Montmorillonite: Properties, Characteristics and its Harnessing in Environmental Applications

Abstract

Montmorillonite (MMT) is a 2:1 dioctahedral clay mineral. Due to all the environmental uses, it is an adaptable clay mineral that garnered much attention. In this chapter, we will highlight the distinctive properties and special qualities of MMT and its crucial function in environmental contexts. In this chapter, we will also explore its remarkable adsorption powers to remove contaminants from water and its contribution to erosion reduction and soil stabilization. This chapter reveals through an in-depth examination how MMT promotes eco-friendly practices and offers effective solutions for reducing pollution and preserving ecological balance. Then, we merged the wide range of characteristics of MMT with the vast array of properties of starch biopolymer to prepare a nanocomposite with a high adsorption capacity. Thus, we found a large adsorption capacity of 341.9 mg/g with a removal rate of 97.7%. Furthermore, we will explore its efficacy in removing ibuprofen drug by modifying it with CTAB/ZnO nps. Additionally, its potential application in the electrochemical detection of NiO₂⁻ will be investigated through the incorporation of TiO₂ and ZnO nps on MMT.

1. Introduction

The MMT is a clay mineral composed of two silica tetrahedral sheets and one alumina octahedral sheet that make up this 2:1 layer phyllosilicate. It belongs to the dioctahedral smectite group. Because of its large specific area, high cationic exchange capacity, and indeed its high adsorption capacity and high porosity, MMT is thought to be as a suitable candidate for many applications. For instance, in drug delivery systems, MMT is employed as a pharmaceutical excipient. Its strong adsorption ability contributes to the improvement of drug entrapment and sustained release. In many formulations, MMT usually maintains medication release by firmly adhering to the drug molecule. Furthermore, MMT increases the rate of hydrophobic drug dissolution and bioavailability [1]. It is found in various environmental applications, including soil remediation and water purification, and is a constituent of environmentally friendly materials [2]. Thus, it is used to adsorb toxic compounds like heavy metals such as $H{g}^{2+},C{r}^{3+},P{b}^{2+},C{u}^{2+},Z{n}^{2+},B{a}^{2+},N{i}^{2+},M{n}^{2+},C{d}^{2+}$ and $A{g}^{+}$[3], synthetic dye as methylene blue [4] and pharmaceutic compounds [5]. However, when compared to other adsorbent materials, MMT might have a comparatively low adsorption capability when used alone. This capability may differ based on several variables, such as specific surface area and capacity of cation exchange. MMT’s specific surface area, the ratio of its surface area to mass, has a major effect on how well it adsorbs different compounds. Increasing the specific surface area of MMT can significantly increase its adsorption capacity [6]. Furthermore, the many kinds of adsorption sites that are found on the surface of MMT are crucial in determining how well it can adsorb substances. Interestingly, certain adsorption sites in MMT draw different kinds of molecules, which increases the material’s capacity to adsorb organic and inorganic compounds [6]. Additionally, the adsorption capacity of MMT is influenced by its chemical composition. It is possible to significantly increase MMT’s adsorption capacity through chemical changes, allowing for a wider variety of adsorbed compounds, as demonstrated in the context of chemical alteration [7].

It underwent an acidic treatment to enhance its specific area and then its adsorption capacity. For example, as indicated by Ravichandran and Sivasankar, MMT had an external specific surface area of 19.0 m²/g [6, 7]. However, after the HCl (0.7 M) treatment, its value dramatically increased to 188.3 m²/g [7, 8]. The treated MMT was then used to adsorb Pb(II), Cd(II), Cu(II), Co(II), and Ni (II) from water [8]. Adding nanoparticles to MMT can also enhance specific surface area by generating more adsorption sites and changing the structure of MMT [9]. It can be metallic nanoparticles such as zinc oxide nanoparticles [10], TiO₂ nanoparticles [11], etc. The modification of MMT by organic products and polymers is another commonly used method for organic products, including solvents such as alcohols, ethers, and ethanol [12]. It can also be modified with plastic polymers such as polyethylene [13] and polystyrene [14] or biopolymers such as chitosan [15], starch [16], silane organic chains, alkyls, amines [16].

In this chapter, we will explore the diverse properties of MMT, rendering it indispensable across various fields. Emphasis will be placed on its intrinsic qualities, showcasing how this naturally occurring mineral is not only supportive of environmentally friendly practices but also presents viable solutions for enhancing water quality, reducing pollution, and preserving nature. A detailed examination will be conducted, focusing on the adsorption of methyl orange dye using MMT modified by octadecylammonium and starch biopolymer [17], removal of ibuprofen by MMT-CTAB/ZnO [18] np with photocatalysis methods, and electrochemical detection of NiO₂⁻ by MMT-TiO₂/ZnO [19], delving into the mechanisms and outcomes involved.

2. Structure of MMT clay mineral

The MMT mineral is a 2:1 phyllosilicate. It is composed of two SiO₄ tetrahedral sheets sandwiching an octahedral sheet [20]. This mineral structure exhibits a dioctahedral phyllosilicate composition wherein, among every three octahedral cavities, two are occupied by a trivalent cation (Al³⁺) [21]. Two planes of oxygen and hydroxide ions organized in a compact assembly formed the octahedral sheet, delineating octahedral cavities—two-dimensional networks of tetrahedra form adjacent to this center sheet. The assembly of octahedral and tetrahedral sheets forms a layer. The space between two layers is called interfoliar space. The thickness of the layer with interfoliar space forms the basal spacing d_00l (Figure 1). MMT can be identified by a doubly periodic repeat of a planar lattice that is centered and has parameters ‘a’ and ‘b’, where b = a√3. The structure has monoclinic symmetry (α = γ = 90°, β$\ne$ 90°) due to the orientation of the two tetrahedral sheets and a space group C2/m [21]. Moreover, MMT exhibits stacking faults, including faults due to translations and random rotations [21]. Generally, all types of phyllosilicates have the same lattice parameters (a, b = a√3) and variable c parameter. This is why we always consider d₀₀₁ when referring to basal spacing.

Figure 1.

MMT crystal structure by VESTA software projected along (010).

Dioctahedral smectite is formed of an octahedral cavity layer around two SiO₄ tetrahedral layers [22]. By stacking oxygen planes, tetrahedral or octahedral cavities were created, resulting in tetrahedral or octahedral layers, respectively. The stability of the layer is maintained by the presence of cations within these cavities. MMT is a 2:1 dioctahedral phyllosilicate in which a trivalent metal ion (Al³⁺) occupies two of the three octahedral cavities. In the tetrahedral layer (Si⁴⁺ → Al³⁺) or the octahedral layer (Al³⁺ → Mg²⁺, Mg²⁺ → Li⁺), isomorphic substitutions can occur [22]. The resulting layers are then negatively charged, and to maintain sheet’s electrical neutrality, compensating cations are placed in the distance between the layers (d_00l).

The clay fraction is composed of three structural units (Figure 2): the layer (7–25 Å), the particle (200–1500 Å), and the aggregate (1.5–16 μm) [24]. This structuring determines two types of porosity: inter-aggregate porosity and intra-aggregate porosity.

Figure 2.

The various types of pore spaces in MMT at different scales [23].

MMT is studied and characterized at various scales using diverse methods. At the nanometric scale, powder X-ray diffraction (PXRD) and small angle X-ray scattering (SAXS) are employed to determine cation position, average of water layer, and stacking modes, which can characterize MMT structure when modified with inorganic or organic compounds and to identify structural changes along c parameter [21].

Fourier transform infrared spectroscopy (FTIR) (500–4000 cm⁻¹) is used to determine the exchange capacity ratio and the dioctahedral type of MMT. Inductively coupled plasma (ICP) is utilized to determine the chemical elements and the amount of oxides in MMT. Electronic microscopy is employed to identify and monitor the morphology of both raw and treated MMT. In fact, it enables the observation of MMT at the particle scale, allowing us to visualize the pores and layers [23].

3. Types of MMT

Multiple types of MMT were distinguished among them via numerous factors:

3.1 Chemical composition

The general formula for MMT is provided as follows [25]:

$$\left({\text{Si}}_{\text{4}}\right)\left({\text{Al}}_{\text{2-y}}{\text{Mg}}_{\text{y}}\right){\text{O}}_{\text{10}}{\left(\text{OH}\right)}_{\text{2}}\text{,}{}_{\text{y}}{\text{M}}^{\text{+}}{\text{.nH}}_{\text{2}}\text{O}$$

The chemical composition of MMT varies slightly depending on where it comes from. Its characteristics may change depending on the elements or cations present and their concentration. Thus, when metal ions bind to the adsorption sites of MMT, they have the potential to replace some of the Al, Ca, or Mg cations within the MMT structure. This can lead to the formation of new minerals with different chemical compositions, subsequently influencing the color of MMT [26].

3.2 Geological origin

The physical and chemical properties of MMT might vary depending on the geological formations or mineral deposits. A naturally occurring mineral, montmorillonite can be found all over the world. It was first discovered in France in 1847 at Montmorillon [25], hence its name. It is difficult to get a precise estimate of the total amount of MMT in the world. The amount of MMT in the earth is determined by a number of factors, such as the concentration of the mineral in the soil, the amount of soil that has been studied and examined, and the amount of MMT that is artificially produced. Furthermore, because MMT is a mineral that readily dissolves into soil, accurate assessment is frequently difficult. All these conditions lead to slight substitutions in the tetrahedral sheet charge, with the charge varying e of 0 and 0.1. Based on their chemical formulae, the regions where MMT is found are listed in Table 1.

Place	Chemical formula
Wyoming/USA [23]	(Ca^2+0.07K^+0.01Na^+0.20)[Al^3+1.53Fe^3+0.18Mg^2+0.26Ti^4+0.01][Si^4+3.96Al^3+0.04]-O10(OH2)
France [26]	(Ca0.14Na0.02)∑ = 0.16 (Al1.66Mg0.36Fe0.04) ∑ = 2.08 (Si3.90Al0.10) ∑ = 4.00O10 (OH)2 1.02H2O
Choushan, Zhejiang Province (China) [27]	(Ca0.10Mg0.08)(Al1.51Fe^3+0.14Mg0.35)(Si4)O10(OH)2·nH2O
Gafsa (Tunisia) [24]	(Si4)(Al1.1 Mg0.4 Fe0.5) O10 (OH)2 M^+ (M is a compensating cation)
Grec-Ca [23]	(Si3.923 Al0.077)(Al1.459 26Ti^4+0.018 Fe^3+0.039Fe2^+0.045Mg0.382) O10 (OH)2 (Ca^2+0.18 Na^+0.03)

Table 1.

MMT types according to geological formation.

3.3 Purity and impurities

Impurities may affect texture, color, and intended uses of MMT clay minerals [27]. Such impurities like traces of heavy metals or other minerals like quartz and calcite, which are identified with XRD, could affect the MMT utilization.

4. Purification of MMT clay mineral

The purification process is very important to determine the structural formula before using the MMT clay mineral.

Generally, there are two stages for MMT purification: treatment with hydrochloric acid (HCl) and the use of NaCl (1 M). These protocols are used to ensure the removal of impurities completely.

The HCl titration method was used to remove CaCO₃ from clay minerals, but the pH must not be lower than 5 as this could damage the structure of the MMT clay mineral. On the other hand, the NaCl purification method allows maximum dispersion of the mineral and removal of all impurities greater than 2 μm, as well as cationic exchange. The purification protocol involved dispersing 1 g of MMT in 10 ml of a 1 M NaCl solution. The mixture was stirred using a magnetic stirrer for 24 h and subsequently centrifuged at 4000 rpm for 10 minutes. The cationic exchange reaction is represented as follows:

$$\text{MMT}-{\text{M}}^{+}+\text{NaCl}\to \text{MMT}-{\text{Na}}^{+}+\text{MCl}$$E1

The recovered solid was then washed many times with distilled water to ensure the entire removal of chloride ions. Finally, it was dried at 60° C at 12 h.

5. Cationic exchange capacity

All or part of the compensating cations can be exchanged with those of a saline solution in contact with the clay mineral. This process, known as cation exchange capacity (CEC), can repetitively occur with various cations in the solution. In order to understand the characteristics of these minerals, particularly their hydration and dispersion properties, introducing the concept of cation exchange capacity becomes necessary. Thus, the unique feature of each 2:1 phyllosilicate lies in its cation exchange capacity, denoting the number of monovalent cations capable of substituting the compensating cations in a silicate to balance the electrical charge of 100 g of calcined mineral [23]. For soils (e.g.), the CEC represents the soil’s reservoir of fertility.

The CEC measurements are conducted using various protocols such as the titration method [28, 29, 30], employing ethylene diamine tetra-acetic acid (EDTA) on MMT-Na converted to its calcium form and subsequently reverted to its sodium form to measure the calcium ions that were liberated [30]. Additionally, the Hofman-Klemen test is employed to measure the CEC involving the loss of the entire cation exchange capacity of MMT saturated with a cation possessing a small ionic radius, such as Li (0.63 Å), after heating to 200°C due to the migration of Li cations to the vacant octahedral site [20, 31]. The CEC of MMT ranges between 80 and 150 meq/100 g [32].

6. Hydration and dehydration

6.1 Hydration

Investigating the hydration process in MMT is crucial to evaluate its ability to encapsulate pollutant molecules in its interlayer space. In fact, the hydration property is defined as the ability of MMT to swell in the presence of water.

The distribution of water in the MMT occurs either at the particle scale defining internal water that leads to the penetration of water into the layers of MMT (interlayer hydration) or in the micropores (interparticle dispersion), or between particles and aggregates, referred to as external water [33]. The interlayer hydration varied according to several factors such as CEC, ionic radius of interlayer cations, pH, pressure, relative humidity (RH), and pH. The average number of water layer in MMT can be more than three layers under such conditions of RH, etc., leading to a change in basal distance [32] estimated through the X-ray diffraction method. In Table 2, some examples of the number of water layers in MMT are provided based on cation exchange and its ionic radius [32]. Meanwhile, the external water is estimated to have an average of 4.5 g in Wyoming-Ca [38].

MMT type	Basal distance d001 (Å)	Ion radius (Å)	Number of water layer	References
MMT-Na	≃11.6–12.9	1.12	1	[9, 34]
MMT-Cs	12.35	1.17	1	[35, 36]
MMT-Cu	12.36	0.71	1	[36]
MMT-Li	14.62	0.63	2	[37]
MMT-Ni	15.08	0.72	2	[36]
MMT-Co	14.88	0.74	2	[36]

Table 2.

Average water layer in various types of MMT.

6.2 Dehydration

MMT can undergo a dehydration process under specific conditions involving the removal of water molecules from the MMT structure through heating. The dehydration process was thoroughly examined using thermogravimetric analysis, revealing two distinct stages. The initial stage, occurring between 100°C and 140°C, is associated with the extraction of pore water (external water) due to the very low interaction energy between water molecules and the MMT structure. The second stage, observed in the temperature range of 500–600°C, corresponds to the dehydration of internal water, attributed to the high interaction energy between the water layer and cations [33]. Water distribution is generally conducted through the desiccation/humectation method. In a cycle of desiccation/humectation of MMT, the gain and loss of internal water molecules are quasi-reversible under certain conditions. However, it can be irreversible with smaller interlayer cations (such as lithium and magnesium) [37, 39]. The water content curve in relation to pressure exhibits hysteresis [37].

The concept of hydration and dehydration is necessary to understand the behavior of MMT and its application in various fields, such as water purification and soil remediation.

7. Adsorption capacity

Adsorption capacity of MMT depends on many factors such as surface area, swelling degree, capacity of cationic exchange, and surface charge. But sometimes, it must be modified to elevate adsorption properties. It can be modified with a cation by the addition of an ammonium or phosphonium-based surfactant to MMT, polymer chains, alkyl chains, amines [40, 41], grafting an organosilane [42], etc. The modification of MMT with an organic compound results in an increase in surface area and facilitates the intercalation of various compounds, including nanoparticles, polymers, catalysis, etc. This modification enhances the potential applications of MMT in environmental contexts Table 3. Adsorption capacity is closely related to the surface area when estimating adsorption sites in MMT.

Compound	Method	Contaminant	Adsorption capacity	Ref.
MMT/chitosan nanocomposite	Adsorption	Methyl orange	123.46 mg/g	[43]
Kappa-carrageenan (Car)/sodium alginate (Alg) biopolymers/Na-MMT	Adsorption	Crystal violet	88.8 mg/g	[44]
MMT/bean starch nanocomposite	Adsorption	Heavy metals: Co, Ni	Co: (94%); Ni: 78%	[45]
MMT/TiO2 nanoparticle	Photocatalyse	Rhodamine B		[46]
Phenanthroline/MMT composite	Electrochemical detection	Pb		[47]
montmorillonite-ZnO	Electrochemical detection	Diltiazem hydrochloride drug		[48]

Table 3.

Various applications of MMT in water remediation.

8. Surface area

Various methods have been employed to estimate and determine the surface area and porosity of MMT clay minerals. The absorption of methylene blue (MB) dye is a commonly utilized procedure [4, 49]. Surface area measurement is also conducted using the Brunauer-Emmett-Teller method, involving the adsorption/desorption of nitrogen at 77 K [50]. Furthermore, investigations into the adsorption of ethylene glycol are carried out. The total surface area value is estimated at 700–800 m²/g [51].

9. Main characterization techniques of MMT clay mineral

Many techniques are used to identify and quantify MMT clay minerals. First, the use of powder X-ray diffraction (PXRD) is often considered the primary technique in an optimal strategy for MMT clay mineral identification. It relies on the application of X-rays to the powdered MMT clay mineral sample [25], following Bragg’s law:

$$2dsin\theta =n\lambda$$E2

where:

$\lambda$: X-ray wavelength.

n: diffraction order

$d$: interplanar spacing

$\theta$: angle of X-ray incidence.

This method allows the identification of the clay mineral structure because the dimension of X-ray wavelength is on the order of atom dimensions (angustrum). It also permits the determination of the position of exchanged cations in the MMT structure and characterizes the stacking modes [25, 38]. Second, the identification of MMT clay minerals is followed by the utilization of electron microscopy techniques such as scanning electron microscopy (SEM) and transmission electron microscopy. These methods enable the visualization of MMT clay mineral morphology and tracking changes that occur after any modifications. They also allow the determination of its chemical composition with energy dispersion X-ray fluorescence (EDXRF), its lattice imaging with high-resolution transmission electron microscopy (HRTEM) in TEM, and its structure by selected area electron diffraction (SAED) in TEM. Additionally, Fourier transform infrared spectroscopy (FTIR) is commonly used, and it is based on the absorption of IR radiation by the MMT sample. This technique involves the vibrations of atoms that constitute the clay mineral structure. By analyzing the positions of absorption bands, it is possible to detect functional groups and identify MMT clay minerals. With FTIR, it is easy to identify the dioctahedral type of MMT. It can indicate exchanged cations and efficiently determines organic intercalated molecules [25]. There are many other complementary techniques such as X-ray photoelectron spectroscopy (XPS), X-ray Absorption Spectroscopy, etc.

10. Montmorillonite modified with octadecylammonium/starch composite (PSA/OMMT) for effective removal of methyl orange

The use of MMT clays to reinforce starchy matrices for packaging and wastewater treatment has been investigated in earlier research [52, 53]. Adding MMT modified with octadecylammonium cation to the porous starch matrix (PSA/OMMT) improves its capacity to remove dyes from aqueous solutions. This improvement is brought about by an increase in the specific surface area, which is made possible by better interactions between the organoclay and polysaccharide. These interactions increase the surface functionality of the composite by resulting from the exfoliation of the organoclay and possible hydrogen bond connection of biopolymer chains [54, 55]. Figure 3 provides a graphical illustration of PSA/OMMT. Prior research has investigated the use of MMT clays to strengthen starchy matrices for various purposes.

Figure 3.

Graphical representation of PSA/OMMT in MO adsorption.

The adsorption capacity of the produced PSA/OMMT composite was evaluated using the anionic dye methyl orange (MO).

The adsorption experiments were conducted by studying kinetic adsorption, isotherm adsorption, and thermodynamic adsorption, but first, many parameters were optimized, which are pH effect, time effect, and adsorption dosage effect.

The removal percentage and adsorption capacity experienced a notable increase at pH 9 with 98.5% and 189.7 mg/g [17], respectively. Consequently, pH 9 was determined as the most effective pH for subsequent experiments. Next, the investigation delved into the reaction time, spanning from 5 to 90 minutes, revealing a swift adsorption phase within 30 minutes with a removal rate of 99.2% and an adsorption capacity of 198.5 mg/g. Furthermore, the study of adsorbent dosage on MO adsorption showed a maximal removal efficiency of 197.7 mg/g (with 20 mg of adsorbent). At those optimized, the analysis of kinetic adsorption results indicated that the PSA/OMMT composite’s adsorption of MO fitted well with the pseudo-second-order model. Then, the investigation of the adsorption isotherms results demonstrated a high fitting to the experimental data compared to the Freundlich model and a predicted adsorption capacity close to the experimental value (344.7 mg/g) [17]. This result suggests a preference for a uniform monolayer adsorption behavior for MO dye molecules. Finally, the study of the thermodynamic effect shows that the adsorption of MO on the PSA/MMT is an exothermic nature. Consequently, PSA/OMMT demonstrates significant potential as an efficient and low cost adsorbent for the treatment of methyl-orange-containing wastewater [17]. Table 4 presents a comparative study of these works and other adsorbents for the adsorption of methyl orange.

Adsorbent compound	Adsorption capacity (mg/g)	References
Zn/Al layered double hydroxide	276.55	[56]
Biochar from grape seeds	111.11	[57]
Mesoporous carbon CMK-3	294.1	[58]
PSA/OMMT (1:10)	344.7	[17]

Table 4.

Adsorption of MO with various adsorbents mentioned in the literature.

11. The efficacy of MMT modified with CTAB/ZnO nanocomposite for the removal of methylene blue dye by photocatalysis

The incorporation of nanoparticles into MMT broadens its range of applications, especially in fields like photocatalysis and electrochemical detection. In this study, MMT was modified with CTAB to increase its interlayer distance. Subsequently, ZnO nanoparticles are incorporated onto the surface of MMT/CTAB. Analysis of XRD, TEM, SEM, and Brunauer Emmett Teller (BET) results revealed an exfoliated structure and an increase in surface area, offering more adsorption sites. The as-prepared material exhibited a notable degradation activity, resulting in a 62% yield in degradation of methylene blue [18]. In Figure 4, a graphical illustration of MMT-CTAB/ZnO nanocomposite.

Figure 4.

Graphical illustration of MMT-CTAB/ZnO nanocomposite.

12. MMT/TiO₂-ZnO nanocomposite for a sophisticated detection system for nanomolar level of the food preservative nitrite in sugar byproducts

An additional important application for MMT intercalated catalysis lies in the determination and surveillance of toxic elements. In this study, TiO₂ is employed as a catalysis for NiO₂⁻ detection, but it can be susceptible to the recombination of electron and hole, thereby affecting the electrochemical and conductivity properties of TiO₂. To address this issue, the addition of ZnO nps is necessary to improve charge transfer and catalytic efficiency. Furthermore, to limit nps agglomeration, which would decrease surface area, the addition of MMT was crucial. MMT also provides an additional adsorption site. This modification serves to immobilize ZnO nps and prevent their agglomeration. Figure 5 displays a graphical representation of MMT-TiO₂/ZnO nanocomposite. The obtained sensor reveals a clear limit of detection at 0.12 nM for NO₂⁻ and it exhibited a sensitivity of 0.78 μM⁻¹. The sensor reveals satisfactory precision and strong selectivity in the detection of NO₂⁻ in commercial sugar byproduct samples without interference from the product’s constituents [19]. Table 5 presents previous studies that have been utilized for the detection of NO₂⁻ exhibiting a low limit of detection (LOD) when compared to MMT-TiO₂/ZnO.

Figure 5.

Graphical representation of MMT-TiO₂/ZnO nanocomposite.

Sensor	LOD	References
Chitosan (CS)/carbon paste electrode (CPE)	0.187 μg/ml	[59]
AgPs-(ionic liquid)IL/CPE	3 mM	[60]
Ag/Cu/MWNTs	0.2 mM	[61]
(Graphene oxide)GO/SDBS/GCPE	1.89 mM	[62]

Table 5.

Determination of NiO₂⁻ with various sensors illustrated in the literature.

13. Conclusions and outlook

To wrap up, MMT is an important clay mineral that has received a lot of interest for its utilization, especially in environmental fields. This chapter draws attention to the properties of MMT, its compatibility with organic compounds, such as octadecylammoinum cation and porous starch biopolymer, and their application in the adsorption of methyl orange. It is mentioned here that the structure of MMT is based on an aluminum octahedral situated between two silica tetrahedral layers. Then, it was pointed out that there are many types of MMT that are differentiated in terms of their chemical composition, geological origin, purity, and impurities. Subsequently, this chapter highlighted the interesting properties of MMT such as high isomorphic substitution and cationic exchange capacity, which are measured in the range of 80–150 meq/100 g of MMT. After that, it was pointed out that the hydratation and dehydratation of MMT varied according to the cation exchange in the interlayer space. It was found that the number of water layers estimated more than three layers for the MMT-Na. Another important property of MMT is the high surface area of MMT for about 800 m²/g, which is initiated through three current methods: methylene blue adsorption, ethylene glycol adsorption, and N₂ adsorption/desorption (BET). All these properties ensure that this clay mineral is highly adaptable for adsorption applications.

Thus, we mentioned the application of the adsorption of the nanocomposite MMT modified with octadecylammonium/porous starch (PSA/OMMT). This work merged the high properties of MMT and the porous starch biopolymer, which decreased MMT’s hydrophilicity and enhanced its adsorption capacity. Indeed, it was found significant adsorption of methyl orange ability as high as 344.7 mg/g, which made that PSA/OMMT, which synthesis essentially by MMT clay mineral, is suitable as an economical and effective adsorbent for treating dyeing wastewater. Furthermore, we have studied its effectiveness in removing the ibuprofen drug by modifying it with CTAB/ZnO np. Then, we explored its potential application in the electrochemical detection of NiO₂⁻ by incorporating TiO₂ and ZnO nps onto MMT. Thus, we find an impressive limit of detection equal to 0.12 nM.

It is interesting to mention that MMT and some MMT-based nanocomposites can be influenced by various environmental conditions such as temperature, humidity, and acidity. Therefore, at high temperatures, they may cease to effectively adsorb or photodegrade contaminants in water. On the other hand, they can degrade over time, reducing their durability and potentially releasing contaminants into the environment upon degradation. To overcome these challenges, it is necessary to optimize their performance. MMT can be modified with non-toxic compounds, such as biopolymers, to enhance its thermal, mechanical, and durability properties, thereby prolonging the duration of adsorption and photodegradation of contaminants and ensuring biodegradation without contaminating the soil over time. Additionally, research into efficient and low-cost materials for industrial-scale applications is essential.

Acknowledgments

I want to thank Mr. Abdesslem Ben Haj Amara and Ms. Hafsia Ben Rhaiem for their invaluable assistance in providing necessary documents and correcting the manuscript and their continuous support. Thanks to Dr. Mohamed Amine Djebbi for his constant support and guidance. I am also grateful to Ramzi Chalghaf for his help. We appreciate all those who contributed, whether directly or indirectly, to the development of this work.

Conflict of interest

The authors declare no conflict of interest.