## 3 Results and Discussion
### DCF and PARX Adsorption Assays
#### 3.2.5 Adsorption Mechanisms  
It is well-known that organic compounds with aromatic rings can establish \(\pi\)-\(\pi\) dispersive interactions with the graphene layers of carbon materials [57; 58]; thus, it must be assumed that this was an important mechanism in the removal of the drugs with both carbons. Since an adsorption process is usually not limited to a single mechanism, it is necessary to go deeper into the adsorbates/adsorbents properties that, together with the results obtained in adsorption assays, allow elucidating the other removal mechanisms  
Figure 9: Effect of temperature on the adsorption capacity of DCF and PARX for ACK and CC carbons (Adsorbent mass = 10 mg; Contact time = 8 h (CC carbon) and 4 h (ACK carbon); PARX and DCF initial concentration = 100 mg L\({}^{-1}\); Solution volume = 25 mL; Solution initial pH = 6.0 (DCF) and 5.5 (PARX)).  
that can be involved. Hydrogen bonding with the electronegative atoms (F, N, and O) of the adsorbate molecules and the electropositive H of the oxygen functional groups [59; 60] is highly probable, particularly for ACK carbon, given the fact that this carbon presented a surface richer in the -OH phenolic groups and carboxyl groups (-COOH). Effectively, the Sips constant (Table 7) associated with PARX removal shows that the molecule, with F and N atoms in its structure [43], has a higher affinity for ACK carbon.  
Electrostatic attraction should also be considered, particularly in the case of the DCF molecule, which was in its anionic form, while both carbons presented positively charged surfaces. However, CC carbon presents a higher pH\({}_{\text{PZC}}\) (Table 3) and, consequently, has a more positively charged surface, establishing stronger electrostatic interactions with the DCF anionic molecule.  
It must be highlighted that the adsorption results correlate poorly with the surface area of adsorbents, since ACK carbon presented a higher surface area and micropore volume (Table 2) than the commercial carbon, but the maximum uptake capacities of DCF and PARX with the two adsorbents were quite comparable. Carbon's pore size and geometry and local energetic environment have a strong influence on the nanoconfinement of the adsorbate molecules [61]. Previous authors have confirmed the critical role of pore size in porous carbons for the adsorption of pharmaceutical molecules [62; 63; 64], evidencing how important the tailoring is of the textural properties. Analyzing the micropore size distribution of the carbons (Figure 1), it seems that CC carbon presents more supermicropores (0.7-2 nm), which are usually more favorable for the adsorption of organic molecules [65]; thus, the pore size effect also played a role on the adsorption of DCF and PARX.  
Comparing the results obtained in this work with the results previously obtained by the authors, in which argon nutshells were submitted to H\({}_{3}\)PO\({}_{4}\) activation [29] and the resulting carbon (ACH) was applied as a removal agent of the same drug molecules, it can be concluded that KOH activation allows obtaining porous carbons with better properties for the removal of this type of adsorbate. Effectively, ACK carbon achieves uptake capacities 46 and 64% higher for DCF and PARX, respectively, compared to ACH carbon. The authors attributed the better performance of ACK carbon to its higher microporosity.