Nanoporous Mg-doped SiO2 nanoparticles with tunable infrared emissivity toward effective radiative cooling coatings
Xingxing Zhang, Xiangdong Gao, Yubing Dong, Yongqing Wu, Deng Duan, Xiangyong Zhao, Xiaomin Li
Abstract
SiO 2 is the hotspot radiative cooling material due to its selective radiation or the Mie resonance effect generated by micro/nanospheres of a specific size. Herein, we demonstrate the modulation of the infrared emissivity of the intrinsic SiO 2 at the atmospheric window by doping Mg 2+ in nanoporous SiO 2 nanoparticles via a modified stöber method. The effects of the Mg-doping on the crystallinity , morphology, infrared emissivity of the nanoparticles and the radiative cooling properties of the corresponding coatings are investigated. Results show that the Mg-doping at a level of 0.226–2.26 % can induce cristobalite nanocrystals after sintering at 1000 ℃, transform the morphology from spheres to irregular nanoporous particles, and improve the infrared emissivity up to 0.96. XPS proves the formation of Mg-O bonds and the change of the binding energy of Si 2p and O 1s, supporting the successful doping of Mg 2+ in the lattice of SiO 2 . All-inorganic Mg-doped SiO 2 coatings on FTO substrates are prepared via tape casting , which exhibit rough and porous microstructure and high solar reflectivity up to ∼86 %, with the thickness of ∼90 µm. The Mg-doping improves the radiative cooling capacity of the coatings obviously, and the best temperature reduction of 17.8 ℃ compared with the empty space is achieved, 3–5 ℃ lower than the pure SiO 2 coating and 4.5 ℃ lower than the commercial SiO 2 coating. Our work offers an effective way to modulate the infrared emission of emitter, enriching the technical measures to improve the overall performance of the sub-ambient radiative cooling devices.