Preparation and Characterization of ‘Green’ Nano Silica from Rice Husks

Abstract

Silica with Nanostructure is a high quality silica that is used in many industrial areas. The study was aimed at preparation and characterization of nanao silica from rice husk by precipitation method. The rice husk ash (RHA) was obtained by washing and burning rice husk (RH) at 700^oC for 2 h in a muffle furnace. The RHA was subjected to Energy dispersive x-ray fluorescence (EDXRF) and silicon content was as high as 36.53 %. Indicating that there was silicon dioxide (silica) in RHA. Rice husk pure silica (RHS) was obtained by alkaline extraction method of 10g of RHA using 2.5 M sodium hydroxide. 9.3 g of RHS was obtained. The FT-IR spectral data which showed Absorption signals at 1069.7 cm^-1, 957.97 cm^-1, 797.7 cm^-1 , 1632.6 cm^{-1  ,}2885.0 – 3900 cm^-1 and 2158.17 cm^-1 , supported that the  substance produced is silica. The RHS was subjected to precipitation by refluxing silica with 6 M HCl and dissolving the substrate in 2.5 M NaOH by continuous stirring for 1 hour on a magnetic stirrer and then concentrated H₂SO₄ was added to adjust pH in the range of 7.5-8.5in order to produce nanosilica. The prepared Rice husk nano silica (RHNS) showed an X-ray diffractogram that has a strong broad peak at  18˚ to 36.5˚(2 ), which the absence of  sharp peak indicates that nanosilica prepared  is amorphous. FT-IR of RHNS support that the substance is silica. The SEM of the RHNS showed aggregates of silica forming fine globules of varied sizes. The EDXRF shows a complete removal of K from the RHA by alkaline treatment.

Keywords: Rice husk, precipitation, EDXRF, FT-IR, SEM ,Rice husk nano silica