Sonochemically-coated transparent wood with ZnO: Passive radiative cooling materials for energy saving applications

Improving the energy efficiency of buildings through the use of enhanced passive radiative cooling materials would have a great relief to the global energy and climate crises. Through a purely solution-based sonochemical synthesis method raising no requirements on temperature and vacuum, we fabricated a ZnO-coated transparent wood (CTW) composite with high emissivity (∼0.91) across infrared wavelengths, allowing great potential for radiative cooling applications. The CTW exhibited a reasonable luminous transmittance (∼66.04% at a film thickness of ∼360 nm) for both visual comfort and luminous purposes. The ZnO coating improves the mechanical (43% enhancement of tensile strength) and thermal insulation (0.157 W.m−1.K−1) properties of the transparent wood substrate, making it a potential replacement for existing glazing materials. Energy-saving simulations for Hong Kong, Shanghai and Chongqing have revealed that CTW can save up to ∼17% more energy than conventional commercial window materials.