# Adsorption of Ag (I) Ions at the Zirconium Phosphate/KNO3 Aqueous Solution Interface
## 3 Results and Discussion
### Electrophoretic Study of the Zirconium Phosphate Samples
The functional groups of the xerogel ZrP after HTT had the most acidic character, the pK\({}_{\mathrm{a2}}\) being 1.5 units lower than the pK\({}_{\mathrm{a2}}\) of the initial sample and hence the pH\({}_{\mathrm{iep}}\) of this sample was 2.2. Figure 3: (**a**). Zeta potential of the zirconium phosphate xerogel samples MWT treated in the 0.001 mol/dm\({}^{3}\) KNO\({}_{3}\) solution as a function of pH. (**b**). Zeta potential of the zirconium phosphate gel samples MWT and MChT treated in the 0.001 mol/dm\({}^{3}\) KNO\({}_{3}\) solution as a function of pH. Adsorption of Ag (I) Ions at the Interface of the ZrP Sample/Solution 0.001 mol/dm\({}^{3}\) KNO\({}_{3}\)  
Zirconium phosphates or titanium phosphates are the adsorbents characterized by the great adsorption affinity for heavy metals [25; 26]. It was found that these adsorbents can practically remove Cd (II) and Zn (II) ions from the solutions with a pH greater than 4. Adsorption of heavy metal cations in the pH range from 2 to 4 increases with the increasing pH due to the exchange of protons in the group's zirconium or titanium phosphate hydroxyl or hydrogen phosphate group. Ag\({}^{+}\) ions can also adsorb to one hydroxyl or phosphate group releasing a proton. Due to the small pH\({}_{\text{\text{\scriptsize{\text{\text{\text{\text{\text{\text{\text{ \text{\text{\text{\text{\text{\text{\text{\text{\texttexttexttexttexttexttexttexttexttexttext  
Figure 4: Comparison of Ag (I) ions adsorption in different zirconium phosphate samples from the solution of the initial concentration, 1 \(\upmu\)mol/dm\({}^{3}\) Ag (I) ions as a function of pH. Figure 5: Comparison of Ag (I) ions adsorption in different zirconium phosphate samples from the solution of initial concentration, 10 \(\upmu\)mol/dm\({}^{3}\) Ag (I) ions as a function of pH. After determining the equilibrium constants and the amount of released protons, the pH values at which 50% of the initial concentration of Ag\({}^{+}\) ions were adsorbed (pH50%) and in the pH range in which the adsorption changes from 90% to 10% (\(\Delta\)pH90-10%) were calculated. The obtained values of pH50% and \(\Delta\)pH90-10% are given in Table 3. As can be seen, with the increase of the initial concentration, the pH50% value shifted towards higher pH values; however, in most cases it did not exceed pH = 4. Similarly, the value of \(\Delta\)pH90-10% exceeded 4 in two cases. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample No** & **Sample Code** & **Ag [I] Conc. (\(\mu\)mol/dm\({}^{3}\))** & \(\text{p}\beta_{n}\)\({}^{*}\) & \(n\) & \(\text{pH}_{\text{50\%}}\) & \(\Delta\text{pH}_{\text{90-10\%}}\) \\ \hline \multirow{2}{*}{**1**} & \multirow{2}{*}{Initial} & 1 & 0.065 & 0.77 & 3.2 & 2.5 \\  & & 10 & 0.033 & 0.66 & 3.3 & 2.9 \\  & & 100 & 0.016 & 0.54 & 3.5 & 3.5 \\ \hline \multirow{2}{*}{**2**} & \multirow{2}{*}{Xerogel} & 1 & 0.040 & 0.55 & 2.8 & 3.5 \\  & & 10 & 0.044 & 0.56 & 2.9 & 3.4 \\  & & 100 & 0.016 & 0.62 & 3.7 & 3.1 \\ \hline \multirow{2}{*}{**3**} & \multirow{2}{*}{Gel} & 1 & 0.045 & 0.58 & 2.8 & 3.3 \\  & & 10 & 0.016 & 0.57 & 3.6 & 3.3 \\ \hline \multirow{2}{*}{**4**} & \multirow{2}{*}{MWT Xerogel} & 1 & 0.141 & 0.73 & 2.6 & 2.6 \\  & & 10 & 0.034 & 0.49 & 2.7 & 3.9 \\ \cline{1-1}  & & 100 & 0.076 & 0.78 & 3.1 & 2.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The equilibrium constants of Ag (I) adsorption and the amount of released H + ions based on the non-stoichiometric exchange model. Figure 6: Comparison of Ag (I) ions adsorption in different zirconium phosphate samples from the solution of initial concentration, 100 \(\upmu\)mol/dm\({}^{3}\) Ag (I) ions as a function of pH.