Synthesis and characterization of high surface area nanosilica from rice husk ash by surfactant-free sol-gel method

A nanosilica powder was obtained by thermal treatment of rice husk ash using the sol-gel method without adding any extra surfactant, and was characterized by several techniques. Fourier transform infrared measurements revealed the similarity of the absorption curves of both standard nanosilica and synthesized nanosilica. From the nitrogen adsorption-desorption analysis followed that the nanosilica showed very high surface area of 653 m(2)/g, total pore volume of 0.64647 mL/g, and narrow pore radius of about 1.98 nm. Scanning electron microscopy of the nanosilica sample dried at 120 A degrees C showed separated particles, while the particles of the sample sintered at 700 A degrees C were aggregated. The analysis of transmission electron microscopy (TEM) micrographs and showed that about 69 % of particles had their sizes in the range of 20-25 nm. X-ray diffraction measurements showed the amorphous nature of the synthesized silica. Applying the Debye-Scherrer formula provided the value of the mean crystallite size around 26 nm which agreed with the one determined from TEM. The purity of the prepared nanosilica was higher than 95 % silica which was confirmed by means of energy dispersive X-ray analysis.