Engineered biochar derived from lemon peel waste for highly efficient removal of organic pollutants from water

The urgent need for efficient decontamination of organic dyes from polluted waters necessitates the search for a low-cost and suitable adsorbent. The large amount of lemon peel residue in actual production can be an ideal raw material for the preparation of adsorbents. Herein, a novel magnetic nanocomposite derived from lemon (Citrus limon L.) peel residue (Fe3O4/Lp-biochar) was successfully synthesized by one-step hydrothermal method and used for the adsorptive capture of methylene blue (MB) in aqueous solution. The prepared Fe3O4/Lp-biochar are spherical with a particle size of 8.3 nm and have a saturation magnetization intensity of 52.9 emu/g and a specific surface area of 64.30 m2/g. It was found that the maximum MB adsorption capacity of 26.36 mg/g by the Fe3O4/Lp-biochar can be achieved when the amount of nanocomposite was 0.10 mg/mL, the system's pH value was 10, the reaction temperature was 25 °C, and the adsorption time was 60 min. Adsorption kinetics of MB on the Fe3O4/Lp-biochar followed the pseudo-second-order kinetic model whilst the Freundlich isotherm model could well simulate the adsorption behavior of MB on magnetic biochar. The adsorption mechanism of MB by the Fe3O4/Lp-biochar predominantly include electrostatic attraction and mesoporous interaction. Furthermore, the Fe3O4/Lp-biochar exhibited a remarkable retention of 94.7% of the initial adsorption efficiency even after the 10th cycle of repeated use. It was concluded that the lemon peel-derived magnetic biochar can be a promising alternative to conventional adsorbents for wastewater treatment.