Photoswitchable Superabsorbency Based on Nanocellulose Aerogels

Abstract

Chemical vapor deposition of a thin titanium dioxide (TiO 2 ) fi lm on lightweight native nanocellulose aerogels offers a novel type of functional material that shows photoswitching between water-superabsorbent and water-repellent states. Cellulose nanofi brils (diameters in the range of 5-20 nm) with native crystalline internal structures are topical due to their attractive mechanical properties, and they have become relevant for applications due to the recent progress in the methods of their preparation. Highly porous, nanocellulose aerogels are here fi rst formed by freeze-drying from the corresponding aqueous gels. Well-defi ned, nearly conformal TiO 2 coatings with thicknesses of about 7 nm are prepared by chemical vapor deposition on the aerogel skeleton. Weighing shows that such TiO 2 -coated aerogel specimens essentially do not absorb water upon immersion, which is also evidenced by a high contact angle for water of 140 ° on the surface. Upon UV illumination, they absorb water 16 times their own weight and show a vanishing contact angle on the surface, allowing them to be denoted as superabsorbents. Recovery of the original absorption and wetting properties occurs upon storage in the dark. That the cellulose nanofi brils spontaneously aggregate into porous sheets of different length scales during freeze-drying is relevant: in the water-repellent state they may stabilize air pockets, as evidenced by a high contact angle, in the superabsorbent state they facilitate rapid water-spreading into the aerogel cavities by capillary effects. The TiO 2 -coated nanocellulose aerogels also show photooxidative decomposition, i.e., photocatalytic activity, which, in combination with the porous structure, is interesting for applications such as water purifi cation. It is expected that the present dynamic, externally controlled, organic/inorganic aerogels will open technically relevant approaches for various applications.

Comparative Study of Aerogels Obtained from Differently Prepared Nanocellulose Fibers

“…[31,32] The NCF aerogels can then be used as templates for inorganic hollow nanotubes [33] and cobalt-ferrite nanoparticles, [34] and further functionalized to achieve ideal electrical, [35] optical [36] and fire-resistant [37] characteristics. The structures and properties of the NCF aerogels are mainly determined by the morphologies and surface properties of the NCF building blocks.…”

Interactions between inorganic nanoparticles and cellulose nanofibrils

“…Additionally, the fibril network can be modified using solid particles (Maneerung et al 2008;Díez et al 2011;Kettunen et al 2011;Olsson et al 2011). Evidently use of easily modifiable non-toxic particles would increase the amount of the potential applications, for example, in functional packaging materials.…”

Functionalization of Nanofibrillated Cellulose with Silver Nanoclusters: Fluorescence and Antibacterial Activity

“…They allow, e.g., strong nanocomposites, nanopaper, thin films by layer-by-layer assemblies, transparent films, ductile aerogels, low gas-barrier properties and wetting modifications. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] On the other hand, various types of nanoparticles have been assembled on the surfaces of macroscopic and nanoscopic cellulose fibers to allow functionalities, such as antibacterial or catalytic activity and permanent colors. [33][34][35][36] In this work, we aim to explore possibilities to bind metal objects even smaller than nanoparticles, i.e., nanoclusters consisting of only a few atoms, on native cellulose nanofibers.…”