Drying and Pyrolysis of Cellulose Nanofibers from Wood, Bacteria, and Algae for Char Application in Oil Absorption and Dye Adsorption

Native cellulose nanofibers (CNF) constitute an abundant resource for pyrolysis leading to char materials offering a wide range of properties and application possibilities. With the aim to produce chars having large surface area and pore volume for dyes adsorption and oil absorption, respectively, we herein explore the slow pyrolysis process of cellulose nanofibers from wood, Cladophora algae and bacteria that were subjected to various drying routes. Whereas algae CNF with their large crystallites lead to high surface area (S-BET) substrates using conventional drying from aqueous suspension, CNF from wood having smaller crystallites requires drying from solvents to reach high S-BET substrates, which results in chars with a good adsorption capacity for both anionic and cationic dyes. Moreover, the porosity of the CNF substrate can be tuned via an ice-templating freeze-drying procedure reaching values as high as 99.7% and corresponding chars capable of absorbing 64-120 g g(-1) of various oils and organic solvents. Besides the absorption/adsorption properties of the chars, we report effects of CNF source and structure on the thermal properties assessed by thermogravimetric and thermomechanical analyses, differential scanning calorimetry, and mass spectrometry, and we identified over 20 decomposition products and 3 expansion events occurring during CNF pyrolysis.