ZnO doped MgHPO4·0.78H2O coating for daytime radiation cooling research
Objects can radiate emission of heat to outer empty space(～3 K)through an atmospheric window(8-13 μm),resulting in a possibility for radiative cooling.In this paper,ZnO doped MgHPO4·0.78H2O powder was synthesized by two-step hydrothermal synthesis method with anhydrous magnesium chloride as magnesium source,sodium pyrophosphate as phosphorus source and zinc oxide as zinc source.Then,ZnO doped MgHPO4·0.78H2O radiative cooling coating was prepared with polyvinyl alcohol(PVA)as film forming agent.The day-time radiative cooling performance of the coating was studied.The results indicate that Mg∶P∶ZnO powder with molar ratio of 1∶1∶0.5 powder has a high reflectance of 93％in the solar spectral region of 0.3-2.5 μm and a high emissivity of 0.91 in the atmospheric window of 8-13 μm.Compared with the undoped ZnO powder,the solar spectral(0.3-2.5 μm)and near-infrared reflectivity(0.76-2.5 μm)are increased by 3％and 7％respective-ly.In the high humidity area,0.5-ZnO coating could achieves a daytime radiative cooling of 3 ℃ below the am-bient air temperature,providing valuable references for its application of radiative cooling coating in the high humidity area.
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