Robust Thermal Stability, Flame Retardancy, and Weather Resistance Cross-Linked Cellulose Aerogel toward High-Performance Passive Radiative Cooling

The frequent occurrence of high temperatures has driven the development of green passive cooling technologies. Traditional passive radiative cooling materials have single performance, insufficient weather resistance and structural stability, and are unable to adapt to outdoor multifunctional thermal management. In this study, cellulose nanofibers were used as the substrate, and silica and methyltrimethoxysilane were incorporated to prepare a composite aerogel. Tests show that the optimal sample has excellent radiation cooling, heat insulation, flame retardancy, hydrophobicity, and sound absorption performance. With a solar reflectance of 93.5% and a mid-infrared emissivity of 94.3%, it provides a maximum outdoor temperature reduction of 15.7 °C. Its minimum thermal conductivity reaches 0.034 W m–1 K–1, offering excellent thermal insulation performance. The total heat release and the rate of heat release were significantly reduced, and flame retardancy was greatly improved. In addition, the sample exhibits a water contact angle of 137.2°, endowing it with favorable self-cleaning properties. The average sound absorption coefficient reaches 0.78 in the broadband range of 1000–6300 Hz, and the noise reduction performance is superior to that of commercial materials. This multifunctional composite aerogel overcomes the performance limitations of traditional materials and offers new insights into the development and application of outdoor integrated thermal management functional materials.