University student designs self-powered sensor from plants

Qi Chen’s research story is full of serendipity. A first-year PhD student at the university’s Zernik campus was chatting with friends about the subjects of her classmates’ research studies. Chen informed them that he was going to research foam-like materials. The stem of a grass-like plant was casually peeled away by a friend, revealing its interior, which appeared to be an open and airy structure. He playfully suggested that Chen might want to go through with it. After putting it in her bag, she promptly forgot about it.

Gui Chen, a macromolecular chemist from the University of Groningen, created a small sensor from a plant he harvested on the university campus. Photo credit: Leonie van Rystok – University of Groningen

Two years later Chen found the herb in his bag. She tried to generate energy from bacteria using foam material as a living habitat. The results weren’t impressive, so she decided to investigate this grass-like plant: soft rush (Juncus effusus L.), a common wetland weed.

Little snowflakes

The texture of the smooth rush stem consists of layers of interlaced stars, resembling tiny snowflakes.

Gui Chen, Ph.D. Student, University of Groningen

These layers are placed on top of each other to form a structure that allows a large amount of air to flow.

Chen added, “My samples were very light. Once, when I closed the samples and opened the lab door, the samples flew away. It looked like snow on the pavement.

Many aquatic or wetland plants have aerenchyma—an open structure—in their interior.

The plant needs this open system to breathe because in moist environments their roots must take oxygen from the air and transport it through the stem.” Chen noted.

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It turns out that this material is a fantastic alternative source for organic plant-based foams.

A small device to put in your shoe

The unique shape of the tiny snowflake on the soft rush stem was also ideal for creating a nanogenerator: a tiny device that generates an electrical charge that can be used as a sensor or power source.

A nanogenerator like this could make the current trend of small wearable electronics more sustainable by replacing batteries that end up in e-waste.

Chen, along with colleagues Wenjian Li and Feng Yan, created a postage stamp-sized nanogenerator that is roughly one millimeter thick. It acts as a motion sensor.

You can put it in your shoe and when you walk, jump or run, it emits a unique signal that we can recognize.

Dina Maniar, study co-author and assistant professor, Faculty of Science and Engineering, University of Groningen

The triboelectric effect that causes a shock when touching a doorknob after walking across a carpet is the basis of this little gadget. It is made up of two small layers with rough edges. A separator keeps the two layers separate, but when pressed, the friction between the layers creates an electric charge, similar to how an electric charge is created when shifting feet on a carpet.

Maniyar noted.It helps convert motion into electrical signals.

On the nanogenerator’s layers, tiny snowflakes from the soft rush plant create a rough, foam-like surface with plenty of pores: perfect for better friction between the layers while being light. This was another serendipitous discovery: Chen dropped his dissolved plant material on aluminum foil and failed to pick it up. The water evaporated, leaving a thin layer with a rough surface reminiscent of tiny snowflakes.

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It can actually be called stable

For years, scientists have been trying to make foam-like polymers from plant cellulose.

Usually, too many resources extract the cellulose, breaking down the structure. Then, a lot of resources go into creating the necessary framework for new products.

Katja Loos, study co-author and professor, Applied Chemistry, University of Groningen

By removing the stem and dissolving it in a simple mixture, Chen was able to maintain the building blocks—the tiny 'snowflakes’—of delicate rush interiors.

She said, „So, we can call it really stable.

This technique used very little energy and no oil-based fossil resources. Chen is also working on a variety of applications, including using soft rush snowflakes as part of a battery and removing contaminants from water.

Chen observed that the local municipality had eliminated soft rush development.

Chen concluded, “Now I just have to cycle a bit more to get it. 'In our lab, it’s not a weed; It is a valuable resource.

Press Notes:

Chen, K., and many others. (2023) Aerenchyma tissue of Juncus effusus L.: a new source for sustainable natural cellulose foams. Cellulose. doi:10.1007/s10570-023-05453-9

Chen, K., and many others. (2023) Juncus effusus L. Lightweight triboelectric nanogenerators based on aerenchyma-derived hollow stellate cellulose films. Advanced functional materials. doi:10.1002/adfm.202304801

Source: https://www.rug.nl

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