Self-Cleaning and Spectral Selective Membrane for Sustainable Radiative Cooling

Radiative cooling materials have attracted great attention due to their superiority in energy-free cooling, especially for outdoor applications. However, outdoor cooling performance is threatened by surface pollution. Herein, we demonstrate a ternary compound system, including polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), boron nitride nanosheets (BNNS), and hydrophobic silicon dioxide (SiO2), to synchronously achieve self-cooling and self-cleaning properties through biomimetically building a lotus-like papillomatous structure. The optimized membrane has a high infrared emissivity of 0.93, a sunlight reflectivity of 97.2%, and a water contact angle of 150.5°and not only efficiently cools the object to a suitable temperature but also protects the membrane from polluting and keeps cooling for a long time. The result shows that the membrane can cool a nonfebrile object by 30.5 and 1.7 °C for noon and night, respectively, and the noon and night-time temperature drops are 10.8 and 13.5 °C for the self-heating object, compared to the bare state. Meanwhile, the membrane always keeps self-cleaning if slurry is splashed onto its surface or it is exposed to slurry. Importantly, the integration of superhydrophobic and radiative cooling properties ensures that the membrane has permanent cooling performance by protecting it from being contaminated, which is significant for outdoor applications.