Dual-mode natural silk nanofiber aerogel with porous layered structure for highly stabilized radiative cooling and heating.

Passive Radiant Cooling and Heating are green and sustainable methods of radiant heat management without consuming additional energy. However, the absorption of sunlight and poor insulation of materials can reduce radiative cooling and also affect radiative heating performance. Herein, we have constructed porous hierarchical dual-mode silk nanofibrous aerogel (SNF) films with high mechanical toughness and stability using silk nanofibers/GO. The porous hierarchical structure endows the cooling side of the dual-mode film with low thermal conductivity (0.034 W·m·K) and high atmospheric window emissivity (92.7 %), with a sub-ambient cooling temperature of up to 9.6 °C under direct sunlight. The heating side of the dual-mode film has a high solar absorptivity (93.8 %) and a low atmospheric window emissivity (11.4 %). The covered air temperature was warmed by 25.5 °C in the simulated cold environment by the ice water bath. Importantly, both sides of the film are hydrophobically modified with FOTS to exhibit self-cleaning properties that protect the surface from contamination and facilitate long-term radiative cooling/heating. The films showed excellent cooling and heating properties even after two months of immersion in different pH solutions. This dual-mode aerogel film has great potential for outdoor applications and can be adapted to radiant heat management in various complex environments.