# Adsorption of Ag (I) Ions at the Zirconium Phosphate/KNO3 Aqueous Solution Interface
## 3 Results and Discussion  
### FTIR Study of the ZrP Samples  
As shown in ref. [17], initial precipitated ZrP is X-ray amorphous. Moreover, its phase composition is preserved after the hydrothermal microwave and mechanochemical modifications although some ordering of the structure takes place [18; 19]. The FTIR spectra of the obtained initial sample and the samples modified as dried xerogel are shown in Figure 1 while those for the samples modified in the form of wet gel are depicted in Figure 2. The bands in the range of 1000-1100 cm\({}^{-1}\) assigned to the asymmetric and symmetric vibrations of the PO\({}_{4}\)\({}^{3-}\) groups as well as those in the range of 400-800 cm\({}^{-1}\) related to the vibrations of the Zr-O bond [10; 11] had the same intensity. [PERSON] et al. analyzed in detail the IR spectra of the samples \(\gamma\)-Zr [O\({}_{3}\)POH]\({}_{2}\)\(\cdot\)H\({}_{2}\)O and \(\alpha\)-Zr [PO\({}_{4}\)] [O\({}_{2}\)P(OH)\({}_{2}\)]\(\cdot\)H\({}_{2}\)O and proved that there are symmetrical and asymmetric vibrations of P-O and P-O-H in the wavenumbers 850-1300 cm\({}^{-1}\)[20]. Only the MWT causes the broadening of the band associated with the vibrations of the phosphate groups in the range of 1300-850 cm\({}^{-1}\), and in particular, increases the intensity of the bands related to P-O-H. The MChT treatment of the gel ZrP sample reduces the share of the intensity of the bands in the peak of the phosphate groups. The presented changes indicate that the MWT treatment causes the most significant changes. Besides, the surface structure is changed as a result of MWT and MChT. Thus, the FTIR spectroscopic studies of the initial and modified samples showed a wide band in the spectra in the wavenumber range 3700-2400 cm\({}^{-1}\) with the maximum around 3450 cm\({}^{-1}\), which is associated with the vibrations of the water molecules and surface OH groups. The band at the wavenumber 1630 cm\({}^{-1}\) is attributed to the bending vibrations of the O-H bond in the water molecule [21; 22]. The spectra for the initial sample and after HTT of gel and xerogel showed a similar course. On the other hand, the samples after both MWT and MChT were characterized by more intense bands in the range of 3700-2400 cm\({}^{-1}\) and the band at the wavenumber of 1630 cm\({}^{-1}\). As can be seen, the intensity of the band at 3450 cm\({}^{-1}\) increased significantly after MWT and MChT. These bands are related to the presence of the adsorbed H\({}_{2}\)O and surface OH groups. The increase of the intensity of this band for the milled sample (Figure 2) may be due solely to a drastic increase in the specific surface area (Table 2). However, a more significant increase in the intensity of this band for the samples after MWT (Figures 1 and 2) is obviously explained not only by an increase in the specific surface area. Figure 1: Comparison of FTIR spectra for the initial (black) and after HTT (violet)- and after MWT (red)-treated xerogel samples [11] [PERSON] et al., 2020. It should be noted that MWT used in this study is the version of HTT. However, the observed effect of microwave treatment on the surface structure (according to the FTIR data) is different from that of the conventional hydrothermal treatment. This may be due \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Label**} & **pHiep** & \multirow{2}{*}{**pKa1**} & **pKa2** \\ \cline{2-3}  & **0.001** & & \\ \hline \multicolumn{3}{c}{Xerogel} \\ \hline Initial & 3.9 & 0.87 & 6.28 \\ Xerogel & 4.1 & 0.52 & 7.24 \\ MWT xerogel & 2.2 & & 4.70 \\ \hline \multicolumn{3}{c}{Gel} \\ \hline Initial & 3.9 & 0.87 & 6.28 \\ Gel & 2.5 & & 5.36 \\ MWT gel & 2.9 & & 5.60 \\ MChT gel & 2.9 & & 5.47 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: pHiep and pKa2 of the surface groups of initial zirconium phosphate and after HTT, MWT, and MChT. Figure 2: FTIR spectra for the initial sample (black) and that after HTT (violet), MWT (cyan), and MChT (blue) of the gel ZrP samples.