons CMK-3 and CMK-1 were prepared from SBA-15 and MCM-48 materials with pore diameters 3.9 nm and 2.7 nm, respectively. When both mesoporous carbons were coated with about 10 wt.% poly(methyl methacrylate) (PMMA), the pore diameters decreased from 3.9 nm to 3.4 nm for CMK-3 and from 2.7 nm to 2.5 nm for CMK-1. These mesoporous carbons containing about 10 wt.% PMMA were studied as adsorbents of Vitamin B 12 (VB12) from water solutions, and their performances were compared with that of pristine CMK-3, CMK-1. Compared with CMK-1, CMK-3 showed higher vitamin B12 adsorption due to a larger mesopore volume, a higher BET surface and a larger pore diameter. After coated with PMMA, both mesoporous carbons showed higher adsorption capacity than pristine materials. The adsorption properties were influenced by the pore structure and surface properties of mesoporous carbons.     

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.     

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.     

有序介孔碳对低浓度气相萘的吸附特性分析

对3种常见有序介孔碳（OMCs）吸附脱除典型气相多环芳烃--萘进行了研究。分别采用吸附等温线模型（Langmuir、Freundlich、Sips）和恒定浓度波动力学模型对吸附等温线和穿透曲进行拟合分析。采用程序升温脱附法通过失重曲线分析了吸附剂的再生性能。结果表明：Langmuir模型和Sips模型能很好地描述低浓度气相萘在OMCs上的静态吸附行为（R² > 99%）,吸附量呈CMK-5 > CMK-3 > FDU-15排列。恒定浓度波动力学模型具有较高的拟合度,介孔促使3种吸附剂对萘分子具有较高的吸附扩散系数。具有微通孔结构的CMK-5和FDU-15表现出更好的再生性能。综合吸脱附动力学分析,CMK-5在3种吸附剂中表现出更好的应用潜能。     

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.