The rice husks thermally treated at 400 °C and 700 °C were investigated by X-ray diffraction. No difference was observed between XRD patterns of TRH700 and TRH400 (Fig. 7). The XRD pattern features two diffused peaks at 2 22° and at 2 44°,which corresponds to the presence of amorphous silica and graphite structures, respectively [35]. As seen From Table 1, the full width at half maximum (FWHM2-Theta) is higher in case of the 400 °C sample,which indicates a smaller size of crystalline carbon. At higher temperatures, the FWHM 2-Theta may decrease due to the destruction of cellulose structures in rice husk. In this sample, probably calcite (CaCO3) was present in small amounts (less than 1.0 %). The integral intensity of the amorphous phase (net Area−cps×2-Theta ) was highest in the 700 °C sample. In summary, it can be concluded from the XRD patterns that thermally treated rice husk mainly consist of amorphous silica.