4. Definition and terms

#### 4.1 Adsorption isotherm

It is the most important measurement made to characterize an adsorbent; it is defined as the relationship between the amount adsorbed, na, and the equilibrium pressure, P, at constant temperature, T [1, 2] (Figure 1)

$$m\_a = f(P)\_T \tag{1}$$

a gas molecule is free to move within the adsorption space, or the instance of immobile adsorption, taking place in the case where the adsorbed molecule vibrates

Synthesis, Characterization, and Adsorption Properties of Nanoporous Materials

For open surfaces, adsorption consists of a layer-by-layer loading process, where

and Nm is the monolayer capacity; as a result, it is understood that we have mono-

They are characterized by their specific surface area, denoted by S, and mea-

external to the micropores. If the adsorbents do not have micropores, the surface area and the outer surface area match; furthermore, the micropore volume is

W is the sum of the micropores and mesopore volumes [32] of the adsorbent, also

<sup>Δ</sup>Dp versus Dp, where Vp is the pore volume accumulated up to the pore width Dp measured in (cc-STP/g Å) [26, 27]. Now it is necessary to state that cc-STP is a unit denoting the amount adsorbed, measured in cubic centimeters at standard

The interfacial layer is the non-homogeneous section of an adsorption system, i.e., between two neighboring bulk phases (Figure 2), where the properties typifying this region are radically dissimilar from, but associated to, the properties of the bulk phases; in which, to deal with this system is assumed that in the ideal reference system, the concentration must be constant up to the Gibbs dividing surface (GDS)

temperature and pressure (STP), that is, 273.15 K and 760 Torr, that is,

/g), in which the surface area is the outer surface, concretely, the area

/g). Lastly, we have the pore size distribution (PSD), i.e., a plot of

layer adsorption when θ < 1 and multiplayer adsorption when θ > 1 [31].

Nm = 1, where θ is the surface recovery

/g), whereas the total pore volume labeled

around an adsorption site [2, 3].

Graphic representation of the adsorption isotherm.

DOI: http://dx.doi.org/10.5772/intechopen.83355

4.4 Monolayers and multilayers

4.5 Porous adsorbents

sured in (m2

Figure 1.

measured in (cm3

1.01325 � <sup>10</sup><sup>5</sup> Pa.

4.6 Magnitude of adsorption

(see Figure 2); been, in an actual system [32]

ΔvP

73

the first layer is filled as in the case when <sup>θ</sup> <sup>¼</sup> na

represented by WMP, measured in (cm3

#### 4.2 Physical and chemical adsorption

The gas adsorption process is normally considered a physical process, named physical adsorption, since the molecular forces involved in this process are usually of the van der Waals type. Meanwhile Chemical adsorption of gases in solid surfaces takes place in the case where during the adsorption process a reaction with exchange of electrons between the solid surface and the gas molecules with the formation of chemical bonds takes place, been, the adsorbent the solid phase and the adsorbate the gas phase [14].

#### 4.3 Mobile and immobile adsorptions

Gas and vapor adsorption in solid adsorbents can be also classified as mobile adsorption, where the first case occurs when the adsorbed molecule is performed as Synthesis, Characterization, and Adsorption Properties of Nanoporous Materials DOI: http://dx.doi.org/10.5772/intechopen.83355

Figure 1. Graphic representation of the adsorption isotherm.

placed, prior to the detector, to eliminate Cu K<sup>α</sup> radiation the one-dimensional

The analytical test was carried out with an equipment similar to a TA, Q-500 instrument; the samples were placed onto a ceramic sample holder suspended from an analytical balance, suspended from an analytical balance; then the temperature was linearly scanned, from 25 to 300 C, at a heating rate of 5 C/min under a pure N2 flow of 100 mL/min. TGA testing process was carried out with a TA, Q-500 instru-

DRIFTS were gathered using equipment similar to a Thermo Scientific Nicolet iS10 FTIR spectrometer. The data of the hydrated and dehydrated samples were collected at a resolution of 4 cm�<sup>1</sup> employing 100 scans per sample; a background, with pure KBr, was in all cases collected before the collection of the spectra. Both the hydrated and dehydrated samples were gathered at room temperature while flowing N2 (Praxair, 99.99%) at a rate of 50 cc/min; while, the dehydration of the studied samples was performed at 100°C for 2 h in N2 flow of 50 mL/min while the sample under test was included in the finger-sample-holder of the IR high temper-

Room-temperature Mossbauer Spectrometry measurements were made with a system similar to a SEECo supplied spectrometer operating at constant acceleration mode with a 50 mCi 57Co γ-ray source in a Rh matrix made by Rietverc GmbH. The 1024-point raw data were folded and analyzed using WMOSS, a public domain Mossbauer spectral analysis program; the calibration was made with reference to α-

It is the most important measurement made to characterize an adsorbent; it is defined as the relationship between the amount adsorbed, na, and the equilibrium

The gas adsorption process is normally considered a physical process, named physical adsorption, since the molecular forces involved in this process are usually of the van der Waals type. Meanwhile Chemical adsorption of gases in solid surfaces

Gas and vapor adsorption in solid adsorbents can be also classified as mobile adsorption, where the first case occurs when the adsorbed molecule is performed as

takes place in the case where during the adsorption process a reaction with exchange of electrons between the solid surface and the gas molecules with the formation of chemical bonds takes place, been, the adsorbent the solid phase and

na ¼ f Pð Þ<sup>T</sup> (1)

pressure, P, at constant temperature, T [1, 2] (Figure 1)

4.2 Physical and chemical adsorption

the adsorbate the gas phase [14].

72

4.3 Mobile and immobile adsorptions

ment, and the samples were placed onto a ceramic sample holder [27].

detector was employed [26].

Applied Surface Science

ature cell [28].

Fe metal [30].

4. Definition and terms

4.1 Adsorption isotherm

3.1 Thermo-gravimetric analysis (TGA)

a gas molecule is free to move within the adsorption space, or the instance of immobile adsorption, taking place in the case where the adsorbed molecule vibrates around an adsorption site [2, 3].
