Fe₃O₄-Impregnated Adsorbent Derived from Lignocellulosic Arachis hypogaea Shell for the Efficient Removal of Cationic Methylene Blue and Crystal Violet Dyes

A magnetically separable adsorbent material was synthesized by impregnating Fe₃O₄ nanoparticles onto Arachis hypogaea (peanut) shells (Fe₃O₄-AHS). This novel composite was systematically characterized and evaluated for its efficacy in adsorbing methylene blue (MB) and crystal violet (CV) dyes from aqueous solution. The physicochemical properties of the adsorbent were determined using a range of analytical techniques, including Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, thermogravimetric analysis, and vibrating sample magnetometry. Various kinetic models were used to assess the time-dependent experimental data, and the pseudo-second-order model showed the best fit for both dyes, as shown by high coefficient of determination values. The Langmuir isotherm model provided the best fit to the adsorption equilibrium data for both dyes. The maximum adsorption capacities were calculated to be 263.158 mg/g for MB and 212.766 mg/g for CV at 303 K. The adsorption processes for both CV and MB onto the Fe₃O₄-AHS were endothermic and spontaneous. In addition, the adsorbent exhibited high reusability, retaining its efficacy for up to 6 consecutive adsorption-desorption cycles. These results collectively suggest that Fe₃O₄-AHS is a promising option for the remediation of dye-contaminated effluent.