*3.2. Static Adsorption Experiments*

#### 3.2.1. Adsorption Isotherm

The adsorption isotherms of chrysin on the Bi-MIPs, Bi-NIPs, Si-MIPs and Si-NIPs at (298 K) with chrysin concentrations of 0.2–1.4 mg/mL are presented in Figure 4. As shown in Figure 4a, the chrysin adsorption property for the Bi-MIPs, Bi-NIPs, Si-MIPs and Si-NIPs increased with increasing chrysin concentration. As the concentration increases, the adsorption difference increases. The Bi-MIPs have the highest adsorption capacity of chrysin, followed by Si-MIPs. These results indicate that the Bi-MIPs and Si-MIPs have specific cavities sizes and specific adsorption capacity for chrysin. By comparing Bi-MIPs, Bi-NIPs, Si-MIPs and Si-NIPs to the adsorption capacity of chrysin, the adsorption capacity of the binary functional monomers was better than that of the single functional monomer, which further indicates that the Bi-MIPs have an excellent application prospect.

To analyze the adsorption mechanism, Langmuir and Freundlich isotherm models were used to fit the experimental data when the adsorption process reached the adsorption equilibrium. The equations of these two models are as follows [46–49].

Langmuir isotherm equation:

$$\frac{1}{\mathcal{Q}\_{\text{e}}} = \frac{1}{\mathcal{Q}\_{\text{m}}} + \frac{1}{\mathcal{K}\_{1}\mathcal{Q}\_{\text{m}}} \times \frac{1}{\mathcal{C}\_{\text{e}}} \tag{4}$$

Freundlich isotherm equation:

$$
\ln \mathcal{Q}\_{\mathbf{e}} = \ln \mathcal{k}\_{2} + \frac{1}{\mathbf{n}} \ln \mathcal{C}\_{\mathbf{e}} \tag{5}
$$

where Ce represents the concentration of chrysin at the adsorption equilibrium (mg/mL); Qe represents the chrysin adsorption amount for the Bi-MIPs, Bi-NIPs, Si-MIPs and Si-NIPs at equilibrium (mg/g); Qm represents the maximum adsorption amount of monolayer cov-

erage (mg/g); K1 represents the Langmuir constant (mL/mg); K2 represents the Freundlich constant; and 1/n represents the dimensionless Freundlich constant.

**Figure 4.** (**a**) Adsorption isotherm of the Bi-MIPs, Bi-NIPs, Si-MIPs and Si-NIPs; (**b**) Langmuir adsorption isotherm of the Si-MIPs and Si-NIPs; (**c**) Freundlich adsorption isotherm of the Si-MIPs and Si-NIPs; (**d**) Langmuir adsorption isotherm of the Bi-MIPs and Bi-NIPs; (**e**) Freundlich adsorption isotherm of the Bi-MIPs and Bi-NIPs.

According to the Langmuir and Freundlich isotherm models, the experimental data were fitted and the parameters are shown in Table 1. The Bi-MIPs are illustrated by comparing the Langmuir and Freundlich equation correlation coefficients (the Langmuir and Freundlich correlation coefficients are 0.9953 and 0.9669, respectively). The isothermal adsorption curve of the Bi-MIPs is better represented by the Langmuir model. The Bi-NIPs, Si-MIPs and Si-NIPs were compared and analyzed by the Langmuir and Freundlich equation correlation coefficients (Langmuir and Freundlich correlation coefficients are 0.9946 and 0.9788, 0.9912 and 0.9736, 0.9905 and 0.9596, respectively), indicating that the Bi-NIPs, Si-MIPs and Si-NIPs with Bi-MIPs have the same degree of compatibility with Langmuir. The isothermal adsorption curves of the Bi-NIPs, Si-NIPs and Si-NIPs are better represented by the Langmuir model. These results indicate that the adsorption of chrysin

on the Bi-MIPs occurs via monolayer adsorption, which shows that the Bi-MIPs can easily adsorb chrysin.


**Table 1.** Parameters of the Langmuir and Freundlich adsorption models.
