Upgrading Agricultural Waste Into Bio‐Based Multifunctional Materials via Selective Oxidation

Abstract Distillers’ spent grains (DG), a major agricultural byproduct of the traditional fermented food industry, remain underutilized due to the lack of efficient value‐added strategies. This study presents an effective approach to upcycle DG into bio‐based multifunctional materials. By selectively oxidizing the cellulose component in DG using sodium periodate (NaIO 4 ), in situ activation of the raw material is achieved. Subsequent hot‐pressing promotes cross‐linking reactions between the oxidized cellulose and lignin, enabling the efficient fabrication of bulk materials. The resulting materials demonstrate excellent mechanical properties (with a maximum tensile strength of 20.25 MPa, Young's modulus of 20.43 GPa, and hardness of 89 HD), thermal stability, and solvent resistance. Notably, owing to the retained lignin, these materials exhibit outstanding photothermal conversion performance (46.08% photothermal conversion efficiency), making them suitable for solar‐thermal‐electric generators (TEGs) for green energy harvesting. Furthermore, the activated DG powder can function as a solvent‐free, bio‐based wood adhesive, exhibiting strong bonding performance (bonding strength up to 2.28 MPa and adhesion energy of 5.21 kJm −2 ) and solvent resistance. This study not only enhances the resource utilization of bio‐waste but also provides a scalable production pathway for cost‐effective, all‐biomass‐based functional materials.