**2. Preparation**

This section of the chapter describes the preparation of organoclay on the laboratory run, with various experimental conditions, clays from different regions, and various kinds of surfactants. Organoclay material is defined as hybrid materials resulting from clay mineral association with surfactant [28].

Surfactant compounds are amphiphilic molecules, meaning they have two parts of different polarity, one hydrophobic is apolar and the other hydrophilic is polar (**Figure 1**).

Clay minerals are fundamentally hydrous alumino-silicates with highly fine particle sizes. Most clay minerals are made by a stack of sheets; these sheets are made by a stack of tetrahedral and octahedral layers that shape the frame of all clay mineral assemblage; the arrangement of these tetrahedral and octahedral layers makes it possible to discern three main types of clay (1:1 or TO type, 2:1 or TOT type, 2:1:1 or TOTO type) [24]. Clay minerals have different types of physical properties like- the CEC, plasticity, hardness, porosity and adsorption ability (**Figure 1**).

Clay organophilization depends on the characterizations (structure, propriety, type, chemical nature…etc.) of the used clay and surfactant. Among the clay

**Figure 1.**

*General structure of a clay mineral [32] and surfactant molecule [33].*

minerals, smectites (2:1 or TOT type), have been widely employed to prepare Organoclay since of their excellent properties. For example, several pieces of research [24, 28, 34] are noted among the expandable clay minerals, montmorillonites were the most popular material for the preparation of organoclays because of their singular properties: charge density, cation exchange capacity (CEC) and swelling ability, its abundance in the ground, and thus its low cost. Thus, Jlassi et al. [24] noted a high CEC of clay and a uniform surface charge density promote clay organophilization; therefore montmorillonites are the most favorable swelling clay for the intercalation of organic species in its interlayer space. The compensating cation size (to be replaced) has an impact on clay organophilization. Indeed, the smaller, more mobile, and more easily hydratable the compensating cation are, the easier the exchange is [24]. For this, the purification of the raw clay in order to obtain sodium clay is an essential step in the preparation of organophilic clays. In Fact, Na<sup>+</sup> cations are very exchangeable compared to K<sup>+</sup> and Ca2+ cations. The net amount of surfactant adsorbed to the clay minerals can exceed the CEC of the clay minerals. Therefore the entire researcher prepares organoclay with a surfactant concentration exceeding the CEC of the clay used [34].

There are some types of organoclay based on the used surfactant; the best-known surfactants are cationic (quaternary alkylammonium, exotic (zwitterionic) and nonionic ones [28]. For cationic and zwitterionic surfactants, organoclays are obtained by the substitution of the inorganic cations located within the interlayer space through cation exchange, whereas these exchange hydrated cations are kept in the case of nonionic compounds, leading to hybrid materials with a dual hydrophilic hydrophobic behavior [28]. Cationic surfactants were principally used for the preparation of organoclay. The quaternary alkylammonium salts are the cationic surfactants the most preferred for the modification of clay minerals where her arrangements depend on both the length of the alkyl chains and the concentration of the amphiphilic molecules [28]. Therefore, currently, there is a significant several of research on the modification of clay minerals with several kinds of quaternary alkylammonium salts on a laboratory scale.

In literature, various methods are used for the preparation of organoclay such as cation exchange, organosilane, iodonium, and diazonium salt grafting. Of the methods of organophilic preparation, cation exchange is the most commonly employed [24, 34]; cation exchange has been used for five decades. This technique aims to exchange interlayer cations of the clay mineral with surfactant [24, 34].

Experimentally, organoclay can be prepared through three routes in humid states by liquid–solid or liquid–liquid interaction with the use of solvents, or by solid-state reaction with solid–solid interaction without the use of any solvents [24, 34]. The first, a solid–solid process, consists of grinding a mixture of clay powders and surfactant that is subsequently heated to ensure the diffusion of surfactant molecules in the interlayer space [24]. The solid-state reactions of clay minerals and ammonium cations were reported in 1990 [34]. The dry process leads to heterogeneous exchanged organoclays. Even if the intercalation of the compounds (cationic or polar molecules), is confirmed by the expansion of the interlayer space identified by following the 00 l reflection through X-ray diffraction (XRD) [35]. But, the absence of solvents preceding the preparation is environmentally good and makes the process more suitable for industrialization [28]. The second is carried out by a liquid–solid process by putting clay, originally powdered, in contact with an organic cation solution at a known concentration. The third method is a liquid–liquid process and consists of mixing dispersed clay slurry with a solution of organic salt. The easiest way for organoclay preparation, which was reported in many studies, is surely in an aqueous solution.

### *Organoclay Nano-Adsorbent: Preparation, Characterization and Applications DOI: http://dx.doi.org/10.5772/intechopen.105903*

Indeed, in solution the presence of water surrounding the exchangeable cations amplifies then repulsive forces at long-range order leading to exfoliation of the phyllosilicates sheets offering total access to the entire specific surface area, making easier the adsorption and interaction with surfactants of which chemical nature control the properties of the organoclays [28].

In a general view of the literature, we note that the synthesis is done in two steps, first The preparation starts with a purification step, which is a long and time-consuming process, leading most of the time to sodium clays [24]; which then facilitates the exchange with the molecule of surfactant in the second step (**Figure 2**):

Pre-treatment of clay minerals: The clay fraction (<2 μm) was separated by sedimentation of the clay suspension (based on Stokes Law calculations), and would remove the larger sized particles (>2 μm). Free carbonate remove by attacks with a solution of hydrochloric acid HCl followed by washing several times with water to remove excess HCL; Organic matter was removed by suspension in H2O2 followed by washing several times with water to remove excess H2O2; finally, treatment with a NaCl solution. This step is essential because firstly it eliminates the impurities (calcite, quartz, etc.) and secondly, it replaces the cations between the sheets with Na + (homoiconic clays). Homoionic clays are made to facilitate exchange; thus avoiding the different degree of exchange and/or competition between the pollutant to be adsorbed and the ions initially present [36].

Preparation of organo-clays: In literature, the most frequently used method is as follows: A given mass in (g) of sodium clay mixes with a given volume in (mL) of a surfactant solution with a concentration multiple of the cation exchange capacity of the sodium clay. This mixture is then stirred for 2 to 24 hours and then centrifuged. The surfactant-modified clay is washed several times with distilled water. The organoclay obtained is dried at 60° C, then ground and sieved (**Figure 2**).

**Figure 2.** *Preparation of organoclay.*

In the literature, most organic clay used in the treatment of water prepares under these conditions: the type of clay used is smectite, the quaternary ammonium ions as surfactant and by an ion-exchange mechanism (Cation exchange); with Surfactant concentration equals 0.5 to 4 times CEC of the clay used.

He et al. [37] used hexadecyltrimethylammonium bromide (HDTMAB) to prepare HDTMA-montmorillonite organoclays to elucidate the relation between the morphology of organoclay and the surfactant packing density within the montmorillonites galleries. The concentrations of HDTMA were 0.5 CEC, 1.5 CEC and 5.0 CEC of montmorillonite, respectively.

Hamdi and Srasra [38] prepared an organo-smectite by cation exchange with hexadecyltrimethylammonium bromide (HDTMAB) at different concentrations (1.0 to 3.0 CEC of clay CEC—cationic exchange capacity). The clay used for preparation was collected from Gabes (southeast of Tunisia).

Msadok et al. [39] modified Tunisian clay with hexadécylpyridinium (HDPy) in a concentration equivalent to 0.5 to 4.0 of cation exchange capacity of purified clay (CEC). This organoclay was also used for application as viscosifier in oil drilling fluid.

Gammoudi et al. [40] studied the influence of exchangeable cation of smectite on surfactant adsorption, Organoclays were prepared Tunisian smectite saturated with Na+ , Ca2+ and Zn2+ ions and the cationic surfactant hexadecyltrimethylammonium bromide.

Yunfei et al. [41] modified sodium montmorillonite by an ion-exchange mechanism using three cationic surfactants: octadecyltrimethylammonium bromide, dimethyldioctadecylammonium bromide, and methyltrioctadecylammonium bromide. These organoclaye were prepared to investigate changes in the surfaces and structures were characterized using X-ray diffraction (XRD), thermal analysis (TG) and infrared (IR) spectroscopy.

Shirzad-Siboni et al. [42] treated montmorillonites with cetyltrimethylammonium bromide (CTAB) by the intercalation method and used it as an adsorbent to uptake herbicide from aqueous solutions.

Guégana and Le Forestierc [43] with the objective of performance evaluation of organoclays for the amoxicillin retention in a dynamic context were modified Na-montmorillonite (Na-Mt) using a set of short and moderate chain surfactant (TMA, BTA, BTMA and TOM), and a long chain organoclay (HDTMA).

De Oliveira and Guégan also prepared organophilic montmorillonite exchanged by various amounts of benzyldimethyltetradecyl ammonium chloride cationic surfactant (BDTAC) up to four times the cation exchange capacity (CEC), to be used for the adsorption of diclofenac [44].

Pandey and De [43] employed a cationic surfactant cetyl tri methyl ammonium bromide (CTAB), wich was prepared in order to explore the adsorption potential of natural bentonite for organic pollutant and anionic molecules.

The solid-state reaction is an alternative route of preparation of organoclays, but it has been less employed than cation exchange. Therefore, **Table 1** summarized 22 important papers in the recent literature, indicating a strong tendency for the use of smectite, quaternary alkylammonium salts and the cation exchange technique to prepare organoclay.

The following sections are organized to study the characterization of these organoclays and their application.


*Organoclay Nano-Adsorbent: Preparation, Characterization and Applications DOI: http://dx.doi.org/10.5772/intechopen.105903*

#### **Table 1.**

*Kinds of clay and surfactant, routes of preparations to prepare organoclay.*
