A robust Janus fibrous membrane with switchable infrared radiation properties for potential building thermal management applications

Abstract

The heating and cooling of buildings consumes a large part of global energy, contributing to aggravating global warming and the energy crisis. Combining heating and cooling functions within the same material without intensive energy input is strongly desired but still waiting to be realized. Herein, a Janus thermal management membrane with a trilayer structure has been prepared using ZnO nanorods array-coated cellulose (ZnO-NRs@cellulose), ultralong MnO₂ nanowires (UL-MnO₂-NWs) and silver nanowires (Ag-NWs) as building blocks. The ZnO-NRs@cellulose fiber layer with a rough surface was fabricated by a hydrothermal process based on the controlled growth of ZnO nanorods on cellulose surfaces. Subsequently, the hydrothermally synthesized UL-MnO₂-NWs and Ag-NWs were filtered onto the ZnO-NRs@cellulose layer in turn, forming a laminated Janus membrane. The Janus membrane exhibited asymmetric radiation properties on each side: the ZnO-NRs@cellulose side of the Janus membrane displayed high solar radiation reflectivity and high infrared emissivity to minimize heat input from the sun and enhance heat dissipation in hot environments, while the Ag-NW side exhibited a relatively high solar radiation absorption rate and low infrared emissivity for enhancing heat input from the sun and reducing the heat radiation loss in cold environments. The introduction of UL-MnO₂-NWs and Ag-NWs into the laminated Janus membrane endowed the membrane with a high tensile stress of 61.4 MPa. Moreover, the strong compatible entanglement between the three layers of the Janus membrane causes satisfactory interface stability. Due to its special asymmetric radiation performance, excellent interfacial compatibility, and high mechanical stability, such a Janus membrane may potentially be useful in energy saving in buildings, personal thermal management and other facilities.