Valorization of spent alkaline battery for the development of carbon dots-decorated ZnO as photocatalyst and supercapacitor material

This study presents a comprehensive valorization strategy for spent zinc-carbon batteries, converting both black mass and graphite rod into high-performance carbon dots-decorated zinc oxide (ZnO-CDs) material for energy storage and photocatalytic applications. Selective alkaline leaching achieved an 82% zinc recovery with minimal co-dissolution of manganese (<0.5%), followed by precipitation and calcination to form crystalline ZnO nanoparticles. Simultaneously, the graphite rod was activated and subjected to oxidative cutting to synthesize fluorescent carbon dots with an absorption peak at 262 nm, which were decorated onto ZnO surfaces. Comprehensive characterization confirmed successful carbon dots incorporation, inducing lattice expansion, crystallite size reduction (13.27–11.5 nm), and band gap narrowing (3.09–3.03 eV). The ZnO-CDs nanocomposite demonstrated superior electrochemical performance with 142 F/g specific capacitance at 10 mV/s (18% enhancement over pristine ZnO) and exceptional photocatalytic activity, achieving 97% methylene blue degradation within 90 min with 68% faster kinetics compared to pristine ZnO. Enhanced performance is attributed to improved charge separation at ZnO/CDs, increased active surface area, enhanced electrical conductivity, and efficient pollutant adsorption. This waste-to-resource approach offers environmental remediation through the complete valorization of batteries, the production of dual-functional nanomaterials, and the practical implementation of circular economy principles through facile aqueous processing. • Spent zinc-carbon battery black mass valorized to ZnO nanoparticles via selective alkaline leaching and calcination. • Selective alkaline leaching achieves 82% zinc recovery with minimal manganese co-dissolution (<0.5%). • Carbon dots decoration enhances ZnO pseudocapacitance in three-electrode supercapacitor configuration. • ZnO-CDs nanocomposite achieves 68% faster methylene blue degradation kinetics than pristine ZnO. • Waste-to-resource approach enables circular economy through dual energy storage and photocatalytic applications.