## 4 Conclusions  
It was shown that JNP-bPEI exhibits both of the desired characteristics: amphiphilicity and capability to absorb metal ions. We have demonstrated that the amphiphilicity of JNPs is key to enabling new ion extraction and recovery technologies. For example, we have demonstrated that amphiphilic JNP-bPEI can operate as (a) standalone ion-extraction agents, capable of absorbing metal ions from water and then transporting these to the surface where they could be collected and (b) as emulsifiers of molten wax to generate a new type of carriers capable of floating on the surface of water but also of metal ion extraction. There are, however, still multiple aspects left to explore. The kinetics of the extraction and recovery processes could be assessed by analyzing the metal content of the solutions as a function of time. With the optimized extraction times, the recyclability experiments using Cr(VI) could be repeated to see if the capacity still degrades. Different metal ions such as Ni(II) or Co(II) could be used to gather more data concerning the extraction and recovery capacities. The selectivity towards certain ions could also be determined--an important parameter when it comes to real-world applications. In future works, the long-term stability of JNP-bPEI-covered wax colloidosomes should be tested. The colloidosomes are only viable carriers if the nanoparticles stay attached to their surfaces even after prolonged agitation. A scale-up of the preparation procedure should also be attempted, with regard to manufacturing at an industrial scale. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/nano12213738/s1](https://www.mdpi.com/article/10.3390/nano12213738/s1)]([https://www.mdpi.com/article/10.3390/nano12213738/s1](https://www.mdpi.com/article/10.3390/nano12213738/s1)). Figure S1: FTIR spectra of polystyrene seed nanoparticles, JNP-CN, JNP-COOH and JNP-bPEI, Figure S2: Zeta potential with pH for JNP-CN and JNP-COOH, Figure S3: SEM images of JNP-CN and JNP-COOH, Figure S4: Zeta potential with pH for JNP-bPEI, Figure S5: SEM images of the homologous series of JNPs functionalized with bPEI, Table S1: Zeta potential of the homologous series of JNP-CN, JNP-COOH and JNP-bPEI, Figure S6: Evolution of the interfacial tension of heptane/water in time in the presence of JNP-bPEI with pH, Figure S7: Interfacial tension of heptane/water in time as a function of JNP-bPEI concentration in water, Figure S8: SEM images of wax colloidosomes prepared with JNP-bPEI 2-4 mL, Figure S9: SEM images of colloidosomes, Figure S10: Performance of JNP-bPEI 2 mL after five consecutive extraction and recovery cycles for Cu(II), Figure S11: Regular and number-normalized Cr(VI) extraction and recovery values for JNP-bPEI 2-4 mL, Figure S12: Regular and number-normalized Cu(II) extraction and recovery values for JNP-bPEI 2-4 mL, Table S2: Metal ion extraction and recovery capacities of the homologous series of JNP-bPEI, Figure S13: Image sequence of colloidosome flotation and images of filtered colloidosomes. Conceptualization, O.P. and A.H.; methodology, O.P. ; software, O.P. ; validation, A.H.; formal analysis, O.P. and A.H.; investigation, O.P. and A.H.; resources, A.H.; data curation, O.P. ; writing--original draft preparation, O.P. and A.H.; writing--review and editing, A.H.; visualization, O.P. and A.H.; supervision, A.H.; project administration, A.H.; funding acquisition, A.H. All authors have read and agreed to the published version of the manuscript. This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI-UEFISCDI, project number PN-III-P4-PCE-2021-0306 (Contract Nr. PCE62/2022). Not applicable. This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI-UEFISCDI, project number PN-III-P4-PCE-2021-0306 (Contract Nr. PCE62/2022). Not applicable.