## 3 Results
### Adsorption Properties of GA-FK Gel  
GA-FK gel was used as an adsorbent, and Fe(III) was used as metal pollutant model to evaluate its adsorption performance in aqueous solution. The removal efficiency was taken as the main index. The initial concentration of pollutant, the dosage of adsorbent, the adsorption temperature, and the adsorption time were investigated. The results are show in Figure 7.  
With the increase in initial concentration, the Fe(III) removal rate decreased gradually (see Figure 7a). So, 300 mg\(\cdot\)L\({}^{-1}\) was chosen as the initial concentration for subsequent experiments. With the increase in adsorption dosage, the Fe(III) removal rate increased but the adsorption capacity decreased (see Figure 7b). Therefore, 0.05 g was selected for subsequent experiments. It can be seen from Figure 7c that the Fe(III) removal rate and adsorption capacity increase first, and then decrease, with the temperature increase, and both reach the maximum value when the temperature is 30 \({}^{\circ}\)C. Therefore, 30 \({}^{\circ}\)C is the optimum adsorption temperature.  
As for adsorption time, it results in complex effects on the Fe(III) removal rate and adsorption capacity, which increases first, then decreases, and then increases again (see Figure 7d). The Fe(III) removal rate reached its first peak (93.7%) at 30 min. The removal rate then decreased to 89.1% at 45 min. Then, the removal rate of Fe(III) increased gradually with the increase in adsorption time. The adsorption of Fe(III) on the GA-FK gel gradually  
Figure 7: Adsorption performance of GA-FK gel to Fe(III) in aqueous solution (pH = 6). **(a)** Effects of Fe(III) initial concentration to removal rate (C\({}_{0}\) = 50–2000 mg\(\cdot\)L\({}^{-1}\); Dos. = 0.05 g; 25 \({}^{\circ}\)C; 30 min); **(b)** effects of adsorbent dosage to removal rate (C\({}_{0}\) = 300 mg\(\cdot\)L\({}^{-1}\); pH = 6; 25 \({}^{\circ}\)C; 30 min); **(c)** effects of temperature to removal rate (C\({}_{0}\) = 300 mg\(\cdot\)L\({}^{-1}\); pH = 6; Dos. = 0.05 g; 30 min); **(d)** effects of time to removal rate (C\({}_{0}\) = 300 mg\(\cdot\)L\({}^{-1}\); pH = 6; Dos. = 0.05 g; 30 \({}^{\circ}\)C).  
reached equilibrium after 90 min. The equilibrium adsorption capacity (\(Q_{e}\)) of GA-FK gel to Fe(III) was 142.2 mg:g\({}^{-1}\) (E = 94.8%). Therefore, it can be concluded that the adsorption process of GA-FK gel to Fe(III) is a two-stage pattern accompanied with swelling. In the first stage, the without-swelling adsorbent (GA-FK gel) is rigid, the rapid physical adsorption is attributed to chemical-modified GA-FK gel, which has a plant of mesopores, affording it more active sites. In the second stage, the adsorbent (GA-FK gel) started swelling in the aqueous environment, it transformed from rigid to flexible. The swelling led to pores disappearing and \(Q_{t}\) decreasing. When the swelling reached equilibrium, the adsorption equilibrium was reestablished. The second stage is the decisive one in all adsorption process. In this stage, the adsorption is non-specific adsorption, which includes the complexation of phenolic hydroxyl group of GA, free amino, and carboxyl of FK with Fe(III).