Waste citrus pseudolimon peels derived biochar assisted magnetic Zn + Al (LDH) nanocomposites for As (III) adsorption

Arsenic (III) ion contamination in water system is a significant and challenging global concern. In this study, agro-waste material, specifically Citrus pseudolimon peels (CP), was utilized as a precursor for the preparation of biochar (CPB). Furthermore, biochar-supported Fe₃O₄-Zn + Al layered double hydroxide (M-CPB/LDH) has been synthesized by simple co-precipitation method for the removal of noxious As (III) ions. The prepared composites undergone instrumental analysis including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) equipped with energy-dispersive X-ray spectroscopy (EDX) and elemental mapping, high-resolution transmission electron microscopy (HRTEM), Brunauer-Emmett-Teller (BET), thermo-gravimetric (TGA), vibrating sample magnetometer (VSM), and X-ray photoelectron spectroscopy (XPS). The surface areas (BET) of CPB and M-CPB/LDH composites were recorded to be 52.49 m²/g and 99.78 m²/g, respectively. The VSM analysis confirmed the ferromagnetic characteristics of M-CPB/LDH composites. The adsorption behavior of CPB, M-LDH and M-CPB/LDH composites was strongly depend on pH, with the maximum As (III) ion uptake recorded at pH 4.0. The sorption of As (III) ion were analyzed by isotherm, kinetics and thermodynamic study. Experimental data obey the Langmuir model (R2 = 0.97–0.99), indicating that As (III) ions exhibits the monolayer adsorption. The kinetic results directed that removal mechanism conformed to pseudo-second-order model, signifying the chemisorption play a major role. The maximum monolayer capacities of CPB, M-LDH and M-CPB/LDH composites for As (III) ions were recorded to be 575.10 mg/g, 624.34 mg/g and 721.34 mg/g, respectively. The maximum adsorption of 88.95%, 92.18%, and 96.76% were achieved for CPB, M-LDH and M-CPB/LDH composites, respectively, at 65 °C under optimal conditions, indicating a endothermic and thermodynamically favorable. Regeneration study demonstrated that adsorbents were effectively recovered using 0.01 mol/L HCl as the desorbing agent. After seven adsorption-desorption cycles, the adsorption remained at 78.19%, 83.13%, and 91.45% for CPB, M-LDH, and M-CPB/LDH composites, respectively. Finally, we summarize that synthesized M-CPB/LDH composite exhibited high efficiency, versatility and economical for As (III) ion removal, making it a promising material for wastewater treatment.