XAFS analysis of the potasium-silica interaction in rice husks

Abstract

The Si K-edge X-ray absorption spectra of three samples obtained from rice husk have been recorded to investigate changes in medium and short range order that could explain the drastic differences in surface area of the samples, from 1 to 260 m 2/g. The recorded differences are similar to those detected in densified silica, where they have been associated with changes in medium range order. Similar changes have been observed in K 2OSiO 2 glasses where the addition of potassium oxide leads to the disruption of SiO 4 network, and the formation of chain like structure of non-bridging oxygen atoms, as increasing the quantity of potassium oxide. This suggests that this behavior is due to the strong interaction between silica and the potassium ions contained in the rice husks, which leads to a dramatic decrease of the specific surface area if K + ions are not removed before the annealing of the sample.