Synthesis of magnetite nanocomposite supported on apple peel-derived activated carbon for removal of methylene blue from aqueous solutions

The pollution of water resources by synthetic dyes from textile effluents is a significant environmental concern. Developing effective adsorbents from renewable resources is a promising strategy for wastewater treatment. This study aimed to synthesize and characterize a novel magnetically separable nanocomposite (Fe3O4−ACAP) from apple peel by-product and evaluate its efficiency for the methylene blue (MB) adsorption from aqueous solutions. AC was obtained from apple peel through chemical activation with NaOH, followed by physical pyrolysis. The Fe3O4 nanoparticles were prepared using the co-precipitation method and loaded onto the AC to yield the Fe₃O₄-ACAP nanocomposite. The prepared material was characterized by XRD, FTIR, SEM, BET surface area analysis, and VSM. Batch adsorption experiments were executed concerning pH between 3 and 11, contact time, adsorbent dose (0.02–0.37 g L-1), different initial MB concentrations (10–100 mg L-1), and temperature (293–323 K). The nanocomposite possessed a high surface area of (706.29 m2 g-1) and good magnetic saturation of 4.1 emu g-1. Allowing for easy and rapid separation from treated water post-use, which is a key feature for practical, large-scale application. The optimal conditions for removal were pH 6.5, contact time = 120 min, adsorbent dose = 0.09 g 100 mL-1 (0.9 g L-1), and temperature = 293 K for an initial concentration of 10 mg L-1, at which maximum MB removal efficiency of 99% was achieved. Adsorption isotherm data fitted best with the Langmuir model, showing monolayer adsorption with a theoretical maximum capacity of 152 mg g-1. The kinetic profile of the adsorption followed a pseudo-second-order model. Thermodynamic analysis, represented by ΔG°<0 and ΔH°= −86.424 kJ mol-1, demonstrated the feasibility and exothermic nature of the process. Fe3O4−ACAP nano composite presented excellent magnetic separability with a very high adsorption capacity derived from agricultural waste. It proved to be an efficient, sustainable, and easily recyclable adsorbent, showing excellent potential for application in removing cationic dyes from industrial wastewater.