## 3 Results and Discussion
### Batch Desorption Studies
#### 3.6.2 Detailed Adsorption Studies
Electrostatic forces had little effect at this stage, and adsorption can be due to any mechanism other than electrostatic interactions. Nonetheless, the study of the impact of pH showed an adsorption capacity between 50 and 60 per cent from pH 4 to 8, which is still very significant. The percentage removal of phenol reached 31% at pH = 11.00. Interfering ions may have outcompeted phenolic molecules for adsorption sites at higher pH values, resulting in the observed adsorption trend. The reduced adsorption capacity towards pH 11.00 is due to the negatively charged adsorbent surface of biochar/rGO/DES-glycerol, which repels phenoxide ions. At pH 10.0, the surface of the biochar/rGO/DES-glycerol and phenol molecules was negatively charged, resulting in an increasing electrostatic repulsion; hence, the reduced adsorption capacity was observed. Figure 8: pH (pzc) of biochar/rGO/DES-glycerol. Isotherm Studies  
The relationship between the number of organic pollutants adsorbed onto biochar/rGO/DES-glycerol and an adsorption isotherm presents the pollutant's concentration at the equilibrium state. The adsorption isotherm investigation also reveals the distribution of adsorbate molecules in the solid and liquid phases at equilibrium. For design and operating purposes, selecting a suitable isotherm model is critical. The models that best describe equilibrium data are found to be suitably derived from the regression analysis with the highest degree of unison. Furthermore, the adsorption isotherm provides critical information about the adsorption process's capabilities for wastewater purification applications. Multiple isotherm models describe equilibrium curves and extract system information from the literature. [PERSON] and [PERSON]'s isotherms were used in this study to describe equilibrium adsorption, and investigated parameters are shown in Table 3. The R\({}^{2}\) closest to 1 indicated that Langmuir was the best-fit model for the experimental data during the adsorption of ZDV and phenol onto biochar/rGO/DES-glycerol. According to empirical models and theoretical evidence, ZDV and phenol adsorption onto biochar/rGO/DES-glycerol were primarily monolayer adsorption. The Langmuir model implies that (i) the adsorption is monolayer and occurs on the adsorbent surface with an equal number of adsorption sites, and (ii) the adsorbed molecules do not interact. The model is appropriate for the adsorption of contaminants in various sites with comparable energies [43]. The maximum ZDV and phenol adsorption capacity on biochar/rGO/DES-glycerol obtained from the Langmuir model is 20.192 mg/g and 61.653 mg/g, respectively. A crucial element of the Langmuir isotherm may be described by a dimensionless constant known as the equilibrium parameter \(R_{L}\). \(R_{L}\) is expressed by the following equation:  
\[R_{L}=\frac{1}{1+K_{L}C_{i}} \tag{9}\]  
\(K_{L}\) is the Langmuir constant, while \(C_{i}\) denotes the initial pollutant concentration. Unfavorable adsorption circumstances are indicated by \(R_{L}\) values larger than one, and RL values between one and zero characterize favorable adsorption conditions. An \(R_{L}\) value of 1 or 0 indicates either linear or irreversible adsorption. The degree of favorability is strongly associated with the irreversibility of the system, offering a qualitative assessment of the interactions between the adsorbent and adsorbate. Table 3 shows that the process has \(R_{L}\) values of 0.984, indicative of favorable adsorption [44]. These findings suggest that the experimental adsorption system is better represented by the Langmuir isotherm (Figure 9A,B), implying that adsorption sites are energetically homogenous. Furthermore, Freundlich R\({}^{2}\) values for both the adsorption of ZDV and phenol were greater than 0.9,