Closed-loop valorization of waste plant biomass into recyclable carbon dots/cellulose hydrogels with pH-triggered multi-stage information encryption capability.

Maximizing the valorization of waste plant biomass into functional materials remains challenging owing to intrinsic structural complexity. Herein, we propose for the first time a broadly applicable strategy to derive all components from a single plant waste source for the construction of functional fluorescent hydrogels with recyclability. Specifically, lignin-derived hydrophobic carbon dots (CDs) and cellulose co-derived from straw are assembled into stable fluorescent hydrogels via solvent-exchange-induced hydrophobic interactions. The infiltration of alkali into the three-dimensional network of hydrogel triggers the dissociation of aggregation-induced emission (AIE) aggregates of CDs, resulting in a blue shift and up to 56% enhancement in fluorescence emission as the pH increases from 7 to 13. Leveraging this pronounced response, the functional hydrogels enable information recording and encryption using alkali as a readily accessible ink, further achieving three-stage information encryption through the integration of three-dimensional structuring and coding. Notably, such sensitive pH-triggered fluorescence behavior is universally observed across hydrogels derived from various lignocellulosic-rich wastes, including corncob, wood sawdust, and peanut shells. Moreover, the hydrogel can be regenerated after use via solvent exchange, or disassembled under alkaline conditions, enabling the recovery of CDs with a yield of 53% while the remaining cellulose matrix undergoes enzymatic degradation. This strategy not only enables the closed-loop valorization of single waste plant biomass but also ensures post-use sustainability, offering a novel promising route toward green functional materials.