4.1. Synthesis of Mesoporous Silica Nanoparticles (MCM-41 Generation)

Mesoporous silica nanoparticles were synthesized using a chemical method [41]. The pH of deionized water (442 mL) was kept at 11 by adding 29% ammonium hydroxide (Sigma-Aldrich Cat. No. 1336-21-6; EMSURE®, Darmstadt, Germany) dropwise. The solution was heated to 50 °C, and 0.279 g of cetyltrimethylammonium bromide (CTAB) (Sigma-Aldrich Cat No. 57-09-0; Calbiochem®, Darmstadt, Germany) was added while stirring continuously. The pH was maintained at 10.3, and the solution was allowed to cool to room temperature. Next, tetramethyl orthosilicate (TMOS, 1.394 mL) (Sigma-Aldrich Cat. No. 78-10-4; Darmstadt, Germany) was added with constant stirring, resulting in turbidity after 2 min. The solution was left to stir overnight, followed by filtration and washing with deionized water. The obtained particles were dried at 90 °C and calcined at 500 °C for 5 h, yielding a white product. The product was finely ground into powder form. The dried powder was refluxed in methanol (100 mL) (Sigma-Aldrich Cat No. 67-56-1; Darmstadt, Germany) with concentrated HCl (1 mL) (Sigma-Aldrich Cat No. 7647-01-0; Darmstadt, Germany) for 24 h at 50 °C to remove the CTAB template. The resulting mesoporous silica nanoparticles (MSN) were isolated by filtration, extensively washed with water and methanol, and then dried at 100 °C for 24 h.