Synthesis and characterization of tin oxide-modified mesoporous silica by the repeated post-grafting of tin chloride

Modification of mesoporous silica with tin oxide was investigated by the repeated post-grafting method, which consisted of the repetition of the cycle of hydroxylation of the surface, grafting of tin(IV) chloride through the reaction with surface hydroxyl groups and calcination in air. The singly SnO2-modified material showed extremely high thermal stability up to 950 degreesC as well as the stability against the treatment in basic solution (pH = 10). With increasing the number of cycles, XRD peak intensity characteristic to the hexagonal mesophase decreased gradually, but the mesoporous structure was maintained up to the third modification. The optical absorption due to tin oxide was emerged by the modification and its absorbance increased with an increase in the modification cycles. The repeated modification with tin oxide caused progressive decreases in specific surface area, mesopore volume and diameter, while no significant change of the hexagonal cell parameter was observed. It was suggested from the enhanced stabilities and the pore-structure change that inner wall and outer surfaces of the mesoporous silica was progressively coated with the tin oxide layer, (C) 2001 Elsevier Science B.V. All rights reserved.