Morphology-controlled synthesis of SiO₂ hierarchical structures using pollen grains as templates

Rape-, sweet potato- and camellia-pollen-templated SiO₂ hierarchical structures with species-specific surface morphologies were prepared through a facile surface sol-gel and succedent calcination process. Various-morphology SiO₂ replicas with complex structures, such as about 50-μm-length and 20-μm-width high-fidelity ellipsoidal replicas with about 5-μm uniform meshes, about 40-μm spheres with 2-μm taper-like protuberances and 15-μm spheres with troughs, were obtained from using rape-, sweet potato- and camellia pollen grains as templates, respectively. The results of N₂ adsorption-desorption isotherms indicate that both rape- and camellia-pollen-templated SiO₂ replicas show type IV-like isotherm with the characteristics of mesoporosity and corresponding Brunauer-Emmett-Teller (BET) surface areas are 10.5 and 5.2 m ²·g^-1, respectively. The Barrett-Joyner-Halenda (BJH) pore size distribution of the rape-pollen-templated SiO₂ replicas presents smaller pores centered at 3.6 nm and bigger pores centered at 8.6 nm with a broad distribution whereas the camelliapollen-templated SiO ₂ replicas display narrow BJH pore size distribution centered at 20 nm. The biofabrication procedure using ubiquitous, inexpensive and environment-friendly pollen grains as a biotemplate holds a promise as a simple route to construct controlled complex porous oxides via simple chemical methods.