Carbon recovered from lithium ion batteries for methylene blue adsorption and environmental remediation

Graphitic carbon recovered from spent lithium-ion battery anodes was investigated as an adsorbent for methylene blue removal, providing a waste-valorization approach based on minimal processing. The material was obtained through acid washing without chemical activation. Adsorption experiments were conducted at different pH values under typical conditions of initial dye concentration of 10–100 mg L -1 , adsorbent dosage of 1 g L -1 , and equilibrium time of 120–150 min, with 24 h adopted to ensure complete equilibrium. Adsorption was strongly pH-dependent, with maximum performance at pH 10 and a Langmuir capacity of 7.25 mg g -1 (R² = 0.998). Thermodynamic parameters (ΔH° = −6.64 ± 0.47 kJ mol -1 , ΔG° ≈ −13 to − 15 kJ mol -1 , ΔS° = +23.4 ± 1.6 J mol -1 K -1 ) confirmed a spontaneous, entropy-driven physisorption process. Kinetic analysis showed increased adsorption rates at higher pH, with the generalized near-equilibrium (GNE) model indicating a PFO-like monoexponential relaxation regime. Enhanced electrostatic interactions were the main driving force, while π–π interactions contributed as a secondary mechanism. XRD and FTIR analyses confirmed graphitic domains and surface functional groups.The material maintained over 90% efficiency after seven regeneration cycles. These results demonstrate that recycled anode-derived graphitic carbon is a promising low-cost adsorbent for dye removal and supports the valorization of battery waste for environmental applications.