## 3 Results and Discussion
### FT-IR Spectroscopic Studies
#### 3.1.4 Ferulic Acid  
FA has a more complex structure compared to VA because it has a group C = C in the aliphatic part of the acid. This is manifested in its vibrational spectrum (Figure 4, Table 4). The interaction of FA with the oxide surface caused a number of changes in the spectra of FA/CeO\({}_{2}\) (Figure 4). Bands 1036 cm\({}^{-1}\) (\(\
u_{\text{s}}\)(C-O-CH\({}_{3}\))) and 1205 cm\({}^{-1}\) (\(\
u_{\text{as}}\)(C-O-CH\({}_{3}\))) [72; 73] for FA/CeO\({}_{2}\) were shifted to 1034 cm\({}^{-1}\) and 1211 cm\({}^{-1}\), respectively. In addition, bands at 1115 and 1178 cm\({}^{-1}\) disappeared in the FA/CeO\({}_{2}\) spectra, which was most likely associated with \(\beta\)(CH\({}_{3}\)) vibrations [72], and a new band appeared at 1124 cm\({}^{-1}\). The intensity of the band 1466 cm\({}^{-1}\) (\(\beta\)(CH\({}_{3}\))) [64; 72] significantly decreased (Figure 4). This indicates the participation of the methoxyl group in the interaction with the nanoceria surface.  
The absorption ratios at 1115 cm\({}^{-1}\) for pure FA in the literature data differ between (\(\beta\)(CH\({}_{3}\))--[72]) and (\(\beta\)(CH)--[74]), as well as the absorption ratios of bands at 1113 cm\({}^{-1}\) for VA (\(\beta\)(CH\({}_{3}\))--[65]) and (\(\beta\)(CH)--[15]). However, these bands all corresponded to (\(\beta\)(CH\({}_{3}\))), while the new bands, which appeared at 1124 cm\({}^{-1}\) for FA/CeO\({}_{2}\) and 1130 cm\({}^{-1}\)--for VA/CeO\({}_{2}\), corresponded to \(\beta\)(CH\({}_{3}\)) vibrations of methoxyl groups involved in the interaction with the surface.  
The interaction of the aromatic OH group of FA with CeO\({}_{2}\) can be evidenced by the absence of bands in the spectra of the FA/CeO\({}_{2}\) samples at 1167 cm\({}^{-1}\)\(\beta\)(OH)\({}_{ar}\)[72] and 1290 cm\({}^{-1}\) (v(CO)\({}_{ar}\)) [72], and the appearance of absorption at 1296 cm\({}^{-1}\) (0.1-0.6 mmol/g). Thus, we can discuss the interaction of FA with the surface of CeO\({}_{2}\) through both methoxyl and phenolic groups.  
The formation of carboxylate complexes of FA on the cerium oxide surface was also detected by the FT-IR spectra of FA/CeO\({}_{2}\) samples (Figure 4). The appearance of bands at 1405 cm\({}^{-1}\) (CO) and 1608 cm\({}^{-1}\) (C = O) may be associated with the formation of monodentate carboxylate complexes (\(\Delta\)v = v(C = O) - v(C-O) = 203 cm\({}^{-1}\)). The band 1608 cm\({}^{-1}\) overlapped with the absorption of the aromatic ring vibration (1601 cm\({}^{-1}\)). The new bands at 1450 cm\({}^{-1}\) (v\({}_{\rm as}\) (COO\({}^{-}\))) and 1502 cm\({}^{-1}\) (v\({}_{\rm as}\)(COO\({}^{-}\))) corresponded to the bidentate chelate complexes, since \(\Delta\)v = 52 cm\({}^{-1}\).  
The C = O vibrations at 1666 and 1691 cm\({}^{-1}\) as well as \(\beta\)(COH) at 1325 cm\({}^{-1}\) and \(\delta\)(COH) at 949 cm\({}^{-1}\) ([64,74] in the spectra of FA/CeO\({}_{2}\) (0.1-0.6 mmol/g) disappeared. The appearance of these and other bands of pure acid in the FA/CeO\({}_{2}\) spectra (0.9-1.2 mmol/g) was due to the formation of intermolecular acid associates. This was confirmed by the presence of absorptions in the region of 2400 cm\({}^{-1}\), which correspond to v(OH) of dimers [64]. FA associates can form on the surface when the number of FA molecules exceeds the available active centers of the oxide surface.  
A significant shift up to 1637 cm\({}^{-1}\) was observed for the absorption band v(C = C) for the FA/CeO\({}_{2}\) samples. Such a type of shift was also found in the interaction of FA with metals [74,75].