Researchers have used metal-organic frameworks and zinc oxide to overcome a major limitation of passive-cooling textiles: delivering strong solar reflection without restricting garments to white.
Researchers in China and Australia have developed an electrospun purple textile that remained 6.2°C cooler than conventional purple cotton and 4.2°C cooler than commercial white cotton under direct sunlight, demonstrating a potential route to coloured garments with passive radiative-cooling properties.
The research, led by Zhengzhou University with Australian collaborators and published in Small on July 21, uses a one-step electrospinning process to incorporate a metal-organic framework (MOF) and zinc oxide nanoparticles into thermoplastic polyurethane fibres.
Colour without surrendering cooling
Most radiative-cooling textiles are white because high solar reflectance limits heat absorption. Purple is particularly difficult because producing the colour requires absorption in the green region, where solar irradiation is strong.
The researchers instead used the MOF as a spectrally selective colourant. Its imidazole and cobalt-nitrogen structure contributes to infrared heat emission, while ZnO nanoparticles increase solar scattering. The resulting textile achieved 96.4% mid-infrared emissivity and 87.6% average solar reflectance, including 90.7% reflectance in the near-infrared region.
When placed over simulated skin outdoors, the fabric reduced maximum daytime temperature by up to 8°C, compared with 4.6°C for white cotton and 2.8°C for conventional purple cotton.
Wearability moves closer
The material was reported to be lightweight, flexible, stretchable and water-vapour permeable, while maintaining cooling performance after 50 washing cycles. It also retained optical performance following accelerated UV exposure equivalent to about 108 days outdoors.
The researchers believe other MOFs with different optical properties could extend the concept to additional colours.
Scale-up is the next hurdle
For textile manufacturers, the innovation addresses a crucial commercial weakness of passive cooling: consumers want colour as well as thermal performance.
However, industrial relevance will depend on electrospinning throughput, MOF and ZnO cost, hand feel, abrasion durability, colour consistency and integration with conventional garment production. If those challenges are resolved, coloured radiative-cooling textiles could find applications in sportswear, workwear and clothing for increasingly hot climates.
