A recyclable, up-scalable and eco-friendly radiative cooling material for all-day sub-ambient comfort

Passive radiative cooling materials provide coldness without energy consumption for all-day thermal comfort by reflecting solar irradiation and emitting heat into the 3 K universe. However, the conventional radiative cooling materials involve complex multilayer structures and unsustainable polymers, showing the non-recyclable disadvantage, which induces resource waste and environmental issues. Herein, we reported a low-cost, scal-able, and eco-friendly radiative cooling material (namely cooling paper), consisting of the delignified, fibrillated cellulose fibers and nano-sized hydroxyapatite (HA) via the mature pulping and papermaking process. The resulting cooled paper can be recycled, and it can be easily deconstructed to harvest cellulose fibers and HA, individually. The recovered source materials can be reused to prepare secondary products that show comparable performance to the original cooling paper, including a high solar reflectance of-94% and an infrared emissivity of-0.95 in the atmospheric transparency window. Such cooling paper enables superior cooling performance with the temperature drop of 6 -8.8 degrees C under directly solar radiation. Based on the EnergyPlus simulation, our cooling paper shows a average cooling energy saving of-29 % in buildings across China. The recyclable cooling paper with high cooling capability and scalability, as well as environmental friendliness, shows promising po-tential for sustainable energy-efficient buildings.

Automated summary

Passive radiative cooling materials offer all-day thermal comfort without energy consumption by reflecting solar radiation and emitting heat into the 3 K universe. However, conventional materials have non-recyclable complex structures and unsustainable polymers, leading to resource waste and environmental issues. This study presents a low-cost, scalable, and eco-friendly radiative cooling material called cooling paper, made from delignified cellulose fibers and nano-sized hydroxyapatite (HA). The resulting paper can be easily recycled and deconstructed to recover cellulose fibers and HA, which can be reused to prepare secondary products with comparable performance. The recyclable cooling paper shows a temperature drop of 6-8.8 degrees C under direct solar radiation and an average cooling energy saving of 29% in buildings across China, indicating its promising potential for sustainable energy-efficient buildings.