Upcycled battery-derived MnO₂ for ultrafast lead removal from wastewater

Waste generation from discarded batteries poses a significant environmental challenge, while lead (Pb²⁺) contamination in water threatens public health and aquatic ecosystems due to its high toxicity, persistence, and non-biodegradable nature, even at trace concentrations. To address these dual issues, this study presents manganese oxide (MnO₂) synthesized from discarded battery materials as a single, highly efficient adsorbent for Pb²⁺ removal from aqueous solutions, demonstrating a sustainable waste-to-waste remediation strategy. The synthesized MnO₂ was comprehensively characterized to confirm its crystalline structure, surface properties. Batch adsorption experiments were conducted to evaluate the effects of contact time, solution pH, adsorbent dosage, initial Pb²⁺ concentration, and temperature on adsorption performance. Notably, the synthesized MnO₂ demonstrated exceptionally rapid adsorption kinetics, removing more than 94% of Pb²⁺ within 1 minute at neutral pH without external pH adjustment, using an adsorbent dosage of 0.125 g L^-1. Kinetic analysis showed that the adsorption follows a pseudo-second-order model, indicating a chemisorption mechanism. Equilibrium data were best fitted by the Langmuir isotherm, suggesting monolayer adsorption with a maximum adsorption capacity of approximately 167.78, 201, and 222 mg g^-1 at 25, 40, and 50 °C, respectively. Furthermore, the MnO₂ demonstrated excellent reusability and performance stability over multiple adsorption-desorption cycles. In addition, the adsorbent maintained high Pb²⁺ removal efficiency in the presence of competing inorganic ions, demonstrating good selectivity and potential applicability in complex water matrices. These findings highlight the potential of battery-derived MnO₂ as a sustainable, low-cost, and highly effective adsorbent for rapid Pb²⁺ remediation in contaminated water.