It has been found that cellulose can be made to conduct electricity when heated to relatively high temperatures under certain conditions.
However, the burning process — called carbonization — can destroy the three-dimensional structures that would make cellulose-derived semiconductors so useful.
A new breakthrough has addressed this problem. In a paper published Tuesday in ACS Nano, the researchers describe a treatment process that makes it possible “to heat the nanopaper without damaging the structures of the paper from the nanoscale up to the macroscale.”
They had to make sure that the process allowed manufacturers to “tune” the nanopaper to have electrical properties suitable for the specific application. In addition, the process had to be gentle enough so that manufacturers can design structures with a lot of surface area and an abundance of pores.
“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,” says material scientist Hirotaka Koga, a co-author of the paper.
The researchers used the nanopaper semiconductor as a sensor to monitor the flow of water vapor through two different types of masks. When attached to a washable mask made of cloth, the sensor could record pulses that were synchronized with exhalations. The water molecules in the wearer’s breath temporarily lowered the electrical resistance of the sensor. When attached to a surgical mask, the sensor didn’t record such pulses. “Only a gradual decrease in sensor resistance was observed, indicating the effective water vapor capture of the surgical mask,” the researchers wrote.
When the researchers attached the nanopaper semiconductor to a glucose biofuel cell, the material demonstrated a power density 14 times higher than that of a commercial graphite sheet.
“The structure maintenance and tunability that we have been able to show is very encouraging for the translation of nanomaterials into practical devices,” Koga says. “We believe that our approach will underpin the next steps in sustainable electronics made entirely from plant materials.”
