*2.3. Sol-Gel Synthesis*

Silica sol was synthesized following the one-stage sol-gel method [31]. Tetraethylorthosilicate (TEOS) and methyltrietoxysilane (MTES) (ABCR GmbH & Co., Karlsruhe, Germany) were used as silica precursors, 0.1 N nitric acid (Merck Millipore, Burlington, MA, USA) and acetic acid (glacial, 100% *v*/*v*, Merck Millipore, Burlington, MA, USA) were used as catalyzers and absolute ethanol (99.9% *v/v*, Merck Millipore, Burlington, MA, USA) was used as solvent. Final silica concentration was 18 g·L<sup>−</sup>1. The sol was synthesized in a thermostatic bath at 40 ◦C under constant stirring at 300 rpm for 3 h. It was stored at 4 ◦C for 24 h before using.
