Synthesis of Silica-Based Materials Using Bio-Residues through the Sol-Gel Technique

This study focused on the use of citrus bio-waste and obtention of silica-based materials through the sol-gel technique for promoting a greener and more sustainable catalysis. The sol-gel method is a versatile synthesis route characterized by the low temperatures the materials are synthesized in, which allows the incorporation of organic components. This method is carried out by acid or alkali hydrolysis combined with bio-waste, such as orange and lemon peels, generated as co-products in the food processing industry. The main objective was to obtain silica-based materials from the precursor TEOS with different catalysts—acetic, citric and hydro-chloric acids and ammonium hydroxide—adding different percentages of lemon and orange peels in order to find the influence of bio-waste on acids/alkali precursor hydrolysis. This was to partially replace these catalysts for orange or lemon peels. The solids obtained were characterized with different techniques, such as SEM, FT₋IR, potentiometric titration and XRD. SEM images were compared with pure silica obtained to contrast the morphology of the acidic and alkali hydrolysis. However, until now, few attempts have been made to highlight the renewability of reagents used in the synthesis or to incorporate bio-based catalytic processes on larger scales.