3.2.2. Kinetic Study

and (6)). The R<sup>2</sup>

tion = 50 mg/L).

nism (Figure 5).

**(L/mg) R<sup>2</sup>**

[70].

**<sup>q</sup>m (mg/g) K.10<sup>2</sup>**

**Acs** 

Figure 4 presents the adsorption kinetics of atenolol on studied carbons. It is clearly observed that the adsorption of AT was faster for samples R1-500 and CAC than that of R2-500 and R3-500 samples and the maximum uptake was reached in approximately 100 min. The quantity adsorbed at equilibrium found in this study (≈65 mg/g) appeared to be better than that reported by N.K Haro et al. (4.0 mg/g) [46]. *C* **2022**, *8*, x FOR PEER REVIEW 11 of 16

**Figure 4.** Adsorption kinetics of atenolol on different activated carbons at 25 °C, initial concentration C0 = 50 mg/L; adsorbent concentration = 50 mg/L (experimental data: symbols; and second-order adsorption kinetic equation: continuous line). **Figure 4.** Adsorption kinetics of atenolol on different activated carbons at 25 ◦C, initial concentration C<sup>0</sup> = 50 mg/L; adsorbent concentration = 50 mg/L (experimental data: symbols; and second-order adsorption kinetic equation: continuous line).

Table 6 compiles the fitting parameters for the kinetic studies using (Equations (5)

mental ones indicated that atenolol uptake onto all adsorbents could be satisfactorily described by the pseudo-second-order model. This same tendency was observed in the ad-

**Table 6.** Parameters obtained from kinetics curves of atenolol (C0 = 50 mg/L; adsorbent concentra-

**First-Order Model Experiment Second-Order Model** 

**(mg/g) q<sup>m</sup>** 

**qexp** 

R1-500 18.77 1.63 0.68 70.92 69.01 6.63 0.99 R2-500 36.51 2.12 0.94 71.27 69.75 2.16 0.99 R3-500 41.61 1.78 0.84 75.53 71.53 2.07 0.99 CAC 19.74 0.20 0.68 74.06 70.45 7.62 0.99

3.2.3. Mechanism of Atenolol Adsorption

larger than 0.99 as well as the calculated qmax values close to the experi-

**(mg/g)** 

The prepared activated carbon is negatively charged, and its surface is rich in oxygenated function. In addition, the pHpzc was found to be about 8. These facts allow the adsorption of atenolol being this last positively charged solution. The species of atenolol would be fixed on the surface of the activated carbon via the interaction H–H and H–O, and the secondary amine group of atenolol as shown in the following proposed mecha-

**K.10<sup>2</sup>**

**(L/mg) R<sup>2</sup>**

Table 6 compiles the fitting parameters for the kinetic studies using (Equations (5) and (6)). The R<sup>2</sup> larger than 0.99 as well as the calculated qmax values close to the experimental ones indicated that atenolol uptake onto all adsorbents could be satisfactorily described by the pseudo-second-order model. This same tendency was observed in the adsorption of atenolol in a novel β-cyclodextrin adsorbent by Duan et al. [69] and the adsorption of atenolol in biocarbon designed from Melia Azedarach stones by Garcia et al. [70].

**Table 6.** Parameters obtained from kinetics curves of atenolol (C<sup>0</sup> = 50 mg/L; adsorbent concentration = 50 mg/L).

