Monolayer assembly of zeolite crystals on glass with fullerene as the covalent linker

Abstract

Glass plates tethered with 3-aminopropyl groups were prepared and fullerene (C60) was mounted onto the amine groups via NH insertion of the terminal amine moiety into one of the double bonds of fullerene. Cubic zeolite-A crystals covered with 3-aminopropyl groups on the external surface were independently prepared by treating the crystals with (3- aminopropyl)triethoxysilane. The zeolite-A crystals readily assembled in the form of monolayers on the fullerene-tethering glass substrates when they were allowed to contact in boiling toluene. The assembled zeolite-A monolayers remained intact even after sonication for 5 min in toluene. In contrast, the assembly of zeolite crystals does not occur if the (ethering of either 3- aminopropyl or fullerene is omitted. Based on the two contrasting results, the monolayer assembly of zeolite crystals on glass is proposed to occur by formation of a large number of propylamine-fullerene-propylamine covalent linkages between each zeolite crystal and the glass substrate. Scanning electron microscope images revealed that zeolite-A crystals assemble with a face pointing normal to the plane of the substrate. The monolayers consist of small domains comprised of about 110 closely packed zeolite-A crystals aligned in uniform three-dimensional orientation. The same procedure also worked well for the monolayer assembly of larger ZSM-5 crystals. Migration of the weakly bound zeolite crystals over the glass substrate driven by a large number of hydrogen bonds between the surface-bound amine groups on the neighboring crystals is proposed to play an important role in inducing the close packing.