Organoclay Nano-Adsorbent: Preparation, Characterization and Applications

Abstract

Organoclay has a tremendous impact on both fundamental studies and practical applications in numerous fields. In this context, this chapter investigates the performance of Organoclay in wastewater treatment. In particular, the adsorption of various hazardous substances has been reviewed. This study aims to give an overview of the preparation methods of Organoclay. The second purpose was to discuss the removal efficiency and reliability of various pollutants by organoclay. The third goal discussed the isotherms and kinetics used for the data interpretation. This work revealed that the characteristics of Organoclay depend mainly on the type of clay used and the nature of the intercalated surfactant. Sorption efficiency was found to depend on the nature of Organoclay, type of pollutant, pH, contact time and the concentration of pollutant.

1. Introduction

Nanotechnology is one of the most prominent promising technologies that offer solutions to different problems in various aspects of our life. In fact, nowadays, nanotechnology used in the synthesis of nanoparticles has attracted great interest in different applications (environment, emerging, industries…etc.) [1, 2, 3]. A healthy environment is a major challenge faced by the world today. In connection with the rapid industrialization, scientists reported the presence of more than 700 carcinogenic and highly toxic inorganic and organic micro pollutants. Toxic inorganic metals included instance chromium, mercury, cadmium, lead…etc. and inorganic oxyanions included fluoride, nitrate, phosphate etc. while organic contaminants included, phenols, dye, hydrocarbons, and pesticides. They are considered persistent environmental pollutants non-biotransformable or non-biodegradable [3]. Mining operations, metal plating facilities, textile industries, fertilizer industries and pharmaceutical industries are the most common sources of these hazardous substances [4, 5, 6, 7, 8]. Consequently, developing efficient techniques for the treatment of effluent fertilizers and industrial before being discharged into the environment is a considerable issue in terms of public health and environmental protection.

The need for sustainable technologies to conserve the environment leads to the development of a lot of technologies in the field of water treatment [9]. In this scenario, research efforts have been conducted to remove these contaminants from wastewater using several methods such as adsorption, electrolysis electrodialysis, ion exchange, reverse osmosis, coagulation and flocculation, and chemical precipitation have demonstrated different degrees of remediation efficiency [9, 10, 11].

Many of these methods, such as coagulation and flocculation, ion-exchange, and reverse osmosis, are expensive and cannot be applied in developing countries. Conventional coagulation methods and chemical precipitation cause secondary contaminants requiring an additional treatment and increasing the treatment cost [3, 11].

Interestingly, adsorption is the most attractive process in developing countries due to its lower cost, easy-to-use and its high efficiency to remove different types of contaminants [3, 12, 13]; thus, the adsorption method produces low quantities of sludge, which is largely produced by other methods (chemical precipitation) [3], but it requires a good choice of adsorbent. Generally, the selection of the useful adsorbent for water treatments is controlled by many factors such as the adsorption capacity of the material toward the target contaminant, cost/efficiency ratio, and the type and concentration of the contaminants present in water [3]. Ideal adsorbents must therefore meet a number of criteria, such as: (1) should be environmentally benign; (2) should demonstrate a high sorption capacity and high selectivity especially to the pollutants occurring in water at low concentration; (3) the adsorbed pollutants can be easily removed from its surface, and (4) should be recyclable [14]. A sorbent with the above characteristics would be considered an excellent adsorbent in wastewater treatment. Efficient adsorbents of biological, organic or mineral origin have been used for wastewater treatment [15, 16]. The most important used adsorbents are agricultural wastes [17], clay minerals [18, 19], modified clays [20, 21], zeolites [22], and activated carbon [23]…etc.

Nanotechnology has great potential for improving the efficiency in preventing water pollution and improving the treatment methods [9]. In fact, the application of nanotechnology in water treatment extends to various fields like nanoscale filtration techniques, adsorption of pollutants on nanoparticles and breakdown of contaminants by nanoparticle catalysis [3, 15].

Among various nanoparticles ‘clay minerals’ generally speaking, clay minerals which are constituted of layered mineral silicates in the nano dimension, are cheap and non- hazardous, and are characterized by high surface reactivity and stability due to their large surface area [24]. Compared with other adsorbent materials, clay minerals with physical adsorption ability and surface chemical activity, are readily available, making them increasing focus as of late [25, 26]. Nevertheless, the adsorption ability of clay is mainly dependent on fundamental traits, for instance, the charge characteristics of the adsorbent, pH, competing ions and pollutant type [18]. Moreover, clays that exhibit the crystal structure and negative charge have restricted their application [27]. In order to overcome these limitations, many studies in recent years have addressed the improvement of the mechanical properties of clay through the use of various types of modifications [21].

Recently, there has been an increasing interest in using organoclay for the removal of contaminants from soil and aquatic environments due to here the large specific surface and a hydrophobic behavior. Indeed, the intercalation of cationic surfactants changes the surface properties from hydrophilic to hydrophobic, greatly increases the specific surface and increases the basal spacing resulting in exposure of more adsorption sites [28, 29], thus, adsorption capacity especially when surfactant loading exceeds the CEC of clay [30]. Organoclay are a group of surfactant modified clays with hydrophobic properties, which have been extensively used in remediation of heavy metals, herbicides and pesticides, organic compounds and anionic contaminants [31].

The overall aim of this chapter was the investigation of the preparation and characterization of organoclay and their capacities to remove various pollutants as well as empirical findings on the equilibrium isotherms and kinetics. The literature for the chapter included published studies on hazardous substances.

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).

Figure 1.

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

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 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⁺ cations are very exchangeable compared to K⁺ 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. 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):

Figure 2.

Preparation of organoclay.

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).

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.

Clay	Surfactant	Concentration	Reference
Smectite	HDPy and HDTMA	0.5 to 3.0CEC	[45]
Bentonite	HDTMA and MTMAB	2CEC	[46]
Montmorillonite	CTAB	1CEC	[42]
Montmorillonites	TMA and HDTMA	40–100% CEC	[47]
Smectite	BDTAC	4.0CEC	[44]
Bentonite	CTAB	—	[43]
bentonite,	HDTMA	2 and 4 CEC	[30]
Bentonite	CTMAB	0.04 to 0.28 CEC	[48]
Bentonite.	CPC	—	[49]
Smectite	HDPy	3.0CEC	[50]
Smectite	HDTMA and (HDPy)	120 and 170% CEC	[51]
Smectite	HDPy	1 to 3 CEC	[52]
Montmorillonites	HDTMA	0.5 to 2CEC	[53]
Montmorillonites	DDAB	—	[54]
Bentonite.	HDPy	—	[55]
Montmorillonites	HDPy	20–400%.	[56]
Montmorillonite	DDTMA and DDDMA)	0.5–2.0 CEC	[57]
Montmorillonite	DTAB and CTAB	1 CEC	[58]
Montmorillonite	BTMA	—	[59]
montmorillonite	HDTMA	20%	[60]
montmorillonite	HDPy	4 CEC	[29]
Bentonite	HDTMA—BTEA	—	[36]

Table 1.

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

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

3. Characterization

Understanding the structure of organoclays is essential for their practical applications. Consequently, after the synthesis of organoclay, the verification of the intercalation of surfactant in the inter-layer space of the clay by comparison before and after intercalation is essential. In literature, various characterization methods were used on the original clays and the organo-modified clays to get information on structure, expansion capacity, layer charge, pore size, crystallite size, charge distribution and pore distribution. The indispensable methods for characterization are X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), Scanning electron micrographs (SEM) and transmission electron microscopy (TEM) and determination of physic-chemical properties (CEC, area-specific, pHpzc … etc.).

3.1 X-ray diffraction (XRD)

Intercalation of organic surfactant between layers of clays greatly changes (increases) the basal spacing of the layers; X-ray diffraction was used to study this Changement. Otherwise, X-ray diffraction (XRD) can give the basal spacing (d₀₀₁) information of the organo-clays which is very important for explaining the intercalation and configuration of surfactant between clay layers. The arrangement of cationic surfactant in the interlayer space of clay minerals was initially deduced in 1969 [34]. Generally speaking, on the basis of XRD results for raw clay the into-foliar cations only form monolayers; but in the case of organoclay, the organic cations (surfactant) may form monolayers, bilayers and paraffin-type layers. The arrangement of organic cations (surfactant) in organoclay depends on the layer charge (=interlayer cation density = packing density of the alkylammonium ions) of the clay mineral and the chain length of the organic ion. On the other hand, with an increasing concentration of added surfactants, the arrangement of surfactant change from monolayer to paraffin-type layers (Figure 3) [24, 28, 34].

Figure 3.

Arrangement of surfactants in the interlayer space of a clay.

For example, Msodok et al. [39] notated that according to the literature, the thickness of the montmorillonite is 9.7 Å and the molecular size of HDPy is approximately 23.1 Å in length and 4.6 Å in height. At a small concentration of the cationic surfactant, the interlayer spacing (d₀₀₁) of 0.5 CEC was 14.4 Å which is attributed to monolayer arrangement. For the 1.0 CEC sample, the basal spacing was 21.96 Å which is assigned to the pseudo-trimolecular arrangement. From 2.0CEC, 3.0CEC and 4.0 CEC data, the basal spacing increased in respect of 0.5 CEC-A with the maximum (d001) was 44.51 Å for 4.0 CEC. These data indicate that the surfactant molecules are located as paraffinic bilayer arrangement in the interlayer space of the montmorillonites (Figure 4) [39]. This result is in accordance with another study [45, 61].

Figure 4.

(A) XRD patterns; and (B) FTIR spectra of clay and organoclays [39].

Also, He et al. [37] and Hamdi and Srasra [38] prepared an organoclay by cation exchange with hexadecyltrimethylammonium bromide at different concentrations. The X-ray diffraction analysis of various organoclays prepared indicates the basal spacings are expanded as expected depending on the surfactant concentrations. After treatment with a surfactant (0.5, 1 and 2 CEC of clay) the peak d001 of smectite at 12.69 Å passed to 17.59, 19.25 and 21.62 Å, respectively. The increase in the basal spacing of sodium clay with HDTMA cations can be attributed to the replacement of the inorganic interlayer cations and their hydration water with HDTMA cations [38].

Xi et al. prepared Organoclays based on halloysite, kaolinite and bentonite and used DRX and IR for characterization. XRD pattern has shown that the exchange of cations by surfactant causes the expansion of different clay layers. The expansion is proportional to the concentrations of HDTMA used and varied between the types of clay. For bentonite modified with 2CEC one dominant reflection at 20.2 Å was noted corresponding to basal spacing with surfactant molecules laying flat between clay mineral layers. But For bentonite modified with 4 CEC two d₀₀₁ spacings were observed at18.5 Å corresponding to the bentonite expanded with HDTMA molecule laying flat between two layers and 35.7 Å attributed to the surfactant molecules at right angles to the clay mineral surface. On the other hand, the HDTMA modified kaolinite and halloysite did not show much change in XRD patterns compared to those of untreated ones [30].

3.2 Fourier transforms infrared spectroscopy (FTIR)

Infrared spectroscopy is a powerful tool for the study of the bonding mechanisms on a molecular scale. In FTIR the cationic surfactant is characterized by the presence of C–N (vibrations in tertiary amines) and C\H stretching bands and aliphatic C\H stretching bands of CH₂. In fact, Fourier transforms infrared spectroscopy (FTIR) will further confirm the presence of organics in the clay materials and offers the additional advantage of confirming the configuration of the organic molecule.

Generally, if examining the spectra of raw clay compared to the organoclay; noting the presence of similar bands between both clay such as (H–O–H stretching, H–O–H bending, stretching mode of Si–O…etc.). Thus, additional bands in organoclay: C–N vibrations of tertiary amines and of C–H stretching bands and aliphatic C–H of CH₂. The intensity and width of the similar and additionally bands of absorbance for raw clay and organoclay exhibit distinct differences. Generally, the decrease of band intensity of the OH stretching and bending vibrations are explained by the replacement of the hydrated cations with cationic surfactants [62], which indicates the change of surface clay to the organophilic character. Thus, the increase of surfactant concentration added in clay engenders a slight shift for the symmetric bands of CH₂. Generally, this shift of CH₂ antisymmetric frequency was used to identify the environment surfactant in the interlayer space of organoclay [45]. The higher frequencies indicate a liquid-like environment while the lower frequencies indicate a solid-like environment.

Using infrared spectroscopy, Gammoudi et al. [45] compared the spectrum of raw clay and organic clay showing the presence of similar bands and new bands in organic clay-like as the peaks at 1463 and 1473 cm⁻¹ indicate the presence of C–N vibrations in tertiary amines and the N–H stretching peak at 3016 cm⁻¹ appeared only after the addition of HDTMA at concentrations greater than 3 CEC and the peak of C\H stretching bands of CH₂ and aliphatic C\H stretching bands. The frequency and the intensity of asymmetric and symmetric stretching bands of CH₂ change with the amount of intercalated surfactant. This indicates that, as the loading surfactant on sodium clay increased, the confined amine chains changed to gauche conformation for trans conformation (to lateral arrangement for paraffin arrangement). This finding is in concordance with previous studies [39] (Figure 4).

Thus in the work of Shirzad-Siboni et al. [42], the comparison of FTIR spectra of organoclay with raw clay exhibits significant changes in some of the peaks. In particular, the shift in the siloxane peak after loading of surfactant, the additional peaks appointed to –CH–stretching vibration, could be observed only in organoclay. Additionally are noted that the band at 3460 cm⁻¹ disappeared after the modification of MMT nonmaterial with CTAB, which indicates the removal of water molecules and the change in the hydrophobicity of MMT nonmaterial. Also, is noted that with the loading of surfactant asymmetric (CH₂) shifts from 2927 to 2922 cm⁻¹ and symmetric (CH₂) shifts slightly from 2856 to 2852 cm⁻¹ for organoclay. This indicates that, in the existence of added surfactant, the confined surfactant chains adopt a fundamentally all-trans conformation. This result clearly reveals that the surface modification of MMT is achieved by surfactants.

3.3 Scanning electron micrographs and transmission electron microscopy

SEM and TEM are used to collect detailed information on the morphology.

Msodek et al. [39] used SEM to determine the change in surface morphology of raw clay upon the intercalation of HDPy surfactant. Results showed that the photomicrography of raw clay exhibits massive and aggregate morphology (Figure 5). While, at low surfactant concentration (1.0 CEC ≤), the particles exhibit a compact form that can be explained by the interactions between the R groups of alkyl chains of surfactant. For the concentrations in exceeded the CEC of clay, the particles were changed to flat layers.

Figure 5.

Photomicrographs of clay and organoclays [39].

Using SEM and TEM, Pandey and De observed that the raw clay (bentonite) showed rough surface morphology however organo-bentonite showed a smooth surface with large size particles.

Thus Shirzad-Siboni et al. [42] employed SEM analysis to evaluate the surface morphology of the raw clay (montmorillonites,MMT) and organoclay (montmorillonite). Results reveal that the surface morphologies of both raw clay and organoclay have an uneven structure with non-uniform size distribution. The MMT shows massive, aggregated morphology, while, after modification, the clay surface was changed to a non-aggregated morphology with severely crumpled structures. Furthermore, the surface of Organoclay was expanded.

3.4 Physicochemical properties

The intercalation of surfactants in clay changes their Physicochemical properties (CEC, pore volume, Pore size, pH_PZC…etc.).

Hamdi et al. noted that specific surface area decreases significantly as a function of the increase of exchanged surfactant in the specimen. The same results were obtained for the CEC and The pore volume (Vp). However, the value of PZC increased with the increase of exchanged surfactant in the raw clay. The SSA decrease indicates a compact packing of larger surfactant molecules between the silicate layers of mineral clay and blocking the passage of nitrogen molecules [63]. The same outcomes were reported by Pandey and De noted that The Pore size, surface area, as well as micro and mesopore volume, was drastically reduced after cationic surfactant treatment (Table 2).

Adsorbent	SBET	Vp	CEC	pHPZC	Pore size	Reference
Organosmectites
0.5CEC	14.83	0.0861	56	7	—	[38]
1CEC	3.42	0.0157	33	7.7	—
2CEC	1.96	0.0006	28	8	—
Bentonite	33.02	0.10	97.6	—	11.52	[43]
CTAB–bentonite	10.40	0.04	—	—	16.11
Na- montmorillonites	29.089	0.035	—		—	[64]
DTAB- montmorillonites	13.345	0.028	—	6.5	—
CTAB- montmorillonites	6.036	0.022	—	11.2	—
Na-Bentonite	36.5		0.52	4.5		[65]
Organoclay	27.9		0.72	7.8

Table 2.

Physicochemical properties of the raw clay and organoclay.

4. Applications

Organoclays have been used in various applications. These applications include adsorbents, rheological control agents, paints, grease, cosmetics, personal care products, and oil well drilling fluids. Currently, an important application of the organoclays is in pollutant adsorption. In fact, a view of the literature shows that various studies have shown that replacing the inorganic exchange cations of clay minerals with organic cations can result in greatly enhanced abilities to remove various contaminants from water:

4.1 Application of organoclay to remove fluoride, phosphate and nitrate

Phosphate, fluoride and nitrate are essential nutrients in the aquatic environment, but excessive phosphate (above 0.02 mg/L), nitrate (above 0.02 mg/L) and Fluoride (above 1.5 mg/L) input may lead to eutrophication (causing degradation of water quality) respectively. Nowadays, the presence of fluoride, phosphate and nitrate in the environment has been identified as one of the acute problems worldwide. Organoclay has been successfully utilized for the removal of nitrate, phosphate and fluoride:

Gammoudi et al. prepared organoclay with smectite using two cationic surfactants (HDPy and HDTMA) for fluoride removal from wastewaters. The optimal condition suitable for defluoridation consists of low fluoride concentration, contact time equal to 6 h and acidic pH. These organoclays showed high removal capacities for fluoride ions [45].

Xi et al. prepared various Organoclays with on halloysite, kaolinite and bentonite for removal of nitrate. The results showed that all these raw clays showed poor adsorption amounts for nitrate. However, when these clays were modified with surfactant HDTMA in 2 or 4 CEC, the removal amounts of these clays were greatly improved. Thus, among all these organoclays, HDTMA modified bentonite showed the best result [30].

Ma and Zhu [48] used inorganic–organo-bentonite which is prepared by replacing the exchangeable inorganic cations with cetyltrimethylammonium bromide (CTMAB) to phosphures from water. The results of this study reveal that inorganic–organo-bentonite can act as a successful adsorbent for removing the phosphures from contaminated water. More than 95% phosphate and 99% phenanthrene were removed from the water within 30 min. The amount of sorbed phosphate increased as pH decreased and the sorption amount increased slightly with an increase in temperature [48].

4.2 Application of organoclay to remove dye

Dyes and pigments are widely used by several industries like plastics, textile, cosmetics…etc. Textile dyeing process is an important source of contamination responsible for the continuous pollution of the environment. In recent years Organo-clays have been attractive for use as selective sorbents for dyes:

Tabak et al. [49] studied the adsorption of the Reactive Red 120 by cetylpyridinium modified Resadiye bentonite (CP-bentonite) prepared by ion exchange at different temperature, force ionique and pH levels. Their results showed that the structural arrangement of cetylpyridinium ions in the CP-bentonite sample, as well as the pH, temperature and ionic strength of the bulk solution, influenced the adsorption of RR 120 dye from aqueous solutions by CP-bentonite [49].

Ma et al. [46] showed that bentonite modified with hexadecyltrimethylammonium bromide could be used as a highly efficient adsorbent for the removal of acid dyes from an aqueous solution. The study reveals that the adsorption capacity of organobentonites is affected by the surfactant alkyl chain length [46].

Gammoudi and Srassra [50] studied the removal of three dyes (methyl orange (MO), indigo carmine (IC) and phenol red (PR) on the surface of Tunisian HDPy-modified; the maximum adsorption capacity from the Langmuir equation was calculated at 227.27, 326.40, and 344.82 mg/g, respectively. The results revealed that the kinetics uptake was fast and equilibrium was attained within 30 min for IC, PR and 60 min for MO.

4.3 Application of organoclay to remove pesticides and herbicide

Shirzad-Siboni et al. [42] were prepare surfactant-modified pillared montmorillonites using cetyltrimethylammonium bromide and used them as adsorbents to remove bentazon from aqueous solutions. Results showed that the maximum adsorption capacity was estimated to be 500 mg/g at pH 3 and room temperature. The removal efficiency at optimum pH 3 was found to increase with the increase in contact time and adsorption dosage, but to decrease with an increase in initial bentazon concentration [42].

Carrizosa et al. [41] examined the adsorption of the herbicide dicamba by organoclays at various concentrations and pH levels. Their results showed that the adsorption capacity of organoclays is favored for high-layer charge and saturation with bulky organic cations close to the CEC.

4.4 Application of organoclay to remove heavy metal

Some heavy metals are notorious water pollutants with high toxicity and carcinogenicity. Heavy metals have been removed from water by adsorption technology using nanoparticles. Organoclay is effective for the removal of various heavy metals. The elimination efficacies of these contaminants are discussed below.

HDTMA modified natural kaolin has been confirmed effective sorbent for Cr (VI) with a maximum adsorption capacity of 27.8 mg/g, while the unmodified natural kaolin was only 0.7 mg/g [60]. Results indicate that most of the adsorption of chromate occurred through the anion exchange of the Br-anion of the HDTMA ion pair [66].

Similarly, the adsorption scheme of oxygen anions of Cr and Mowas studied with bentonite modified by cetylpyridine bromide (CPBr). The equilibrium adsorption capacity of Mo (VI) of 1.4 mmol/g quantity to double the capacity of Cr(VI) (0.7 mmol/g), indicating that Mo (VI) was removed on organic bentonite in the form of polynuclear anions [67].

4.5 Application of organoclay to remove pharmaceutical contaminants

Various researches have reported the successful elimination of pharmaceutical pollutants using organoclay:

Saitoh and Shibayama synthesized organo-clays: Didodecyldimethylammonium bromide (DDAB)-montmorillonite which was used for the removal of 1β-lactam antibiotics from water. The study showed that the removal of antibiotics increased with increasing the amount of organoclay added and the amount of DDAB sorbed on MT. Thus, the authors postulated that the Didodecyldimethylammonium bromide (DDAB)-montmorillonite (MT) organoclay was a useful sorbent not only for the removal of β-lactam antibiotics from water but for their eco-friendly degradation [54].

Polubesova et al. [68] examined tetracycline and sulfonamide antibiotics sorption by the BDMHDA modified montmorillonite. Their results indicated that BDMHDA modified montmorillonite is very efficient for water purification from tetracycline and sulfonamide antibiotics [68].

Guégan and Le Forestier [47] used modified montmorillonite with tetramethyl ammonium (TMA) and hexadecyl trimethyl ammonium (HDTMA) cationic surfactants as adsorbents for the retention of amoxicillin (AMX) [47].

4.6 Application of organoclay to remove hydrocarbons

Masooleh et al. [53] studied the performance of a organically modified nanoclay for petroleum hydrocarbon adsorption. The obtained results that the adsorption capacity of the organoclay was clearly higher than that of the unmodified clay and the hydrocarbons the adsorption capacity was in the range of 4 to 10 g of adsorbent. Also, adsorption equilibrium was attained within 1 h.

4.7 Application of organoclay to remove phenol

Park et al. [57] prepared two types of organoclays from different surfactants (DDTMA and DDDMA) for the adsorption of phenolic compounds. This study revealed the potential utility of the organoclays as adsorbents for the uptake of industrial pollutants in environmental applications.

Zhang et al. [64] were prepared organoclays using withdodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB); were used as adsorbents for 4-chlorophenol and 2,4-dichlorophenol. This study demonstrates that the adsorption process is affected by the initial solution pH and temperature.

4.8 Application of organoclay to remove radioactive

Bentonite clay is suggested as a buffer material in various concepts for repositories for high-level radioactive waste. Two different mechanisms have been established to study the importance of the ionic balance between the interlayer space of montmorillonites and an external solution: the Donnan equilibrium and the ion exchange equilibrium [69].

Yang et al. [55] synthesized Hexadecylpyridinium Chloride Monohydrate modified bentonite (HDPy-bent) and used it as an adsorbent to remove-99 (99Tc). Results are demonstrated that the HDPy-bent is a low-cost sorbent which can efficiently eliminate Technetium-99 from wastewaters.

Li et al. [58] examined the efficacy of organoclay as sorbents to bind iodide (I⁻) and iodate (IO₃⁻) from groundwater. Results showed that these sorbents were highly effective at removing I⁻ and IO₃ from groundwater under oxic conditions, with the adsorption capacity up to 30 mg I/g sorbent.

Some studies, evaluate the efficiency and capability of organoclay to simultaneously remove various pollutants from wastewater:

Yahya et al. [61] used smectitic clay modified using cationic surfactant (hexadecylpyridinium for the removal of fluoride and phosphate single and industrial aqueous solutions. The results show low adsorption ability for fluoride and phosphate ions comparing the case of single solutions. Thus, the selectivity of fluoride is better than phosphate and with coexisting chloride, sulfate ions and other cations.

Xiaoying et al. [36] are studying the possibility of organoclays used to simultaneously remove amoxicillin (AMX) and Cu (II) from wastewater. Results showed that the adsorption of AMX onto organ-bentonite was 6 times higher than that using bentonite (control), while adsorption of Cu (II) on organ-bentonite showed comparable results as that using bentonite. The simultaneous adsorption of AMX and Cu (II) onto organ-bentonite occurred through partition for AMX and ion-exchange for Cu (II). More than 34.8% AMX and 43.6% Cu (II) were removed from industrial wastewater, indicating its great potential removal of mixed organic and metal contaminants.

Oyanedel-Craver et al. [36] were studying the feasibility of using hexadecyltrimethylammonium bentonite clay (HDTMA-clay) and benzyl triethylammonium bentonite clay (BTEA-clay) for simultaneous sorption of benzene and one of four heavy metals (Pb, Cd, Zn and Hg). Results showed that both organoclays tested had dual sorptive properties for both heavy metals and an organic contaminant. But, sorption of Pb, Cd, and Zn on both BTEA- and HDTMA-clay decreases in the presence of benzene relative to the sorption obtained without benzene present.

Generally, the predominant mechanism of the adsorption of dye, inorganic oxyanions (fluoride, phosphate nitrate) is an ion exchange [46, 51, 61] (Figure 6). The mechanisms mainly include electrostatic adsorption of heavy metal, redox, ion exchange, precipitation, coordination (chelation), as well as surface complexation. For heavy metals, the mechanisms mainly include surface complexation, redox, ion exchange, precipitation, coordination (chelation) and electrostatic adsorption (Figure 7) [26].

Figure 6.

Mechanism of pollutant (P) uptake in organoclay.

Figure 7.

Adsorption mechanisms of functional organoclays for heavy metal ions [26].

Table 3 represents various applications of organoclay for the removal of wastewaters pollutants by adsorption.

Pollutants	Removing capacities	Isotherm study	Kinetics study	Mechanism	Reference
Dye	144.08–249.62	—	—	ion-exchange	[46]
Dye	227.27–344.82	Langmuir	pseudo-second order	ion-exchange	[50]
Dye	81.97	Langmuir	pseudo-second order	ion-exchange	[49]
Dye	324.36–399.74	Freundlich	pseudo-second order	—	[65]
Heavy metal	11.970	Langmuir	pseudo-second order	Complexation	[70]
Heavy metal	—	Freundlich	pseudo-second order	ion-exchange	[71]
Herbicide	500 mg/g	Langmuir	pseudo-second order	—	[42]
Nitrate	(0.287 meq/g	Langmuir	pseudo-second order	—	[72]
Chromate-molybdate	0.7–1.4 mmol/g	—	pseudo-second order	ion-exchange	[73]
chlorophenols	458.2–585.80	Langmuir	pseudo-second order	Complexation	[64]
Phenol	—	Freundlich	pseudo-second order	various mechanisms	[57]
Iodide and iodate	21.1–27.	Langmuir	—	—	[58]
Antibiotics	96–99.9%	Langmuir	—	—	[68]
Fluoride	14.02	Langmuir	pseudo-second order	ion-exchange	[45]
Nitrate	2.63–15.38	Langmuir	pseudo-second order	ion-exchange	[74]
Dey	49.53 mg g^−1	—	—	—	[43]
Nitrate-perchlorate	0.6–1.1 mmolg^−1	Langmuir	pseudo-second order	—	[29]
Phosphate-fluoride	11.36–27.77	Langmuir	pseudo-second order	ion-exchange	[61]
Amoxicillin-Cu(II)	34.8–43.6%	Langmuir; Freundlich	pseudo-second order pseudo-first order	partition; ion-exchange	[60]

Table 3.

Applications of organoclay for the elimination of water pollutants by adsorption.

5. Conclusion

The study of organoclays is a vast field and shows immense potential to be explored. This chapter describes the various ways of preparation of organoclays with the use of cationic surfactants (quaternary alkyl ammonium). Generally, organoclay is obtained by the replacement of the inorganic cations through cation exchange with surfactant. Organoclay can be made using a variety of clay minerals; however, smectite is the most commonly used due to its specific properties. Thus, quaternary ammonium cations are most commonly used as surfactants.

A detailed understanding of the structure of organoclay is of importance in its design and applications. In this chapter, FTIR, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) has been employed to provide insights into the interlayer structure and morphology of organoclay. The details are as follows:

• XRD patterns show that the interlayer spacing increased with the increase of the added surfactant concentration.

• FTIR spectra confirm these results were by the changes in frequencies and intensities of symmetric and antisymmetric stretching bands of -CH₂.

• The intercalation of surfactants in clay decreases the specific surface area, CEC and pore volume. However, increases the value of pH ZPC.

Using SEM and TEM indicate that the raw clay showed rough surface morphology however organoclay showed a smooth surface with large size particles.

Organoclays can be used in various applications including adsorbent systems in the environmental field. These adsorbents display interesting adsorption properties for several organic compounds, especially hydrophobic chemicals.

Despite the potential interest in environmental applications, the use of organoclays appears to be limited to batch experiments but has not yet been explored under dynamic conditions that reduce the efficiency of adsorption.

Finley, overall, in this chapter researchers suggest that the Organoclay could be considered a cheap and efficient adsorbent for the removal of most of the chemical pollutants from wastewater that could be of socioeconomic and environmental relevance.