Scientific discovery: you won't believe what you can do with this fruit

The pomelo is a large citrus fruit commonly grown in Southeast and East Asia. It has a very thick peel that is usually thrown away, creating a large amount of food waste. In a new study, researchers at the University of Illinois at Urbana-Champaign in the US are exploring ways to use the biomass of pomelo peels to create tools that could power small electrical devices and monitor biomechanical movements.

Research Progress

The rind of a pomelo has two main parts: a thin outer layer and a thick, white inner layer.

The white part is soft and feels like a sponge when you squeeze it. Some people have used pomelo rinds to extract compounds for essential oils or pectin, but the researchers wanted to take advantage of the rind’s natural porous, spongy structure.

“If we can recycle the rind into higher-value products rather than just throwing it away, we can not only reduce waste from pomelo production, consumption and juicing, but also create more value from food and agricultural waste,” said study co-author Yi-Cheng Wang, assistant professor in the Department of Food Science and Human Nutrition in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois.

A pomelo fruit typically weighs between 1 and 2 kilograms. Its peel makes up 30 to 50 percent of that weight.

The researchers separated the peel from the pulp and removed the outer layer. The remaining thick, porous white peel was cut into smaller pieces and freeze-dried to preserve its unique three-dimensional porous structure, then stored under varying humidity conditions.

After analyzing the peel’s chemical composition and mechanical properties, the research team used it to create devices that can convert mechanical energy into electricity and act as Kaii-powered motion sensors.

How did the research work?

These devices work on the principle of contact electrification, which is quite simple and experienced every day.

For example, when we touch a doorknob in the winter, we sometimes feel a shock—an example of contact electrification, where static electricity is generated by the transfer of charges when two surfaces are rubbed together.

The researchers used pomelo peel biomass and a plastic polyimide film as two triboelectric materials that come into contact when an external force is applied.

They attached a copper foil electrode to each material and evaluated how well the devices converted mechanical energy into electricity.

By tapping these pomelo peel-based devices, the researchers were able to turn on about 20 light-emitting diodes (LEDs). They also showed that a calculator or sports watch could be powered solely by these mechanical forces, without external electrical energy, when the device was integrated with an energy management system, including an energy storage unit.

Sensors attached to various parts of the body were able to monitor biomechanical movements, such as joint movements and gait patterns. Movements of different body parts caused contact electrification between the triboelectric layers, generating specific electrical signals corresponding to different movements. This opens up great potential for healthcare and physical rehabilitation professionals.

"This work reveals exciting opportunities to convert food waste into value-added devices and materials. This could help reduce waste and replenish non-renewable resources, thereby contributing to long-term sustainability. We will continue to explore more options for recycling food and agricultural waste," said Y. C. Wang.