Bio-based foams with multifunctional photothermal, fire-resistant, and CO2 capture properties

To meet the growing demand for sustainable, fire-resistant, and thermally functional materials, this study develops multifunctional bio-based foams composed of naturally abundant clay minerals and cellulose nanofibers (CNFs). The foams are fabricated via freeze-drying and carbonized to enhance photothermal activity and flame resistance. Varying clay-to-CNF ratios reveal that clay improves structural retention during pyrolysis, reducing volume shrinkage from 85% in neat CNF foams to 10–14% in hybrids. The carbon–clay network significantly enhances compressive modulus and energy absorption, while thermogravimetric analysis confirms improved thermal stability. Despite carbonization, thermal conductivity remains low (0.041–0.058 W·m -1 ·K -1 ), supporting insulation applications. The carbonized foams exhibit strong photothermal response, reaching surface temperatures above 80 °C under solar irradiation, and demonstrate CO 2 adsorption up to 12.4 ± 0.6 mg·g -1 . Life cycle assessment (LCA) highlights substantial environmental advantages, reducing climate change potential from 19.18 to 0.76–1.16 kg CO 2 -eq·kg -1 in clay–CNF hybrids, alongside benefits in acidification, ecotoxicity, eutrophication, water use, and land occupation. These findings establish clay–CNF carbon foams as competitive alternatives to both synthetic insulation materials and pure nanocellulose porous structures, offering high volume retention upon carbonization while achieving a balanced combination of thermal, mechanical, fire-safe, and environmental performance.