Growth of fractal aggregates during template directed SAPO-34 zeolite formation

We describe the hydrothermal synthesis of zeolite SAPO-34 nanoparticles using an amine terminated polymamidoamine dendrimer template. The formation and growth of the zeolite intermediate nanoaggregastes, investigated in situ by small angle X-ray scattering (SAXS), originates porous aggregates with a characteristic fractal structure. A core-shell approach for the analysis of SAXS data allows to correlate the templating action of the dendrimers with the zeolite growth process during the hydrothermal synthesis, and indicates that incorporation of zeolite in the dendrimers surface is the dominant mechanism in the first 3 h. The shape transition of the SAXS profile at the late stage of the synthesis has been connected with an aggregation process among primary units that leads to the formation of large clusters. Analysis of the log-log plot of the SAXS spectra during the late stages of synthesis indicates the presence of two linear regions that are connected with the fractal characteristics of the generated aggregates. The formation of large supramolecular assemblies was finally verified by scanning electron microscopy (SEM) analysis which evidenced the presence of large aggregates with visible surface roughness and distributed pores. The main finding of our results puts novel insight in the development of organic-inorganic nanostructured materials based on mesoporous frameworks as well as stimulates the investigation of alternative protocols for the assembly mechanism of novel bio-inspired pourous materials with new characteristics and properties.