Synthesis, Characterization, and Adsorption Performance of (Mg _0.4 Co _0.4 Mn _0.2 )Fe ₂₋₂ <i> _x </i> Sm <i> _x </i> Sn <i> _x </i> O ₄ Nanoparticles for the Removal

Abstract Water contamination by heavy metal ions poses a significant environmental threat. This study investigates (Mg 0.4 Co 0.4 Mn 0.2 )Fe 2−2 x Sm x Sn x O 4 (0.000 ≤ x ≤ 0.050) ferrite nanoparticles (NPs) as eco‐friendly adsorbents for Cu(II), Cr(III), Fe(III), and Zn(II). X‐ray powder diffraction (XRD) confirmed sample purity, with crystallite size decreasing from 20.28 to 13.31 nm as x increased. Scanning and transmission electron microscopies revealed irregular morphology, whereas energy‐dispersive X‐ray showed successful dopant incorporation into the ferrite lattice. Brunauer–Emmett–Teller analysis indicated a surface area increase from 76.5 to 91.4 m 2 /g with doping. X‐ray photoelectron spectroscopy identified oxidation states, and Fourier transform infrared spectroscopy confirmed the spinel structure. Doping also increased the direct bandgap energy from 3.224 to 3.245 eV and decreased Urbach energy from 0.374 to 0.352 eV. The NPs achieved high removal efficiencies for Cr(III) at 93.3%, Fe(III) at 98.8%, and Zn(II) at 80.6%, though removal of Cu(II) was minimal. The optimal adsorption performance was observed at x = 0.050. Adsorption followed second‐order kinetics and fit the Langmuir isotherm.