## 3 Results and Discussion
### Adsorption Kinetics  
As mentioned earlier, L and VX exhibit consistently high adsorption rates with little variation observed over different adsorption times. This could be attributed to the adsorption mechanism being physical adsorption, where high adsorption efficiency was achieved through dispersion forces between molecules. Moreover, the magnetic composite nanomaterials possessed a high surface area and mesoporous structure, allowing for a large number of compounds to attach to the adsorption material's surface.  
To assess the kinetics of the adsorption process, two models as the pseudo-first-order model (PFO) and the pseudo-second-order model (PSO) were employed. PFO and PSO were recognized as the classical kinetic models and had been widely applied to investigate the adsorption mechanism by magnetic nanoparticles [46]. These models are described by Equations (3) and (4), respectively. The correlation coefficient (\(R^{2}\)) was used to evaluate the goodness of fit for the adsorption kinetic models.  
The pseudo-first-order kinetic model assumed that the reaction rate of adsorption was directly proportional to the first power of the adsorbate concentration. The expression of the equation is as follows:  
\[\mathrm{q_{t}}=\mathrm{q_{e}}(1-\mathrm{e^{-K_{1}t}}) \tag{3}\]  
where \(\mathrm{q_{t}}\) is the amounts of GB and GD adsorbed (mg/g) at any time t (min), \(\mathrm{q_{e}}\) is the amounts of phenolic compounds adsorbed (mg/g) at equilibrium, and \(\mathrm{K_{1}}\) (min\({}^{-1}\)) is the equilibrium rate constant of pseudo-first-order sorption.  
On the other hand, the pseudo-second-order model indicated that the adsorption of GB and GD compounds on MGONCs depended on the square of the number of available active sites of the adsorbent [44]. The expression of the equation is as follows:  
\[\frac{\mathrm{t}}{\mathrm{q_{t}}}=\frac{1}{\mathrm{K_{2}q_{e}^{2}}}+\frac{ \mathrm{t}}{\mathrm{q_{e}}} \tag{4}\]  
where \(\mathrm{K_{2}}\) is the rate constant for pseudo-second-order kinetics (g/mg\(\cdot\)min).  
The calculated kinetics constants and correlation coefficients for the pseudo-first-order (PFO) and pseudo-second-order (PSO) models are presented in Figures 13 and 14 and Table 1. The results indicated that the correlation coefficients (\(R^{2}\)) for the PFO model were relatively low, with \(R^{2}\) values of 0.90089 for GB and 0.86907 for GD. This suggested that the adsorption of GB and GD from MGONCs does not conform well to the PFO model.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & \multicolumn{3}{c}{**PFO**} & \multicolumn{3}{c}{**PSO**} \\ \cline{2-7}  & \(\mathbf{R^{2}}\) & \(\mathbf{K_{1}}\) (min\({}^{-1}\)) & \(\mathbf{q_{e}}\) (mg/g) & \(\mathbf{R^{2}}\) & \(\mathbf{K_{2}}\) (g\(\cdot\)mg\({}^{-1}\cdot\)min\({}^{-1}\)) & \(\mathbf{q_{e}}\) (mg/g) \\ \hline GB & 0.90089 & 0.73516 & 0.0909 & 0.99742 & 8.82163085 & 0.103125 \\ GD & 0.86907 & 0.52878 & 0.0680 & 0.98594 & 6.79722099 & 0.081349 \\ \hline \end{tabular}
\end{table}
Table 1: Fitting parameters of adsorption kinetic models.  
On the other hand, the correlation coefficients obtained for the PSO model were acceptable, with \(R^{2}\) values of 0.99742 for GB and 0.98594 for GD. These higher \(R^{2}\) values indicated that the PSO model was more suitable for describing the adsorption of GB and GD on MGONCs. The results suggested that the adsorption mechanism is primarily a chemical process. MGONCs contain a significant number of -COOH and -OH groups, which enable favorable electrostatic adsorption and hydrogen bonding between the hydroxyl groups and the active functional groups present in MGONCs.