275 / 2022-09-20 15:03:26

Geopolymer-based sub-ambient daytime radiative cooling coating

Geopolymer,daytime radiative cooling,alkali activation,sub-ambient

Sub-ambient daytime radiative cooling coating (SDRCC) is an appealing thermal management technology that has great potential for alleviating the global warming and urban heat island effect. The radiative cooling effect can be achieved by engineering a surface with a high solar reflectance as well as a high emittance in the sky transparent window (infrared atmospheric window). Over the past few years, various types of polymeric SDRCCs have been developed. However, they may face problems of environmental ageing under UV, moist and fire due to their organic nature. In this study, an ambient-cured inorganic alkali-activated geopolymer (AAGP)-based daytime radiative cooling coating was synthesized with the modification of barium sulphate (BaSO₄) and nano-silica (SiO₂) particles (Fig. 1). The optical and physicochemical properties were systematically investigated. The chemical composition, functional groups as well as surface morphologies of the raw materials and the formed geopolymer coating were characterized by XRD, FTIR and EDS. The microstructural of the section of the AAGP cooling coating was presented by false-colored SEM (Fig. 3). The developed AAGP coating exhibited a high infrared emissivity of 0.9491 and solar reflectance of 97.6%. When exposed to direct sunlight and based on a self-made field test setup (Fig. 5),  the coating’s surface was found to be able to cool down up to 8.9 ℃ below the ambient air temperature under Hong Kong’s climate (Fig. 4). Due to the inherit advantages of an inorganic coating over its organic counterpart, the developed AAGP coating is expected to be able to broaden the applicability of the SDRCC technology for efficient thermal management and energy saving purpose.