Circular economy in action: transforming spent alkaline batteries into ZnO-based photocatalysts for water purification.

The rapid accumulation of spent alkaline batteries poses a pressing environmental challenge due to their hazardous components. In response, this study introduces a sustainable upcycling strategy that transforms battery-derived manganese and zinc oxides into high-efficiency photocatalytic materials. By incorporating silver (Ag) and graphitic carbon nitride (g-C3N4), a series of ZnO-based nanocomposites was synthesized and thoroughly characterized using XRD, FTIR, BET, TGA-DSC, UV-Vis spectroscopy, and SEM. Among them, the ZnO-g-C3N4 composite exhibited the most remarkable performance, achieving 97.42% degradation of Methylene Blue and 91.77% of Crystal Violet under visible light within 240 min. This outstanding activity is attributed to enhanced surface area, improved charge separation, and expanded visible-light absorption via bandgap narrowing. Furthermore, the catalyst demonstrated excellent reusability, maintaining over 84% degradation efficiency after four cycles. This research not only addresses the dual issues of electronic waste and water pollution but also exemplifies a circular economy approach aligned with multiple Sustainable Development Goals (SDGs), particularly those focused on clean water, responsible production, and climate action. The findings highlight the viability of repurposing hazardous waste into functional materials for environmental remediation.