Simultaneous fabrication of carbon microspheres, lignin/silica nanohybrids, and cellulose nanostructures from rice husk

Rice husk (RH) is one of the inevitable byproduct of rice production. It has been generated with an enormous amount every year. Biorefinery concept-assisted transformation of rice husk into high-value materials received significant attention. Thus, in this present study, we have developed an integrated biorefinery approach for converting rice husk into different micro/nanostructured materials, including carbon microspheres (CMs), lignin/SiO2 nanohybrids (LSNHs), and cellulose nanostructures (CNs) simultaneously. The rice husk was treated with dilute hydrochloric acid at 120 degrees C under 15 lbs pressure. The dilute acid treatment disintegrates the RH structure and releases the hemicellulose. The obtained liquid hemicellulose fraction was subjected to hydrothermal carbonization at 180 degrees C for 24 h. After hydrothermal treatment, the obtained solid fraction was subjected to alkali treatment. Lignin/SiO2 and cellulose were extracted from liquid and solid fractions after alkali treatment, respectively. The obtained cellulose was transformed into CNs using an acid hydrolysis process. The TEM images of the RH-derived carbon material showed spherical aggregates in shape with 500-1000 nm diameter. The LSNHs have 20-50 nm silica nanoparticles dispersed on the lignin matrix. The CNs TEM image displays fibrillated structure with 600-1000 nm in length and 25-40 nm width. The RH-derived materials reduced cell viability slightly and altered the cellular and nuclear morphology in FaDu cells. Our study results indicate that fabricated materials can be applicable for various biomedical applications.