3.2.3. Mechanism of Atenolol Adsorption

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 mechanism (Figure 5). *C* **2022**, *8*, x FOR PEER REVIEW 12 of 16

**Figure 5.** Adsorption mechanism of atenolol on activated carbon. **Figure 5.** Adsorption mechanism of atenolol on activated carbon.

**4. Conclusions** 

maceutical drugs and further environmental applications.

Activated carbons with a well-developed porosity were prepared from *Stipa tenacisssima* leaves by chemical activation with phosphoric acid at different activation conditions.

area and, especially, the total pore volume. The obtained results confirm that a 450 °C activation temperature and an impregnation ratio of 2 are suitable for obtaining an activated carbon with a surface area of 1503 m2/g and pore volume of 0.59 cm3/g. The synthesized activated carbons R1-500, R2-500, and R3-500 showed a good adsorption capacity for atenolol removal. The maximum adsorption capacities reached the value of 110 mg/g and showed a similar adsorption capacity as the commercial activated carbon from Darco. The equilibrium and adsorption kinetics results were satisfactorily fitted to Freundlich and Langmuir models and also to the second-order kinetic adsorption equation. Consequently, our findings suggest that a good quality activated carbon could be easily produced by one-step chemical activation with phosphoric acid from cheaper and sustainable raw materials such as *Stipa tenacisssima* leaves, and suitable for the elimination of phar-
