Alginate/soy protein isolate aerogels as biodegradable oil absorbents: representing a sustainable approach

Background Accidental oil spills threaten ecosystems and water resources, while synthetic absorbents like polypropylene contribute to long‐term pollution. This study explores the potential of a novel biodegradable hybrid biopolymer composed of sodium alginate (ALG) and soy protein isolate (SPI) for oil spill remediation. The ALG/SPI aerogel absorbent was synthesised via a sol–gel method. Surface modification of the ALG/SPI to enhance its hydrophobicity was performed through two techniques: (i) liquid immersion and (ii) scCO 2 adsorption. The reusability, biodegradation, and toxicity tests of the ALG/SPI absorbent were evaluated, aligning with the growing concern about sustainability and reliance on synthetic or non‐biodegradable materials. Results ALG/SPI aerogels biodegraded rapidly (80–86% mass loss in 5 weeks) while maintaining buoyancy after oil uptake. MTMS silanisation with both techniques produced superhydrophobic/oleophilic surfaces (water contact angles: surface 124–143°, cross‐section 118–146°), enhancing oil selectivity and performance. The optimised 1% ALG/1.5% SPI (ALG/SPI 1:1.5) exhibited the highest contact angle of 143 o , achieving 89.8% oil–water separation efficiency with 13‐cycle reusability through MTMS liquid immersion. FTIR, TGA, and FESEM post‐testing supported an environmentally benign profile, positioning ALG/SPI aerogels as a promising alternative to synthetic absorbents. Conclusion The ALG/SPI 1:1.5 aerogel exhibited excellent buoyancy, stable absorption across 40–120 °C, and superior environmental performance compared to synthetic sponges. With liquid immersion giving the highest hydrophobicity and scCO₂ adsorption showing potential as a greener solvent‐free alternative with comparable wettability properties, ALG/SPI emerges as a sustainable substitute for synthetic oil absorbents.