Structural analysis and transformation of biosilica during lignocellulose fractionation of rice straw

• Silica/lignin-polysaccharides interactions are proposed during fractionations.
• The capacity to bind/store silica is in order of lignin > polysaccharides > lipids.
• Silica is bounding with chemical fractions in form of Si(OR)x, SiOSi, and SiOx.

This study focused on the interfacial combination of silica and lignin-polysaccharides during lignocellulose fractionation of rice straw using scanning electric microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD) techniques. Silica was deposited on the exterior surface of rice straw in the form of Si(OR)x, SiOSi, SiOx, and SiC respectively, while not in the form of elemental Si. After delignification and alkalization, silica was deposited on the surface of polysaccharide with a more regular pattern. It is due to that silica reacted with polysaccharide to form SiOx and Si(OR)x during the decomposition of lignin and hemicellulose, leading to the remained framework structure of crystalline cellulose. After the decomposition of polysaccharide, silica was embedded into lignin fragments, and shown as an amorphous opal. For silica-lignin, SiOSi was gradually transferred to Si(OR)x instead of SiC. The capacities of the fractionated components to bind or store silica were in order of lignin > polysaccharides > lipids. Moreover, the fractionated components of rice straw were associated with the different ultrastructural forms of the silica.