Hierarchically Porous Cellulose-Based Radiative Cooler for Zero-Energy Food Preservation

This paperreports an energy-free biomass-based radiativecooling film, which will be critically demand in sustainable low-temperaturefood preservation. Lowtemperature preservation is an essential route to extend thefood shelf life but remains challenging due to its increasing energyconsumption and carbon emission, as well as the need for decentralizedfood preservation. Passive radiative cooling, which can dissipatean object's thermal energy through an atmospheric transparencywindow to ultracold outer space without consuming any energy, providesa sustainable route for food preservation. Here, a hierarchicallyporous (0.006-10 mu m) cellulose acetate/zinc oxide (CA/ZnO)nanocomposite film is constructebased on water-assisted induced phaseseparation to achieve passive cooling without any energy input. Thefilm with 30 wt % ZnO concentration achieves subambient temperaturecooling through high solar reflectivity (97.0%) and high mid-infraredemissivity (94.0%), achieving a daytime temperature drop of 13.8 degrees Cunder strong solar illumination. When used in food packaging, theCA/ZnO film can decrease the temperature of enoki mushrooms by upto 18 degrees C under direct sunlight. The preservation temperaturereduction outperforms other commercially available food packagingmaterials, which can extend strawberries storage time to 9 days. Meanwhile,the film also demonstrates excellent antimicrobial, self-cleaning,and reusable properties. This energy-free cooling film has great potentialin food preservation as well as other applications where a controlledenvironmental temperature is required.