1. Introduction

The concept of "adsorption" was recommended by Kayser in 1881 to explain the growth in concentration of gas molecules on the adjacent surface of a solid adsorbent, an effect previously noted by Fontana and Scheele in 1777 [1]. In particular, majority of adsorbents useful for industrial applications have pores with hole dimensions in the nanometer region; in this pore-size zone, adsorption is on the one hand a significant methodology for the characterization of porous materials; to be exact, gas adsorption offers evidence concerning the mesopore area, volume and size of the pores together with the energetics of adsorption [2]. Also, gas adsorption is a vital unitary operation for sustainable energy and pollution abatement

#### Applied Surface Science

applications of nanoporous materials along with the industrial uses, where materials like metal organic framework molecular sieves, metal organic frameworks, Prussian blue analogues, mesoporous molecular sieves, pillared clays, silica, alumina, active carbons, titanium dioxides, magnesium oxides, carbon nanotubes together with zeolites and related materials are the most widely studied and applied adsorbents in Science and Technology [3].

the hydrolysis of a silicon alkoxide, formally a silicic acid ether; then, the global reaction continues as a condensation polymerization to form high molecular weight

Synthesis, Characterization, and Adsorption Properties of Nanoporous Materials

These materials are normally synthesized in hydrothermal conditions using solutions that are composed of sodium hydroxide, sodium silicate and sodium aluminate, where three steps are observed during the synthesis process, i.e., induction, nucleation, and crystallization, which determine the specific zeolite produced by the applied reactants, along with the parameters used, such as temperature, pH,

In this case, the aluminosilicate synthesis is complemented with the addition of structure-directing agents (SDA), such as quaternary ammonium cations, linear or cyclic ethers, and coordination compounds. been, the first high-silica zeolites, that is, ETA, EU, NU, and the ZSM series, patented in the late 1960s, or early 1980s [20]; moreover, high silica zeolite can be as well synthesized using ethanol and seeds of the desired phase [21]; meanwhile, Microporous aluminophosphate molecular sieves, that is, non-aluminosilicate zeolites; such as: SAPO molecular sieves were obtained by incorporation of Si in the AlPO framework, while MeAPO molecular sieves are obtained by the inclusion of Ga, Be, Va, Co, Fe, Mg, Mn, Zn in the AlPO

framework obtaining between others: gallophosphates, zincophosphates,

Active Carbon prepared with wood, lignite, peat, coconut, eucalyptus lignin, and apricot, cherry and olive stones under physical (a) and chemical activation (b)

a. carbonization at 800–1000°C under inert gas, and activation under oxidizing

b.chemical activation requires a treatment with: sulfuric acid, phosphoric acid, zinc chloride, potassium hydroxide at 400–1000°C, followed by the elimination of the dehydrating agent by meticulous washing.

Prussian blue analogues (PBAs) [26, 27] and nitroprussides (NPs) [28] are produced by mixing solutions of K3[Fe(CN)6], for the synthesis of Prussian blue analogues, and Na2[Fe(CN)5NO] for the synthesis of nitroprussides with a nitrate

The X-ray Diffraction (XRD) methodology was used to determine the crystalline phases present in the natural and synthesized materials, together with the investigation of the nucleation and growth process during the synthesis of different materials to be used as adsorbents, ion exchangers and catalysts [29]. The XRD tests were carried out, at room temperature using a stage similar to an Anton Paar HTK-1200 N with an equipment similar to a Bruker D8 Advance system in a Bragg-Brentano vertical goniometer configuration, the angular measurements being made applying steps of 0.01° from 5 to 80°, using a Cu anode tube together with a Ni filter

of the corresponding metal to get the corresponding PBAs and NPs.

beryllophosphates, vanadophosphates and ferrophosphates [22].

agents, as a rule, carbon dioxide or water vapor.

polysilicates, which connect together to produce a gel [17].

2.4 High silica and non-aluminosilicate zeolites

2.3 Aluminosilicate zeolites

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

and time [18, 19].

methods; i.e. [23–25]:

3. Characterization

71

In addition to their adsorption properties, nanoporous materials are a group of advanced materials with other excellent properties and applications in many fields, for example, waste water treatment [4–6], ionic conduction [7], ionic exchange [8], gas separation [9], membranes [10], catalysts [11], catalyst supports [12] and detergency [13].

The classification of the different pore widths of porous adsorbents was carried out by the International Union of Pure and Applied Chemistry (IUPAC); in this classification, adsorbent materials are categorized as those with pore diameters greater than 50 nm, named macroporous adsorbents, while mesoporous materials show pore diameters between 2 and 50 nm that are termed microporous; those adsorbents showing pore diameters between 0.3 and 2 nm, where, the pore width, Dp, is defined as equal to the diameter in the case of cylindrical shaped pores, and as the distance between opposite walls in the case of slit-shaped pores [14].

In addition, the clean surface of an adsorbent is characterized by the fact that the atoms that produce the surface have non-saturated bonds, fact producing an adsorption field above this surface; been the adsorption field the cause of the formation of a stockpile of molecules close to the adsorbent surface; this effect, i.e., adsorption, is a universal propensity of surface systems, given that throughout this process a reduction of the surface tension is experienced by the solid; been, adsorption the term applied to describe this process; whereas for the opposite, the term desorption is used [1].

Now it is necessary to state that the occupation of the adsorption space by adsorbed molecules in complex porous systems occurs roughly in the following form: initially, micropore filling takes place, with the adsorption process being controlled almost totally by the interaction of the adsorbed molecules with the pore walls; thereafter, at higher pressures, the external surface is covered, which is a monolayer and a multilayer adsorption on the walls of mesopores, and open macropores take place. Finally, capillary condensation occurs in the mesopores [2]. On the other hand, dynamic adsorption is a mass transfer between a mobile, solid, or liquid phase, and the adsorption bed packed in a reactor, been necessary to carry out the dynamic adsorption, a reactor, where the adsorption process will occur in the reactor adsorbent packed bed, been, the adsorbents normally used for these applications are active carbons, zeolites and related materials, silica, mesoporous molecular sieves, alumina, titanium dioxide, magnesium oxide, clays, and pillared clays [3].
