## 3 Results and Discussion
### Batch Desorption Studies
#### 3.6.2 Detailed Adsorption Studies
This supports the concept that the adsorption of ZDV and phenol onto biochar/rGO/DES-glycerol resulted from several adsorption processes involving simultaneous reactions such as hydrophobic, \(\pi\)-\(\pi\) interactions, and H-bonding between the adsorbate molecules and the adsorbents. The rate-controlling step of the adsorption process was determined using the intra-particle diffusion model (IPD). In addition, the rate-controlling step is generally the slowest step in the sorption process, and this stage can be attributed to external mechanisms or to the sorption process itself. The result obtained from Figure 11 reveals that the plot did not pass through the origin, and it is nonlinear. As a result, this confirms that intra-particle diffusion was not the only rate-controlling step [18]. This demonstrates that the sorption of ZDV and phenol onto biochar/rGO/DES-glycerol might be a multistep and heterogeneous process. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & **Conc** & \begin{tabular}{c} **PFO** \\ **qe (mg g\({}^{-1}\))** \\ \end{tabular}  & \begin{tabular}{c} **K\({}_{1}\)** \\ **(min\({}^{-1}\))** \\ \end{tabular}  & \begin{tabular}{c} **R\({}^{2}\)** \\ **qe (mg g\({}^{-1}\))** \\ \end{tabular}  & \begin{tabular}{c} **PSO** \\ **(g (mg min)\({}^{-1}\))** \\ \end{tabular}  & \begin{tabular}{c} **K\({}_{2}\)** \\ **(mg g\({}^{-1}\)h\({}^{-12}\))** \\ \end{tabular}  & \begin{tabular}{c} **IPD K\({}_{diff}\)** \\ **(mg g\({}^{-1}\)h\({}^{-12}\))** \\ \end{tabular}  & \ \begin{tabular}{c} **C** \\ **(mg g\({}^{-1}\))** \\ \end{tabular}  & \begin{tabular}{c} **R\({}^{2}\)** \\ **(mg g\({}^{-1}\))** \\ \end{tabular}  \\ \hline ZDV & 5 & 8.881 & 0.044 & 0.961 & 10.324 & 0.005 & 0.983 & 0.686 & 1.121 & 0.963 \\ \hline  & 10 & 14.941 & 0.041 & 0.742 & 17.327 & 0.003 &  
Regeneration/Desorption Studies  
It is critical to prevent secondary waste generation by dumping (contaminated) adsorbents into the environment. The reusability of adsorbents was investigated to renew and isolate the pollutants. The regeneration study was conducted for five cycles of adsorption and desorption tests. This experiment was carried out by adding 0.50 g of the adsorbent Biochar/rGO/DES-glycerol to 40 mL of 10 mg L\({}^{-1}\) of ZDV and 100 mg L\({}^{-1}\) phenol solutions, respectively. The solutions were agitated for 24 h at room temperature on an orbital shaker at a speed of 200 rpm. After filtering the solutions, the pollutant's equilibrium concentration was determined. The saturated adsorbents were dried in an oven at 80 \({}^{\circ}\)C. Exactly 0.05 g of saturated adsorbents were weighed in conical flasks, 10 mL of ethanol (desorbing solvent) was added, and the flasks were stirred for 30 min. The starting concentration of the contaminants desorbed was calculated using the collected filtrates. The desorption efficiency was calculated using Equation (2). The regeneration test achieved 96% to 49% efficiencies for the recovery of Biochar/rGO/DES-glycerol using ZDV and 93% to 50% using phenol, respectively (Figure 12). These percentage desorption results prove that the recovery of biochar/rGO/DES-glycerol by ZDV and phenol can be achieved. The adsorbent can be reused for up to five cycles during the adsorption of ZDV and four cycles for the adsorption of phenol. The characterization of biochar/rGO/DES-glycerol by FTIR showed a difference between the original material before and after adsorption/regeneration. As shown in Figure 13A for the adsorption of ZDV, the previously observed peak at 2848 cm\({}^{-1}\) corresponding to the CH\({}_{2}\) functional group appeared less intense after adsorption and post-regeneration of the adsorbent material. The broad bands at 1422 cm\({}^{-1}\) and 3530 cm\({}^{-1}\)-3151 cm\({}^{-1}\) belonging to O=C-O alkoxy and -OH functional groups, respectively, have been completely removed from the surface of the adsorbent post-adsorption and regeneration.