**1. Introduction**

The growth of humanity and the development of science and technology are causing an environmental disorder due to the pollution of water by a number of pollutants including synthetic dyes, which have a complex molecular structure, which makes them more stable and difficult. These dyes are discharged with the liquid effluents, which are most of the time directly discharged into watercourses without prior treatment [1]. These colored discharges pose a great threat to human health and the environment because many of the dyes are toxic. Therefore, it is very important to develop efficient methods for the removal of dyes from aqueous media.

Traditional processes such as biological processes give unsatisfactory results due to the composition of these releases of toxic and dyestuffs, which are difficult to biodegrade; on the other hand, physicochemical processes, which include coagulationflocculation, oxidation, and membrane filtration, have been widely studied and have revealed a high efficiency in water discoloration [2, 3]. These techniques have proven to be very effective, but their high cost has prompted many researchers to try other cheaper and abundant materials. Adsorption, as a flexible, simple, and inexpensive approach, can be used for the removal of pollutant chemical species. Every day researchers describe new ways and elaborate a new adsorbent on the basis of good selectivity for a chemical species or for the low cost of the process. The elimination of dyes in aqueous solutions by adsorption on different solid materials, in particular on activated carbon, has been the subject of much work [4–6]. The adsorption of dyes on activated carbon has been found to be very effective, but its use remains limited due to the difficulties of its regeneration and its high cost [7].

For this reason, the use of clay as an adsorbent is of great interest because of its effectiveness, its accessible cost, and its abundance. From this perspective, lot of research has been done on clays and all have shown their depollution efficiency toward dyes [8, 9]. The importance given to these materials is granted to their abundant availability in nature and their great capacity of retention of various pollutants, which is offered by their structure in sheets, which gives a large specific surface toward the adsorption [10, 11].

In this context, our choice focused on clay, which is an adsorbent material found in abundance in Morocco, is effective and more economical. The use of clays for the depollution of waters contaminated by dyes requires a good knowledge of their mineralogical characteristics and of the mechanism of adsorption of these pollutants. On the other hand, Natural Safiot Clay (NSC) materials could be an attractive alternative for the adsorption of various pollutants from wastewater due to their low cost, their lamellar structure, which provides high specific surface areas, thermal stability, high cation exchange capacity, abundance, and high adsorption capacity [12–14].

Generally, most of the studies carried out to eliminate cationic dyes are carried out on single dyes [15], which lead us to study the possibility of eliminating a mixture of two dyes at the same time, close to the real conditions of effluents in the environment, because industrial discharges are a complex mixture of several pollutants.

Recently and with computer development, quantum chemistry calculations are widely used in studies of dye adsorption [16, 17]. A lot of research has been carried out on this theoretical approach; in particular since the appearance of their efficiencies in the study of adsorption mechanisms on the one hand, and the study of behavior of dyes with respect to the adsorbent surface on the other hand [18, 19]. The theoretical reactivity indices based on density functional theory (DFT) have become a powerful

*Use of Natural Safiot Clay for the Removal of Chemical Substances from Aqueous Solutions… DOI: http://dx.doi.org/10.5772/intechopen.101605*

and informative tool for studying organic reactivity and for describing intermolecular interactions [20, 21].

The purpose of this study was to demonstrate the ability of Natural Safiot Clay to remove some mixture industrial dyes such as Basic blue 9 and Basic yellow 28 from single and binary aqueous solutions. This allows optimizing the cost of the process and the quantity of the adsorbent used in the adsorption process to have a multiple removal efficiencies of different pollutants instead of one [22, 23]. In this study, the possibility of adsorption of Basic blue 9 (BB9) and Basic yellow 28 (BY28) in the single and binary system has been studied experimentally and theoretically using density functional theory (DFT) and molecular dynamics simulations (MDS), In order to explain the competitiveness between the two dyes on active sites and their reactivity, check if the experimental results are in good correlation with the theoretical results.

## **2. Materials and methods**

### **2.1 Preparation of natural safiot clay**

The Natural Safiot Clay (NSC) used in this work is collected from a natural basin in the region of Safi in Morocco for removal of Basic blue 9 and Basic yellow 28 from aqueous solutions and used without any prior activation. Samples were ground and sieved to obtain very fine particle sizes and washed with distilled water to ensure the removal of dust and any soluble impurities may exist.

### **2.2 Preparation of dyes solutions mixture**

Basic blue 9 (BB9) and Basic yellow 28 (BY28) as representative cationic dyes were purchased from Sigma-Aldrich with a purity of 99% and used without further purification. The chemical structures of the studied dyes are given in **Figure 1**.

### **2.3 Experimentation conditions of adsorption studies**

For single and binary system, several stock solutions 100 mg/L of BB9 and BY28 dyes have been prepared by mixing calculated volumes of the stock solutions of each dye and accurately diluting it with distilled water. The NSC and mixture of dyes are shaken in batch experiments at various parameters such as the amount of natural safiot clay (5 mg–35 mg), initial dye concentration (10 mg–40 mg/L), and initial solution pH (2–12). The working solutions' pH was adjusted to the desired values with dilute HCl (0.1 M) or NaOH (0.1 M) using a pH-Meter HANNA 5222. After stirring of a prescribed contact time, the solution is filtrated using filter syringe, and the maximum absorbance value of BB9 and BY28 is measured using spectrophotometer UV– Visible (JENWAY 6300) at 663 and 438 nm, respectively, as shown in **Figure 2**.

The percentage removal and the quantity adsorbed qe (mg/g) of dye on NSC were calculated using the following equation:

$$\%Removaldye = \frac{C\_0 - C\_\epsilon}{C\_0} \, \* 100 \tag{1}$$

$$q\_{\epsilon}(m\text{g/g}) = \frac{\text{C}\_0 - \text{C}\_{\epsilon}}{m} \ast V \tag{2}$$

**Figure 1.** *Chemical structures of BB9 and BY28.*

Where C0 (mg/L) and Ce (mg/L) represent the concentration of BB9 and BY28 at initial and equilibrium, respectively, V (L) is the volume of solution, and W (g) is the weight of adsorbent used.
