Scalable, Flexible, and UV-Resistant Bacterial Cellulose Composite Film for Daytime Radiative Cooling

Radiative cooling, a passive cooling technology, functions by reflecting the majority of solar radiation (within the solar spectrum of 0.3-2.5 mu m) and emitting thermal radiation (within the atmospheric windows of 8-13 mu m and 16-20 mu m). Predominantly, synthetic polymers are effectively utilized for radiative cooling while posing potential environmental hazards due to their complex components, toxicity, or nonbiodegradation. Bacterial cellulose, a natural and renewable biopolymer, stands out due to its environmentally friendly, scalability, high purity, and significant infrared emissivity. In this work, we developed a bacterial cellulose-based composite film (BCF) with a cross-linked network structure by a facile agitation spraying method to achieve enhanced and sustainable radiative cooling performance. The BCF exhibited superior optical properties and environmental tolerance, with a notable infrared emissivity of 94.6%. As a result, the thermal emitter demonstrates a substantial subambient cooling capacity (11:00 to 13:00, maximum drop of 7.15 degrees C, average drop of 4.85 degrees C; 22:00 to 2:00, maximum drop of 2.7 degrees C, average drop of 2.32 degrees C). Additionally, the BCF maintained stable emissivity after 240 h of continuous UV irradiation. Furthermore, BCF can effectively preserve the freshness of fruits under intense solar irradiation. Hence, BCF with high radiative cooling performance presents a broad application prospect in building energy conservation, solar cells efficiency enhancement, and food transportation packaging.