Self-cleaning and anticorrosive pompon chrysanthemum-like hollow silica nanosphere@boron nitride nanosheets hierarchical coating for highly efficient daytime passive radiative cooling

Passive radiative cooling as an effective energy-saving cooling technology has attracted enormous attention. However, the fabrication of the materials with highly efficient passive radiative cooling capability for practical applications still remains a challenge. Herein, a pompon chrysanthemum-like hierarchical structure is fabricated by in-situ growth of boron nitride nanosheets on the surfaces of hollow silica nanospheres (h-SiO₂@BNNSs). The as-obtained h-SiO₂@BNNSs can tightly stacked together on the surface of aluminum oxide plate to form a h-SiO₂@BNNS coating with an average solar radiation reflectivity of ∼0.80 and an average selective infrared emissivity of ∼0.85. These good solar radiation reflectivity and high selective infrared emissivity, combining with the multistage scattering among randomly distributed BNNSs, endue the h-SiO₂@BNNS coating a highly efficient passive radiative cooling capability. The indoor simulated radiative cooling performance test shows that the h-SiO₂@BNNS coating can achieve a temperature decrease of ∼8.5 °C at the constant solar irradiance of ∼800 W m⁻². Subsequently, the outdoor measurement further demonstrates this capability showing an average temperature decrease of ∼8.5 °C with a maximum value of ∼10.0 °C on a clear day and an average temperature decrease of ∼9.0 °C with a maximum value of ∼11.7 °C on a slight cloudy day, respectively. Besides, the h-SiO₂@BNNS coating also possesses self-cleaning and anticorrosive performances, ensuring the stability and durability of the coating utilized in different environments. This work provides a feasible pathway for the fabrication of efficient passive radiative cooling materials by reasonable combination of the solar reflection, scattering and selective infrared emission.