Nanoscale or even sub-nm scale cellulose channels allows for interesting interaction among cellulose, water and ions. As a demonstration, the transport of sodium ions within the molecular chains were demonstrated which was utilized to achieve a high ionic thermoelectric performance (T. Li, et al, Nature Materials 18, 6, 2019).

The dimension of the ion transport channels shows excellent tunability via structural engineering. This opens up an exciting new direction using abundant bio-materials—cellulose for fluidic applications. Taking nanofluidics for example, nanoscale ion channels exhibit among fibrillated cellulose and elementary cellulose fibers with a dimension of 2 nm to 50 nm. Wood with numerously aligned nanoscale channels can thus be used as an ion regulation membrane from which an electrically gated ionic transistor was demonstrated with an exchange of electrical signal and ion signal (T Li, et al, Science Advances 5, 2, 2019).

With the aid of advanced characterization methods including small angle neutron scattering and small angle X-ray scattering as well as fundamental understanding of the process-structure-property-application relationship via molecular engineering, enormous opportunities in a myriad of new directions can be foreseen.

Buildings represent the largest energy sector. Building energy efficiency must be considered as a part of our sustainable energy strategy. With innovative functionalization, wood can be made as an extremely attractive energy efficient building material. Several wood technologies were developed including transparent wood, thermal insulation nanowood, and radiative cooling wood.

Taking cooling wood for example, it features an effective back-scattering of sunlight and minimum absorption coefficient for the realization of the sub-ambient radiative cooling, providing a perpetual path to dissipate heat into the universe via the atmospheric transparency window without energy consumption. The cooling wood is directly derived from mesoporous natural wood. The material exhibits continuous cooling effect with a mechanical strength > 400 MPa and a specific tensile strength of 334.2 MPa cm³/g. The high strength is attributed to the physical entanglement of microscale wood cells and the maximized interaction among aligned nanofibers via hydrogen bonding (T. Li, et al, Science, 364, 6442, 2019) .