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

Glass plates tethered with 3-aminopropyl groups were prepared and fullerene (C-60) 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 tethering 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.