Freeze-Thaw Adhesion-Driven Fabrication of Fire-Resistant Janus Aerogels with Switchable Radiative Cooling/Heating...

Passive radiative cooling and solar heating have emerged as ecofriendly and renewable strategies for thermal management, attracting widespread attention. Nevertheless, conventional materials are predominantly optimized for single static conditions and cannot meet the thermal comfort requirements under fluctuating temperatures across cold and hot seasons. To address this issue, this study proposed a dual-mode PVA-based Janus aerogel, which achieved interfacial bonding between a cooling layer (PVA/HNT@TiO₂) and a heating layer (PVA/MXene). This design integrated efficient radiative cooling and solar heating in one material, aiming to achieve thermal regulation in space and perennial energy savings. The synergistic enhancement of HNT@TiO₂ nanoparticles and the three-dimensional porous structure endowed the cooling layer with a high solar reflectance of 92.83% and an atmospheric window infrared emissivity of 94.15%. On the heating side, benefiting from the excellent photothermal properties of MXene and the light-trapping effect induced by the porous structure, the solar absorption rate reached 79.54%. Outdoor tests demonstrated that in cooling mode, the cooling side significantly reflected sunlight and emitted infrared radiation, achieving a maximum subambient temperature drop of 8.52 °C; in heating mode, the heating side absorbed sunlight, causing a temperature increase of 4.96 °C. By simply flipping the Janus aerogel mechanically, effective thermal management over a wide temperature range was realized, with performance surpassing that of reported works. Furthermore, owing to the strong interfacial bonding and physical cross-linking between nanoparticles and the PVA matrix, the compressive strength of the Janus aerogel 3 was increased by 93.1% compared to pure PVA, and its compressive modulus was 40.6 times higher. More importantly, relative to pure PVA aerogel, Janus aerogel 3 exhibited reductions of 30.1% in peak heat release rate, 33.7% in peak smoke production rate, 39.2% in total smoke production, and 30.9% in peak CO production rate, indicating outstanding fire safety performance. This was attributed to the ability of HNT@TiO₂ and MXene to form a protective char layer reinforced by metal oxides and to catalyze the conversion of toxic gases, thereby further suppressing combustion behavior. By integrating switchable thermal regulation, superior fire safety, and mechanical robustness, this study establishes the potential of Janus aerogels as safe, durable, smart building envelopes for year-round energy efficiency.