# Gemini Surfactant as a Template Agent for the Synthesis of More Eco-Friendly Silica Nanocapsules
## 3 Results and Discussion
### Ecotoxicity  
Ecotoxicity data (I/LC\({}_{50}\)) are summarized in Table 3. Respective dose-response curves supporting these results are presented in a Supplementary Material (Figure S1). Both nanomaterials were toxic towards the tested microalgae and harmful towards the tested crustaceans [30]. However, SiNC_CTAB was more toxic than the novel SiNC_QSB2-12, for all tested species, statistically significant (\(p<0.05\)) in the case of the diatom _P. tricornutum_ (up to 3.5-times more toxic) and _T. chuii_ (+25%) (Table 3). It has been suggested that the toxicity of silica nanocapsules may be associated with traces of cationic surfactants used during synthesis [10]. This is in accordance with FTIR data which confirm the presence of cationic surfactant residues in both nanomaterials. Previous studies by researchers from the University of Aveiro have shown that CTAB has 20-times higher toxicity towards _P. tricornutum_ than gemini surfactant QSB2-12 [25]. These results prompted the decision to replace CTAB with QBS12, leading to the development of the work presented in this paper. \begin{table}
\begin{tabular}{c c c} \hline  & **S\(\mathbf{\ddot{B}}\)ET** & **Pore Size** \\  & **[m\({}^{2}\)/g]** & **[nm]** \\ \hline SiNC\_CTAB & 719 & 4.4 \\ SiNC\_QSB2-12 & 603 & 5.9 \\ \hline \end{tabular}
\end{table} 
Table 2: Textural properties of SiNC_CTAB and SiNC_QSB2-12. Figure 6: TG profile of SiNC_CTAB and SiNC_QSB2-12. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Marine Species**} & \multicolumn{3}{c}{**I/IC\({}_{50}\) [mg/L]**} & \multirow{2}{*}{**\(p\)-Value**} & \multirow{2}{*}{**F-Test to Compare Variances D Pr, DFd**} & \multirow{2}{*}{\(p\)-Value**} \\ \cline{2-2} \cline{5-6}  & **(95\% CI)** & & & & **Variances D Pr, DFd** \\ \hline \multirow{2}{*}{_Namachloropsis gaditana_} & 8.51 & 9.69 & \multirow{2}{*}{1.2230} & \multirow{2}{*}{0.2282} & 94.91 & \multirow{2}{*}{\textless{}0.0001} \\  & (6.76–10.7) & (9.48–9.91) & & & 20, 22 & \\ \hline \multirow{2}{*}{_Tetraselmis chuli_} & 7.41 & 9.26 & \multirow{2}{*}{3.3437} & \multirow{2}{*}{0.0014} & 17.28 & \multirow{2}{*}{\textless{}0.0001} \\  & (7.37–7.45) & (8.97–9.55) & & & 19, 22 & \\ \hline \multirow{2}{*}{_Phaodactylum tricurrentum_} & 2.37 & 8.30 & \multirow{2}{*}{2.1350} & \multirow{2}{*}{0.0386} & 14.84 & \multirow{2}{*}{\textless{}0.0001} \\  & (1.75–3.23) & (2.69–15.61) & & & 22, 20 & \\ \hline \multirow{2}{*}{_Artemia salin_} & 23.0 & 25.4 & \multirow{2}{*}{0.6126} & \multirow{2}{*}{0.5451} & 8.42 & \multirow{2}{*}{0.0003} \\  & (20.6–25.7) & (18.4–35.0) & & & 14, 14 & \\ \hline \hline \end{tabular} Data are presented as median growth inhibition concentration (72 h-IC\({}_{50}\)) and median lethal concentration values (48 h-IC\({}_{50}\)), and respective 95% confidence intervals (CI). D Pr—degrees of freedom numerator. DPd—degrees of freedom denominator.  
\end{table} 
Table 3: Toxicity of synthesized reference (SiNC_CTAB) and newly developed (SiNC_QSB2-12) silica nanocapsules towards marine species and statistical comparison of I/LC\({}_{50}\) through \(t\)-tests and F-tests per tested species. Figure 7: (**a**) Nitrogen adsorption–desorption isotherms and (**b**) pore size distribution of silica nanocapsules. There are some ecotoxicity data available in the literature for CTAB-based silica nanocapsules. For the diatom _P. tricrorutum_ IC\({}_{50}\) ranges from 2.03 mg/L [10] to 3.67 mg/L [13], for microalgae _N. gaditana_ IC\({}_{50}\) is 1.15 mg/L [10], while for the crustacean _A. salina_ SiNC_CTAB are harmful (LC\({}_{50}\) = 12.2 mg/L [34]) or non-toxic (LC\({}_{50}\) > 100 mg/L [10]). The results obtained in the present work agree with the literature data, particularly in the case of diatoms and crustaceans. There is a difference for the microalgae _N. gaditana_, which may be associated with different amounts of the cationic surfactant still adsorbed to the silica nanocapsules surface. Sustainability is, nowadays, one of the main challenges in materials science.