## 3 Results and Discussion
### Adsorption Study  
Figure 3 shows the effect of contact time on the nitroimidazole adsorption onto SiC NPs, for the initial concentration, \(C_{0}=30\) mg\(\cdot\)L\({}^{-1}\). Nitroimidazole adsorption rapidly increased with time and then reached equilibrium. The contact time required to reach equilibrium was almost 20 min. The removal rate of the adsorbate is higher in the beginning because of the large surface area of the adsorbent available for adsorption, which gradually decreased with the progress of time. The pH of the solution strongly influences adsorbents' surface charge and the ionization of other species present in the aqueous solution. While hydrogen and hydroxyl ions are strongly adsorbed, the adsorption of other ions is often affected by the pH of the solution. Figure 4 shows the effect of pH on nitroimidazole removal by adsorption on SiC NPs at an initial concentration of 30 mg\(\cdot\)L\({}^{-1}\), in the pH range of 1 to 11. The adsorption capacity of nitroimidazoles by SiC NPs increased with increasing  
Figure 3: Effects of contact time on the adsorption of nitroimidazoles onto SiC NPs (\(C_{0}=30\) mg/L, \(T=25\)\({}^{\circ}\)C; adsorbent dose = 0.1 g, pH = 8). Figure 2: Transmission electron microscopy (TEM) **(A)** and scanning electron microscopy (SEM) images **(B)** of SiC nanoparticles. pH, and reached a maximum value at pH 8. A slight decrease in nitroimidazole removal was often observed at a pH greater than 9. Extensive investigations on nitroimidazole adsorption have revealed that its uptake strongly depends upon the concentration and nature of the electrolyte ionic species added to the ion bath [36; 37]. The effect of inorganic salt (KCl) on the adsorption rate of nitroimidazole on SiC NPs was investigated. However, the presence of inorganic salt did not influence the adsorption rate of nitroimidazole. These results confirm that the interactions involved in adsorption are not electrostatic. A dimensionless constant separation factor \(R_{L}\) is defined, to determine whether an adsorption is favorable or not. Adsorption is irreversible when \(R_{L}\) is 0; favorable when \(R_{L}\) is between 0 and 1; linear when \(R_{L}\) is 1; and unfavorable when \(R_{L}\) is greater than 1. \(R_{L}\) is defined as follows:  
\[R_{L}=\frac{1}{1+K_{L}C_{0}}, \tag{8}\]  
All of the computed values of \(R_{L}\) were in the range of 0.5-0.6 for SiC NPs, thereby confirming that the adsorption processes for all of the four different nitroimidazole antibiotics investigated here are favorable. The adsorption kinetics describe the rate of the uptake of the nitroimidazoles on the silicon carbine nanoparticles synthesized here. The mechanism and the potential rate-controlling steps involved in the adsorption were examined using three kinetic models, namely, pseudo-first order (Equation (2)), pseudo-second order (Equation (3)), and intraparticle diffusion (Equation (4)). The parameters \(k_{1}\) and \(q_{e}\) for the pseudo-first order kinetic model were determined from the slope and intercept of the plots of \(\ln(q_{e}-q_{t})\) versus \(t\), and are reported in Table 3, along with the values of the correlation coefficient \(R^{2}\). The values range from 0.95 for RNZ to 0.97 for MNZ. Moreover, the predicted values of \(q_{e}\) are significantly different from the actual experimental values. This suggests that nitroimidazole adsorption onto SiC NPs cannot be described by the pseudo-first order kinetic model. Parameters of other kinetic models are also listed in Table 3. It is obvious that the pseudo-second order kinetic model is capable of accurately describing the experimental data of nitroimidazole adsorption. In this case, the model parameters, i.e., \(k_{2}\) and \(q_{e}\), were obtained from the slope and intercepts of plots of \((t/q_{t})\) versus \(t\), as shown in Figure 6. The correlation coefficients (\(R^{2}\)) of linear plots have high values, which suggest that nitroimidazole adsorption onto SiC NPs follows the pseudo-second order kinetic model.