An Intelligent, Recyclable, Biomass Film for Adaptive Day-Night and Year-Round Energy Savings

Passive radiative cooling is a zero-energy technology vital for mitigating the energy crisis. However, achieving intelligent thermal management across varying weather conditions (day/night and summer/winter) while maintaining sustainability is a significant challenge. Here, a recyclable biomass film engineered for adaptive, year-round energy conservation is introduced. This film utilizes porous acetyl cellulose (AC) as a cooling-side matrix, enabling efficient radiative cooling during hot days (8.5 °C reduction) and minimizing overcooling on cold nights (only 2.5 °C reduction). This performance is facilitated by high solar reflectance (96.3%) and broad-spectrum infrared emission (95.4%), optimizing atmospheric thermal regulation. The reverse side, coated with carbon black (CB), demonstrates superior solar heating (20.9 °C increase), allowing for effortless switching between cooling and heating by flipping the film. Further, the film employs a solvent-responsive ethyl cellulose (EC) adhesion, ensuring durability, complete recycling, and reuse. With ultraviolet (UV) resistance, self-cleaning, and durability, coupled with intelligent thermal management, this work provides new ideas for advanced radiative heat management materials, enabling adaptive control during both daytime/nighttime and summer/winter.