Effect of wash solvents on salt removal in rice husk derived nano-silica

Precipitated nano-silica powders were prepared from rice husk ash by a method combining a sodium silicate based sol-gel process and traditional precipitation process. The transition of silica sol into silica gel (hydrogel) also produces undesirable sodium salt as a byproduct trapped in the gel microscopic pores. Three types of wash solvents used for the salt removal process were tap water, water + ethanol, and water+acetone. The extent of salt removal achieved after the washing process was evaluated using scanning electron microscopy with energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Our initial investigation found that the water+ethanol mixture was most effective for salt removal. A reason for this could be that due to the lower surface tension of ethanol as compared to acetone, the mixture was more effective in penetrating the gel pores to dissolve the salt.