Effect of rare earth doping on the structural, magnetic and photocatalytic properties of newly synthesized nanocrystalline rare earth doped Ruddlesden–Popper oxides LnSrFe0.5Co0.5O4 (Ln = La, Nd, Sm, Gd)

Abstract

The Ruddlesden–Popper (RP) oxides in a high grade of purity are generally prepared at high temperature and that is why there are few reports on their nanocrystalline state. These oxides may show good photocatalytic activity in nanocrystalline form because of higher surface area and better morphology. In this context, we are reporting rare earth doped nanocrystalline RP phases LnSrFe_0.5Co_0.5O₄ (Ln = La, Nd, Sm, Gd), which are highly efficient in removing hazardous organic dye pollutants from wastewater both in unitary and ternary solutions. The impact of rare earth ion doping on the structural, magnetic, and optical characteristics of LnSrFe_0.5Co_0.5O₄ has also been comprehensively investigated via different characterization methods. The Rietveld refinement analysis confirmed the formation of single-phase samples having tetragonal symmetry that crystallised in the I4/mmm space group. The refinement results revealed that with heavier rare earth ion doping, there was a continuous decrease in the value of the unit cell parameters and the cell volume. Dominant anti-ferromagnetic (AFM) interactions were seen in each of these compounds, along with the presence of weak ferromagnetic (FM) interactions due to the co-existence of the super-exchange (Co³⁺–O–Fe³⁺) FM and (Co³⁺–O–Co³⁺, Fe³⁺–O–Fe³⁺) AFM interactions. The band gap values of all these nanophases lie in the range of 1.53–1.62 eV, making them suitable photocatalysts for dye degradation. The photocatalytic activity of the synthesised nanophases was assessed using cationic (methylene blue and rhodamine B) and anionic (methyl orange) pollutants as well as their mixture. It has been observed that the Nd-doped catalyst showed better deterioration efficacy for rhodamine B dye, i.e., 99% in 40 min, followed by 84%, 87%, and 85% for the La, Sm, and Gd phases in the same time period, respectively. The results of photocatalytic activity have been interpreted on the basis of bandgap energy values and photoluminescence (PL) intensity.