# Gelatin-Siloxane Hybrid Monoliths as Novel Heavy Metal Adsorbents
## 3 Results and Discussion
### Resistance of Gelatin Beads to Shaking in Water Solutions
#### 3.6.1 Effect of Contact Time  
Information on the kinetics of metal uptake is crucial for the selection of appropriate conditions for batch metal removal process. The adsorption rate of copper, lead and cadmium ions was investigated. The adsorption rates of these metal ions on studied hybrids were rather slow and within 3 h about 50% of the metal ions in solution was removed (Figure 6). In the case of the gelatin-siloxane monolith GS 1:1, the rate of metal adsorption is much lower (Figure 7). It was observed that the rate of Cd(II), Cu(II) and Pb(II) adsorption depends on the agitation speed, however too vigorous agitation may lead to the destruction of hybrid monoliths. Therefore, the stirring speed was limited to 90 rpm to avoid rapid disintegration of the monoliths. Figure 7 shows the concentrations of metals  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Type of Solution**} & \multicolumn{2}{c}{**Composition of Hybrid**} & \multicolumn{2}{c}{**pH**} & \multirow{2}{*}{**Disintegration Time [hours]**} \\  & **Monoliths (Gelatin:Siloxane)** & & & **Initial** & **After 1 h** & **After 2 h** \\ \hline Cu(II) & 1:1 & 2.26 & - & - & \textgreater{}48 \\ Cu(II) & 2:1 & 2.26 & - & - & \textgreater{}24 \\ Cu(II) & 3:1 & 2.26 & 4.58 & 6.01 & 8 \\ Cu(II) & 4:1 & 2.26 & 4.47 & 5.82 & 6 \\ Cu(II) & 6:1 & 2.26 & 6.15 & 6.98 & 2 \\ Cu(II) & 8:1 & 2.26 & 4.42 & 5.78 & 3 \\ water & 4:1 & 5.05 & 9.64 & 9.57 & 5 \\ water & 6:1 & 5.05 & 9.77 & 9.69 & 2 \\ water & 8:1 & 5.05 & 9.73 & 9.70 & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The disintegration time of gelatin–siloxane monoliths.  
Figure 5: Stability of the monolith depending on the mass ratio of gelatin to siloxane, (\(\blacktriangledown\)–copper, \(\blacksquare\)–distilled water), measured with agitation speed of 90 rpm.  
in aqueous solutions measured after adsorption on gelatin-siloxane hybrid GS 1:1. The study was carried out to determine the time when the process would reach equilibrium. Measurements were made after 3, 5, 9, 12, 15 and 18 h of shaking the samples. The obtained results clearly showed that the adsorption occurs quickly in the initial period and then the process slows down. It was also observed that the adsorption of metals ions in the studied period of time is higher for GS 2:1 in comparison to GS 1:1. The experiments were completed after 18 h to avoid the breakdown of hybrid monoliths. A slight decrease in adsorption observed for GS 2:1 in case of lead and cadmium after 18 h of shaking may indicate the beginning of the monoliths' disintegration, although there were no visible changes in their structure. A decrease in adsorption was not observed for the GS 1:1 hybrid, probably due to its higher stability in aqueous solutions (see Table 2).  
Figure 6: Effect of contact time on the adsorption of Cu(II)(\(\blacklozenge\)), Pb(II) (\(\blacksquare\)) and Cd(II) (\(\blacktriangle\)) on gelatin-siloxane monoliths GS 2:1 (initial concentration of metals–10 mg/L; initial pH = 2.6; agitation speed–90 rpm; mass of adsorbent monoliths 0.32 \(\pm\) 0.02 g; temperature 23 \(\pm\) 1.0 \({}^{\circ}\)C).  
Figure 7: Effect of contact time on the adsorption of Cu(II) (\(\blacklozenge\)), Pb(II) (\(\blacksquare\)) and Cd(II) (\(\blacktriangle\)) on gelatin–siloxane monoliths GS 1:1 (initial concentration of metals–10 mg/L; initial pH = 2.6; agitation speed–90 rpm; mass of adsorbent monoliths 0.32 \(\pm\) 0.02 g; temperature 23 \(\pm\) 1.0 \({}^{\circ}\)C).  
Figure 8 shows the photos of hybrid monoliths after the adsorption process (18 h) for each studied metal ion. The color of the monolith after copper adsorption was intense blue and no changes were observed in the case of adsorption of other metals.