## 3 Results and Discussion
### Synthesis of MIP on Terbium Nitrate
#### 3.2.3. Sorption and Desorption Properties of the MIPs and NIPs  
The sorption properties of the MIPs are based on their specific structure. These properties are explained by the processes of selective recognition of molecules in the presence of other molecules. It is caused by the presence of the molecular imprints that are created during the synthesis of the MIP polymer. The characteristic of the template determines the specificity, and hence, the ability of the MIP to adsorb specific molecules. Figure 8: SEM picture of the MIP based on terbium(III) nitrate. Figure 9: SEM picture of the NIP. Thus, the sorption and desorption properties of the MIPs ensure their use in various fields, such as chromatography, sensors, catalysts, membrane processes, etc. In this regard, in this work, research was conducted on the adsorption and desorption of Tb from MIP and NIP. For this purpose, the wavelength of the solutions of terbium with a concentration of 0.5 g/100 mL was determined. The wavelength was 281 nm. After that, 10 mL of each metal solution was prepared, and the MIP and NIP were placed into them in a glass filter. Then, using a spectrophotometer, the absorbance of the solution was measured every 15 min throughout 3 h. After 24 h, a control measurement was carried out. Along with the sorption of Tb on the MIP, the sorption on the NIP was also carried out on a comparative basis. The changing of the terbium concentration during sorption by the MIP and NIP is shown in Figure 10. From this graph, we can see that for the MIP, the sorption was active for 2 h and reached a concentration of 0.353 g/100 mL in a sorbent, and then, the value was constant. For the NIP, the sorption was active for more than 1 h, and after that, the value reached 0.050 g/100 mL in a sorbent and become constant. Based on the results in Figure 10, in order to evaluate the adsorption efficiency of the MIP and NIP, the sorption degree and sorption capacity were calculated. The following equations were used for the calculations of the sorption parameters:  
Sorption degree:  
\[\eta=\frac{C_{0}-C_{equilibrium}}{C_{0}}\times 100\%\]  
where C\({}_{0}\) is an initial concentration of terbium nitrate in a solution, g/100 mL; and C\({}_{\text{equilibrium}}\) is a concentration of terbium nitrate in a solution at a certain time interval, g/100 mL. Sorption capacity:  
\[Q=\frac{\left(C_{0}-C_{equilibrium}\right)\times V_{solution}}{m_{solvent}}\]  
where C\({}_{0}\) is an initial concentration of terbium nitrate in a solution, g/100 mL; C\({}_{\text{equilibrium}}\) is a concentration of terbium nitrate in a solution at a certain time interval, g/100 mL; V\({}_{\text{solution}}\) is a volume of solution of terbium nitrate taken for sorption experiments, mL; and m\({}_{\text{sorbent}}\) is a mass of MIP/NIP taken for sorption experiments, g.  
Figure 10: Change of the concentration of Tb during adsorption: in the solution studied (**a**); and in the MIP and NIP (**b**). The sorption degree of terbium on the MIP and NIP is shown on Figure 11, while the sorption capacity of the MIP and NIP is shown on Figure 12. From the data, we can conclude that the most active sorption is observed during 120 min (2 h); the sorption degree is 70.80% for MIP and 9.95% for NIP; and the sorption capacity is 3.54 g/g for MIP and 0.50 g/g for NIP. The Tb sorption character is different for MIP and NIP--in the case of NIP, the activity of sorption is observed at one hour, after what the values of the concentration and sorption properties become constant. Also, control measurements after 24 h were performed, and the values of the sorption parameters are presented in Table 7. Based on the results, it can be concluded that the adsorption efficiency of the MIP is seven times greater than that of the NIP. Figure 11: Sorption degree of the MIP and NIP in relation to Tb. Figure 12: Sorption capacity of the MIP and NIP in relation to Tb.