Porosity ultramicropores

The results presented in this section confirm that an adequate pore size is more important than a high surface area for an optimization of the capacitance values. For the production of compact systems, an important objective is to limit as much as possible the useless porosity in order to enhance the volumetric capacity. Moderately activated carbons, with pores at the boarder of the ultramicropore region, e.g., 0.7-0.9 nm, are the most profitable for ions electrosorption. 

Porosity is divided by IUPAC (Rouquerol et al. 1994), based on pore size, into the following groups macropores (>50 nm), mesopores (2-50 nm), and micropores (<2 nm). Microporosity may then be subdivided into three subsequent categories supermicropores (1.4-2.0 nm), micropores (0.5-1.4 nm), and ultramicropores (<0.5 nm). Both mineral and organic soil components have pores with different diameter. The holes and channels in the polymer chain of humic substances as well as the interlayer space of the layered mineral have an important role in determining the specific surface area. The size of the interlayer space of layered minerals in a dry state is a few tenths of nanometers, so they are considered as micropores. 

Zhuravlev, Gorelik, and co-workers (77, 80,120-122,143) carried out kinetic studies of water vapor adsorption and isotopic exchange (D2O + =Si-OH) for different types of amorphous silica. A relationship was established between the nature of the porosity and the shape of the kinetic curve. For example, for bidispersed silica gels containing both wide mesopores and very fine ultramicropores, the kinetic plot consists of two sections a very short period due to the mass transfer of water vapors through transport mesopores, and a very long period (tens of hours) due to the diffusion of water molecules inside very fine pores that have diameters comparable with that of the water molecule. Thus, such plots provide information on the type of pores present in the silica sample. 

The use of CO2 adsorption at 273 K for the characterization of (ultra)microporous carbons has been repeatedly proposed as an alternative to of Ni at 77 K in view of the well-kimwn activated diffusion limitations to N2 adsorption at 77 K in carbon ultramicropores [28], Mesurement of CO2 adsorption at high pressures [29] afforded a comparison of CO2 (273 K) and N2 (77 K) adsorption at similar adairption potentials, and led to the conclusion that similar mechanisms operate for these two adsorptives at the temperatures indicated. More recently, Lozano-Castelld et al. [30] have reviewed this topic and provided additional examples for the useMness of CO2 adsorption to characterize microporous carbons. Aigon is another usefiil adsorptive for carbon porosity characterization, whose application to ACFs has also been discusssed recently [31]. 

Increasing the hydroxide content in the treatment often increases the micropore volume and the formation of mesopores, while an increase in nitrogen flow enhances ultramicropore volume and homogenous porosity, yielding molecular... 

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