Semiconducting nanomaterials with 3D network architectures have large surface areas and lots of pores, making them ideal for adsorption, separation and sensing applications. Moreover, achieving outstanding functionality and end-use adaptability while simultaneously addressing electrical characteristics and constructing effective micro and macro-scale structures remains a challenge.
Researchers from Osaka University have created a nanocellulose paper semiconductor in partnership with The University of Tokyo, Kyushu University and Okayama University that allows for both nano-micro-macro-trans-scale designability of 3D structures and extensive tunability of electrical properties. Their results have been reported in the journal ACS Nano.
Cellulose is a wood-derived material that is both natural and easy to obtain. Nanocellulose (cellulose nanofibers) can be manufactured into sheets of stretchable nanocellulose paper (nanopaper) with A4-sized dimensions. Although nanopaper does not produce energy, it can be made to do so by heating it. However, the nanostructure can be disrupted as a result of this heat exposure.
As a result, the researchers designed a treatment procedure that allows them to heat the nanopaper without causing damage to the paper’s structures from the nanoscale to the macroscale.
An important property for the nanopaper semiconductor is tunability because this allows devices to be designed for specific applications. We applied an iodine treatment that was very effective in 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.
Hirotaka Koga, Study Author, Osaka University
The researchers employed origami (paper folding) and kirigami (paper cutting) techniques to demonstrate the nanopaper’s macro flexibility in a fun way. A bird and a box were folded, shaped like an apple and a snowflake was punched out, and laser cutting was used to create more elaborate constructions. This highlighted the level of detail attainable as well as the heat treatment’s lack of damage.
Nanopaper semiconductor sensors built into wearable devices to detect inhaled moisture breaking through facemasks and dampness on the skin are examples of successful uses. The nanopaper semiconductor was also employed as an electrode in a glucose biofuel cell, which generated enough energy to light a tiny lamp.
Koga, also an associate professor, states, “The structure maintenance and tunability that we have been able to show is very encouraging for the translation of nanomaterials into practical devices. We believe that our approach will underpin the next steps in sustainable electronics made entirely from plant materials.”
Koga, H., et al. (2022) Nanocellulose Paper Semiconductor with a 3D Network Structure and Its Nano–Micro–Macro Trans-Scale Design. ACS Nano. doi.org/10.1021/acsnano.1c10728.