Device demonstrations with the nanopaper semiconductor. (a) Wearable sensor for monitoring exhaled water vapor leaking from face masks. (b) Glucose biofuel cell for energy generation. Image: 2022 Koga et al. Nanocellulose paper semiconductor with a 3D network structure and its nano-micro-macro trans-scale design. ACS Nano.
Device demonstrations with the nanopaper semiconductor. (a) Wearable sensor for monitoring exhaled water vapor leaking from face masks. (b) Glucose biofuel cell for energy generation. Image: 2022 Koga et al. Nanocellulose paper semiconductor with a 3D network structure and its nano-micro-macro trans-scale design. ACS Nano.

Semiconducting nanomaterials with 3D network structures have high surface areas and lots of pores that make them excellent for applications involving adsorbing, separating and sensing. However, simultaneously creating useful micro- and macro-scale structures and controlling their electrical properties, while also achieving excellent functionality and end-use versatility, remains challenging.

Now, researchers at Osaka University in Japan, along with colleagues at The University of Tokyo, Kyushu University and Okayama University, also in Japan, have developed a nanocellulose paper semiconductor that allows both trans-scale designability of its 3D structures and wide tunability of its electrical properties. The researchers report their work in a paper in ACS Nano.

Cellulose is a natural and easy-to-source material derived from wood. Cellulose nanofibers (nanocellulose) can be made into sheets of flexible nanocellulose paper (nanopaper) with dimensions like those of standard A4. While nanopaper does not normally conduct an electric current, heating can introduce semiconducting properties. Unfortunately, this exposure to heat can also disrupt the nanostructure.

The researchers have therefore devised a treatment process that allows them to heat nanopaper without damaging its structure, from the nanoscale up to the macroscale.

“An important property for the nanopaper semiconductor is tunability because this allows devices to be designed for specific applications,” explains Hirotaka Koga from Osaka University. “We applied an iodine treatment that was very effective for protecting the nanostructure of the nanopaper. Combining this with spatially controlled drying meant that the pyrolysis treatment did not substantially alter the designed structures and the selected temperature could be used to control the electrical properties.”

The researchers used origami (paper folding) and kirigami (paper cutting) techniques to demonstrate the flexibility of this nanopaper at the macrolevel. A bird and box were folded, shapes including an apple and a snowflake were punched out, and more intricate structures were produced by laser cutting. This demonstrated the level of detail possible, as well as the lack of damage caused by the heat treatment.

Examples of successful applications included nanopaper semiconductor sensors incorporated into wearable devices for detecting exhaled moisture breaking through facemasks and moisture on the skin. The nanopaper semiconductor was also used as an electrode in a glucose biofuel cell, which generated sufficient energy to power a small lightbulb.

“The structure maintenance and tunability that we have been able to show is very encouraging for the translation of nanomaterials into practical devices,” says Koga. “We believe that our approach will underpin the next steps in sustainable electronics made entirely from plant materials.”

This story is adapted from material from Osaka University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.