Nano-graphitic biochar from pyrolyzed lemon peel as an efficient adsorbent for cationic dye removal from aqueous solutions.

The valorization of agricultural waste into effective adsorbents presents a promising strategy for sustainable wastewater remediation. This study investigates the conversion of lemon peel (LP), a common biowaste, into nano-graphitic biochar (NGB). Evaluating both materials as green adsorbents for the removal of the cationic dye Basic Fuchsin (BF). FTIR, SEM, and XRD were used to characterize the NGB. The obtained data confirm graphitization, high porosity, and exfoliated morphology compared to raw LP. The batch adsorption experiment conditions, pH, adsorbent dose, contact time, initial dye concentration, and temperature, have been optimized. NGB demonstrated exceptional performance, achieving 99.2% removal efficiency within just 5 min at optimal conditions (pH 7, 0.1 g adsorbent dose), significantly outperforming raw LP (86.4%). Isotherm analysis revealed that adsorption onto LP followed the Freundlich model (R2 = 0.972), indicating heterogeneous, multilayer adsorption. In contrast, NGB adsorption was best described by the Temkin model (R2 = 0.988), suggesting a uniform distribution of binding energies. Kinetic data were accurately fitted to a pseudo-second-order model, and thermodynamic parameters confirmed a spontaneous exothermic physisorption process. Furthermore, NGB exhibited excellent regeneration, maintaining 97.3% efficiency after five adsorption-desorption cycles. Application to spiked real water samples (groundwater, saline wells) yielded recovery rates up to 96%, underscoring its practical potential.