From waste to value: valorising biorefinery waste as a sustainable crosslinker for nanoparticle synthesis.

Valorising biorefinery residues is a key issue to ensure the complete recycling of such byproducts. In this study, we isolated humic-like substances (HLS) from a lignin-rich biorefinery waste and employed them as crosslinkers to synthesize chitosan nanoparticles (NPs). Comprehensive solid- and liquid-state NMR analyses revealed the heterogeneous nature of HLS, which were rich in hydroxyl, phenolic, and carboxyl groups, these functions being involved in promoting NP formation via ionotropic gelation, as highlighted by Infrared Spectrometry. Dynamic light scattering indicated NP size variations (164-1103 nm) depending on HLS:chitosan ratios, with lower HLS concentrations yielding the smallest particles, while higher HLS levels led to aggregation phenomena. Scanning electron microscopy showed spherical morphology for HLS-based NPs, regardless of the HLS:chitosan ratio assayed. The radical scavenging capacity of the NPs showed a dose dependency on HLS concentration, highlighting the role of phenolic groups in HLS as primary hydrogen donors. Overall, this work introduces a rapid, simple, and sustainable approach to increase the reliability of biorefineries by converting their waste into eco-friendly nanomaterials with radical scavenging properties. The proposed system advances circular economy-oriented green nanotechnology and shows potential for applications in various research fields, such as agricultural, food and environmental sectors.