Highly pure amorphous silica nano-disks from rice straw

White ash, containing majority of SiO2 with trace amounts of Al2O3, CaO, MgO, K2O, P2O5, etc., was successfully produced by heating rice straw at 10 °C/min and holding at 250, 325 and 575 °C to facilitate decomposition and gasification of the organics while avoiding auto-ignition. Highly pure amorphous silica was derived from the resultant rice straw ash by a base dissolution and acid precipitation process at a 90.8% yield (or 11.47% from rice straw). The SiO2 chemical composition was confirmed by EDS and FTIR and the amorphous nature by XRD. Freeze-drying of silica gel produced mesoporous silica powders with a 5.8 nm average pore size (2 to 22 nm pore size distribution) and very high specific surface (509.5 m2/g BET and 637.0 m2/g BJH) and pore volume (0.925 cm3/g). These silica powders were dispersible in water and shown to consist of nano-disks with an average 172 nm diameter and 3.09 nm thickness as measured by TEM and AFM, respectively.

Highly pure amorphous silica powders derived from rice straw were dispersible in water and shown to consist of nano-disks with an average 172 nm diameter and 3.09 nm thickness.Figure optionsDownload as PowerPoint slideHighlights
► Pure amorphous silica was successfully extracted from rice straw.
► Mesoporous silica powders have very high specific surface and pore volume.
► Silica powders were dispersible in water and dried to nano-disks.
► The nano-disk is 172 nm in diameter and 3.09 nm in thickness.