A facile, single-step synthesis of flowery shaped, pure/lithium-doped 3D iron oxides

Abstract

The shape-dependent surface properties of iron oxides are being paid increasing attention for their many advanced and synergistic applications. The present investigation deals with the preparation of pure and lithiated 3D iron oxide through a simple and single-step synthesis route. The nano-hierarchical flowers were synthesized by adopting a semi-aqueous ligated system. Here, the reagent played a double role for ligation as well as for precipitation. In the absence of lithium, goethite and ferrihydrite phases were formed, whereas formation of a mixture of hematite and ferrihydrite was observed in its presence, confirming participation of Li in phase transformation of goethite/ferrihydrite to hematite. With the progress of time, flowery shaped nanoparticles developed. Mössbauer spectroscopy revealed Li ion-induced formation of an α-Fe₂O₃ phase. Single-phase hematite was formed on annealing at 500 °C. The Li-doped iron oxide sample has high surface area and has a sharp distribution peak centered at 19.13 nm, showing homogeneity of the pores. On calcination of the sample at 400 °C, the surface area decreased; however, pore size distribution remained unchanged, which was an unusual trend. The annealed sample (500 °C) possessed bimodal (small and large) mesopore distribution. The fluoride adsorption behaviour and magnetic properties of the as-synthesized and annealed Li-doped samples are discussed. Magnetic properties of the samples suggest that incorporation of Li resulted in an increase of coercivity due to stabilization of the domain. The unique surface behaviour of the present samples can be further examined for other high end applications. The present synthesis strategy has the advantage of producing shape-controlled hierarchical materials with tunable surface properties, which promises the further development of other functional materials.