Formation Of Carboxylic Acid Group

As it was demonstrated in Figure 2, the peaks at 1703 and 1727 cm-1 in the MPS-comprising nanohybrids appeared, while the peak at 1745 cm-1 vanished. Through the formation of MPS-comprising nanohybrids, the observation of the new absorption bands (1707 and 1727 cm-1 ) concomitant of the absorption at 1733 cm-1 may be owing to the formation of ester groups through the reaction between carboxylic acid groups of PAA oligomers and silanol groups of silica moieties 12. Besides, in SiO2/PAA hybrids, the O-H bands were broadened with the increase of silica content from 30 to 40 and 40 wt % and gradually shifted from 3100 cm-1 to 3150 cm-1, respectively (Figure 2). These observations may be the consequence of the strong hetero-associated hydrogen bonds …show more content…
Thus, a successful surface modification with amino groups can be confirmed by the coexistence of bands at about 3200, 1650 and 1150 cm−1, which means it corresponded to the N–H, –C(=O)–N–H secondary amine bond and C–N–C secondary amine moiety, respectively. The formation of the secondary amine bond may be attributed to the attachment between amine groups and the carboxyl groups 13,14. Moreover, as it is revealed by the FT-IR spectra, the copolymers showed no absorption in the characteristic C=C bond region at 1628 cm−1 which can be attributed to the absence monomer …show more content…
The interpretation of the obtained EIS spectra can be made by numerical fitting and the use of equivalent circuits depicted in Figure 7(b) and Zsimp Win software (version 3.21). As shown in Figure7(a). the Nyquist plot for the bare GCE exhibited a very small semicircle, which suggested a low [Fe(CN)6]-3/-4 transfer resistance. Whereas P(AA-co-EHA)/ silica nanohybrids were modified onto the bare GCE surface, the [Fe(CN)6]-3/-4 transfer resistance values (Rc, Table2) increased dramatically, which showed poor electron transfer ability of the nanohybrids. The resistance value of P(AA-co-EHA)/ silica-modified electrodes containing APTS (121.9 Ωcm2) and lower silica content decreased obviously in comparison with resistance value (2671 Ωcm2) of the modified electrodes comprising MPS with higher amount of SiO2. These results were in agreement with the results from CVs. Meanwhile, since the Bode and Phase diagrams of the modified electrode had two peaks and inflection points, respectively two capacitive responses and resistances can be considered. Hence, in the quantitative interpretation of the EIS results, the Cc and RC are capacitance and resistance of the P(AA-co-EHA)/ silica nanohybrid on the GCE and the Cdl and Rct represent the capacitance of the double layer and the resistance of the