*6.1. Composites of Nanocellulose and Carbon Nanofibers*

Carbon nanofibers can be created by carbonization of cellulose nanofibers originating from bacterial nanocellulose [21,23,161], urea [161], filter paper [162] or plant-derived cellulose [22,24]. Another method of preparing carbon nanofibers is chemical vapor deposition (CVD; [25]). These carbon nanofibers can be further combined with other carbon nanoparticles, mainly graphene. For example, a composite paper consisting of nitrogen-doped carbon nanofibers, reduced graphene oxide (rGO) and bacterial cellulose was designed as a high-performance, mechanically tough, and bendable electrode for a supercapacitor. The bacterial nanocellulose in this paper is exploited both as a biomass precursor for the creation of carbon nanofibers by pyrolysis and as a supporting substrate for the newly-created material [21]. In another study, highly conductive freestanding cross-linked carbon nanofibers, derived from bacterial cellulose in a rapid plasma pyrolysis process, were used as substrates for the growth of vertically-oriented graphene sheets for constructing alternating current filtering supercapacitors [23]. A small amount of rGO can also act as an effective initiator of carbonization of cellulose nanofibers through microwave treatment [24]. Carbonization of aerogels, prepared from a mixture of PVA, cellulose nanofibers and GO by freeze-drying, enhanced the hydrophobic properties, the specific surface area and the adsorption capacity of these aerogels. These materials then became suitable candidates for oil-water separation and environmental protection [22]. In addition to graphene, cellulose-derived carbon nanofibers can be combined with various other nanoparticles and nanostructures, such as Pt nanoparticles for methanol oxidation reaction [161], TiO2 films and Fe3O4 nanoparticles for lithium ion batteries [162], tin oxide (SnO) nanoparticles for lithium-sulfur batteries [163] or NiCo2S4 nanoparticles for hydrogen evolution reaction [164]. Carbon nanofibers are also promising for biomedical applications, particularly bone tissue engineering. Their nanoscale diameter produced a nanoscale surface roughness of their compacts or of their composite with poly-lactic-*co*-glycolic acid (PLGA). This nanoroughness promoted preferential adhesion of osteoblasts from other cell types, particularly fibroblasts, which could prevent fibrous encapsulation of bone implants [25].
