# Study on Dicyandiamide-Imprinted Polymers with Computer-Aided Design
## 2 Results and Discussion
### Adsorption Property of the MIPs  
To obtain a MIP with good adsorption capacity for DCD, a series of MIPs and non-imprinted polymers (NIPs) were prepared using different functional monomers, imprinting molar ratios, and cross-linkers. The adsorption experiments were designed and performed on the basis of the results of theoretical calculations.  
First of all, MIPs were prepared using different functional monomers (MAA, AM, IA, and MBA), when the best imprinting molar ratios of their own were applied and PETA was used as the cross-linker. As shown in Figure 4A, the MIPs with different functional monomers exhibit different adsorption capacities. The MIP, with MAA as the functional monomer, shows the highest adsorption capacity. The sequence for different functional monomers is MAA \(>\) AM \(>\) IA \(>\) MBA, according to the adsorption quantities. Thus, the MAA is the best monomer in our studies for DCD-MIP preparation.  
Figure 4: Adsorption capacities of MIPs and NIPs with different functional monomers (**A**); different imprinting ratios (**B**); and different cross-linking agents (**C**). Adsorption conditions: MIPs or NIPs, 20.0 mg; DCD methanol solution, 100 mg/L, 10.00 mL; 4 h.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Species** & **EGDMA** & **DVB** & **PETA** & **TRIM** \\ \hline DCD & \(-36.49\) & \(-34.92\) & \(-33.61\) & \(-53.30\) \\ MAA & \(-23.63\) & \(-16.02\) & \(-43.58\) & \(-37.54\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Binding energies (\(\Delta E_{\rm B2}\)) between DCD as well as MAA and different cross-linkers at the M062X/6-31G(d,p) level (kJ/mol).  
In order to confirm the best molar ratio for DCD to MAA, the MIPs with different imprinting ratios were prepared, when MAA was used as the functional monomer and PETA was used as the cross-linker. As shown in Figure 4B, the MIP, whose molar ratio of DCD to MAA is 1:5, shows the maximum adsorption quantity. The order of different molar ratios is 1:5 > 1:4 > 1:6 > 1:3, according to the adsorption quantities.  
Then, the experiments for the choice of cross-linker were carried out. In Figure 4C, the MIP was prepared using PETA as the cross-linker with the maximum adsorption quantity, when MAA was the monomer and the molar ratio of DCD to MAA is 1:5. The sequence of cross-linkers is PETA > DVB > TRIM > EGDMA, according to the adsorption quantities, which may indicate that PETA is the best cross-linker in our study.  
To fully evaluate the adsorption properties of the MIPs, a series of NIPs were prepared and used for adsorbing DCD, and then their adsorption capacities were compared with that of the MIPs. These NIPs were prepared through the same process as the preparations of MIPs, excepting the absence of the template (DCD). As shown in Figure 4A-C, the adsorption quantities of the MIPs are always significantly higher than that of the corresponding NIPs, which may be explained by the fact that the MIPs contain the imprinted cavities which match the DCD molecules.  
Finally, on the basis of above experimental results, a DCD-MIP was prepared using MAA as the functional monomer and PETA as the cross-linker, and the molar ratio of DCD to MAA is 1:5. The scanning electron microscope (SEM) photograph of the DCD-MIP is shown in Figure 5A. The average diameter of the MIP microspheres is about 300 nm. In order to obtain the information about the DCD binding characteristics of the DCD-MIP, the adsorption behavior of the DCD-MIP was investigated. The initial DCD concentrations were in the range of 10 to 120 mg/L. A Scatchard plot was used to evaluate the adsorption property of the DCD-MIP. As shown in Figure 5B, the Scatchard plot is a single straight line, which might indicate that the binding sites of the MIP toward DCD are equal in the studied concentration range. The linear regression equation is \(Q/C\) = 0.2618 \(-\) 0.0150Q. On the basis of this equation, it can be concluded that the \(K_{\mathrm{d}}\) value and \(Q_{\mathrm{max}}\) value of the DCD-MIP are 66.67 mg/L and 17.45 mg/g, respectively.