New Insights Into Method Development and Characterization of Amorphous Silica From Wheat Straw

Abstract

Amorphous silica, a specialised silicate adsorbent is extensively extracted from agricultural residues for application in various environmental domains. Wheat straws are a rich source of silica that have earlier been overlooked however demand for value addition. The study presents an innovative approach to extracting silica from wheat straw and standardising the extraction process to produce clean product. The sodium silicate solution and the amorphous silica synthesis were obtained by modifying the template mediated sol–gel method. Optimum temperature, concentration and pH were identified for the cleaner production of silica with maximum yield and favourable adsorbent characteristics. The crystallographic properties analysed by the X-Ray Diffraction revealed the amorphous nature of silica extracted from ash at 650 °C for 4 h. The structure of phytolith present in the wheat straw was observed in the form of articulated elongate undulate epidermal phytolith under scanning electron microscopy. The Energy Dispersive X-ray spectrum exhibited higher amount of silica (Si %) of 70.10% with a minimal percentage of potassium (9.96%). The sharp bend at 1025 cm−1 is attributed to the siloxane (Si–O-Si) vibrations in Fourier transform infrared spectroscopic graph of amorphous silica. The specific surface area measurements of amorphous silica showed type II isotherm curve with a hysteresis of H3 type. The optimum conditions derived to produce amorphous silica were 3 M NaOH and 3 M H2SO4 at pH 9.

Recent Advances on Porous Siliceous Materials Derived from Waste

“…The management of agro-industrial waste is one of the tools to mitigate the impact of agriculture production and, in this context, an analysis of the scientific literature highlighted the possibility of recovering SiO 2 from them. Among the different precursors obtained from agricultural sources, the majority of the studies reported the use of sugar cane bagasse [ 75 ], bamboo leaves [ 76 ], wheat straw [ 77 , 78 ], corncob [ 79 , 80 ], and rice husk [ 30 , 81 , 82 , 83 , 84 ]. In particular, rice husk is the most promising precursor due to its high abundance (the worldwide annual rice production is approx.…”

“…120 million tons [ 85 ]). Rice husk composition depends on variety, origin, climate, and geographical location [ 86 ]; however, with respect to other biomasses, its initial SiO 2 content can reach values >90 wt.% of the total inorganic residue ( Table 1 ) [ 75 , 76 , 77 , 78 , 79 , 80 , 82 , 84 , 87 ].…”