Hierarchical SiO₂@Cellulose Nanofiber Aerogels With Synergistic Optical-Thermal Regulation for High-Performance Passive Cooling.

Abstract

Passive radiative cooling offers a sustainable pathway for thermal management by minimizing solar absorption while maximizing mid-infrared (MIR) emission through the atmospheric transparency window. However, parasitic heat gain substantially compromises its net cooling efficiency. Here, we report a reversible xanthation-mediated strategy to fabricate hierarchical SiO₂@cellulose nanofiber aerogels that synergistically integrate broadband solar reflectivity, high MIR emissivity, and low thermal conductivity. The xanthation chemistry enables uniform, in situ anchoring of ∼300 nm SiO₂ nanospheres along nanofibers, creating a distinctive 'pearl-necklace' morphology, while directional ice-templating further constructs lamellar hierarchical porous networks that suppress nonradiative heat transfer. The optimized aerogel exhibits an average solar reflectance of 95.6%, a MIR emissivity of 95.3% within the 8-13 µm atmospheric window, and an ultralow thermal conductivity of 0.028 W m^-1K^-1. Under 1000 W m^-2 solar irradiance, it achieves a time-averaged subambient cooling of 3.7°C and a net temperature reduction of 24.9°C compared to polystyrene foam, while extending refrigeration thermal cycling by 47.3%. This work provides a scalable material design framework for monolithic integration of optical selectivity and thermal insulation, offering a promising sustainable solution for energy-efficient buildings, cold-chain logistics, and next-generation thermal management systems.