## 3 Results and Discussion
### Characterization of MIPs and NIPs
#### 3.2.2 Surface Area Measurement via Nitrogen Adsorption-Desorption Analysis  
The surface area of MIPs and NIPs were measured with nitrogen adsorption-desorption analysis. Listed in Table 2 are the structure parameters of MIPs, NIPs, and their silica substrate, including the surface area and average pore diameter. Results showed that the specific surface area for silica gel was only 14.29 m\({}^{2}\) g\({}^{-1}\). In comparison with silica gel, there was a significant increase of surface area for MIP2 (268.2 m\({}^{2}\) g\({}^{-1}\)) and NIP2 (31.53 m\({}^{2}\) g\({}^{-1}\)). However, for bulk polymerization, MIP1 had much lower (seven times lower) surface area compared to that of NIP1 (13.9 m\({}^{2}\) g\({}^{-1}\) versus 91.1 m\({}^{2}\) g\({}^{-1}\)). This implied surface layer imprinting was beneficial for increasing the specific surface area for molecular imprinting. By sol-gel surface layer imprinting, the specific surface area of MIP2 was seven times higher than that of NIP2. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Samples** & **BET Surface Area (m\({}^{2}\) g\({}^{-1}\))** & **Average Pore Diameter (nm)** \\ \hline NIP1 & 91.1 & 6.57 \\ MIP1 & 13.9 & 40.4 \\ Silica gel & 14.29 & 23.07 \\ (spherical 500 nm) & 31.53 & 22.29 \\ MIP2 & 268.2 & 5.542 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: **Brunauer – Emmett-Teller** BET surface area and average pore diameter of MIPs and NIPs and silica gel supports. bound gossypol had occupied most of the binding sites; eventually, the adsorption reached equilibrium. Such rapid adsorption was desirable for its application. For the sol\(-\)gel process without adding the silica gel support, adsorption kinetic experiments were carried out by using a 300 mg L\({}^{-1}\) gossypol solution in methanol for MIP3 and NIP3 at time intervals of 0 to 200 min. Figure 3A3 shows the overall kinetic curve of MIP3 was similar to that of MIP2 but with much lower adsorption capacity than that of MIP3. The equilibrium times, adsorption capacities, and IF of MIP1, MIP2, and MIP3 are summarized in Table 3. For MIP1, it took as long as 720 min to reach equilibrium. However, for MIP2 and MIP3, the adsorption equilibrium time was much shorter. Results showed that the sol-gel and surface layer imprinting promoted the diffusion of the template to the binding sites. The consequence of this was more complete removal of templates and lower mass transfer resistance compared to traditional bulk MIPs. The differences in kinetic and \(Q_{e}\) between MIP1 and MIP2 could also be related to the different affinity of monomers used for MIP synthesis--not only to morphological aspects. Figure 3: **(A)** Adsorption kinetics of MIPs and NIPs; **(B)** two kinetic models by nonlinear fitting for MIPs (**A1**: bulk polymerization: 10 mg of absorbents in 5.0 mL of 300 mg\(\cdot\)L\({}^{-1}\) gossypol solution from 0 to 900 min; **A2**: sol\(-\)gel and surface layer imprinting: 10 mg of absorbents in 5.0 mL of 300 mg\(\cdot\)L\({}^{-1}\) gossypol solution from 0 to 900 min; **A3**: sol\(-\)gel without adding silica gel: 10 mg of absorbents in 5.0 mL of 300 mg\(\cdot\)L\({}^{-1}\) gossypol in methanol from 0 to 200 min). In addition, the IF value of MIP2 was 2.53, which was much higher than that of MIP1 (IF = 1.14) and MIP3 (IF = 1.22), indicating a better imprinting effect of the surface molecular imprinting. Overall, the faster adsorption kinetics, decent binding capacity, and improved imprinting effect demonstrated the merits of silica gel as the supporting material in the preparation of molecular imprinted materials. A comparison of the kinetics of adsorption behaviors of MIPs and NIPs by different imprinting approaches for gossypol is presented in Figure 3B1-B3), and the corresponding kinetic parameters and correlation coefficients are summarized in Table 4. The two most common kinetic models--the pseudo-first-order and the pseudo-second-order models [51; 52]--were employed to analyze the kinetic data.