¿ìè¶ÌÊÓƵ

Unwanted citrus fruit peel could be re-purposed into ultra-light sponges that can clean up oil spills, while also reducing food waste.

Fengzhi Tan at Dalian Polytechnic University in China gathered the discarded peel of pomelos, a large citrus fruit similar to a grapefruit. They chipped off the yellow skin, leaving only the spongy pith, which they ground and dried into a powder.

Then they added a liquid silicon-based compound and heated it to 80°C for 12 hours and then 60°C for 24 hours to turn it into an aerogel – a type of material so light and porous that it can float on air.

These ultralight materials are also very strong, so they have been suggested as possible heat shield materials for spacecraft. Cellulose-based aerogels, like this new one, are known to be good for soaking up oil and have been made from cotton, corn stalks and leaves, and banana peels.

In this pomelo-peel-based aerogel, the internal pores are 10 to 1000 nanometres wide, and they make up most of the material. This is on the larger end of the scale as far as pore size goes for aerogels. Scanning electron microscope images reveal that the porosity – or the fraction of empty space to actual material – is up to 98.6 percent. Thin filaments of fibre from the citrus peel crisscross to make the layers between the pores.

The team tested whether the aerogel could remove kerosene from water. They found that water formed droplets on the surface of the material, while kerosene was quickly and completely absorbed. They also put dyed kerosene into a beaker of water and dipped the aerogel inside. After 1 minute, the kerosene was entirely soaked up.

The team tested the same sample of the aerogel in consecutive experiments and found that it retained nearly 94 per cent of its capacity to soak up oil after 10 cycles, suggesting the material could be used multiple times.