Superhydrophobic cellulose nanofiber aerogel composites with thermal insulation and solar absorption recycled from waste sugarcane bagasse pith

Sugarcane bagasse pith (SBP) represents the primary waste from bagasse-based paper mill and sugar industry. Due to the lack of interweaving ability, SBP is often overlooked or utilized for low-efficiency boiler combustion. Such practices not only result in environmental pollution but also represent a significant loss of abundant cellulose resources. Herein, SBP served as a potential source for cellulose nanofiber extraction, enabling the assembly of multifunctional composite aerogels through a facile fabrication strategy. Initially, 2,2,6,6tetramethylpiperidine-1-oxyl (TEMPO) radical-mediated oxidized cellulose nanofiber (TOCNF) was extracted from SBP. The extracted TOCNF with small diameter (3.22 nm) and stable suspension (zeta potential=- 51.3 mV) served as the structural skeleton of multifunctional aerogels. Subsequently, pomethylsilsesquioxane (PMSQ) was in-situ grafted onto the surface of TOCNF to achieve "rigid-flexible" composite nanofibers, which were integrated with TiN to form aerogel precursors, ultimately yielding modified TiN/TOCNF aerogels through directional freeze-casting drying. The resultant aerogel exhibits ordered arrangement and layer-to-layer support structures, displayed a low density (12.1 mg/cm3) and high porosity (99.4 %). Moreover, the light weight aerogel demonstrated superhydrophobicity (water contact angle of 155.8 degrees), outstanding mechanical properties that can maintain low deformation loss of 9.4 % at 50 % strain under cyclic compression, low thermal conductivity (30.82 mW center dot m- 1 center dot k- 1), and high solar absorptivity (90.3 %). The facile construction strategy of SBP-derived cellulose nanofiber aerogel proposed in this work provides a potential path for eco-friendly development of waste SBP cellulose resources.