Rice (Oryza satiVa), which is a member of the family
Gramineae, typically constitutes 20-22% of its total produce
in the form of rice husk, and a great deal of rice husk is presently
disposed off by rice mill industry as waste. The presence of
silicon as SiO2 in rice has been well known since 1938.15
Interestingly, the highest SiO2 content in rice is observed in its
husk, which varies from 8.7% to 12.1%, averaging close to
10.6%.16a However, the silica present in rice husk is in a
hydrated amorphous form14,16b similar to that present in most
of the other entities in the biosphere. While there have been
some studies on the dissolution of amorphous silica present in
rice hull ash (RHA) to octasilicate anions under ambient
conditions,16b to our knowledge there have been no attempts at
harnessing the enormous amount of amorphous silica present
in rice husk (a cheap agro-based waste material) and its roomtemperature
biotransformation into crystalline silica nanoparticles.
In this Article, we address this issue and describe how
naturally deposited amorphous biosilica in rice husk can be
bioleached and simultaneously biotransformed into high value
crystalline silica nanoparticles