Ultra-Lightweight and Reinforced ZnO/Cellulose Hierarchical Aerogel for Thermal Insulation

Abstract Cellulose aerogels (CA) with high porosity and environmental sustainability are expected to replace traditional petroleum-based insulation materials. However, the efficient thermal insulation and mechanical reinforcement of cellulose aerogel still face challenges. We develop zinc oxide/cellulose (ZnO/CA) aerogels through a straightforward strategy involving the dissolution of cellulose in a sodium hydroxide-urea solution followed by directional freezing. Specifically, the sodium hydroxide-urea solution disrupts the intermolecular and intramolecular hydrogen bonds within cellulose, converting its crystalline structure from cellulose I to cellulose II. The temperature gradient during directional freezing induces a uniformly ordered, three-dimensional layered porous structure with ultra-low density (0.071–0.102 g/cm³) and high porosity (97.14–98.02%). Importantly, The compressive modulus of the ZnO/CA aerogel reaches 917.43 kPa, while its thermal conductivity is as low as 0.0138 W·m− 1·K− 1, indicating high compressive strength and excellent thermal stability. Within the ZnO/CA aerogel framework, the overall emissivity in the infrared band is below 0.5, effectively reducing thermal radiation intensity. On an 80°C hot target, the surface radiation temperature of the aerogel drops to as low as 38°C. Furthermore, ZnO/CA aerogel-coated fabrics exhibit a 74% increase in insulation compared to untreated cotton fabric and demonstrate effective insulation for various heat sources. The lightweight, reinforced ZnO/CA aerogel offers new possibilities for developing wearable insulating devices and high-performance thermal insulation materials.