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The uniqueness of this work is the comparison of manganese ferrites/ polyaniline (Mn x Fe 3 À x O 4 /PANI) produced using K 2 S 2 O 8 as an oxidant for aniline with the efficacy of spinel manganese ferrite with various Mn 2+ ratios for the polymerization of aniline. The structural and morphological properties of the nanocomposites were characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) techniques. XRD results confirmed the formation of a single-phase cubic spinel structure with a lattice constant of approximately 8.3 Å. The surface enriched by Mn 2+ exhibited an enhanced valence of +3 and +4, increased lattice oxygen content, facilitated ferrite reduction, and improved the oxidative performance of Fe 3+ . The saturation magnetization decreased with an increase in Mn +2 ratios and PANI contents. The nanocomposites exhibited excellent adsorption of Lanaset Brown B dye, which was investigated as a model textile dye. Various adsorption capacities (q max ) for the nanocomposites were calculated in a range of 122.39-215 mg/ g, depending on the synthesis conditions. Optimization parameters, such as pH, adsorbent dose, and initial concentration, as well as reusability, were described. The Langmuir isotherm is a better model for describing the adsorption process of the nanocomposites. An evaluation of thermodynamic parameters suggests the sorption process is feasible, spontaneous, and endothermic. K E Y W O R D S adsorption, green synthesis, Lanaset Brown B dye, Mn x Fe 3Àx O 4 /PANI, polyaniline nanocomposites

M AGNETIC nanocomposites loaded with antimicrobial drugs have grown in popularity for treating infectious diseases due to their magnetic properties and the ability to penetrate bacteria cells. In this research, Cu x Fe 3-x O 4 nanoparticles and Cu x Fe 3-x O 4 /PANI nanocomposites were synthesized, characterized, and examined for their antimicrobial activity. The in-situ oxidative polymerization of aniline in the presence of Cu x Fe 3-x O 4 nanoparticles produced Cu x Fe 3-x O 4 /PANI nanocomposites with distinct spinel ferrites. XRD, FT-IR, VSM, SEM, EDX, TEM, and XPS techniques confirmed the successful synthesis of the Cu x Fe 3-x O 4 /PANI nanocomposites. The analysis of magnetization patterns of Cu x Fe 3-x O 4 /PANI nanocomposites revealed their superparamagnetic characteristics. With increasing Cu 2+ ratios, both the pure copper ferrites nanoparticles and the Cu x Fe 3-x O 4 /PANI nanocomposites exhibited enhanced antimicrobial effects against gram-positive (Staph), gram-negative (E. coli, P. aeruginosa, and K. pneumoniae), and fungi such as (C. albicans), which is consistent with decreasing the order of crystal size (nm) and the lattice strain, where crystal size and lattice strain decreased with increasing Cu 2+ ratio. SEM micrographs revealed changes in bacterial shape, deformation of fungal cell walls, and bacterial and yeast colonies collapsing. Furthermore, the nanocomposites are more effective against gram-negative bacteria and Candida albicans than gram-positive bacteria, displaying the alteration of bacterial shape, fungal cell wall deformation, and collapsing bacterial and yeast colonies. The results presented an approach for using Cu x Fe 3-x O 4 and Cu x Fe 3-x O 4 /PANI as an alternative promising antimicrobial agent against several multidrugresistant microbes.