Green Radiative Cooling and Antimicrobial Materials Based on Polylactic Acid Oligomer Hexagonal Microspheres

Thermal management relying on passive radiative cooling materials can result in remarkable energy savings and greenhouse gas emissions reductions compared with traditional air conditioner-based cooling. However, few of these materials are degradable; thus, their disposal may generate a new environmental problem. At the same time, the COVID-19 pandemic and other infectious diseases have raised requirements for hygienic and antimicrobial performance. In this work, we use a facile solvent evaporation method to prepare a novel hierarchically porous polylactic acid oligomer (PLAO) coating that exhibits a radiative cooling effect, broad-spectrum antimicrobial properties, and degradability (with a degradation rate of 99.5% after 28 days). The radiative cooling effect is attributed to the hexagonal microsphere geometry and nanotexture of the polylactic acid oligomer (PLAO) crystals, which enhance reflectivity in the solar spectrum through a multiple scattering effect and exhibit high emissivity in the mid-infrared atmospheric window. The hierarchically porous PLAO coating material achieves an apparent temperature reduction of 6.8 °C under solar-spectrum irradiation (AM 1.5). The material also shows broad-spectrum antimicrobial and antiviral properties against coronaviruses (including the COVID-19 virus), with a reduction rate of 99.99% after 20 min; Gram-positive and Gram-negative bacteria, with a reduction rate of 99.99% after 1 h; fungi, with a reduction rate of 98.4% after 1 h; and multidrug-resistant bacteria, against which it produces a 0.22 cm inhibition ring after 12 h.