Structural Perturbations in Mesoporous Silica Microspheres Prepared Using Cationic Organosilanes.

Mesoporous MSU silica microspheres were prepared by the hydrolysis of tetraethoxysilane (TEOS) in mildly acidic aqueous nonionic surfactant solutions in the presence of small amounts (molar percentage tip to 1.25% with respect to TEOS) of cationic organotrialkoxysilanes (N-((trimethoxysilyl)propyl)-N,N,N-trimethylammonium chloride, N-((trimethoxysilyl)propyl)-N, N,N-tributylanimonium chloride, and N-((trimethoxysilyl)propyl)-ammonium chloride). The incorporation of increasing amounts of cationic organotrialkoxysilanes results in the formation of microspherical MSU silica with increasingly perturbed mesopore structure (bimodal pore size distributions in the 30-120 angstrom range) and increasingly textural morphology. Functionalized derivatives of the microspheres were prepared by the substitution of TEOS with 3-mercaptopropyl-trimethoxysilane (MPTMS) in the synthesis mixture. Gold ion adsorption studies were performed on the resulting microspheres, which showed that mildly perturbed microspheres, maintaining an adequate degree of uniformity in their mesopores, had optimal adsorption capacity and improved adsorption kinetics compared with both unperturbed and highly perturbed microspherical mesostructures.