# Reduction of Water Color in a Spinning Disc Reactor
## 4 Discussion  
### FTIR Spectra of Adsorbents before and after Dye Adsorption in the SD Setup  
The FTIR spectra (Figure 7) indicate whether the dye adsorption onto each studied adsorbent took place and also allow for a few remarks on the dye and each adsorbent structure before and after treatment by the SD technology for possible discoloration:  
* The peak at 3608 cm\({}^{-1}\) can be seen in the spectrum of the pure dye (1), it being assigned to N-H in the amine groups due to strong stretching vibrations, since no OH was present in the dye structure. In addition, the peak at 3555 cm\({}^{-1}\) from ZnAlLDH structure was assigned to strong OH stretching vibrations, and the ones at 3571 and 3104 cm\({}^{-1}\), from the ZnAlLDH loaded with dye (ZnAlDH-dye), were assigned to OH stretching vibrations in the LDHs structure or water molecules and to the aromatic benzene nucleus of adsorbed dye, respectively. The peaks at 3453 cm\({}^{-1}\) from the TiO\({}_{2}\) structure, and also at 3454 cm\({}^{-1}\) from the structure of TiO\({}_{2}\) loaded with dye, were assigned to OH stretching vibrations in the TiO\({}_{2}\)-based adsorbent and water molecules, and the same considerations were made for the peaks at 3621 cm\({}^{-1}\) from the Al\({}_{2}\)O\({}_{3}\) structure and 3598 cm\({}^{-1}\) from the Al\({}_{2}\)O\({}_{3}\)-dye structure, but no significant dye adsorption inside of the used adsorbent was shown. * The peak at 2441 cm\({}^{-1}\) for the ZnAlLDH structure after treatment in the SD setup was assigned to the presence of a carboxylic acid (COOH) originating from the studied dye structure adsorbed onto adsorbent surface. * The 1630 cm\({}^{-1}\) peak for the TiO\({}_{2}\) structure was assigned to the strong stretching vibrations of C=N double bonds in the aromatic species adsorbed on it. * The strong deformation vibrations at 1441 and 1428 cm\({}^{-1}\) from the structure of the ZnAlLDH before and after treatment in the SD experimental setup were assigned either to the C-H deformation vibrations from the dye structure, indicating dye adsorption onto the solid adsorbent surface, or to the aliphatic hydroxyl group deformation due to the adsorbent and water molecules. The peaks at 1304 cm\({}^{-1}\) from the ZnAlLDH structure after treatment and at 1370 cm\({}^{-1}\) from the TiO\({}_{2}\) structure after treatment in the SD experimental setup could be assigned either to the O=S=O in the sulfonic groups of the studied dye as result of antisymmetric stretching vibrations, or to NO\({}_{2}\) deformation vibrations due to the active sites of the dye adsorbed onto the TiO\({}_{2}\) sur \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Solid Material Tested**} & \multirow{2}{*}{**SD Treatment Status**} & **Relevant Peaks (cm\({}^{-1}\))/Its Magnitude** \\  & & **(s—Strong; m—Medium; w—Weak)** \\ \hline \multirow{2}{*}{RR dye (1)} & \multirow{2}{*}{no} & 3608 sh, 2093 s, 1641 sh, 1517 s, 1256 s, 1161 m, 1065 s, 891 w, 650 s, \\  & & 378 s, 267 s \\ \hline \multirow{2}{*}{ZnAlLDH} & Before & 3555 sh, 1441 s, 1027 s, 642 s, 485 s, 375 s, 306 s, 260 m \\  & (2) & 3571 sh, 3104 w, 2441 m, 1428 s, 1304 s, 1121 m, 1011 s, 644 s, 581 m, \\  & (3) & 488 s, 373 s, 309 m, 266 m, 226 m \\ \hline \multirow{2}{*}{TiO\({}_{2}\)} & Before (5) & 3453 sh, 1630 w, 898 s, 373 s, 308 s, 265 s \\ \cline{2-3}  & After (4) & 3454 sh, 1370 w, 919 s, 371 s, 261 s \\ \hline \multirow{2}{*}{Al\({}_{2}\)O\({}_{3}\)} & Before (6) & 621 sh, 977 s, 428 m, 374 s, 301 w, 248 s \\ \cline{2-3}  & After (7) & 3598 sh, 977 s, 360 s, 308 s, 264 s \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Representative peaks in the FTIR spectra. face with the help of water molecules.