 of pesticide adsorption is given in Table 4. In addition, the other two-parameter isotherms (Dubinin-Radushkevich and Temkin) were also tested and the fitted curves including the isotherm parameters are presented in Figure S1 and Table S1. Amongst two-parameter isotherm models, the Freundlich model provides a good description of imidacloprid adsorption with a higher correlation coefficient (R 2 ) of 0.9770 than that of the Langmuir model (R 2 > 0.9750). The results indicate that the BC has a heterogeneous distribution of surface energy for imidacloprid adsorption [64]. In contrast, the Langmuir isotherm (R 2 > 0.975) fits the experimental adsorption data of acetamiprid and methomyl better than the Freundlich isotherm according to the values of R 2, suggesting the monolayer with the uniform heat of adsorption without interaction between the pesticide adsorbed molecules [65]. Furthermore, the maximum adsorption capacities calculated from the Langmuir model are 32.42, 14.75, and 4.78 mg g −1 for methomyl, imidacloprid and acetamiprid, respectively. Three-parameter isotherms, Sips and Redlich-Peterson, were also tested to amplify the R 2 and for their fittingness to explain the pesticide adsorption on BC.
The Redlich-Peterson model gave the highest R 2 for acetamiprid (0.9942) and methomyl (0.9940) adsorption, implying that it is the better fitting model. However, it is unable to simulate the adsorption behaviors because the values for β were greater than one for both acetamiprid and methomyl adsorption [66]. Thus, the Sips model was well-fitted to all pesticide adsorption data with R 2 values greater than 0.9900, suggesting the heterogeneous surface adsorption of pesticides on BC [36]. The value of n s obtained from the Sips isotherm for methomyl adsorption was higher than one, suggesting that the Sips isotherm tended to resemble the Freundlich model. This indicates the multilayered adsorption of methomyl on the BC surface. saturation coverage on the adsorption sites [63]. Thus, adsorbent loadings of 5 g L −1 for methomyl and acetamiprid and 0.5 g L −1 for imidacloprid were chosen to study the adsorption isotherms and adsorption kinetics of the pesticide removal in aqueous media by the BC material.

Adsorption Isotherm
From the adsorption isotherms in Figures 3 and 4, the equilibrium concentrations (Ce) of methomyl were found to be lower than the those from other pesticide treatments due to the higher adsorption capacity of methomyl of the BC surface. Fitted curves of the adsorption isotherms computed by the two-and three parameter adsorption models, are included in Figures 3 and 4, respectively, whereas the information obtained from fitting the experimental data of pesticide adsorption is given in Table 4. In addition, the other two-parameter isotherms (Dubinin-Radushkevich and Temkin) were also tested and the fitted curves including the isotherm parameters are presented in Figure S1 and Table S1. Amongst two-parameter isotherm models, the Freundlich model provides a good description of imidacloprid adsorption with a higher correlation coefficient (R 2 ) of 0.9770 than that of the Langmuir model (R 2 > 0.9750). The results indicate that the BC has a heterogeneous distribution of surface energy for imidacloprid adsorption [64]. In contrast, the Langmuir isotherm (R 2 > 0.975) fits the experimental adsorption data of acetamiprid and methomyl better than the Freundlich isotherm according to the values of R 2, suggesting the monolayer with the uniform heat of adsorption without interaction between the pesticide adsorbed molecules [65]. Furthermore, the maximum adsorption capacities calculated from the Langmuir model are 32.42, 14.75, and 4.78 mg g −1 for methomyl, imidacloprid and acetamiprid, respectively. Three-parameter isotherms, Sips and Redlich-Peterson, were also tested to amplify the R 2 and for their fittingness to explain the pesticide adsorption on BC.   saturation coverage on the adsorption sites [63]. Thus, adsorbent loadings of 5 g L −1 for methomyl and acetamiprid and 0.5 g L −1 for imidacloprid were chosen to study the adsorption isotherms and adsorption kinetics of the pesticide removal in aqueous media by the BC material.

Adsorption Isotherm
From the adsorption isotherms in Figures 3 and 4, the equilibrium concentrations (Ce) of methomyl were found to be lower than the those from other pesticide treatments due to the higher adsorption capacity of methomyl of the BC surface. Fitted curves of the adsorption isotherms computed by the two-and three parameter adsorption models, are included in Figures 3 and 4, respectively, whereas the information obtained from fitting the experimental data of pesticide adsorption is given in Table 4. In addition, the other two-parameter isotherms (Dubinin-Radushkevich and Temkin) were also tested and the fitted curves including the isotherm parameters are presented in Figure S1 and Table S1. Amongst two-parameter isotherm models, the Freundlich model provides a good description of imidacloprid adsorption with a higher correlation coefficient (R 2 ) of 0.9770 than that of the Langmuir model (R 2 > 0.9750). The results indicate that the BC has a heterogeneous distribution of surface energy for imidacloprid adsorption [64]. In contrast, the Langmuir isotherm (R 2 > 0.975) fits the experimental adsorption data of acetamiprid and methomyl better than the Freundlich isotherm according to the values of R 2, suggesting the monolayer with the uniform heat of adsorption without interaction between the pesticide adsorbed molecules [65]. Furthermore, the maximum adsorption capacities calculated from the Langmuir model are 32.42, 14.75, and 4.78 mg g −1 for methomyl, imidacloprid and acetamiprid, respectively. Three-parameter isotherms, Sips and Redlich-Peterson, were also tested to amplify the R 2 and for their fittingness to explain the pesticide adsorption on BC.    In contrast, the n s values from the Sips isotherm for imidacloprid and acetamiprid are close to one, indicating that the adsorption behavior of imidacloprid and acetamiprid on BC dominantly occurs through monolayer adsorption. Thus, it is clearly seen that the Sips model gave the best fit of the experimental data based on the appropriate constants and correlation coefficients, possibly due to its ability to predict wide ranges of adsorbate concentration [36].

Adsorption Kinetics
The adsorption kinetics of pesticide adsorption on the BC material were studied using the initial pesticide concentration of 50 ppm at 25 • C, sorbent dosages of 5 g L −1 (acetamiprid and methomyl) and 0.5 g L −1 (imidacloprid). Notably, as seen in Figure 2c, it is unnecessary to use a high BC dosage for imidacloprid adsorption. The kinetics of methomyl, imidacloprid, and acetamiprid adsorption on the eucalyptus wood-derived BC ( Figure 5) showed that adsorption of the pesticides rapidly occurred during the first 0.5 h, 2 h, and 3 h of adsorption for removal of imidacloprid, acetamiprid, and methomyl, respectively, and were subsequently followed by a slower rate until equilibrium was reached (at about 1 h for imidacloprid and 6 h for acetamiprid and methomyl). The fast adsorption at the initial stage possibly resulted from the large amount of unoccupied active sites on the biochar's surface and the strong interaction force between pesticide molecules and the surface functional groups of the sorbent [67]. The saturation of active sites and weak interaction force possibly led to the sorption equilibrium after the adsorption process was continuously carried out. To better understand the mechanism of pesticides adsorbed on the BC, three non-linear kinetic models, namely pseudo-first order, pseudo-second order, and Elovich, were applied to analyze the experimental data from the batch experiments.
Pseud-second order (PSO) is given as: where k 1 (h −1 ) is the PFO adsorption rate constant, k 2 (g (mg h) −1 is the PSO rate constant, q e and q t (mg g −1 ) are the amount adsorbed at equilibrium and the amount adsorbed at time "t", respectively [68,69]. The Elovich model can be described as in Equation (9).
Minerals 2022, 12, x FOR PEER REVIEW 10 of 18 the BC, three non-linear kinetic models, namely pseudo-first order, pseudo-second order, and Elovich, were applied to analyze the experimental data from the batch experiments. Pseudo-first order (PFO) is given in Equation (7).
Pseud-second order (PSO) is given as: where k1 (h −1 ) is the PFO adsorption rate constant, k2 (g (mg h) −1 is the PSO rate constant, qe and qt (mg g −1 ) are the amount adsorbed at equilibrium and the amount adsorbed at time "t", respectively [68,69