## 3 Results and Discussions
### Metal Ion Extraction by JNPs Supported by Wax Colloidosomes  
The wax colloidosomes obtained by stabilizing the molten wax with JNP-bPEI were also employed in the metal ion extraction and recovery cycles, see Figure 5.  
As already mentioned, the great advantage of these materials, JNPs and JNP decorated colloidosomes, is the ability to employ them in interfacial extraction technologies, with the main benefit of ease of deployment, collection and recovery from the water's surface and re-deployment on the surface of the water for the subsequent metal ion extraction/recovery cycles. To test the versatility of these JNPs-decorated wax colloidosomes in such technologies, we have deployed them for Cu(II) extraction. The graph in Figure 6A shows the extraction efficiencies \(q_{\text{e}}\) for three consecutive cycles from fresh 10 mM Cu(II) solutions,as described in the experimental section. In a different experiment, two portions of 6 g of colloidosomes were used to extract Cu(II) from the same 10 mL solution with an initial concentration of 10 mM. After the first extraction cycle, the concentration of copper in the solution was reduced to 4 mM and after the second extraction cycle, the concentration of Cu(II) decreased further to 0.3 mM, see Figure 6B,C. The numbers are in good agreement with the extraction capacities \(q_{\mathrm{e}}\) calculated by the \"differential concentration\" method: (\(q_{\mathrm{e}}\)\(\approx\) 0.55 mg/g Colloidosome \(\approx\) 8.7 \(\mathrm{\SIUnitSymbolMicro mol/g}\)\(\approx\) 52 \(\mathrm{\SIUnitSymbolMicro mol\) Cu(II)/6 g Colloidosome; 10 mL soln. with c = 10 mM \(\rightarrow\) 100 \(\mathrm{\SIUnitSymbolMicro mol\) Cu(II)). The photographs in Figure 6B,C clearly demonstrate that a floating layer of 6 g of wax colloidosomes decorated with JNP-bPEI 3 mL, placed above a water solution of Cu(II) ions, and after brief shaking to ensure the wetting of the nanoparticles, is capable of almost complete interfacial extraction of the ions overnight. Next, the metal-loaded colloidosomes can be easily collected from the water's surface and dried; see the color change from white to blue of colloidosomes, before and after the Cu(II) metal ion extraction in the photographs of Figure 6B,C. The experiments were limited only to extraction, to demonstrate the working principle and versatility of wax colloidosomes and a recovery cycle for Cu(II) was not made. It is important to note that the amphiphilicity and the interfacial activity of JNP-bPEI are important for both emulsification and to ensure the proper orientation of the Janus lobes at the surface of wax colloidosomes. In this case, good amphiphilic behavior ensures that the hydrophobic PS Janus lobe is oriented toward the wax surface, while the hydrophilic lobe covered with bPEI provides a large surface area for capturing metal ions. Therefore, this aspect is crucial in designing water-floating colloidosomes and employing them in the interfacial extraction of metal ions. Furthermore, for a quantitative interpretation of the absorption capacity, both JNP-bPEI and JNP-bPEI-covered wax colloidosomes were employed in the extraction and recovery of the Cr(VI) comparative study. Thus, for the preparation of wax colloidosomes, 50 mg JNP-bPEI and 500 mg wax were used. Since not all colloidosome surfaces are fully covered it is reasonable to assume that the entire quantity of JNPs is incorporated into the surface of the wax, which for colloidosomes with an average radius of 15 \(\mathrm{\SIUnitSymbolMicro m}\), results in a mass fraction of \(m_{\mathrm{JNP}}/m_{\mathrm{Colloidosome}}\) = 10%.