Biogenic silica nanoparticles (25−30 nm in
diameter) were synthesized from rice husks. The characterizations
revealed that the silica nanoparticles were composed
of smaller primary particles (ca. 4.2 nm in diameter), and their
clustering led to a porous structure with a surface area of 164
m2/g. Under the controlled melting catalyzed by K+, such silica
nanoparticle clusters can gradually fuse to form semicrystalline
porous silica frameworks with tunable pore size and structural
integrity.