Synthesis of amino-functionalized MCM-41 via direct co-condensation and post-synthesis grafting methods using mono-,di- and tri-amino-organoalkoxysilanes

摘要

Amino-functionalized mesoporous MCM-41 materials were synthesized directly by co-condensation of 3-aminopropyltrimethoxysilane(N silane),[1-2-aminoethyl)-3-aminopropyl]trimethoxysilane(NN silne)or 1-[3-(trimethoxysilyl)propyl]diethylenetriamine(NNN silane)with tetraethyl orthosilicate.The maximum proportions of N,NN and NNN silanes in the Si sources for obtaining the hexagonally structured funcitonalized silica were 0.5,0.4,respectively.the ~(29)Si MAS NMR measurements of the materials thus obtained indicte that the Si atoms containing Si-C bonds accounted for 26.0 17.0 and 7.8 Si mol(percent)of the total silicons,respectively.By comparing with the results form the elemental analyses and the argentometric present on the surface,but some of them were in the wall of the hexagonal channels.Amino-functionalized MCM-41 samples were also synthesized via a post-synthesis grafting on dehydrated MCM-41.At the maximum level of silylation wiht N,NN and NNN silanes,Si atoms containing Si-C bonds of about 20.6,19.2 and 17.9 Si mol(percent),respectively,were obtained,indicating that he surface coverage of amino-organoalkoxysilanes anchored ot silanol groups on the surface of MCM-41 were almost the same,irrespective of the size of the amino-organoalkoxysilanes.The adsorption experiments of Co~(2+) and Fe~(3+) were conducted in order to methods,and some differences in the activity of amino groups derived from N,NN and NNN silanes were found.The cations adsorbed on the amino-functionalzied samples via the co-condensation method were increased with an increase in the surface density of amino groups regardless of the amino-organoalkoxysilanes.When N and NN silanes were grafted onto the surface of MCM-41,theadsorption capacity was increased with an increase in the surface density of amino groups.However,when NNN silane was anchored ot the surface,the adsorption capacity was decreased with an increase in the surface density of the amino groups.these results imply tht the locations of the amino groups introducedc to the silica via the direct co-codensation and the post-synthesis grafting methods are clearly different.