Identification of structural and optical properties and adsorption performance of (Cd_0.4Ni_0.4Mn_0.2)Fe_2-xRu_xO₄ nanoparticles for the removal of Congo red dye

In the field of industrial wastewater treatment, the application of highly efficient methods such as adsorption is crucial for effectively eliminating dangerous pollutants before effluent discharge. Ferrite nanoparticles (NPs) have emerged as promising candidates for the efficient and sustainable removal of dyes from wastewater. Therefore, the synthesis, characterization, and application of (Cd0.4Ni0.4Mn0.2)Fe2-xRuxO4 (0 <= x <= 0.04) NPs as adsorbents for the removal of Congo Red (CR) dye, is reported in this study. The X-ray powder diffraction (XRD) analysis has confirmed the purity of the samples with a very small amount of hematite phase. The prepared NPs have pseudo-spherical morphology and average particle size in the range of 12-17 nm. Furthermore, the elemental compositions, estimated from the energy dispersive x-ray (EDX) measurements, indicate the homogenous distribution of elements and the substitution of the Fe3+ host ions by the Ru3+ dopant. As the Ru content increases from 0.00 to 0.04, S-BET increases from 52.39 to 78.34 m(2)/g, respectively. Furthermore, the pore diameter, ranging between 12.71 and 18.38 nm, reveals the mesoporous nature of the prepared samples. The direct and indirect bandgap energy, calculated from UV-vis spectroscopy analysis, is in the range of 3.049-3.232 eV and 1.894-2.642 eV, respectively. The adsorption performance of the prepared NPs for the removal of CR dye solution was investigated by varying the contact time, adsorbent amount, pH, and reaction temperature. The adsorption process follows a second-order kinetic model and the NPs with x = 0.015 revealed the highest adsorption rate with a rate constant k(2) = 2.7 x 10(-3) g.mg(-1).min(-1). The optimum experimental conditions, achieved in the presence of 80 mg of (Cd0.4Ni0.4Mn0.2)Fe1.985Ru0.015O4 NPs at 308 K and in the acidic medium at pH = 3.45, result in the removal of 87.5 % of CR dye after 60 min. After applying several non-linear adsorption isotherm models, mainly Langmuir, Freundlich, and Temkin isotherms, the experimental data were well-fitted with the Temkin isotherm model. The strong interactive force between CR and (Cd0.4Ni0.4Mn0.2)Fe1.985Ru0.015O4 nanoparticles is revealed from the high value of b(T) knowing that b(T) = 182.91 J.mol(-1).