(340c) Hierarchical Porous Silica Nanoparticles From Rice Husks

Biogenic silica nanoparticles were synthesized using rice husks (RHs) as the raw material via controlled pyrolysis. The characterization results showed that the morphology of the synthesized silica was highly related to the pre-treatment of RHs and the pyrolysis conditions. Particularly, potassium cations in RHs were found to catalyze the melting of silica, during which the amorphous silica were converted to crystalline phase. Two hours of pyrolysis at 700 °C appeared to be ideal to synthesize silica nanoparticles with a diameter of ca. 20-30 nm. Higher temperature and longer duration of pyrolysis led to undesired melting of silica nanoparticles, while too low a temperature cannot effectively remove carbonous residues. The small angle X-ray scattering characterization further revealed that the silica nanoparticles were composed of smaller primary particles, and the clustering of the primary particles leads to a porous structure. The N₂ sorption characterization results confirmed the above morphology, and showed that the prepared porous silica nanoparticles had a specific surface area of ca. 164 m²/g. Under the controlled melting catalyzed by K⁺ cations, such silica nanoparticle clusters can gradually fuse to form crystalline porous silica frameworks with tunable pore size. The implication of the present findings is discussed.