Natural adsorption of methylene blue by waste fallen leaves of Magnoliaceae and its repeated thermal regeneration for reuse

In this study, waste fallen leaves of Magnolia denudate (MDL), Magnolia grandiflora (MGL) and Michelia figo (MFL) were used as adsorbent for removing soluble methylene blue (MB) from aqueous solution. Results showed that the maximum adsorption capacity of MDL, MGL, and MFL were determined to be 185.19 mg/g, 149.25 mg/g, and 238.10 mg/g, which was higher than other reported leaf-based materials. It was found that the adsorption of MB by fallen leaves was a spontaneous and endothermic process, which could be described by Langmuir isotherm (R2 > 0.995) and pseudo-second-order kinetics (R2 > 0.992). Moreover, an environmentally friendly thermal method was applied for regeneration of used adsorbents, by which used MFL was converted to stable MFL-biochar with satisfactory adsorption capacity (139.40 mg/g) for three consecutive cycles. Electrostatic attraction between MB and carboxyl groups was identified as the main mechanism of the observed adsorption. Overall the article provided a novel material as well as regeneration method for potential environmental-sustainable dye wastewater treatment. [Display omitted] •Fallen leaf of Magnolia figo (MFL) was employed for MB removal.•The maximum adsorption capacity of MFL reached 238.10 mg/g.•Used MFL could be converted to biochar for reuse.•79.54% of MB was removed after 3-cycles of reuse.•Adsorption and regeneration mechanisms were illustrated.