Molecular resolution of zeolite surfaces as imaged by atomic force microscopy

An atomic-force microscope (AFM) has been used to probe the surfaces of several natural zeolite crystals with know crystal structures. Scolecite, stilbite, and faujasite have been studied, and their AFM images have been compared with models based on their crystal structure data. In all cases, a particular Miller plane of the crystal was imaged with the AFM. Scolecite crystal was imaged in air along the (001) surface, and twinning, which had been confirmed by single-crystal X-ray diffraction, was observed on a molecular scale. Stilbite (010) was imaged in 0.1 m NaOH aqueous solution; both large and molecular-scale images of the surface were obtained. The AFM image agreed well with the model of the (010) surface. Faujasite was imaged along the (111) surface and showed a rough surface consistent with cleavage through the four rings joining the sodalite unit. These observations demonstrate the utility of AFM for the characterization of zeolite surface structure and that it may lend itself to observing processes at the surfaces, such as surface reconstruction (manuscript in preparation) and ion exchange.