Preparation of carboxyethyltin group-functionalized highly ordered mesoporous organosilica composite material with double acid sites

A series of highly ordered mesoporous ethane-bridged organosilica composite materials functionalized by carboxyethyltin group, SnR–Si(Et)Si– X (SnR and Si(Et)Si denote [Sn(CH 2 ) 2 COOH] 3+ and ethane-bridged organosilica groups, respectively), were successfully designed through one-step co-condensation–hydrothermal method. The pore morphology and textural properties, Sn(IV) coordination environment, the type of acid site, Brönsted and Lewis acid strength were systematically characterized by LXRD, TEM observation, N 2 porosimetry measurements, MAS NMR ( 29 Si, 13 C, 119 Sn), UV–Vis diffuse reflectance spectrum, as well as 1 H and 31 P MAS NMR, FT-IR analysis of adsorbed pyridine, acid–base titration. Composite materials SnR–Si(Et)Si– X possess Brönsted and Lewis acid sites, which originates from –COOH in [Sn(CH 2 ) 2 COOH] 3+ group and bridging OH in [Si(OH)SnR] group as well as tetrahedral coordination framework Sn(IV) in the open configuration [SnR(SiO) 3 (OH)], respectively. The above 2D hexagonal mesoporous structure with unique textural properties, double acid sites (Brönsted and Lewis acid sites) and hydrophobic surface make SnR–Si(Et)Si– X exhibit excellent acid catalytic activity, reusability and water tolerance toward ketalization of cyclohexanone with glycol in absence of azeotrope agent at low temperature.