**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].

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].

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

#### **Figure 3.**

*Arrangement of surfactants in the interlayer space of a clay.*

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

#### **Figure 4.** *(A) XRD patterns; and (B) FTIR spectra of clay and organoclays [39].*

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<sup>−</sup><sup>1</sup> indicate the presence of C–N vibrations in tertiary amines and the N–H stretching peak at 3016 cm<sup>−</sup><sup>1</sup> 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**).

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

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<sup>−</sup><sup>1</sup> 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<sup>−</sup><sup>1</sup> and symmetric (CH2) shifts slightly from 2856 to 2852 cm<sup>−</sup><sup>1</sup> 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.
