Effect of Temperature and Method of Synthesis on Morphology and Phase Transition of Amorphous and Crystalline Nano Silica Extracted from Mission Grass (Pennisetum Polystachion)

Bio silica nanoparticles are well accepted candidates in the field of material science. The present study conveys that Mission grass (MG) is a potential source of bio silica and to best of our knowledge no studies have been reported so far in connection with the extraction of silica from MG. Herein, we have demonstrated the synthesis of nano silica from MG by acid leaching and sol gel method. The effect of annealing temperature of MG and method of synthesis on the morphology and phase transition were studied. Four forms of silica viz 600 °C Acid Leached Silica (600ALS), 600 °C Sol Gel Silica (600SGS), 850 °C Acid Leached Silica (850ALS), 850 °C Sol Gel Silica (850SGS) have been synthesized through acid leaching and sol gel process. The 600SGS possess an average size of 40–100 nm and are found to be in amorphous form, whereas 850 SGS is more agglomerated with size of more than 100 nm and is in crystalline form. A similar trend is also observed in the case of silica nanoparticles that were obtained from the acid leached process. The phase purity as well as the crystalline nature of the all samples are studied by using XRD, FT-IR, FESEM-EDS. Crystallinity Indices are calculated and was highest for 850SGS (82%) and the lowest for 600SGS (43%). From the EDS data, it was found that the percentage of silica was the highest (95.61%) for 600SGS and the lowest (91.95%) for 850ALS. The thermogravimetric studies revealed that the crystalline silica (850 SGS) is more hygroscopic than amorphous silica, but later has more internal water due to its porous nature. Hence, it can be utilized as an excellent moisture absorber.