Flexible and eco-friendly films, with enhanced dielectric properties and the potential for energy storage applications, have been fabricated from ammonia-functionalized graphene oxide (NGO) nanoplatelets and wood-based cellulose nanofibrils (CNF) vs. (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) pre-oxidized (carboxylated) CNFs (TCNF) by the solvent casting method. Various CNF-NGO (CNG) and TCNF-NGO (TCNG) composite films prepared with 0.5–3 wt% of NGO were analysed structurally by FTIR and XRD spectroscopy, and evaluated optically by UV-Vis spectroscopy. The morphological analysis using SEM showed good dispersibility of the NGO sheets in the randomly-distributed CNF, and the dense and parallel-oriented TCNF cellulose nanofibrils. Such a synergistic effect of both components contributed to ultra-strong and ultra-stiff composite films with good mechanical and thermal stability, although they were more brittle with a smoother surface and lower transmittance for the TCNF based films, due to the stronger physico–chemical interactions with NGO. The dielectric performance was verified with a higher (3 wt%) NGO loading capacity, which resulted in a dielectric constant of ∼46 vs. ∼52, and conductivity of ∼2.07 × 10⁻⁴ S m⁻¹ vs. 3.46 × 10⁻⁴ S m⁻¹ for CNG vs. TCNG films, respectively, at a frequency of 1 MHz, showing greater enhancement than other reported studies. Cyclic voltammetry and electrochemical impedance studies reveal the energy storage ability and electrochemical performance of the composite films, under kinetic- and diffusion-controlled processes for the CNG, and under a kinetic-controlled process for the TCNG films.

The conventional isolation of cellulose nanofibers (CNFs) process involves high energy input which leads to compromising the pulp fiber’s physical and chemical properties, in addition to the issue of elemental chlorine-based bleaching, which is associated with serious environmental issues. This study investigates the characteristic functional properties of CNFs extracted via total chlorine-free (TCF) bleached kenaf fiber followed by an eco-friendly supercritical carbon dioxide (SC-CO₂) treatment process. The Fourier transmission infra-red FTIR spectra result gave remarkable effective delignification of the kenaf fiber as the treatment progressed. TEM images showed that the extracted CNFs have a diameter in the range of 10–15 nm and length of up to several micrometers, and thereby proved that the supercritical carbon dioxide pretreatment followed by mild acid hydrolysis is an efficient technique to extract CNFs from the plant biomass. XRD analysis revealed that crystallinity of the fiber was enhanced after each treatment and the obtained crystallinity index of the raw fiber, alkali treated fiber, bleached fiber, and cellulose nanofiber were 33.2%, 54.6%, 88.4%, and 92.8% respectively. SEM images showed that amorphous portions like hemicellulose and lignin were removed completely after the alkali and bleaching treatment, respectively. Moreover, we fabricated a series of cellulose nanopapers using the extracted CNFs suspension via a simple vacuum filtration technique. The fabricated cellulose nanopaper exhibited a good tensile strength of 75.7 MPa at 2.45% strain.

The fabrication of superadsorbent for dye adsorption is a hot research area at present. However, the development of low-cost and highly efficient superadsorbents against toxic textile dyes is still a big challenge. Here, we fabricated hydrophobic cellulose nanofiber aerogels from cellulose nanofibers through an eco-friendly silanization reaction in liquid phase, which is an extremely efficient, rapid, cheap, and environmentally friendly procedure. Moreover, the demonstrated eco-friendly silanization technique is easy to commercialize at the industrial level. Most of the works that have reported on the hydrophobic cellulose nanofiber aerogels explored their use for the elimination of oil from water. The key novelty of the present work is that the demonstrated hydrophobic cellulose nanofibers aerogels could serve as superadsorbents against toxic textile dyes such as crystal violet dye from water and insulating materials for building applications. Here, we make use of the possible hydrophobic interactions between silane-modified cellulose nanofiber aerogel and crystal violet dye for the removal of the crystal violet dye from water. With a 10 mg/L of crystal violet (CV) aqueous solution, the silane-modified cellulose nanofiber aerogel showed a high adsorption capacity value of 150 mg/g of the aerogel. The reason for this adsorption value was due to the short-range hydrophobic interaction between the silane-modified cellulose nanofiber aerogel and the hydrophobic domains in crystal violet dye molecules. Additionally, the fabricated silane-modified cellulose nanofiber hydrophobic aerogels exhibited a lower thermal conductivity value of 0.037 W·m⁻¹ K⁻¹, which was comparable to and lower than the commercial insulators such as mineral wools (0.040 W·m⁻¹ K⁻¹) and polystyrene foams (0.035 W·m⁻¹ K⁻¹). We firmly believe that the demonstrated silane-modified cellulose nanofiber aerogel could yield an eco-friendly adsorbent that is agreeable to adsorbing toxic crystal violet dyes from water as well as active building thermal insulators.