Effect of divalent cations (Co2+ and Ni2+) on microstructure, physical properties and application of Nd

Abstract

The nanocrystalline samples Nd_1–xM_xFeO₃ (x = 0.0 and 0.1; M: Co²⁺ and Ni²⁺) were prepared using the citrate combustion method. The X-ray diffraction (XRD) pattern confirmed that the nanoparticles were synthesized in an orthorhombic structure. The particle size of Nd_1–xM_xFeO₃ is in the range of 29–59 nm. The selected area electron diffraction (SAED) indicates the samples were prepared in a polycrystalline nature. The samples Nd_1–xM_xFeO₃ (x = 0.0 and 0.1; M: Co²⁺ and Ni²⁺) have antiferromagnetic behavior. The Fe³⁺ spins are aligned antiparallel, forming the antiferromagnetic (AFM) properties, which are affected by many factors such as the bond angle between the Fe³⁺ (Fe³⁺–O^2––Fe³⁺) and the Dzyaloshinskii-Moriya (D-M) interaction. The doping of Co²⁺ and Ni²⁺ ions in NdFeO₃ enhances the magnetic properties of the NdFeO₃. The saturation magnetization (M_s) of Nd_0.90Co_0.10FeO₃ increases 1.8 times more than that of NdFeO₃. The exchange bias field (H_EX) of the Co-doped sample is two times greater than that of NdFeO₃. The magnetic anisotropy constant (K) of the 10 % Co-doped sample increases by 11 factors compared to that of NdFeO₃. The Tauc plot illustrates that the samples have a direct optical transition. The divalent cation substitution (Co²⁺ and Ni²⁺) decreases the optical band gap of NdFeO₃, leading to the recommendation of using the samples Nd_0.90Co_0.10FeO₃ and Nd_0.90Ni_0.10FeO₃ in photocatalysis of dye degradation from water. The removal efficiencies of Cr⁶⁺ at pH = 6 are 88.06 %, 85.54 %, and 85.52 % for the samples NdFeO₃, Nd_0.90Co_0.10FeO₃, and Nd_0.90Ni_0.10FeO₃, respectively. The Freundlich isotherm mode is the best-fit model for NdFeO₃ to adsorb Cr⁶⁺ ions from aqueous solutions.