Highly pure amorphous silica nano-disks from rice straw

White ash, containing majority of SiO ₂ with trace amounts of Al ₂O ₃, CaO, MgO, K ₂O, P ₂O ₅, 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 SiO ₂ 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 5.8nm average pore size (2 to 22nm pore size distribution) and very high specific surface (509.5m ²/g BET and 637.0m ²/g BJH) and pore volume (0.925cm ³/g). These silica powders were dispersible in water and shown to consist of nano-disks with an average 172nm diameter and 3.09nm thickness as measured by TEM and AFM, respectively.