Pore size distribution porous carbons

Sosin KA and Quinn DF. Using the high pressure methane isotherm for determination of pore size distribution of carbon adsorbents. J. Porous Mat., 1995 1(1) 111-119. 

The basic assumption of constant radius of every single pore is the same for the capillary condensation technique as for the mercury intrusion technique. Thus the satisfactory agreement of the pore size distribution of carbon obtained [18] by mercury intrusion and capillary condensation in an overlapping region of pore radii between 50 and 300A implies only that the same idealized structure is derived. A method of capillary condensation which is not based on the assumption of the shape of the pores was suggested by Brunauer, Mikhail and Bodor [19] recently. The application of this method to porous electrodes has not been reported so far. 

Supports. The principal component of a typical catalyst is the porous support (49,50). Most supports are robust soHds that can be made with wide ranges of surface areas and pore size distributions. The most widely appHed supports are metal oxides others are carbon, kieselguhr, organic polymers, and zeoHtes. 

Fig. 3.23 shows pore volume distributions of some commercially important porous materials. Note that zeolites and activated carbon consist predominantly of micropores, whereas alumina and silica have pores mainly in the me.sopore range. Zeolites and active carbons have a sharp peak in pore size distribution, but in the case of the activated carbon also larger pores are present. The wide-pore silica is prepared specially to facilitate internal mass-transfer. 

The activation with KOH of selected parent materials under appropriate process conditions (temperature, time, reagent ratio) can provide highly porous carbons of controlled pore size distribution and surface chemistry, also suitable for use as electrode materials in supercapacitors. 

Fig. 4.4 NLDFT Pore size distribution (NLDFT-PSD) in porous carbons with high voiume of uitra- and super-micropores (V = 0.4-0.7 crn g" ), and mesopores 1.2-1.4 cm g ).Li/Ci...

This work is about the development of a new porous composite material [18] which consists of a silica network intercrossed with a carbon network of high activity, being both networks independent and self supported. This new composite was obtained by the sol-gel method, it has an open pore size distribution curve characterized by a big sharpened zone near the 1000 A diameter, and it possess a high thermal stability. 

To achieve a significant adsorptive capacity an adsorbent must have a high specific area, which implies a highly porous structure with very small micropores. Such microporous solids can be produced in several different ways. Adsorbents such as silica gel and activated alumina are made by precipitation of colloidal particles, followed by dehydration. Carbon adsorbents are prepared by controlled burn-out of carbonaceous materials such as coal, lignite, and coconut shells. The crystalline adsorbents (zeolite and zeolite analogues are different in that the dimensions of the micropores are determined by the crystal structure and there is therefore virtually no distribution of micropore size. Although structurally very different from the crystalline adsorbents, carbon molecular sieves also have a very narrow distribution of pore size. The adsorptive properties depend on the pore size and the pore size distribution as well as on the nature of the solid surface. 

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... 

On the other hand, for the microporous carbons with pore size distribution (PSD) with pore fractality, the pore fractal dimensions56,59,62 which represent the size distribution irregularity can be theoretically calculated by non-linear fitting of experimental adsorption isotherm with Dubinin-Astakhov (D-A) equation in consideration of PSD with pore fractality.143"149 The image analysis method54,151"153 has proven to be also effective for the estimation of the surface fractal dimension of the porous materials using perimeter-area method.154"159... 

Because of their biocompatibility, chemical stability, high thermal and electrical conductivity, sorption ability, tuneable surfaces area, pore-size distribution and straightforward functionalization chemistry, porous carbons have found application in diverse topical areas such as sensors, fuel cells, hydrogen storage, and sorption.39 11 One particular property that distinguishes porous carbon from porous silica materials is the electrical conductivity of the former that has no counterpart in siliceous-based scaffoldings. This feature opens the route for certain applications... 

Since adsorption is essentially a surface phenomenon, a practical adsorbent must have a high specific surface area, which means small diameter pores. Conventional adsorbents such as porous alumina, silica gel, and activated carbon have relatively wide pore size distributions, spanning the entire range from a few angstroms to perhaps 1 /xm. For convenience the pores are sometimes divided into three classes ... 

FIGURE 2.20 Pore size distributions in various porous carbons. 

Porous carbon materials mostly consist of carbon and exhibit appreciable apparent surface area and micropore volume (MPV) [1-3], They are solids with a wide variety of pore size distributions (PSDs), which can be prepared in different forms, such as powders, granules, pellets, fibers, cloths,... 

Seaton NA, Walton JPRB, and Quirke N. A new analysis method for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements. Carbon, 1989 27(6) 853-861. 

Porous carbonaceous materials are important in many application areas because of their remarkable properties, such as high surface areas, chemical inertness, and good mechanical stability. Carbon molecular sieves that are amorphous and microporous are commercially important for the separation of nitrogen from air, and activated carbons with a wide pore size distribution are also useful adsorbents for various applications. 

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