Enhanced Adsorption of Malachite Green Dye Using Fe3O4-MgO Nanoparticles Loaded with Phragmites Stems Powder: Characterization, Kinetic, and Isotherm Studies

Abstract

A novel adsorbent was produced from Phragmites australis stems (Ph-St) into a magnetic nanocomposite (Ph-St/Fe₃O₄-MgO) through chemical treatment for effective removal of malachite green (MG) from aqueous medium. Characterization via SEM, EDX, FTIR, BET, and XRD confirmed the efficient deposition of Fe₃O₄-MgO magnetic nanoparticles on Ph-St, forming a cubic spinel structure. The BET surface areas were 4.4985 m²/g for Ph-St and 8.8789 m²/g for Ph-St/Fe₃O₄-MgO. The nitrogen (N₂) adsorption isotherm was classified as type IV. The effect of several factors on adsorption was examined, including temperature, dose, pH, and contact time. Adsorption experiments showed optimal MG removal at pH 7, with an equilibrium time of 20 min. Kinetic analysis revealed that the pseudo-second-order (PSO) model best described the adsorption process compared to the pseudo-first-order (PFO) and intraparticle diffusion (IPD) models. Experimental data for the Ph-St adsorbent correspond well to the Langmuir model and the Freundlich model for Ph-St/Fe₃O₄-MgO at the optimum temperature of 328 K, with maximum adsorption capacities of 33.823 and 104.711 mg/g, respectively. Positive ΔH° and ΔS° values indicated an endothermic and disordered process. The ΔG° values indicate spontaneous adsorption for both adsorbents. These results suggest that magnetic nanocomposites provide an effective solution for reducing water pollution.