*2.4. In Batch Equilibrium Experiments*

The CH adsorption capacities were calculated as qt (mg·g−1) at different contact times (t), by applying Equation (1) [13,14,16].

$$\mathbf{q}\_{\rm t} = \frac{\mathbf{C}\_0 - \mathbf{C}\_{\rm t}}{W} \times \mathbf{V}\_{\rm \prime} \tag{1}$$

where V represents the Kp solution volume (herein 15 mL), W is the dried chitosan adsorbent mass (g), and C0 and Ct (mg·L<sup>−</sup>1) represent the initial Kp concentration and the Kp concentration at time t.

A fixed amount of CH (150 mg) was added to flasks containing 15 mL of Kp solution at two initial concentrations (1 <sup>×</sup> 10−<sup>5</sup> M and 5 <sup>×</sup> 10−<sup>6</sup> M, corresponding to ~2.5 mg·L−<sup>1</sup> and ~1.25 mg·L−1, respectively). The adsorption was performed under continuous stirring at 250 rpm, and UV–Vis absorption spectra were recorded to evaluate the Kp removal efficiency and the chitosan adsorption capacities from water. Furthermore, the effect of adsorbent amount was also explored, changing its mass from 35 mg to 200 mg. In this case, the Kp concentration was maintained at 1 <sup>×</sup> 10−<sup>5</sup> M. The effects of solution ionic strength and changes in pH values (ranging from 3 to 12) on the adsorption process were also studied.
