Macroporous carbon

The physical and chemical activation processes have been generally employed to prepare the porous carbons.18"35 However, the pore structures are not easily controlled by the activation processes and the size of the pores generated by the activation processes is limited to the micropore range only. Recently, much attention has been paid to the synthesis of meso/macroporous carbons with various pore structures and pore size distributions (PSD) by using various types of such inorganic templates as silica materials and zeolites.17,36 55... 

The meso/macroporous carbons have attracted much attention in their application as electrode materials in EDLCs, since the meso/macropores promote the formation of an effective doublelayer or the transfer of ions into the pores, resulting in the increases in the electrolyte wettability and the rate capability.67,68 In this regard, there has been considerable research targeted towards developing the synthetic methods of novel meso/macroporous carbons.17,36"55,69 72 Various types of such inorganic templates as silica materials and zeolites are widely used for the synthesis of the meso/macroporous carbons, since it was revealed17,36"55 that these inorganic templates contribute to the formation of the meso/macropores with various pore structures and broad PSD. 

Figure 1. Plots of differential pore volume against pore diameter calculated from the N2 gas adsorption isotherms obtained from meso/macroporous carbon specimens I (-0-), II (- -), and III (-A-) using Barrett-Joyner-Halenda (BJH) method. Reprinted with permission from G. -J. Lee and S. -I. Pyun, Carbon, 43 (2005) 1804. Copyright 2005, with permission from Elsevier.

Adsorption on macroporous carbons proceeds via multilayer formation in such a manner that the amount adsorbed increases gradually as the relative pressure increases, and then the multilayer build-up near the saturation vapor pressure may be abrupt. This unrestricted monolayer-multilayer adsorption gives rise to Type II and III isotherms. In this case, the adsorption and desorption... 

On the other hand, for the mesoporous carbons, the gas adsorption process changes with increasing relative pressure as follows first monolayer-multilayer adsorption on the pore surfaces, then capillary condensation in the mesopoies, and finally multilayer adsorption on the outer surfaces in sequence (Types IV and V isotherms). Therefore, the adsorption process for the mesoporous carbons is initially similar to that for the macroporous carbons, but at higher relative pressures the amount adsorbed rises very steeply due to the capillary condensation in the mesopoies. 

The present article first provided the brief overview of the synthetic methods of the porous carbons. In order to prepare the microporous carbons with high surface area, the physical/chemical activation methods have been widely used for a long time.18"35 Recently, the meso/macroporous carbons with various pore structures are prepared by templating methods by using various templates and changing sol-gel reaction conditions, e.g., pH, amount of template, and gelation temperature.17,36 55... 

In order to control the pore texture in carbon materials, blending of two kinds of carbon precursors, the one giving a relatively high carbonization yield and the other having a very low yield, was proposed and called polymer blend method [112], This idea gave certain success to prepare macroporous carbons from poly(urethane-imide) films prepared by blending poly(amide acid) and phenol-terminated polyurethane prepolymers [113]. By coupling this polymer blend method with... 

It should be noted that the t-plot analysis shows a very small amount of micropores in the sample studied, which is due to the use of the mesophase pitch as the carbon precursor. It is known that many precursors, e.g., sucrose and polyfurfuryl alcohol, infiltrate well siliceous templates but after carbonization give meso- or macroporous carbons with complementary microporosity. This is not the case for the mesophase pitch, which is used to synthesize carbon fibers that are nonporous materials. 

Kang S., Yu J. S., Kruk M. and Jaroniec M., Synthesis of an ordered macroporous carbon with 62 nm spherical pores that exhibit unique gas adsorption properties. Chem. Commun. (2002) pp. 1670-1671. 

Terzyk A.P, Rychlicki G., Empirical relationship describing energetics of adsorption at low coverages of macroporous carbons, J. Thermal Anal., 55 (1999) pp 1011-1020. 

It was stated, that macroporous carbons of plant origin show better properties in dynamic than in static conditions. It is cormected with relationship of quantity of macropores and diffusion rate. Greater differences in classsification are observed at lower equilibrium concentrations (0,1 and 0,01 mg/dm ) in static adsorption. Therefore direct factors of Freundlich s isotherms influencing adsorption capacities at different concentrations should be considered. It was stated that angle of slope, adsorption rate in static conditions, shape of breaktrough curves in dynamic conditions... 

Lai, C.-Z., Fierke, M.A., Stein, A., and Buhlmann, P. 2007. Ion-selective electrodes with three-dimensionally ordered macroporous carbon as the solid contact. Analytical Chemistry 79, 4621-1626. 

Chapter 27 Sorption of Viscous Organics by Macroporous Carbons... 

Here, the sorption of viscous organics, heavy oils, different oils such as engine and cooking oils, and also biomedical fluids are discussed on macroporous carbon materials, mainly three kinds of materials, i.e., exfohated graphite, carbonized fir fibers, and carbon fiber felts. The recovery of sorbed heavy oils from macroporous carbon materials is also discussed. 

So far, mats of some polymers, such as poly(propylene) and poly(urethane), have been used for the sorption of spilled oil. Their maximum sorption capacity is about 10-30 g of heavy oil per 1 g of polymer [35]. However, they sorb water, as well as heavy oil, and show no special selectivity for heavy oils. Therefore, the effective sorption capacity of the polymer mats for heavy oils floating on water must be lower than the figures mentioned above. Some natural sorbents prepared from cotton fibers, milkweed flosses, and kenaf plants were reported to have rather high sorption capacity and certain potential for oil recovery and sorbent reusability [35—41]. The sorption capacity of macroporous carbon materials, exfoliated graphite, and carbonized fir fibers, is very high in comparison with these materials. Preferential sorption of oils is an advantage of carbon materials in addition to their high sorption capacity. 

Certain possibilities of these macroporous carbon materials to be used for the protection of environment from heavy oil pollutions and the reuse of spilled heavy oils were demonstrated. 

Fig. 4.11 Three-dimensionally ordered macroporous carbon by using monodispersed silica template and polyimide...

Fig. 4.12 Scanning electron micrograph of three-dimensionally macroporous carbon prepared by three-dimensionally macroporous polyimide...

Fig. 4.13 Preparation process of three-dimensionally ordered macroporous carbon with controlled pore size distribution by using monodispersed polystyrene and silica beads...

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