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.