# Gemini Surfactant as a Template Agent for the Synthesis of More Eco-Friendly Silica Nanocapsules
## 4 Conclusions  
Silica nanocapsules based on gemini surfactant QSB2-12 were successfully synthesised and characterized.  
The synthesis is performed in a one-stage process where the toxic commercial cationic surfactant CTAB is replaced by a less toxic gemini surfactant QSB2-12. Changing surfactants allows the reduction, by 50%, of the number of moles used to obtain a stable microemulsion and does not hinder the formation of the nanomaterials. Moreover, the present results show that replacing the surfactant does not significantly change the structure and properties of silica nanocapsules.  
Ecotoxicity tests show that nanocapsules based on CTAB are significantly more toxic than nanocontainers prepared with gemini surfactant for two (out of four) species and slightly more toxic for the other two. Both nanomaterials are classified as toxic (microalgae) and harmful (crustacean). The present study shows that by choosing a template surfactant carefully, environmentally safer silica nanocapsules can be designed. Nonetheless, further research is still needed.  
To the best of our knowledge, the safe-by-design approach for silica nanocapsules synthesis is addressed in this work for the first time. Following this approach allows us to obtain not only environmentally friendly nanomaterials but also prevent the use of toxic surfactants and decrease the number of used chemicals, thus being aligned with the concept of green chemistry [37].  
The following are available online at [[http://www.mdpi.com/2076-3417/10/22/8085/s1](http://www.mdpi.com/2076-3417/10/22/8085/s1)]([http://www.mdpi.com/2076-3417/10/22/8085/s1](http://www.mdpi.com/2076-3417/10/22/8085/s1)), Figure S1. Dose-response curves of the microalgae _Nannochloropsis gaditana_ and _Tetraselmis chuii_, the diatom _Phaodactylum tricrorutum_ and the crustacean _Artemia salina_ exposed to tested cationic surfactants.  
Conceptualization, O.K., R.M. and J.T.; Methodology, O.K., R.M. and I.S.; Investigation, O.K, I.S. and J.F.; Resources, O.K. and R.M.; Data Curation, O.K. and J.F.; Writing--Original Draft, O.K.; Writing--Review & Editing, I.S., R.M., S.L. and J.T.; Visualization, O.K. and J.F.; Project administration, O.K.;Funding acquisition, O.K.; Validation, R.M.; Supervision: R.M., S.L. and J.T. All authors have read and agreed to the published version of the manuscript.  
**Funding:** [PERSON] received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 792945 (EcoGemCoat). [PERSON] was hired under the Scientific Employment Stimulus--Individual Call (CEECIND)/01329/2017), funded by national funds (OE), through FCT, in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of 29 August, changed by Law 57/2017, of 19 July. This work was developed under the framework of the NANOGREEN project (CIRCNA/BRB/0291/2019), funded by the Portuguese Foundation for Science and Technology (FCT) through national funds (OE). This work was also carried out in the framework of SMARTAQUA project, which is funded by the Foundation for Science and Technology in Portugal (FCT), the Research Council of Norway (RCN-284002), Malta Council for Science and Technology (MCST), and co-funded by European Union's Horizon 2020 research and innovation program under the framework of ERA-NET Cofund MarTERA (Maritime and Marine Technologies for a new Era). This work was developed within the scope of the project CICECO-Aveiro Institute of Materials (UIDB/50011/2020; UIDP/50011/2020) and CESAM-Centre for Environmental and Marine Studies (UIDB/50017/2020 + UIDP/50017/2020) financed by national funds.  
**Conflicts of Interest:** The authors declare no conflict of interest.