Cellulose-Based Hierarchical Porous Membranes Integrating Temperature-Adaptability and Superhydrophobic Self-Cleaning for All-Season Passive Radiative Cooling

Abstract Passive radiative cooling offers a sustainable pathway for building thermal management, yet its practical deployment is severely hindered by two critical limitations, namely, static cooling-induced overcooling in cold environments and optical deterioration due to outdoor fouling. Herein, we construct a cellulose-based hierarchically porous material that integrates thermochromic switching with superhydrophobic self-cleaning. Specifically, thermochromic microcapsules (TMCs) are integrated into a tailored cellulose acetate porous network structure via a solvent-template-assisted evaporation-induced phase separation strategy with scalable potential. Crucially, this architecture not only generates extensive Mie-scattering sites to maximize solar reflectance but also mechanically anchors the TMCs within the structure, thereby mitigating the embrittlement typically observed in highly filled composites. Consequently, the resulting membrane exhibits excellent mechanical properties even at a high TMC loading of 30 wt %, achieving a tensile strength of 21.9 MPa and an elongation at break of 34.3%. Meanwhile, the membrane achieves autonomous optical switching, modulating solar reflectance from 96.2% in the hot state to 80.8% in the cold state, while maintaining a high infrared emissivity of 95.0%. Field tests demonstrate superior climate adaptability, i.e., the membrane yields a cooling of 12.3 °C under intense solar irradiance and effectively suppresses overcooling by maintaining a 6.6 °C thermal advantage over the static radiative cooling film in cold environments. Furthermore, to ensure long-term fidelity, a superhydrophobic feature is introduced (contact angle ∼152°), endowing the surface with exceptional self-cleaning capabilities that preserve optical performance against dust accumulation. This work synergizes adaptive thermoregulation with environmental durability, offering a scalable, eco-friendly solution for next-generation smart building envelopes.