# Role of Functional Monomers upon the Properties of Bisphenol A Molecularly Imprinted Silica Films
## 3 Results and Discussion
### Batch Rebinding of BPA on BPA-MIP and NIP Films  
The rebinding studies of BPA consisted of adsorption kinetics analysis and isotherm batch adsorption assays, carried out for the two types of BPA-MIP films (i.e., BPA-MIP\({}_{\text{MPTES}}\) and BPA-MIP\({}_{\text{DAMOT}}\)) and their corresponding blank NIP\({}_{\text{MPTES}}\) and NIP\({}_{\text{DAMOT}}\) as references. The specificity for BPA uptake was assessed by calculating the adsorption capacities, Q (mg/g) and imprinting factors, F of films (Figure 7a,b). From this point of view, the quantification of bonded BPA was conducted indirectly by determining the un-bonded BPA from the supernatants at 278 nm (characteristic wavelength for BPA absorbance). Figure 7a shows the adsorption kinetics of the two BPA-MIP films and their corresponding blank NIPs from a 0.20 g/L BPA solution. The adsorption capacity of all films increased rapidly in the first 20 min, especially for the BPA-MIP films. This trend was followed by a plateau after which the binding equilibrium (Qe) was attained, at 60 min. The NIP films presented similar adsorption profiles over time compared to BPA-MIP films  
Figure 6: Optical properties of BPA-MIP films compared to their corresponding NIP in terms of (**a**) Refractive index, n, variation measured in the 200–1000 nm spectral range and (**b**) Measured transmittance spectra as a function of wavelength, in the 250–900 nm range. and attained lower values for the adsorption capacity due to the lack of specific binding sites. More importantly, the imprinting factor (F) of BPA-MIP\({}_{\text{MPTES}}\) (Figure 7b) was 3.03 in the first 5 min, indicating not only excellent imprinting of BPA but also the recommended time of contact for attaining the most specific adsorption of BPA. As a result, the following isothermal adsorption of BPA in ethanol was determined after only 5 min of contact with the two types of films, in a concentration range varying from 0.08 to 0.2 g/L. As shown in Figure 8, the rebinding amounts of BPA increased gradually with the increasing BPA concentration. The rebinding of BPA, for both BPA-MIP films, exhibited an incremental increase of the adsorption capacity values [28]. As expected, the bonded amount of BPA to the MIP was higher than the one bonded to the NIP. Considering that the concentration of BPA feed solution (Ci) was varied between 0.08-0.20 g/L, the maximum adsorption capacity values were registered at 0.20 g/L, for both the BPA-MIP\({}_{\text{MPTES}}\) and NIP\({}_{\text{MPTES}}\) (Qmax 11.98 and 3.96 mg g\({}^{-1}\), respectively). This high difference in BPA binding affinity to the BPA-MIP and NIP clearly indicated the role of the imprinting in the formation of specific binding sites. Moreover, comparing the adsorption capacity values of the two imprinted films, it was observed that BPA-MIP\({}_{\text{DAMOT}}\) registered a maximum adsorption capacity of 8.78 mg/g for the same BPA feed solution (Ci = 0.20 g/L). These results highlighted the impact of the film thickness and the discrete porous structure of BPA-MIP\({}_{\text{DAMOT}}\) film upon the rebinding performance. [PERSON] et al. [2] reported a maximum BPA adsorption of silica MIPs nanospheres of 444.6 umol g\({}^{-1}\) and [PERSON] and [PERSON] [31] reported a Qmax of 170 mg g\({}^{-1}\). Hence, in this case, it seems like thinner films are more efficient for rebinding BPA and the maximum capacities are in good agreement with other reported values. Considering that the best results were obtained for thinner BPA-MIP\({}_{\text{MPTES}}\) films, it was expected to have better performances for NIP\({}_{\text{MPTES}}\) vs. NIP\({}_{\text{DAMOT}}\) films. Thereby, it seemed like the different growth mechanism of the organosilica matrix upon BPA addition somehow affected the following binding properties of BPA-MIP\({}_{\text{DAMOT}}\) films as compared to the MIP/NIP system with MPTES.