Stöber silica was synthesized by hydrolysis and condensation of tetraethylorthosilicate (TEOS) catalyzed by ammonia. In a typical synthesis, a solution of 3.0 mL of aqueous ammonia, 7.28 mL of water and 50 mL of ethanol have been prepared. Subsequently, 5.6 mL of TEOS were added, and the solution was stirred for 2 hours at room temperature. The ethanol solution was then evaporated at 60 °C for 5 hours and finally the precipitate was dried at 80 °C for 2 hours.23 The sample was named Stöber.
MCM‐41 silica was synthesized by dissolving cetyl trimethylammonium bromide CTAB, 15.12 g, Sigma Aldrich, ≥98 %) in 38 mL of deionized water and then heating the solution at 50 °C. Tetramethylammonium hydroxide (TMAOH, 8.94 mL, Sigma‐Aldrich) was then added, and after 30 minutes silica fumed (5.0 g, Aldrich, 99.8 %) was introduced. After 1 h the gel was transferred in a Teflon cup (125 mL capacity) of an autoclave (Anton PAAR 4748) and heated in an oven at 120 °C for 72 h. After the hydrothermal treatment, the sample was filtered, washed with deionized water and dried overnight at 120 °C. The material was calcined under air flow at 600 °C for 5 h (1 °C/min heating ramp) in order to remove completely the CTAB surfactant.24 The sample was named MCM‐41.
MCM‐41 silica was synthesized by dissolving cetyl trimethylammonium bromide CTAB, 15.12 g, Sigma Aldrich, ≥98 %) in 38 mL of deionized water and then heating the solution at 50 °C. Tetramethylammonium hydroxide (TMAOH, 8.94 mL, Sigma‐Aldrich) was then added, and after 30 minutes silica fumed (5.0 g, Aldrich, 99.8 %) was introduced. After 1 h the gel was transferred in a Teflon cup (125 mL capacity) of an autoclave (Anton PAAR 4748) and heated in an oven at 120 °C for 72 h. After the hydrothermal treatment, the sample was filtered, washed with deionized water and dried overnight at 120 °C. The material was calcined under air flow at 600 °C for 5 h (1 °C/min heating ramp) in order to remove completely the CTAB surfactant.