2.3.4. Dye Adsorption Studies

The adsorption properties of the samples were evaluated using methylene blue (MB) in batch mode. Stock aqueous solutions of MB (0.2–10 mM) were prepared at pH 6 under ambient conditions. For each different set of 3-dram glass vials, adsorbents (ca. 10 mg) were added along with the MB solution (10 mL) at variable dye concentration (0.2–10 mM). The vials were sealed with parafilm and mixed in a horizontal shaker for 24 h at 130 rpm. After mixing for 24 h, the system reached equilibrium and the samples were centrifuged, where the supernatant containing MB was analyzed using UV-vis spectrophotometry. The optical absorbance of MB was determined using a Shimadzu UV-vis spectrophotometer (Bio-RAD FTS-40 IR spectrophotometer, Bio-Rad Laboratories, Inc., Philadelphia, PA, USA) at the maximum absorbance (λmax = 662 nm) to yield a calibration curve across a concentration

range of dye (0.1–10 mM) [14]. The dye adsorption properties of the samples were evaluated by measuring the concentration of unbound MB in the supernatant phase.

## Adsorption of Methylene Blue (MB)

The molar absorptivity of methylene blue (ε-MB) was estimated by the Beer–Lambert law using linear calibration plots and compared against literature values. UV-Vis spectroscopy can be used to determine residual levels of MB in solution after the adsorption process from the experimental value of ε-MB. Adsorption was carried out for all composites at ambient conditions, where the uptake of dye by the composites was determined from the difference between the initial dye concentration (*Co*) and the residual dye concentration (*Ce*), as described by Equation (1).

$$Q\_{\varepsilon} = \frac{(\mathbb{C}\_{\varepsilon} - \mathbb{C}\_{o}) \times V}{m} \tag{1}$$

*Co* (mmol) and *Ce* (mmol) are defined above, where *V* (L) is the volume of dye solution, m is the mass of the adsorbent (g), and Qe is the dye uptake by per mass of adsorbent (mmol/g) at equilibrium.
