*2.9. X-ray Diffraction (XRD)*

Raw OPEFB, OPEFB cellulose and OPEFB microcrystalline cellulose were analyzed by using a Bruker D2 Phaser X-Ray diffractometer (Billerica, MA, USA) using Cu Kα X-rays. The samples were tested by using a scan rate of 0.1 s per step from 2θ = 10–40◦ . The crystallinity index (CrI) of all samples was calculated according to the following equation:

$$\text{Crystallimit Index (CrI)} = \frac{\text{I} - \text{I}'}{\text{I}} \times 100 \tag{1}$$

where: I = the height of the intensity for the crystalline peak measured at 2θ = 22–23◦ .; I'= the height of the intensity for the amorphous peak measured at 2θ = 18–19◦ .

The basal spacing and crystallinity of the nano-bentonite (before and after ultrasonication) were analyzed using a Bruker D2 Phaser X-ray diffractometer with Cu Kα X-rays. The samples were tested using a scan rate of 0.1 s per step from 2θ = 5–40◦ . The XRD data were analyzed by using high score plus software. The basal spacing of the nano-bentonite was calculated by using Bragg's Law (nλ = 2d sin θ).
