Porous macroscopic chitosan-alloy/oxide hybrid beads derived from spent LiNi0.5Mn0.3 Co0.2O2 batteries for rapid heterogeneous Fenton-like wastewater purification

Simultaneous management of spent lithium-ion batteries and dye-wastewater remains challenging. This study proposes a simple strategy to valorize both electrodes of spent LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532) batteries. Through a one-stage thermal synthesis, a high-performance Fenton-like catalyst was fabricated and incorporated into a chitosan biopolymer matrix to form macroscopic composite granules. Comprehensive characterizations revealed a porous, sponge-like structure with active centers comprising a synergistic mixture of Mn, Ni, and Co oxides and a Ni-Co alloy. The composite (synthesized at 750 °C, containing 30 wt% active material) exhibited near-complete crystal violet (CV) degradation rapidly, with an apparent rate constant nearly 13 times higher than that of the pristine chitosan beads. This superior performance is likely attributed to a synergistic mechanism, in which the chitosan/carbon matrix acts as an adsorption pool to enrich local pollutant concentrations, thereby facilitating close contact with active sites. This arrangement facilitates the localized attack of reactive oxygen species—generated at the alloy/oxide interface via an accelerated interfacial electron-transfer process—on the target dye molecules. Notably, LC–MS analysis suggested a CV degradation pathway involving sequential N -demethylation and oxidative transformation. Furthermore, optimal performance occurred at pH 9.0, 45 °C, 0.6 g L −1 catalyst dosage, and 10–15 mM H 2 O 2 . Additionally, the macroscopic catalyst exhibited favorable reusability over five consecutive cycles, retaining approximately 92% of its initial CV removal efficiency. Crucially, transition metal leaching remained extremely low, fully complying with stringent environmental discharge standards, thereby highlighting the potential applicability of this material for sustainable applications.