溶胶凝胶法多孔炭材料的制备及其表征

以十六烷基三甲基溴化胺(CTAB)稳定过的商业硅溶胶为模板硅源、蔗糖为炭前体、运用溶胶凝胶法制备了多孔炭材料。并采用低温N2等温吸脱附、X射线衍射等对材料的结构进行了测试与表征。结果表明:CTAB的加入使所得的多孔炭孔径分布更加集中,由于炭化温度较低,所得的炭材料仍为无定形结构。     

The characterization of porous electrodes by impedance measurements

Impedances of a gold-powder and a Raney-gold electrode were measured over a wide frequency range, and were found to be very similar to those of cylindrical pore of finite depth. The simulation calculation for sphere-packed electrode impedance was performed. It was observed that even though each sphere-layer shows the impedance related to an occluded pore-shape, the overall impedance is similar to that of a cylindrical pore electrode. When the penetration depth approaches the pore depth, the shape of the pore wall has little influence on the impedance. Thus, impedance measurement techniques can be applied to porous electrodes of more intricate pore-texture, and evaluate the radius, depth and pore number of its equivalent cylindrical pore electrode. These values determined for a Raney-gold electrode are in very good agreement with those determined by other methods. The case of a more realistic fuel cell electrode such as Raney-nickel with a metal-electrolyte-gas system, was also tentatively examined.     

铸型炭化法制备多孔炭材料的研究进展

铸型炭化法开辟了多孔炭材料制备研究的一个全新领域,近年来已成为能够最有效控制多孔炭材料结构的方法。本文概述了传统方法制备多孔炭材料的不足,重点综述了以硅胶、黏土、沸石和中孔硅分子筛为铸型制备多孔炭材料的最新研究进展,展望了铸型炭的应用前景,最后指出了铸型炭化法在制备多孔炭领域尚待开展的研究工作。     

Usefulness of CO2 adsorption at 273 K for the characterization of porous carbons

Characterization of microporous solids (activated carbons and carbon molecular sieves) has been carried out by N₂ (subatmospheric pressures) and CO₂ adsorption (at subatmospheric and high pressures) at 77 and 273 K, respectively. Because the relative fugacity range covered by our CO₂ study is similar to the relative pressure range covered with N₂, a suitable comparison of both adsorptives can be made. The results of such comparison show that both adsorptives give the same micropore size distribution (MPSD) for open porosity activated carbons. This observation confirms that the adsorption mechanism of both adsorptives is similar. However, carbon molecular sieves, with very narrow microporosity, cannot be characterized by N₂ at 77 K, due to the existence of diffusional problems. This is also extensive to many other carbon materials, such as carbon fibers and activated carbons with low degree of activation. As a consequence, in this type of samples, N₂ adsorption at 77 K is useless to determine neither the micropore volumes of the narrowest porosity nor their micropore size distributions (MPSD). In this work, the usefulness of CO₂ for the characterization of carbon molecular sieves and activated carbons with different activation degrees is demonstrated. In addition, examples of applications that cannot be explained from N₂ adsorption but yes by CO₂ are presented. As a result, we strongly encourage the use of CO₂ (i.e. at 273 K) as a complement to N₂ adsorption at 77 K.     

Preparation and characterization of porous carbons from PAN-based preoxidized cloth by KOH activation

Porous carbons (PCs) were prepared from PAN-based preoxidized cloth with potassium hydroxide (KOH) as active reagent by the chemical activation method. The PCs have been systematically studied by the adsorptions of nitrogen, benzene and iodine. It has been found that the process parameters such as weight ratio of KOH to the starting material, activation temperature and activation time are crucial for preparing high quality PCs. A series of PCs with high BET surface area and well-developed porous structure in which micropores are dominant were obtained with less KOH and shorter activation time in comparison to the traditional methods. The optimum conditions for preparing PCs with high BET surface area from PAN-based preoxidized cloth were given, and the relationships between pore structure and adsorption property of PCs were explored.     

溶胶-凝胶法碳源对多孔炭材料孔隙结构的影响

以正硅酸乙酯(TEOS)为模板硅源,β-环状糊精和可溶性淀粉分别为碳前驱体,运用溶胶-凝胶法制备了多孔炭材料。利用低温N2等温吸脱附、X射线衍射、高倍扫描电子显微镜等对所得炭材料的结构进行了测试与表征,结果表明,β-环糊精为碳源的样品主要孔径分布在2~3 nm;以可溶性淀粉为碳源的样品孔径呈双峰分布,即孔径集中在3.7 nm和5~20 nm,但由于炭化温度较低,所得的炭材料仍为无定形结构。     

Chemically activated fungi-based porous carbons for hydrogen storage

A set of porous carbons has been prepared by chemical activation of various fungi-based chars with KOH. The resulting carbon materials have high surface areas (1600–2500 m²/g) and pore volumes (0.80–1.56 cm³/g), regardless of the char precursors. The porosities mainly derived from micropores in activated carbons strongly depend on the activation parameters (temperature and KOH amount). All activated carbons have uniform micropores with pore size of 0.8–0.9 nm, but some have a second set of micropores (1.3–1.4 nm pore size), further broadened to 1.9–2.1 nm as a result of increasing either the activation temperature to 750 °C or KOH/char mass ratio to 5/1. These fungi-based porous carbons achieve an excellent H₂ uptake of up to 2.4 wt% at 1 bar and −196 °C, being in agreement with results from other porous carbonaceous adsorbents reported in the literature. At high pressure (ca. 35 bar), the saturated H₂ uptake reaches 4.2–4.7 wt% at −196 °C for these fungi-based porous carbons. The results imply a great potential of these fungi-based porous carbons as H₂ on-board storage media.     

Designed synthesis of porous carbons for the separation of light hydrocarbons

The separation of light hydrocarbon mixtures (C₁-C₃) generated from petrochemical industry is vital and challenging process for obtaining valuable pure chemical feedstocks. In comparison to the energy intensive conventional separation technologies (cryogenic distillation, absorption and hydrogenation), the adsorptive separation is considered as a low energy cost and high efficiency process. Porous carbons have been demonstrated as excellent adsorbents for the separation of light hydrocarbons, owing to their designable structure and tailorable properties. This review summarizes the recent advances of using porous carbons as adsorbents for the separation of light hydrocarbons, including methane/nitrogen, methane/alkane, methane/carbon dioxide, ethylene/ethane and propylene/propane. We discuss the separation mechanisms and highlight the material features including pore structure, surface chemistry and target molecular properties that determine the separation performance. Furthermore, the challenges and development direction associated with carbonaceous adsorbents for light hydrocarbon separation are discussed, meanwhile the guidelines for the design of porous carbons are proposed.     

Green synthesis of templated porous carbons

Porous carbon materials such as activated carbons are widely used industrially for the purposes of purification, decolourization, deodorization, and gas storage, among others. Routes for the synthesis of these materials employing templates have increasingly attracted attention due to the ease of manipulating the characteristics of the final product. In the present work, a simple synthesis method was applied for the production of highly porous carbon materials using commercial sugar as the carbon source, Aerosil silica as a template, and deionized water. The synthesis procedure was as follows: (I) Gel formation; (II) carbonization of the gels; (III) removal of the silica template; (IV) activation. The materials were characterized by N₂ and CO₂ physisorption, Raman spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy, and thermogravimetric analysis. The aging time had an important influence on the specific area and porosity of the material, with physisorption analysis revealing a high specific area and pore volume. The activation procedures further contributed to significantly increasing the specific area (up to 1158 m² g⁻¹) and pore volume (up to 1.65 cm³ g⁻¹). The X-ray diffractograms and Raman spectra identified the formation of semi-crystalline structures in the material, with the presence of a random distribution of graphite and graphene oxide, in addition to amorphous carbon. FTIR analysis showed the presence of bands corresponding to aromatic groups. The results demonstrated that it was possible to obtain materials with excellent potential for use in different industrial sectors using simple raw materials and a technique that is easy to reproduce.     

偏氯乙烯共聚物/纳米水滑石复合材料及多孔炭的制备与表征

采用原位悬浮聚合和熔融加工制备了不同纳米水滑石含量的偏氯乙烯-丙烯酸甲酯(VDC-MA)共聚物/纳米水滑石复合材料,并通过高温炭化和模板消除得到多孔炭材料。采用电镜、X射线衍射、N₂吸脱附法表征了复合材料和多孔炭的结构。结果表明,纳米水滑石含量≤6.25%（质量）时,纳米水滑石基本以初级粒子均匀分散在VDC-MA共聚物基体中,并在炭化过程中转化为金属氧化物;金属氧化物可经酸洗去除,起到模板致孔作用;同时VDC-MA共聚物炭化过程形成大量微孔,因此得到的多孔炭具有微孔和中孔分布。当炭化温度较低时(600～700℃)相似文献   

Hierarchical porous carbons with high performance for supercapacitor electrodes

A series of hierarchical porous carbons (HPCs) were prepared by a combination of self-assembly and chemical activation. Pore-structure analysis shows that micropores can be generated within the mesopore wall of mesoporous carbon in a controllable manner during activation. As evidenced by cyclic voltammetry, galvanostatic charge/discharge cyclings and frequency response measurements, HPCs show superior capacitive performances to hard-templated ordered mesoporous carbons, which can be attributed to the generated pore surfaces that play most important role in the formation of double-layer capacitance and to their unique hierarchical porous structure that favors the fast diffusion of electrolyte ions into the pores. Of special interest is the fact that HPCs maintains 180 F/g at high-frequency of 1 Hz.     

A new analysis method for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements

A new analysis method has been developed for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements. The method is based on a molecular model for the adsorption of nitrogen in porous carbon. It allows, for the first time, the distribution of pore sizes to be determined over both the micropore and mesopore size ranges using a single analysis method. In addition to carbons, this method is also applicable to a range of adsorbents, such as silicas and aluminas.     

S-enriched porous polymer derived N-doped porous carbons for electrochemical energy storage and conversion

Porous polymers have been recently recognized as one of the most important precursors for fabrication of heteroatom-doped porous carbons due to the intrinsic porous structure, easy available heteroatom-containing monomers and versatile polymerization methods. However, the heteroatom elements in as-produced porous carbons are quite relied on monomers. So far, the manipulating of heteroatom in porous polymer derived porous carbons are still very rare and challenge. In this work, a sulfur-enriched porous polymer, which was prepared from a diacetylene-linked porous polymer, was used as precursor to prepare S-doped and/or N-doped porous carbons under nitrogen and/or ammonia atmospheres. Remarkably, S content can sharply decrease from 36.3% to 0.05% after ammonia treatment. The N content and specific surface area of as-fabricated porous carbons can reach up to 1.32% and 1508 m²·g⁻¹, respectively. As the electrode materials for electrical double-layer capacitors, as-fabricated porous carbons exhibit high specific capacitance of up to 431.6 F·g⁻¹ at 5 mV·s⁻¹ and excellent cycling stability of 99.74% capacitance retention after 3000 cycles at 100 mV·s⁻¹. Furthermore, as the electrochemical catalysts for oxygen reduction reaction, as-fabricated porous carbons presented ultralow half-wave-potential of 0.78 V versus RHE. This work not only offers a new strategy for manipulating S and N doping features for the porous carbons derived from S-containing porous polymers, but also paves the way for the structure-performance interrelationship study of heteroatoms co-doped porous carbon for energy applications.     

Preparation and performance of anatase-loaded porous carbons for water purification

Fine particles of photoactive anatase-type TiO₂ were loaded on activated carbon and carbon spheres through the hydrolysis of titanium oxysulfate under autogenous hydrothermal conditions. Their photoactivity and adsorptivity were evaluated separately by the measurements of relative concentration of methylene blue (MB) and iminoctadine triacetate (IT) remained in the solution either in the dark or under UV irradiation. Activated carbon could adsorb a large amount of MB but only a small amount of IT, and carbon spheres could adsorb only a small amount of MB. Loading of anatase under hydrothermal conditions was found to occur preferentially at the entrance of pores on the surface of substrate carbon in the beginning of deposition and to result in the reduction of specific surface area and consequently of the adsorption rate of MB. Further hydrothermal treatment was found to give homogeneous coverage of the surface of activated carbon by anatase fine particles. By UV irradiation after the saturation of adsorption in the dark, a marked decrease in concentration of MB and IT was observed, which recovered a high adsorptivity of activated carbon. Through repetitive measurements of concentration decrease in the solution in the dark and under UV irradiation, it was proved that MB and IT, which were adsorbed in the dark, could be decomposed under UV irradiation.     

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.     

An approximation method for the effectiveness factor in porous catalysts

An efficient method for computing approximate value of the effectiveness factor is presented. The method is developed for an arbitrary rate expression and for three representative catalyst shapes, namely, an infinite slab, an infinite cylinder and a sphere. In the method, two new asymptotic expansions for small and large Thiele moduli are developed and joined together at an intermediate value of the Thiele modulus, which can be calculated by a simple equation. The approximation is highly accurate for small and large Thiele moduli, and it has small or negligible errors for intermediate values of the Thiele modulus. As demonstrated with examples, the approximation method is fast, straightforward and is a dependable alternative to numerical methods for computing exact values of the effectiveness factor.     

溶胶凝胶法N,N-二甲基甲酰胺对多孔炭孔隙结构的影响

以正硅酸乙酯(TEOS)为模板硅源,蔗糖为碳前体,添加N,N-二甲基甲酰胺(DMF)作为控制干燥化学助剂(DCCA),运用溶胶凝胶(Sol-Gel)法制备多孔炭材料。通过SEM和低温N2等温吸脱附等手段对材料的结构进行了测试与表征,结果表明:在优选工艺条件后,成功地制得了无龟裂混合干凝胶,溶硅去模后多孔炭材料孔径主要集中分布在2～7nm。     

Phenol adsorption on porous and non-porous carbons

Phenol physisorption on a series of porous and non-porous amorphous carbons was studied at 298 K. Grand Canonical Monte Carlo computer simulations were performed to simulate phenol adsorption from the gas phase. Phenol is adsorbed in a solid-like state within the pores and there is no well-developed multilayer regime. The ‘t’ plot method was adapted to phenol adsorption and the results obtained are in agreement with the model solids employed. The simulated adsorption isotherms were compared with experimental results obtained for adsorption from aqueous solutions of phenol. BET surface areas were calculated. Other characteristics of the adsorption system analyzed were: adsorption energy distribution functions, density profiles, distribution of molecules according to gas-solid energy, and local isotherms.     

Sulfur-doped porous carbons: Synthesis and applications

Heteroatom doping of carbon materials may become the “Next Big Thing” in materials science further enhancing research concerning carbon nanostructures. In particular, the S-doped porous carbons have gained a great deal of attention in the last few years. They are already proven to be versatile functional materials with a wide range of potential applications, including heterogeneous catalysis, sorption, as well as in the areas of energy conversion and storage. To date, a few approaches have been developed to intrinsically blend sulfur into the carbon matrix. Yet there is still a need to design new porous structures with controllable porosity and well defined chemical status of sulfur doped into the carbon matrix. In this review, we summarize recent reports on the preparation of S-doped carbons, with special emphasis on porous carbons with intrinsically doped sulfur. The effect of S-doping on the properties determining applications is delineated. Special attention is paid to differentiate between elemental sulfur impregnation, intercalation, surface functionalization and S bulk doping of porous carbons. To this end, synthesis and applications of S-impregnated, S-functionalized and S-intercalated carbons are shortly discussed before the intrinsically S-doped carbons are presented in detail. The importance of the sulfide –C–S–C– system for the properties of S-doped carbon is stressed. At the very end, Se-doped carbons are shortly presented as a promising next generation of chalcogen-doped carbon.