Starch gel templating of spongelike macroporous silicalite monoliths and mesoporous films

Silicalite nanoparticles and starch gel templates have been used to fabricate zeolite materials with a hierarchical micro/meso/macropore organization. Two methods were investigated. First, macroporous monoliths consisting of a continuous mesoporous framework of microporous silicalite were prepared by incorporating 50-nm-sized zeolite nanoparticles into freshly prepared viscous starch gels, followed by air-drying and calcination. Macropore sizes between 0.5 and 50 mum were achieved by varying the amount of starch and the starch/silicalite weight ratio. Mesoporous thin films of microporous silicalite, 2-15 mum in thickness, were also prepared by using gels containing low concentrations (2 wt %) of starch. Second, starch sponges with high internal macroporosities were prepared by freezing and thawing of starch gels and were then infiltrated with colloidal suspensions of silicalite nanoparticles and air-dried to produce silicalite-starch foams with pores up to 100 mum across depending on the starch concentration and the silicalite loading. The zeolite nanoparticles were deposited as coherent layers on the thin walls of the starch framework, which could be removed by calcination without significant disruption of the silicalite framework. In general, the methods described are facile, low in cost, and environmentally benign and can be readily extended to other inorganic materials with macroporous architectures, provided that suitable nanoparticle building blocks are available.