Janus graphene-Al2O3: aramid hybrid fabric for multifunctional passive cooling and flame retardancy

Abstract Aramid is an ideal substrate for protective equipment in extreme environments due to its excellent mechanical strength, intrinsic flame retardancy, and high-temperature resistance. However, the functional design of traditional aramid fabrics has long been confined to mechanical protection properties, and little work has been reported on the modification of aramid fabric for passive radiative cooling (PDRC) and unidirectional moisture transport properties. In this study, a Janus fabric was engineered by coating graphene- and hexadecyltrimethoxysilane (HDTMS)-impregnated aramid with an Al 2 O 3 layer. The hydrophilic Al 2 O 3 side had a high solar reflectance (~ 89%) that effectively blocked most of the incident heat, while the hydrophobic graphene/HDTMS side absorbed and transmitted infrared radiation (~ 87%), promoting the dissipation of body heat. The skin microenvironment temperature was reduced by 2.0 °C compared to that of the aramid fabric in a non-sweating indoor environment due to the high infrared emissivity of graphene and by about 10.3 °C compared to that of the aramid fabric in a non-sweating outdoor thermal environment. In a sweaty outdoor thermal environment, the skin microenvironmental temperature change of the fabric was 1.0 °C lower than that of aramid (8.9 °C) due to the effective solar radiation reflectivity of the Al 2 O 3 layer and the effective wicking properties of the overall Janus fabric. Notably, the fabric maintained its performance under UV exposure and retained fire resistance, enabling applications such as building fireproofing. This approach promotes the development of cost-effective, flexible inorganic PDRC materials for sustainable cooling solutions.