Nanostructured biological materials inspire the creation of materials with tunable mechanical properties. Strong cellulose nanofibrils derived from bacteria or wood can form ductile or tough networks that are suitable as functional materials. Here, we show that freeze-dried bacterial cellulose nanofibril aerogels can be used as templates for making lightweight porous magnetic aerogels, which can be compacted into a stiff magnetic nanopaper. The 20-70-nm-thick cellulose nanofibrils act as templates for the non-agglomerated growth of ferromagnetic cobalt ferrite nanoparticles (diameter, 40-120 nm). Unlike solvent-swollen gels and ferrogels, our magnetic aerogel is dry, lightweight, porous (98%), flexible, and can be actuated by a small household magnet. Moreover, it can absorb water and release it upon compression. Owing to their flexibility, high porosity and surface area, these aerogels are expected to be useful in microfluidics devices and as electronic actuators.

The electrical conductivity of reduced graphene oxide (rGO) obtained from graphene oxide (GO) using sodium borohydride (NaBH) as a reducing agent has been investigated as a function of time (2 min to 24 h) and temperature (20 °C to 80 °C). Using a 300 mM aqueous NaBH solution at 80 °C, reduction of GO occurred to a large extent during the first 10 min, which yielded a conductivity increase of 5 orders of magnitude to 10 S m. During the residual 1400 min of reaction, the reduction rate decreased significantly, eventually resulting in a rGO conductivity of 1500 S m. High resolution XPS measurements showed that C/O increased from 2.2 for the GO to 6.9 for the rGO at the longest reaction times, due to the elimination of oxygen. The steep increase in conductivity recorded during the first 8-12 min of reaction was mainly due to the reduction of C-O (e.g., hydroxyl and epoxy) groups, suggesting the preferential attack of the reducing agent on C-O rather than C[double bond, length as m-dash]O groups. In addition, the specular variation of the percentage content of C-O bond functionalities with the sum of Csp and Csp indicated that the reduction of epoxy or hydroxyl groups had a greater impact on the restoration of the conductive nature of the graphite structure in rGO. These findings were reflected in the dramatic change in the structural stability of the rGO nanofoams produced by freeze-drying. The reduction protocol in this study allowed to achieve the highest conductivity values reported so far for the aqueous reduction of graphene oxide mediated by sodium borohydride. The 4-probe sheet resistivity approach used to measure the electrical conductivity is also, for the first time, presented in detail for filtrate sheet assemblies' of stacked GO/rGO sheets.

The effect of using different zinc salts on size, morphology and photoluminescence of ZnO nanoparticles in high-yield aqueous precipitation synthesis.